Coordinated by CRHEA-CNRS research laboratory, this monthly newsletter is produced by Knowmade with collaboration from the managers of GANEX groups. The newsletter presents a selection of newest scientific publications, patent applications and press releases related to III-Nitride semiconductor materials (GaN, AlN, InN and alloys)

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Cluster of Excellence (Labex, 2012-2019) GANEX is a cluster gathering French research teams involved in GaN technology. The objective of GANEX is to strengthen the position of French academic players in terms of knowledge and visibility, and reinforce the French industrials in terms of know-how and market share. www.ganex.fr

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GANEX Newsletter No. 42 July 2016

III-N Technology

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GANEX | Newsletter No. 42 - III-N Technology 2

METHODOLOGY

Each month

250+ new scientific publications

120+ new patent applications

20+ new press releases

Sources 10+ scientific journal editors

Elsevier, IOP, IEEE, Wiley, Springer, APS, AIP, AVS, ECS, Nature, Science …

10+ specialist magazines Semiconductor Today, ElectoIQ, i-micronews,

Compound Semiconductor, Solid State Technology … 5+ open access database: FreeFulPDF, DOAJ …

Patent database: Questel-Orbit

Selection by III-N French

experts

GANEX monthly newsletter

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TABLE OF CONTENTS (clickable links to chapters)

SCIENTIFIC PUBLICATION ................................................................................................................... 4

GROUP 1 - LEDs and Lighting ................................................................................................................... 4

GROUP 2 - Laser and Coherent Light ....................................................................................................... 7

GROUP 3 - Power Electronics ................................................................................................................. 10

GROUP 4 - Advanced Electronics and RF ............................................................................................... 14

GROUP 5 – MEMS and Sensors .............................................................................................................. 17

GROUP 6 - Photovoltaics and Energy harvesting ................................................................................... 22

GROUP 7 - Materials, Technology and Fundamental............................................................................. 24

PRESS RELEASE ................................................................................................................................ 38

PATENT APPLICATION ...................................................................................................................... 54

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SCIENTIFIC PUBLICATION Selection of new scientific articles

GROUP 1 - LEDs and Lighting Group leader: Benjamin Damilano (CRHEA-CNRS)

Information selected by Benjamin Damilano (CRHEA-CNRS)

Nitride-Based UV-LEDs and Their Application UVphotonics NT GmbH, c/o Ferdinand-Braun-Institut, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany Optik & Photonik http://dx.doi.org/10.1002/opph.201600020

A wide range of applications utilize ultraviolet (UV) light in the UVB (280 — 320 nm) and UVC range (< 280 nm). Among them are disinfection of water, air, and surfaces, sensing applications, plant growth lighting, and material processing. While currently some of these applications are already being accessed by using conventional mercury discharge lamps, the use of semiconductor UV-LEDs promises to revolutionize the market by expanding the range of possible applications and making them more efficient. For this, the available range of wavelengths, the LED efficiency and their output power need to be increased. This article describes the technology of nitride-based UV-LEDs and their applications. Metallic nanostructures for efficient LED lighting Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla (CSIC-US), 41092 Sevilla, Spain Light: Science & Applications http://dx.doi.org/10.1038/lsa.2016.80

Light-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light–matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured

metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination. Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany OSRAM Opto Semiconductors GmbH, Leibnizstraße 4, 93055 Regensburg, Germany Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany J. Appl. Phys. http://dx.doi.org/10.1063/1.4953254

We investigate industrial-grade InGaN/GaN quantum wells (QWs) emitting in the green spectral region under high, resonant pumping conditions. Consequently, an ubiquitous high energy luminescence is observed that we assign to a polarization field Confined Hole Continuum (CHC). Our finding is supported by a unique combination of experimental techniques, including transmission electron microscopy, (time-resolved) photoluminescence under various excitation conditions, and electroluminescence, which confirm an extended out-of-plane localization of the CHC-states. The larger width of

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this localization volume surpasses the QW thickness, yielding enhanced non-radiative losses due to point defects and interfaces, whereas the energetic proximity to the bulk valence band states promotes carrier leakage. Investigating the origin of efficiency droop by profiling the voltage across the multi-quantum well of an operating light-emitting diode Department of Nano-Photonics Engineering, Korea University, Seoul 136-713, South Korea Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4953401

Efficiency droop is a phenomenon in which the efficiency of a light-emitting diode (LED) decreases with the increase in current density. To analyze efficiency droop, direct experimental observations on the energy conversion occurring inside the LED is required. Here, we present the measured voltage profiles on the cross section of an operating LED and analyze them with the cross-sectional temperature profiles obtained in a previous study under the same operation conditions. The measured voltage profiles suggest that with increases in the injection current density, electron depletion shifts from the multi-quantum well through an electron blocking layer to the p-GaN region. This is because electron leakage increases with increases in current density. Development of High Power, Large Area, Deep Ultraviolet Light Emitting Devices Using Dynamic Microplasma Excitation (MIPE) of AlGaN Multiple Quantum Wells Research Organization of Science and Technology, Ritsumeikan University, Kusatsu City, Shiga Prefecture, Japan Electronics and Communications in Japan http://dx.doi.org/10.1002/ecj.11768

We have succeeded in developing a new dynamic microplasma-excited deep ultraviolet light emitting device using aluminum gallium nitride (AlGaN) multi-quantum wells (MIPE). The operating principle is completely different from that of current injection-type deep ultraviolet light emitting diodes. We have created a 12 × 5.5 cm

device with a power of about 1 W at a wavelength of 325 nm. We can achieve panel-type laminar-flow water purification and cleaning systems that can be alternatives to the use of mercury lamps as a DUV light source, since these cannot be used under the Minamata Treaty. The wavelength region from 210 nm to 250 nm realized in this device opens new fields of academic research and areas of application, in which the decomposition of materials that are difficult to break down, the synthesis of new materials, including a new H2 battery cell, and disinfection of water are possible. Patterned Ga2O3 for current blocking and optical scattering in visible light-emitting diodes Department of Mechanical Engineering, University of Houston, Houston, TX, USA Metamaterial Electronic Device Research Center, Hongik University, Seoul 121-791, Korea Physica status solidi (a) http://dx.doi.org/10.1002/pssa.201600240

Patterned gallium oxide (Ga2O3) using one-step patterning followed by oxygen plasma treatment on a p-GaN layer can function as both current-blocking and optical-scattering regions for uniform current spreading and improved light-extraction efficiencies. The results showed that the optical output power of the LED with patterned Ga2O3 increased by 16.8% at 60 mA compared to that of conventional LEDs. Numerical studies on light tracing and emission pattern, and external quantum efficiency evaluation support the improvement of both uniform current spreading and light-extraction efficiencies by patterned Ga2O3. Depth-specific optogenetic control in vivo with a scalable, high-density μLED neural probe Institute of Photonics, Dept. of Physics, SUPA, University of Strathclyde, Glasgow G1 1RD, UK Scientific Reports http://dx.doi.org/10.1038/srep28381

Controlling neural circuits is a powerful approach to uncover a causal link between neural activity and behaviour. Optogenetics has been widely adopted by the neuroscience community as it

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offers cell-type-specific perturbation with millisecond precision. However, these studies require light delivery in complex patterns with cellular-scale resolution, while covering a large volume of tissue at depth in vivo. Here we describe a novel high-density silicon-based microscale light-emitting diode (μLED) array, consisting of up to ninety-six 25 μm-diameter μLEDs emitting at a wavelength of 450 nm with a peak irradiance of 400 mW/mm2. A width of 100 μm, tapering to a 1 μm point, and a 40 μm thickness help minimise tissue damage during insertion. Thermal properties permit a set of optogenetic operating regimes, with ~0.5 °C average temperature increase. We demonstrate depth-dependent activation of mouse neocortical neurons in vivo, offering an inexpensive novel tool for the precise manipulation of neural activity. Horizontally assembled green InGaN nanorod LEDs: scalable polarized surface emitting LEDs using electric-field assisted assembly Department of Chemistry, Kookmin University, Seoul 136-702, Korea Scientific Reports http://dx.doi.org/10.1038/srep28312

In this study, we report the concerted fabrication process, which is easy to transform the size of active emitting area and produce polarized surface light, using the electric-field-assisted assembly for horizontally assembled many tiny nanorod LEDs between two metal electrodes. We fabricate the millions of individually separated 1D nanorod LEDs from 2D nanorod arrays using nanosphere lithography, etching and cutting process of InGaN/GaN LED structure on a flat sapphire substrate. The horizontally assembled InGaN-based nanorods LED device shows bright (~2,130 cd/m2) and uniform polarized (polarization ratio, ρ = ~0.61) green emissions from large area (0.7 cm × 0.6 cm) planar surface. The realization of a horizontally assembled nanorod LED device can prove the concept of an innovative idea to fabricate formable and scalable polarized surface LED lighting.

Monolithic Broadband InGaN Light-emitting Diode Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Pok Fu Lam, Hong Kong ACS Photonics http://dx.doi.org/10.1021/acsphotonics.6b00269

A monolithic non-phosphor broadband-emission light-emitting diode is demonstrated, comprising a combination of high-density micro-structured and nano-structured InGaN-GaN quantum wells fabricated using a top-down approach. Broadband emission is achieved by taking advantage of low-dimensional-induced strain-relaxation of highly-strained quantum wells, combining light emitted from strain-relaxed nano-tips at wavelengths shorter than the as-grown by as much as 80 nm with longer-wavelength light emitted from the larger non-relaxed microdisks. The localized emission characteristics have been studied by spatially-resolved near-field photoluminescence spectroscopy which enabled both the photoluminescence intensity and spectrum from individual nano-tips to be distinguished from emission at the larger-dimensioned regions. Distinctive blue-green-yellow emission can be observed from the electroluminescent device, whose continuous broadband spectrum is characterized by CIE coordinates of (0.39, 0.47) and color rendering index of 41. Emission can be tuned by adjusting the relative densities of nano-tips and microdisks along the linear color gamut defined by their respective CIE coordinates.

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GROUP 2 - Laser and Coherent Light Group leader: Bruno Gayral (CEA)

Information selected by Knowmade

Aluminum nitride electro-optic phase shifter for backend integration on silicon Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, #08-02, Innovis, 138634, Singapore Optics Express http://dx.doi.org/10.1364/OE.24.012501

An AlN electro-optic phase shifter with a parallel plate capacitor structure is fabricated on Si using the back-end complementary metal-oxide-semiconductor technology, which is feasible for multilayer photonics integration. The modulation efficiency (Vπ⋅Lπ product) measured from the fabricated waveguide-ring resonators and Mach-Zehnder Interferometer (MZI) modulators near the 1550-nm wavelength is ∼240 V⋅cm for the transverse electric (TE) mode and ∼320 V⋅cm for the transverse magnetic (TM) mode, from which the Pockels coefficient of the deposited AlN is deduced to be ∼1.0 pm/V for both TE and TM modes. The methods for further modulation efficiency improvement are addressed. Recent progress of AlGaN deep-UV LEDs and LDs Riken, Japan Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_SI.2016.STh1L.1

We discuss on recent progress and future prospects of AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) and laser diodes (LDs) which have been realized by developing crystal growth techniques for AlN and AlGaN semiconductor thin-films. Hybrid Perovskite Vertical-Cavity Surface-Emitting Laser Deploying Nanoporous GaN Dielectric Reflector Technology Brown University, United States Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_SI.2016.SW1M.2

Microstructure optimized, solution-grown perovskite thin film with high optical gain is sandwiched between two nanoporous GaN-based DBRs forming a vertical cavity. Low threshold spectrally and spatially coherent near infrared lasing is achieved by optical pumping. Planar Metal-GaN Spiral Nanowire Cavities for High Circular Dichroism Lasing Action National Chiao Tung University, Taiwan Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_SI.2016.SF2O.6

The compact and energy-efficient planar metal-GaN spiral nanowire cavity lasing device has been demonstrated with high circularly polarized UV laser light at 364 nm and the circular dichroism performance enhanced to dissymmetry factor of +1.4. Exciton-polariton laser Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau 2028, Republic of Moldova Low Temp. Phys. http://dx.doi.org/10.1063/1.4948615

We present a review of the investigations realized in the last decades of the phenomenon of the Bose-Einstein condensation (BEC) in the system of two-dimensional cavity polaritons in semiconductor nanostructures. The conditions at which the excitons interacting with cavity photons form new type of quasiparticles named as polaritons are described. Since polaritons can form in a microcavity a weakly interacting Bose gas, similarly to the exciton gas in semiconductors, the microcavity exciton-polariton BEC emerged in the last decades as a new direction of the exciton BEC in solids, promising for practical applications. The high interest in BEC of exciton-polaritons in semiconductor microcavities is related to the ultra-low threshold lasing which has been demonstrated, in particular, for an electrically injected polariton laser based on

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bulk GaN microcavity diode working at room temperature. Effectiveness of inserting an InGaN interlayer to improve the performances of InGaN-based blue-violet laser diodes State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China Chinese Optics Letters https://www.osapublishing.org/col/abstract.cfm?uri=col-14-6-062502

Electron leakage still needs to be solved for InGaN-based blue-violet laser diodes (LDs), despite the presence of the electron blocking layer (EBL). To reduce further electron leakage, a new structure of InGaN-based LDs with an InGaN interlayer between the EBL and p-type waveguide layer is designed. The optical and electrical characteristics of these LDs are simulated, and it is found that the adjusted energy band profile in the new structure can improve carrier injection and enhance the effective energy barrier against electron leakage when the In composition of the InGaN interlayer is properly chosen. As a result, the device performances of the LDs are improved. Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany OSRAM Opto Semiconductors GmbH, Leibnizstraße 4, 93055 Regensburg, Germany Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany J. Appl. Phys. http://dx.doi.org/10.1063/1.4953254

We investigate industrial-grade InGaN/GaN quantum wells (QWs) emitting in the green spectral region under high, resonant pumping conditions. Consequently, an ubiquitous high energy luminescence is observed that we assign to a polarization field Confined Hole Continuum (CHC). Our finding is supported by a unique combination of experimental techniques, including transmission electron microscopy, (time-

resolved) photoluminescence under various excitation conditions, and electroluminescence, which confirm an extended out-of-plane localization of the CHC-states. The larger width of this localization volume surpasses the QW thickness, yielding enhanced non-radiative losses due to point defects and interfaces, whereas the energetic proximity to the bulk valence band states promotes carrier leakage. On the formation of cleaved mirror facets of GaN-based laser diodes—A comparative study of diamond-tip edge-scribing and laser scribing Ferdinand-Braun-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany J. Vac. Sci. Technol. B http://dx.doi.org/10.1116/1.4953885

The formation of cleaved mirror facets of GaN-based laser diodes on c-plane GaN substrates is investigated using either diamond-tip edge-scribing or laser scribing with a skip-and-scribe method. The yield of properly cleaved facets was significantly improved to around 80% when using the laser skip-and-scribe method instead of diamond scribing. In addition, the cleavage planes of laser scribed samples showed fewer terraces than those of diamond scribed samples. The performance of broad area laser diodes with proper facet quality is shown to be independent of the scribing methods studied. Design of free-standing GaN strip waveguide and grating couplers College of Telecommunication and Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003, China Optik - International Journal for Light and Electron Optics http://dx.doi.org/10.1016/j.ijleo.2016.05.104

Gallium Nitride (GaN) based fully cut through free-standing planar photonic device was presented. Waveguide, grating couplers and supporting structure were designed by analytical calculation and finite element method (FEM) simulation. Optimized crossing structure and grating coupler with 0.4 dB intersection loss and 1 dB coupling loss at telecommunication band was obtained

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respectively. Mechanical stability was optimized by static and modal structure simulation. This work illustrates the potential of free-standing GaN photonic structure which will enable new functions for planar photonic devices. It also provides the possibility of monolithic integration of planar photonic and light sources on III–V active platforms. Chemically assisted ion beam etching of laser diode facets on nonpolar and semipolar orientations of GaN Materials Department, University of California, Santa Barbara, CA 93106, USA Semiconductor Science and Technology http://dx.doi.org/10.1088/0268-1242/31/7/075008

We demonstrate a vertical (<1° departure) and smooth (2.0 nm root mean square line-edge roughness (LER)) etch by chemically assisted Ar ion beam etching (CAIBE) in Cl2 chemistry that is suitable for forming laser diode (LD) facets on nonpolar and semipolar oriented III-nitride devices. The etch profiles were achieved with photoresist masks and optimized CAIBE chamber conditions including the platen tilt angle and Cl2 flow rate. Co-loaded studies showed similar etch rates of ~60 nm min−1 for (20-2-1), (20-21) and m-plane orientations. The etched surfaces of LD facets on these orientations are chemically dissimilar (Ga-rich versus N-rich), but were visually indistinguishable, thus confirming the negligible orientation dependence of the etch. Continuous-wave blue LDs were fabricated on the semipolar (20-2-1) plane to compare CAIBE and reactive ion etch (RIE) facet processes. The CAIBE process resulted in LDs with lower threshold current densities due to reduced parasitic mirror loss compared with the RIE process. The LER, degree of verticality, and model of the 1D vertical laser mode were used to calculate a maximum uncoated facet reflection of 17% (94% of the nominal) for the CAIBE facet. The results demonstrate the suitability of CAIBE for forming high quality facets for high performance nonpolar and semipolar III-N LDs.

Suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells Grünberg Research Centre, Nanjing University of Posts and Telecommunications, Nanjing 210003, China Optical Materials Express http://dx.doi.org/10.1364/OME.6.002366

In this paper, we report on the fabrication and characterization of a suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells (MQWs) on a GaN-on-silicon platform. Both silicon removal and back wafer etching are conducted to achieve the suspended waveguide photodetector combination. The light illumination measurements experimentally demonstrate that the metallization stacks can serve as the bottom metal mirror to reflect the incoming light back for re-absorption, leading to an improved photocurrent response. The out-of-plane light can couple into the suspended waveguide and propagate as a confined optical mode, resulting in an induced photocurrent. The photodetector exhibits two operation modes. The peak values of the responsivity spectra for the suspended waveguide photodetector are located around 401 nm at 3 V bias and 435 nm at 0 V bias, respectively. These results pave a promising way to develop the suspended waveguide photodetector for diverse applications in the visible wavelength region.

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GROUP 3 - Power Electronics Group leader: Frédéric Morancho (LAAS-CNRS)

Information selected by Frédéric Morancho (LAAS-CNRS) and Yvon Cordier (CRHEA-CNRS)

Design and fabrication of a 1.2 kV GaN-based MOS vertical transistor for single chip normally off operation School of Electrical, Computer, and Energy Engineering, Arizona State University, AZ, Tempe 85287, USA Physica status solidi (a) http://dx.doi.org/10.1002/pssa.201532575

We report a novel design to achieve normally off, high voltage power switch using an “all-GaN” vertical MOS-gate transistor (MOSVFET). In this structure, two MOS gates were formed vertically on the sidewalls of the pillar, whose opposite ends were connected to the source and drain of the device. The design space and associated performance based on 2D drift-diffusion model is discussed highlighting the trade-off between blocking voltage (Vbl), on resistance (Ron), and threshold voltage (Vth). An optimized device structure was proposed with more than 1.2 kV blocking capability and normally off behavior. With proper design of the drift region thickness and doping, the corresponding Ron was as low as 2.8 mΩ cm2. The role of key parameters such as bulk GaN mobility, channel mobility, gate to gate distance (Lgtg) and gate length (Lg) on the Ron, Vbl, leakage current, and Vth were also examined. The effect of mobility on the device performance and the role of the bulk GaN material was analyzed utilizing the model to create a comprehensive design space for achieving low-loss switching. Characterization of capture cross sections of interface states in dielectric/III-nitride heterojunction structures Research Center for Integrated Quantum Electronics, Hokkaido University, Kita-13 Nishi-8, Kita-ku, 060-8628 Sapporo, Japan Surface Physics and Nanostructures Department, Institute of Physics-CND, Silesian University of Technology, Konarskiego 22B, 44-100 Gliwice, Poland J. Appl. Phys. http://dx.doi.org/10.1063/1.4952708

We performed, for the first time, quantitative characterization of electron capture cross sections σ of the interface states at dielectric/III-N heterojunction interfaces. We developed a new method, which is based on the photo-assisted capacitance-voltage measurements using photon energies below the semiconductor band gap. The analysis was carried out for AlGaN/GaN metal-insulator-semiconductor heterojunction (MISH) structures with Al 2O3, SiO2, or SiN films as insulator deposited on the AlGaN layers with Al content (x) varying over a wide range of values. Additionally, we also investigated an Al 2O3/InAlN/GaN MISH structure. Prior to insulator deposition, the AlGaN and InAlN surfaces were subjected to different treatments. We found that σ for all these structures lies in the range between 5×10−195×10−19 and 10−1610−16 cm2. Furthermore, we revealed that σ for dielectric/AlxGa1− xN interfaces increases with increasing x. We showed that both the multiphonon-emission and cascade processes can explain the obtained results. Electrical and Thermal Stability of ALD-Deposited TiN Transition Metal Nitride Schottky Gates for AlGaN/GaN HEMTs Department of Materials Science and Engineering, University of Maryland, College Park, College Park, Maryland 20742, USA ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0211607jss

TiN, a transition metal nitride, has been evaluated as an electrically and thermally stable Schottky gate material for AlGaN/GaN high electron mobility transistors. HEMTs with 75 nm TiN gates deposited via atomic layer deposition at 350°C exhibited improved static and dynamic on-state characteristics compared to Ni/Au-gated HEMTs. Reverse bias gate stressing indicated a higher critical voltage and higher breakdown voltage for the TiN-gated HEMTs. The TiN gated devices exhibited stable DC operation after annealing at

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temperatures as high as 800°C, while the Ni/Au gates exhibited significant degradation after annealing above 500°C and failed catastrophically at 800°C. The opportunity for bulk GaN power device, technology and application Huga Optotech Inc., USA 2016 International Symposium on VLSI Technology, Systems and Application (VLSI-TSA) http://dx.doi.org/10.1109/VLSI-TSA.2016.7480532

GaN-based wide band-gap semiconductors have attracted much attention due to their excellent properties, such as high breakdown electric field, high power switching efficiency and high thermal stability. Besides, the inherent polarization is built in AlGaN/GaN hetero-junction structure, and further promises higher sheet carrier density (ns) in the two dimensional electron gas (2DEG), as well as a diminution of on-state resistance (Ron) for power switching applications. In particular, the loss at high frequency (about 1MHz) was lower than Si device by a factor of 10. It's means that high frequency operation is a strong probability for GaN device. In other words, the system size and weight can be reduced drastically by using GaN device because of smaller filter and less passives. Nevertheless, there is still lack of suitable substrates for GaN-based devices to develop fully their superiorities. In recent decades, many studies of the growth of GaN-based epilayers on a variety of substrates, such as sapphire, SiC, bulk GaN, and Si, had been published. Among the aforementioned substrate materials, bulk GaN is regarded as a relatively promising substrate for use in GaN-based epitaxy due to homo-epitaxial growth. It was well-known that the largest obstacle for the development of GaN-on-GaN power device is the substrate. Typically, free-standing GaN substrate today are fabricated by hydride vapor phase epitaxy (HVPE) using MOCVD-grown GaN-on-sapphire template. However, the threading dislocation densities (TDDs) are still ranging from 3??106???1??107 cm???2. On the other hand, many papers pointed out that leakage would be easily occurred from channel to substrate through threading dislocations (TDs), accelerate degradation of GaN

power device, and have a well-documented negative impact on GaN power device lifetime. Consequently, TDDs below 104 cm???2, as are available in GaAs and should be available in true bulk GaN, are often regarded as being necessary for vertical GaN-on- GaN power devices. The physical mechanism on the threshold voltage temperature stability improvement for GaN HEMTs with pre-fluorination argon treatment Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119260 A*STAR Institute of Microelectronics, Singapore 117685 Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4953573

In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (VTH) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al2O3 gate dielectrics. For the MIS-HEMT with FPT only, its VTH drops from 4.2 V at room temperature to 0.5 V at 200 °C. Alternatively, for the device with APT-then-FPT process, its VTH can retain at 2.5 V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable VTH makes this device suitable for high power applications. The depth profile of the F atoms in Al2O3, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al2O3 surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al2OxFy cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al2O3 bandgap when

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APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described. Deep traps and instabilities in AlGaN/GaN high electron mobility transistors on Si substrates National University of Science and Technology MISiS, Leninskiy pr. 4, Moscow 119049, Russia J. Vac. Sci. Technol. B http://dx.doi.org/10.1116/1.4953347

Deep traps were studied in multiple-finger AlGaN/GaN transistors with broad periphery by means of current–voltage and capacitance–voltage characteristics, reverse deep level transient spectroscopy, deep level transient spectroscopy with electrical (DLTS) and optical DLTS injection, and current DLTS (CDLTS) with gate voltage and drain voltage pulsing. Deep electron traps with activation energies of 0.25, 0.36, 0.56, and 0.8–0.9 eV are found to be responsible for variations in threshold current with applied gate bias. These traps also give rise to current transients observed at different temperatures in CDLTS. The 0.25 and 0.56 eV centers are most likely located at the AlGaN/GaN interface. The 0.25 eV state is believed to be nitrogen vacancy-related, the 0.36 eV level is of unknown origin, the 0.56 eV level is likely due to point defects enhanced in the presence of dislocations, and responsible for low luminescence efficiency of nonpolar n-GaN and for degradation of GaN transistors and light-emitting diodes and light-emitting diodes, while the 0.8 eV-level has been attributed to either interstitial Ga or N. Hole-trap-like relaxations in CDLTS were observed at temperatures higher than ∼300 K and attributed to hole traps near Ev + 0.9 eV located in the buffer layer. These have previously been assigned to either gallium vacancy-oxygen acceptor complexes (VGa-O)2− or carbon on nitrogen site acceptor (CN −) complexes. These results show that the stability of GaN-based high electron mobility transistors on Si is still dominated by the high concentration of point defects present in the material.

Oxide interfacial charge engineering towards normally-off AlN/GaN MOSHEMT Department of Electronics & Communication Engineering, National Institute of Technology, Silchar 788010, India Materials Science in Semiconductor Processing http://dx.doi.org/10.1016/j.mssp.2016.06.008

In this paper a detail insight into the role of oxide/barrier interfacial charges (Nox) for shifting the threshold voltage (VT) of AlN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMTs) is gained. A model is developed for VT considering all possible charges arise at different interfaces. To validate the model the proposed device is simulated by considering different insulators and Nox into account. It is very fascinating to observe that VT is highly sensitive towards change in Nox at higher oxide dimensions, whereas at lower dimensions Nox has very negligible effect. Normally-off operation can be achieved by increasing or decreasing Nox in MOSHEMT with Al2O3 or HfO2 as gate dielectric respectively. AlGaN/GaN high-electron-mobility transistor technology for high-voltage and low-on-resistance operation Graduate School of Engineering, University of Fukui, Fukui 910-8507, Japan Japanese Journal of Applied Physics http://dx.doi.org/10.7567/JJAP.55.070101

In this paper, we give an overview of the recent progress in GaN-based high-electron-mobility transistors (HEMTs) developed for mainstream acceptance in the power electronics field. The comprehensive investigation of AlGaN/GaN HEMTs fabricated on a free-standing semi-insulating GaN substrate reveals that an extracted effective lateral breakdown field of approximately 1 MV/cm is likely limited by the premature device breakdown originating from the insufficient structural and electrical quality of GaN buffer layers and/or the GaN substrate itself. The effective lateral breakdown field is increased to 2 MV/cm by using a highly resistive GaN substrate achieved by heavy Fe doping. Various issues relevant to current collapse are also discussed in

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the latter half of this paper, where a more pronounced reduction in current collapse is achieved by combining two different schemes (i.e., a prepassivation oxygen plasma treatment and a field plate structure) for intensifying the mitigating effect against current collapse. Finally, a novel approach to suppress current collapse is presented by introducing a three-dimensional field plate (3DFP) in AlGaN/GaN HEMTs, and its possibility of realizing true collapse-free operation is described. Step buffer layer of Al0.25Ga0.75N/Al0.08Ga0.92N on P-InAlN gate normally-off high electron mobility transistors Compound Semiconductor Device Laboratory, Department of Material Science and Engineering, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan Semiconductor Science and Technology http://dx.doi.org/10.1088/0268-1242/31/7/075006

Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al0.25Ga0.75N/Al0.1Ga0.9N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/Al0.25Ga0.75N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm−1). At a drain bias of 15 V, the current density reached 263 mA mm−1. The explored structure is promising owing to tunable positive threshold

voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices. Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using Double Buried p-Type Layers Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 Chinese Physics Letters http://dx.doi.org/10.1088/0256-307X/33/6/067301

A novel AlGaN/GaN high electron mobility transistor (HEMT) with double buried p-type layers (DBPLs) in the GaN buffer layer and its mechanism are studied. The DBPL AlGaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8 μm.

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GROUP 4 - Advanced Electronics and RF Group leader: Jean-Claude Dejaeger (IEMN)

Information selected by Jean-Claude Dejaeger (IEMN) and Yvon Cordier (CRHEA-CNRS)

Petahertz frequency operation with gallium nitride semiconductor NTT Basic Research Laboratories, Japan Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_QELS.2016.FTu3N.6

We demonstrate optical drive with 1.16-PHz frequency using gallium nitride (GaN) wide-bandgap semiconductor. An isolated attosecond pulse with coherent broadband spectrum reveals dipole oscillation with 860-as periodicity in the GaN electron and hole system Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes Department of Physics, College of Science for Girls, University of Dammam (UOD), Saudi Arabia Chinese Physics B http://dx.doi.org/10.1088/1674-1056/25/6/067304

In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga(1−x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current–voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga(1−x)N width, and the aluminum concentration x Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current–voltage (I–V) characteristic strongly depends on aluminum concentration x Al.

It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. Prospects of gallium nitride double drift region mixed tunneling avalanche transit time diodes for operation in F, Y and THz bands Electron Devices Group at the School of Physics, Sambalpur University, Jyoti Vihar, Burla, Sambalpur–768019, Odisha, India Journal of Semiconductors http://dx.doi.org/10.1088/1674-4926/37/5/054001

The potential of GaN as a wide band gap semiconductor is explored for application as double drift region mixed tunneling avalanche transit time (MITATT) diodes for operation at 120 GHz, 220 GHz and 0.35 THz using some computer simulation methods developed by our group. The salient features of our results have uncovered some peculiarities of the GaN based MITATT devices. An efficiency of more than 20% right up to a frequency of 0.35 THz (from the GaN MITATT diode) seems highly encouraging but a power output of only 0.76 W is indicative of its dismal fate. The existence of a noise measure minimum at the operating frequency of 0.35 THz is again exhilarating but the value of the minimum is miserably high i.e. more than 33 dB. Thus, although GaN is a wide band gap semiconductor, the disparate carrier velocities prevent its full potential from being exploited for application as MTATT diodes. Monolithically integrated enhancement/depletion-mode AlGaN/GaN HEMTs SRAM unit and voltage level shifter using fluorine plasma treatment Key Laboratory for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China

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Journal of Semiconductors http://dx.doi.org/10.1088/1674-4926/37/5/055002

A GaN-based E/D mode direct-couple logic 6 transistors SRAM unit and a voltage level shifter were designed and fabricated. E-mode and D-mode AlGaN/GaN HEMTs were integrated in one wafer using fluorine plasma treatment and using a moderate AlGaN barrier layer heterojunction structure. The 6 transistors SRAM unit consists of two symmetrical E/D mode inverters and two E-mode switch HEMTs. The output low and high voltage of the SRAM unit are 0.95 and 0.07 V at a voltage supply of 1 V. The voltage level shifter lowers the supply voltage using four Ni-AlGaN Schottky diodes in a series at a positive supply voltage of 6 V and a negative supply voltage of −6 V. By controlling the states of inverter modules of the level shifter in turn, the level shifter offers two channel voltage outputs of −0.5 and −5 V. The flip voltage of the level shifter is 0.76 V. Both the SRAM unit and voltage shifter operate correctly, demonstrating the promising potential for GaN-based E/D mode digital and analog integrated circuits. Several considerations are proposed to avoid the influence of threshold voltage degradation of D-mode and E-mode HEMT on the operation of the circuit. Study of source access resistance at direct current quiescent points for AlGaN/GaN heterostructure field-effect transistors School of Physics, Shandong University, Jinan 250100, China J. Appl. Phys. http://dx.doi.org/10.1063/1.4953645

The AlGaN/GaN heterostructure field-effect transistor (HFET) with 100 nm gate length was fabricated. An improved method is proposed to determine the value of the source access resistance corresponding to each direct current quiescent points in the saturation region of the current-voltage characteristics. The increase in the source access resistance with drain-source current has been studied, taking into account several main scattering mechanisms, including polarization Coulomb field (PCF) scattering, polar-optical-phonon scattering, piezoelectric scattering, and interface roughness scattering. It is

found that PCF scattering plays a very important role in the source access resistance of AlGaN/GaN HFETs. The PCF scattering component of source access resistance decreases with the increase in drain-source current. Current transport mechanism in graphene/AlGaN/GaN heterostructures with various Al mole fractions School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center (SPRC), Chonbuk National University, Jeonju 54896, Republic of Korea AIP Advances http://dx.doi.org/10.1063/1.4953917

The current transport mechanism of graphene formed on AlxGa1−xN/GaN heterostructures with various Al mole fractions (x = 0.15, 0.20, 0.30, and 0.40) is investigated. The current–voltage measurement from graphene to AlGaN/GaN shows an excellent rectifying property. The extracted Schottky barrier height of the graphene/AlGaN/GaN contacts increases with the Al mole fraction in AlGaN. However, the current transport mechanism deviates from the Schottky-Mott theory owing to the deterioration of AlGaN crystal quality at high Al mole fractions confirmed by reverse leakage current measurement. Gold-free contacts on AlxGa1-xN/GaN high electron mobility transistor structure grown on a 200-mm diameter Si(111) substrate Division of Microelectronics, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore J. Vac. Sci. Technol. B http://dx.doi.org/10.1116/1.4952403

The authors report on the fabrication and characterization of low-temperature processed gold-free Ohmic contacts for Al xGa1−xN/GaN high electron mobility transistors (HEMTs). The HEMT structure grown on a 200-mm diameter Si(111) substrate is used in this study. Using the Ti/Al/NiV metal stack scheme, the source/drain Ohmic contact optimization is accomplished through the variation of Ti/Al thickness ratio and thermal annealing conditions. For an optimized

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Ti/Al stack thickness (20/200 nm) annealed at 500 °C for 30 s with smooth contact surface morphology, a specific contact resistivity of ∼6.3 × 10−6 Ω cm2 is achieved. Furthermore, with gold-free Ni/Al gates, the fabricated HEMTs exhibit I ON/I OFF ratio of ∼109 and a subthreshold swing of ∼71 mV/dec. The demonstrated gold-free contact schemes thus provide a solution toward the implementation of GaN-based HEMT process on a Si foundry platform.

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GANEX | Newsletter No. 42 - III-N Technology 17

GROUP 5 – MEMS and Sensors Group leader: Marc Faucher (IEMN) Information selected by Knowmade

Optical phonon modulation in semiconductors by surface acoustic waves Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany Instituto de Física “Gleb Wataghin”, Unicamp, 13083-859 Campinas-SP, Brazil Phys. Rev. B http://dx.doi.org/10.1103/PhysRevB.93.195212

We investigate the modulation of optical phonons in semiconductor crystals by a surface acoustic wave (SAW) propagating on the crystal surface. The SAW fields induce changes on the order of 10−3 in the time-averaged Raman peak intensity by optical phonons in Si and GaN crystals. The SAW-induced modifications in the intensity of the Raman lines are dominated by the modulation of the longitudinal optical (LO) phonon energy by the SAW strain field. We show that while the strain field of the excited Rayleigh SAWs changes the LO phonon energy, it does not mix it with the transversal optical modes. In addition to the previous contribution, which is of a local character, the experiments give evidence for a weaker and nonlocal contribution attributed to the spatial variation of the SAW strain field. The latter activates optical modes with large wave vectors and, therefore, lower energies. The experimental results, which are well described by theoretical models for the two contributions, prove that optical phonons can be manipulated by SAWs with μm wavelengths. Hot electron generation by aluminum oligomers in plasmonic ultraviolet photodetectors Department of Electrical and Computer Engineering, Florida International University, 10555 W Flagler St., Miami, Florida 33174, USA Optics Express http://dx.doi.org/10.1364/OE.24.013665

We report on an integrated plasmonic ultraviolet (UV) photodetector composed of aluminum Fano-

resonant heptamer nanoantennas deposited on a Gallium Nitride (GaN) active layer which is grown on a sapphire substrate to generate significant photocurrent via formation of hot electrons by nanoclusters upon the decay of nonequilibrium plasmons. Using the plasmon hybridization theory and finite-difference time-domain (FDTD) method, it is shown that the generation of hot carriers by metallic clusters illuminated by UV beam leads to a large photocurrent. The induced Fano resonance (FR) minimum across the UV spectrum allows for noticeable enhancement in the absorption of optical power yielding a plasmonic UV photodetector with a high responsivity. It is also shown that varying the thickness of the oxide layer (Al2O3) around the nanodisks (tox) in a heptamer assembly adjusted the generated photocurrent and responsivity. The proposed plasmonic structure opens new horizons for designing and fabricating efficient opto-electronics devices with high gain and responsivity. HgNO3 sensitivity of AlGaN/GaN field effect transistors functionalized with phytochelating peptides Department of Materials Science and Engineering, North Carolina State University, 1001 Capability Drive Raleigh, North Carolina 27606, USA AIP Advances http://dx.doi.org/10.1063/1.4953806

This study examined the conductance sensitivity of AlGaN/GaN field effect transistors in response to varying Hg/HNO3 solutions. FET surfaces were covalently functionalized with phytochelatin-5 peptides in order to detect Hg in solution. Results showed a resilience of peptide-AlGaN/GaN bonds in the presence of strong HNO3 aliquots, with significant degradation in FET ID signal. However, devices showed strong and varied response to Hg concentrations of 1, 10, 100, and 1000 ppm. The gathered statistically significant results indicate that peptide terminated AlGaN/GaN devices are

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capable of differentiating between Hg solutions and demonstrate device sensitivity. Laterally vibrating resonator based elasto-optic modulation in aluminum nitride Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA APL Photonics http://dx.doi.org/10.1063/1.4945356

An integrated strain-based optical modulator driven by a piezoelectric laterally vibrating resonator is demonstrated. The composite structure consists of an acoustic Lamb wave resonator, in which a photonic racetrack resonator is internally embedded to enable overlap of the guided optical mode with the induced strain field. Both types of resonators are defined in an aluminum nitride (AlN) thin film, which rests upon a layer of silicon dioxide in order to simultaneously define optical waveguides, and the structure is released from a silicon substrate. Lateral vibrations produced by the acoustic resonator are transferred through a partially etched layer of AlN, producing a change in the effective index of the guided wave through the interaction of the strain components with the AlN elasto-optic (p) coefficients. Optical modulation through the elasto-optic effect is demonstrated at electromechanically actuated frequencies of 173 MHz and 843 MHz. This device geometry further enables the development of MEMS-based optical modulators in addition to studying elasto-optic interactions in suspended piezoelectric thin films. Impact of layer and substrate properties on the surface acoustic wave velocity in scandium doped aluminum nitride based SAW devices on sapphire Institute of Sensor and Actuator Systems, TU Wien, 1040 Vienna, Austria Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4953259

This paper investigates the performance of surface acoustic wave (SAW) devices consisting of reactively sputter deposited scandium doped aluminum nitride (ScxAl1-xN) thin films as

piezoelectric layers on sapphire substrates for wireless sensor or for RF-MEMS applications. To investigate the influence of piezoelectric film thickness on the device properties, samples with thickness ranging from 500 nm up to 3000 nm are fabricated. S 21 measurements and simulations demonstrate that the phase velocity is predominantly influenced by the mass density of the electrode material rather than by the thickness of the piezoelectric film. Additionally, the wave propagation direction is varied by rotating the interdigital transducer structures with respect to the crystal orientation of the substrate. The phase velocity is about 2.5% higher for a-direction compared to m-direction of the sapphire substrate, which is in excellent agreement with the difference in the anisotropic Young's modulus of the substrate corresponding to these directions. Piezoelectric tuning of narrowband perfect plasmonic absorbers via an optomechanic cavity School of Optics and Electronic Information, Huazhong University of Science and Technology, Whuan 430074, China Optics Letters http://dx.doi.org/10.1364/OL.41.002803

Optical antennas enable the control of light–matter interaction on the nanometer scale. Efficient on-chip electrical switching of plasmonic resonances is a crucial step toward the integration of optical antennas into practical optoelectronic circuits. We propose and numerically investigate the on-chip low-voltage linear electrical tuning of a narrowband optical antenna perfect absorber via a piezoelectric optomechanic cavity. Near unity absorption is realized by an array of gold nanostrip antennas separated from a membrane-based deformable backreflector by a small gap. A narrow linewidth of 33 nm at 2.58 μm is realized through the coupling between the plasmonic mode and photonic mode in the cavity-enhanced antenna structure. An aluminum nitride piezoelectric layer enabled efficient actuation of the backreflector and therefore changed the gap size, allowing for the tuning of the spectral absorption. The peak wavelength can be shifted linearly by 250 nm with 10 V of tuning voltage,

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and the tuning range is not limited by the pull-in effect. The polarization dependence of the nanostrip antenna coupled with the optomechanic cavity allows the use of our device as a voltage tunable polarization control device. [GaN(Mg)-Cs]:[O-Cs] model for the Negative Electron Affinity GaN (0001) surface School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China Optik - International Journal for Light and Electron Optics http://dx.doi.org/10.1016/j.ijleo.2016.05.140

Because of the limitations of the existing Negative Electron Affinity (NEA) photocathode surface emission models, [GaN(Mg)-Cs]:[O-Cs] photoemission model based on dual-dipole model is established, which can explain the photoemission mechanism of the NEA GaN photocathode well. Cs, O adsorption process on the GaN (0001) surface during the activation is discussed, and the GaN(Mg)-Cs dipole layer is found having a unified direction which is conducive for photoelectron escaping, so photocurrent has a significant increase when Cs is introduced. There is not a unified direction for the O-Cs dipole layer. Because of the surface defects, part of the O-Cs dipoles have the direction which is conducive for photoelectron escaping, and the photocurrent has a modest growth after introducing O. Finally, the performance of GaN and GaAs photocathode are compared based on the photoemission model, and the reason of better stability of NEA GaN photocathode is interpreted. Memristive GaN ultrathin suspended membrane array National Research and Development Institute in Microtechnology, Str. Erou Iancu Nicolae 126A, Bucharest 077190, Romania Nanotechnology http://dx.doi.org/10.1088/0957-4484/27/29/295204

We show that ultrathin GaN membranes, with a thickness of 15 nm and planar dimensions of 12 × 184 μm2, act as memristive devices. The

memristive behavior is due to the migration of the negatively-charged deep traps, which form in the volume of the membrane during the fabrication process, towards the unoccupied surface states of the suspended membranes. The time constant of the migration process is of the order of tens of seconds and varies with the current or voltage sweep. Loss reduction of leaky surface acoustic wave by loading with high-velocity thin film Graduate Faculty of Interdisciplinary Research, University of Yamanashi, Kofu 400-8511, Japan Japanese Journal of Applied Physics http://dx.doi.org/10.7567/JJAP.55.07KD11

The propagation properties of a leaky surface acoustic wave (LSAW) on rotated Y-cut X-propagating lithium niobate (YX-LN) substrates loaded with an aluminum nitride (AlN) thin film with a higher phase velocity than that of the substrate were investigated theoretically and experimentally. From the theoretical calculation, it was found that the minimum attenuation can be obtained at a certain thickness of the AlN thin film for a cut angle ranging from 0 to 60° because the cut angle giving the minimum attenuation shifts toward a smaller cut angle as the film thickness is increased. The propagation properties of an LSAW on several rotated YX-LN substrates were measured by using an interdigital transducer (IDT) pair with a wavelength λ of 8 µm, and the predicted shifts of the minimum attenuation toward a smaller cut angle were demonstrated experimentally. For 0° and 10°YX-LN samples, the measured insertion loss and propagation loss were markedly reduced by loading with the AlN thin film. A larger electromechanical coupling factor (16.9%) than that at the cut angle giving zero attenuation without a film and a propagation loss less of 0.02 dB/λ were obtained simultaneously at a film thickness of 0.125 λ for the 10°YX-LN sample. AlScN thin film based surface acoustic wave devices with enhanced microfluidic performance College of Information Science and Electronic Engineering, Zhejiang University and Cyrus Tang Centre for Sensor Materials and Applications, 38 Zheda Road, Hangzhou 310027, People's Republic of China

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Faculty of Engineering and Environment, University of Northumbria, Newcastle upon Tyne, NE1 8ST, UK School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK Journal of Micromechanics and Microengineering http://dx.doi.org/10.1088/0960-1317/26/7/075006

This paper reports the characterization of scandium aluminum nitride (Al1−x Sc x N, x  =  27%) films and discusses surface acoustic wave (SAW) devices based on them. Both AlScN and AlN films were deposited on silicon by sputtering and possessed columnar microstructures with (0 0 0 2) crystal orientation. The AlScN/Si SAW devices showed improved electromechanical coupling coefficients (K 2, ~2%) compared with pure AlN films (<0.5%). The performance of the two types of devices was also investigated and compared, using acoustofluidics as an example. The AlScN/Si SAW devices achieved much lower threshold powers for the acoustic streaming and pumping of liquid droplets, and the acoustic streaming and pumping velocities were 2  ×  and 3  ×  those of the AlN/Si SAW devices, respectively. Mechanical characterization showed that the Young's modulus and hardness of the AlN film decreased significantly when Sc was doped, and this was responsible for the decreased acoustic velocity and resonant frequency, and the increased temperature coefficient of frequency, of the AlScN SAW devices. Suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells Grünberg Research Centre, Nanjing University of Posts and Telecommunications, Nanjing 210003, China Optical Materials Express http://dx.doi.org/10.1364/OME.6.002366

In this paper, we report on the fabrication and characterization of a suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells (MQWs) on a GaN-on-silicon platform. Both silicon removal and back wafer etching are conducted to achieve the suspended waveguide photodetector combination. The light illumination measurements

experimentally demonstrate that the metallization stacks can serve as the bottom metal mirror to reflect the incoming light back for re-absorption, leading to an improved photocurrent response. The out-of-plane light can couple into the suspended waveguide and propagate as a confined optical mode, resulting in an induced photocurrent. The photodetector exhibits two operation modes. The peak values of the responsivity spectra for the suspended waveguide photodetector are located around 401 nm at 3 V bias and 435 nm at 0 V bias, respectively. These results pave a promising way to develop the suspended waveguide photodetector for diverse applications in the visible wavelength region. Graphene–aluminum nitride NEMS resonant infrared detector Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, USA Microsystems & Nanoengineering http://dx.doi.org/10.1038/micronano.2016.26

The use of micro-/nanoelectromechanical resonators for the room temperature detection of electromagnetic radiation at infrared frequencies has recently been investigated, showing thermal detection capabilities that could potentially outperform conventional microbolometers. The scaling of the device thickness in the nanometer range and the achievement of high infrared absorption in such a subwavelength thickness, without sacrificing the electromechanical performance, are the two key challenges for the implementation of fast, high-resolution micro-/nanoelectromechanical resonant infrared detectors. In this paper, we show that by using a virtually massless, high-electrical-conductivity, and transparent graphene electrode, floating at the van der Waals separation of a few angstroms from a piezoelectric aluminum nitride nanoplate, it is possible to implement ultrathin (460 nm) piezoelectric nanomechanical resonant structures with improved electromechanical performance (>50% improved frequency×quality factor) and infrared detection capabilities (>100× improved infrared absorptance) compared with metal-electrode counterparts, despite their reduced

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volumes. The intrinsic infrared absorption capabilities of a submicron thin graphene–aluminum nitride plate backed with a metal electrode are investigated for the first time and exploited for the first experimental demonstration of a piezoelectric nanoelectromechanical resonant thermal detector with enhanced infrared absorptance in a reduced volume. Moreover, the combination of electromagnetic and piezoelectric resonances provided by the same graphene–aluminum nitride-metal stack allows the proposed device to selectively detect short-wavelength infrared radiation (by tailoring the thickness of aluminum nitride) with unprecedented electromechanical performance and thermal capabilities. These attributes potentially lead to the development of uncooled infrared detectors suitable for the implementation of high performance, miniaturized and power-efficient multispectral infrared imaging systems. Highly selective and sensitive phosphate anion sensors based on AlGaN/GaN high electron mobility transistors functionalized by ion imprinted polymer Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, P. R. China Scientific Reports http://dx.doi.org/10.1038/srep27728

A novel ion-imprinted electrochemical sensor based on AlGaN/GaN high electron mobility transistors (HEMTs) was developed to detect trace amounts of phosphate anion. This sensor combined the advantages of the ion sensitivity of AlGaN/GaN HEMTs and specific recognition of ion imprinted polymers. The current response showed that the fabricated sensor is highly sensitive and selective to phosphate anions. The current change exhibited approximate linear dependence for phosphate concentration from 0.02 mg L−1 to 2 mg L−1, the sensitivity and detection limit of the sensor is 3.191 μA/mg L−1 and 1.97 μg L−1, respectively. The results indicated that this AlGaN/GaN HEMT-based electrochemical sensor has the potential applications on phosphate anion detection.

Enhanced Hydrogen Detection Sensitivity of Semipolar (112¯2)(112¯2) GaN Schottky Diodes by Surface Wet Etching on Schottky Contact Department of Chemical Engineering, Dankook University, Yongin 448-701, Korea J. Electrochem. Soc. http://dx.doi.org/10.1149/2.1161608jes

We report on the enhanced hydrogen sensing characteristics of surface-etched Pt Schottky diodes fabricated on semipolar (112¯2)(112¯2) GaN films using photo-electrochemical wet etching. The surface-etched Pt Schottky diodes showed a rapid sensing response to 4% hydrogen, as well as a full recovery to their initial current level after removing the hydrogen from the ambient. They also demonstrated stable and reproducible current changes with a reasonable linearity in response to H2 concentrations of 0.5∼4% in increments of 0.5%. The hydrogen sensitivity of Pt Schottky diodes on semipolar (112¯2)(112¯2) GaN could therefore be improved by incorporating surface etching on the Schottky contact area using KOH solutions. This rough surface is expected to improve hydrogen detection sensitivity due to the presence of more available adsorption sites, resulting in effective variations of the Schottky barrier height.

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GROUP 6 - Photovoltaics and Energy harvesting Group leader: Eva Monroy (INAC-CEA)

Information selected by Knowmade

Analysis of loss mechanisms in InGaN solar cells using a semi-analytical model School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4953006

InGaN semiconductors are promising candidates for high-efficiency next-generation thin film solar cells. In this work, we study the photovoltaic performance of single-junction and two-junction InGaN solar cells using a semi-analytical model. We analyze the major loss mechanisms in InGaN solar cell including transmission loss, thermalization loss, spatial relaxation loss, and recombination loss. We find that transmission loss plays a major role for InGaN solar cells due to the large bandgaps of III-nitride materials. Among the recombination losses, Shockley-Read-Hall recombination loss is the dominant process. Compared to other III-V photovoltaic materials, we discovered that the emittance of InGaN solar cells is strongly impacted by Urbach tail energy. For two- and multi-junction InGaN solar cells, we discover that the current matching condition results in a limited range of top-junction bandgaps. This theoretical work provides detailed guidance for the design of high-performance InGaN solar cells. Enhanced water splitting with silver decorated GaN photoelectrode Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK Journal of Physics D: Applied Physics http://dx.doi.org/10.1088/0022-3727/49/26/265601

By means of a cost-effective approach, we demonstrate a GaN-based photoelectrode decorated with self-organized silver nano-islands employed for solar powered hydrogen generation, demonstrating 4 times increase in photocurrent compared with a reference sample without using

any silver. Our photoelectrode exhibits a 60% incident photon-to-electron conversion efficiency. The enhanced hydrogen generation is attributed to a significantly increased carrier generation rate as a result of strongly localized electric fields induced by surface plasmon coupling effect. The silver coating also contributes to the good chemical stability of our photoelectrode in a strong alkali electrolyte. This work paves the way for the development of GaN and also InGaN based photoelectrodes with ultra-high solar hydrogen conversion efficiency. Optical transitions in GaNAs quantum wells with variable nitrogen content embedded in AlGaAs International Center for Young Scientists, National Institute for Materials Science, 305-0047 Tsukuba, Japan AIP Advances http://dx.doi.org/10.1063/1.4953894

We investigate the optical transitions of GaN xAs1−x quantum wells (QWs) embedded in wider band gap AlGaAs. A combination of absorption and emission spectroscopic techniques is employed to systematically investigate the properties of GaNAs QWs with N concentrations ranging from 0 – 3%. From measurement of the photocurrent spectra, we find that besides QW ground state and first excited transition, distinct increases in photocurrent generation are observed. Their origin can be explained by N-induced modifications in the density of states at higher energies above the QW ground state. Photoluminescence experiments reveal that peak position dependence with temperature changes with N concentration. The characteristic S-shaped dependence for low N concentrations of 0.5% changes with increasing N concentration where the low temperature red-shift of the S-shape gradually disappears. This change indicates a gradual transition from impurity picture, where localized N induced energy states are present, to alloying picture, where an impurity-band is formed. In the highest-N sample,

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photoluminescence emission shows remarkable temperature stability. This phenomenon is explained by the interplay of N-induced energy states and QW confined states. Limiting factors on the semiconductor structure of III–V multijunction solar cells for ultra-high concentration (1000–5000 suns) Instituto de Energía Solar, Universidad Politécnica de Madrid, Madrid, Spain Progress in Photovoltaics: Research and Applications http://dx.doi.org/10.1002/pip.2791

The main limiting factors of multijunction solar cells operating under ultra-high concentration (>1000 suns) are examined by means of 2D physically based numerical modelling. The validation of the model is carried out by fitting calibrated light concentration measurements. Because the series resistance is the most important constraint in the electrical performance of the solar cell under ultra-high irradiance, it is analysed and quantified detailing different contributions such as: (i) the electrical properties of the emitter; (ii) window layer of the top cell; and (iii) the band discontinuities formed at heterojunctions. We found the role of window layer to be important at very high concentrations (above 700 suns), while at ultra-high concentrations, (above 1000 suns) a gain in efficiency (~ 1% absolute) can be obtained by a proper structural design of the window layer. In the case of the heterojunctions included in the multijunction solar cell, the impact of a high-band offset can be mitigated by increasing the doping level density thus favouring the tunnelling effect. Moreover, the influence of different recombination mechanisms and high-injection effects at ultra-high irradiance is discussed. Finally, an optimisation of the complete solar cell taking into account the ohmic contacts to work under ultra-high irradiances (from 1000 to 5000 suns) is presented as well as the implications on the use of ultra-high irradiance in different multijunction solar cell architectures.

Efficiency Enhancement of InGaN-Based Solar Cells via Stacking Layers of Light-Harvesting Nanospheres King Abdullah University of Science & Technology (KAUST), Computer, Electrical and Mathematical Sciences and Engineering Division, Thuwal, 23955-6900, Saudi Arabia Scientific Reports http://dx.doi.org/10.1038/srep28671

An effective light-harvesting scheme for InGaN-based multiple quantum well solar cells is demonstrated using stacking layers of polystyrene nanospheres. Light-harvesting efficiencies on the solar cells covered with varied stacks of nanospheres are evaluated through numerical and experimental methods. The numerical simulation reveals that nanospheres with 3 stacking layers exhibit the most improved optical absorption and haze ratio as compared to those obtained by monolayer nanospheres. The experimental demonstration, agreeing with the theoretical analyses, shows that the application of 3-layer nanospheres improves the conversion efficiency of the solar cell by ~31%.

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GROUP 7 - Materials, Technology and Fundamental Group leader: Jean-Christophe Harmand (LPN-CNRS)

NANO

Information selected by Jesús Zúñiga Pérez (CRHEA-CNRS)

Piezotronic Effect Modulated Heterojuction Electron Gas in AlGaN/AlN/GaN Heterostructure Microwire School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, Guangdong Engineering Technology Research Center of Optoelectronic Functional Materials and Devices, Institute of Optoelectronic Materials and Technology, South China Normal University, Guangzhou, China Advanced Materials http://dx.doi.org/10.1002/adma.201601721

The piezotronic effect is applied to modulate the physical properties of heterojunction electron gas and thus tune the electric transport in AlGaN/AlN/GaN heterostructure microwires. At room temperature, the conductance is increased by 165% under −1.78% compressive strains, and reduced by 48% under 1.78% tensile strains; at 77 K, this modulating effect is further improved by 890% and 940% under compressive and tensile strains, respectively. Direct Growth of High-Power InGaN/GaN Quantum-Disks-in-Nanowires Red Light-Emitting Diodes on Polycrystalline Molybdenum Substrates King Abdullah University of Science and Technology, Saudi Arabia Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_SI.2016.STu3R.8

The first high-power InGaN/GaN quantum-disks-in-nanowires red (λ=705 nm) light-emitting diodes on metal substrates was demonstrated. The low turn-on voltage and high power were achieved through the direct growth of high-quality nanowires on TiN/Ti/Mo stack.

Nucleation and core-shell formation mechanism of self-induced InxAl1−xN core-shell nanorods grown on sapphire substrates by magnetron sputter epitaxy Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden Vacuum http://dx.doi.org/10.1016/j.vacuum.2016.05.022

Nucleation of self-induced InxAl1−xN nanorod and core-shell structure formation by surface-induced phase separation have been studied at the initial growth stage. The growth of well-separated core-shell nanorods is only found in a transition temperature region (600 °C ≤ T ≤ 800 °C) in contrast to the result of thin film growth outside this region (T < 600 °C or T > 800 °C). Formation of multiple compositional domains, due to phase separation, after ∼20 nm InxAl1−xN epilayer growth from sapphire substrate promotes the core-shell nanorod growth, showing a modified Stranski-Krastanov growth mode. The use of VN seed layer makes the initial growth of the nanorods directly at the substrate interface, revealing a Volmer-Weber growth mode. Different compositional domains are found on VN template surface to support that the phase separation takes place at the initial nucleation process and forms by a self-patterning effect. The nanorods were grown from In-rich domains and initiated the formation of core-shell nanorods due to spinodal decomposition of the InxAl1−xN alloy with a composition in the miscibility gap. Selective-area growth of GaN nanowires on SiO2-masked Si (111) substrates by molecular beam epitaxy Department of Physics, University of Crete, P. O. Box 2208, 71003 Heraklion, Greece Institute of Electronic Structure and Laser, Foundation for Research and Technology–Hellas, N. Plastira 100, 70013 Heraklion, Greece Max-Planck-Institut für Eisenforschung, Max-Planck-Straße 1, 40237 Düsseldorf, Germany

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J. Appl. Phys. http://dx.doi.org/10.1063/1.4953594

We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO2 mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm. Selective Area Growth and Characterization of GaN Nanorods Fabricated by Adjusting the Hydrogen Flow Rate and Growth Temperature with Metal Organic Chemical Vapor Deposition Research and Development Center for Semiconductor Lighting, Chinese Academy of Sciences, Beijing 100083 Schools of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 State Key Laboratory of Solid State Lighting, Chinese Academy of Sciences, Beijing 100083 Chinese Physics Letters http://dx.doi.org/10.1088/0256-307X/33/6/068101

GaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen (H2)/nitrogen (N2) and growth temperature of the selective area growth (SAG) method with metal

organic chemical vapor deposition (MOCVD). The SAG template is obtained by nanospherical-lens photolithography. It is found that increasing the flow rate of H2 will change the GaN crystal shape from pyramid to vertical rod, while increasing the growth temperature will reduce the diameters of GaN rods to nanometer scale. Finally the GaN nanorods with smooth lateral surface and relatively good quality are obtained under the condition that the H2:N2 ratio is 1:1 and the growth temperature is 1030°C. The good crystal quality and orientation of GaN nanorods are confirmed by high resolution transmission electron microscopy. The cathodoluminescence spectrum suggests that the crystal and optical quality is also improved with increasing the temperature. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions ISOM-ETSIT, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4954742

Series of GaN nanowires (NW) with controlled diameters (160–500 nm) and heights (420–1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In

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addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established. Horizontally assembled green InGaN nanorod LEDs: scalable polarized surface emitting LEDs using electric-field assisted assembly Department of Chemistry, Kookmin University, Seoul 136-702, Korea Scientific Reports http://dx.doi.org/10.1038/srep28312

In this study, we report the concerted fabrication process, which is easy to transform the size of active emitting area and produce polarized surface light, using the electric-field-assisted assembly for horizontally assembled many tiny nanorod LEDs between two metal electrodes. We fabricate the millions of individually separated 1D nanorod LEDs from 2D nanorod arrays using nanosphere lithography, etching and cutting process of InGaN/GaN LED structure on a flat sapphire substrate. The horizontally assembled InGaN-based nanorods LED device shows bright (~2,130 cd/m2) and uniform polarized (polarization ratio, ρ = ~0.61) green emissions from large area (0.7 cm × 0.6 cm) planar surface. The realization of a horizontally assembled nanorod LED device can prove the concept of an innovative idea to fabricate formable and scalable polarized surface LED lighting.

NON/SEMI POLAR Information selected by

Philippe De Mierry (CRHEA-CNRS) Investigation of Semi-Polar GaN Grown on (0001) C-plane Nano-Sized Patterned-Sapphire Substrates National Taiwan University, United States Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_AT.2016.JTh2A.78

This paper reported the growth of semi-polar GaN epi-layers on (0001) c-plane nano-sized patterned-sapphire substrates (c-NPSSs). In addition, the impact of c-NPSSs on the quality of semi-polar film had also been studied.

Analysis of low efficiency droop of semipolar InGaN quantum well light-emitting diodes by modified rate equation with weak phase-space filling effect School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287, U.S.A. AIP Advances http://dx.doi.org/10.1063/1.4954296

We study the low efficiency droop characteristics of semipolar InGaN light-emitting diodes (LEDs) using modified rate equation incoporating the phase-space filling (PSF) effect where the results on c-plane LEDs are also obtained and compared. Internal quantum efficiency (IQE) of LEDs was simulated using a modified ABC model with different PSF filling (n0), Shockley-Read-Hall (A), radiative (B), Auger (C) coefficients and different active layer thickness (d), where the PSF effect showed a strong impact on the simulated LED efficiency results. A weaker PSF effect was found for low-droop semipolar LEDs possibly due to small quantum confined Stark effect, short carrier lifetime, and small average carrier density. A very good agreement between experimental data and the theoretical modeling was obtained for low-droop semipolar LEDs with weak PSF effect. These results suggest the low droop performance may be explained by different mechanisms for semipolar LEDs. Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells School of Physics and Astronomy, Photon Science Institute, University of Manchester, M13 9PL Manchester, United Kingdom Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4954236

We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 1011 cm−2 pulse−1 per quantum well; also

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both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density. Chemically assisted ion beam etching of laser diode facets on nonpolar and semipolar orientations of GaN Materials Department, University of California, Santa Barbara, CA 93106, USA Semiconductor Science and Technology http://dx.doi.org/10.1088/0268-1242/31/7/075008

We demonstrate a vertical (<1° departure) and smooth (2.0 nm root mean square line-edge roughness (LER)) etch by chemically assisted Ar ion beam etching (CAIBE) in Cl2 chemistry that is suitable for forming laser diode (LD) facets on nonpolar and semipolar oriented III-nitride devices. The etch profiles were achieved with photoresist masks and optimized CAIBE chamber conditions including the platen tilt angle and Cl2 flow rate. Co-loaded studies showed similar etch rates of ~60 nm min−1 for (20-2-1), (20-21), and m-plane orientations. The etched surfaces of LD facets on these orientations are chemically dissimilar (Ga-rich versus N-rich), but were visually indistinguishable, thus confirming the negligible orientation dependence of the etch. Continuous-wave blue LDs were fabricated on the semipolar (20-2-1) plane to compare CAIBE and reactive ion etch (RIE) facet processes. The CAIBE process resulted in LDs with lower threshold current densities due to reduced parasitic mirror loss compared with the RIE process. The LER, degree of verticality, and model of the 1D vertical laser mode were used to calculate a maximum uncoated facet reflection of 17% (94% of the nominal) for the CAIBE facet. The results demonstrate the suitability of CAIBE for forming high quality facets for high performance nonpolar and semipolar III-N LDs.

Improved Semipolar (11bar 22) GaN Quality Grown on m-Plane Sapphire Substrates by Metal Organic Chemical Vapor Deposition Using Self-Organized SiN x Interlayer Key Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi'an 710071 Chinese Physics Letters http://dx.doi.org/10.1088/0256-307X/33/6/068102

The effect of a self-organized SiNx interlayer on the defect density of (11bar 22) semipolar GaN grown on m-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffraction. The SiNx interlayer reduces the c-type dislocation density from 2.5 × 1010 cm−2 to 5 × 108 cm−2. The SiNx interlayer produces regions that are free from basal plane stacking faults (BSFs) and dislocations. The overall BSF density is reduced from 2.1 × 105 cm−1 to 1.3 × 104 cm−1. The large dislocations and BSF reduction in semipolar (11bar 22) GaN with the SiNx interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of (11bar 22) semipolar GaN. Enhanced Hydrogen Detection Sensitivity of Semipolar (112¯2)(112¯2) GaN Schottky Diodes by Surface Wet Etching on Schottky Contact Department of Chemical Engineering, Dankook University, Yongin 448-701, Korea J. Electrochem. Soc. http://dx.doi.org/10.1149/2.1161608jes

We report on the enhanced hydrogen sensing characteristics of surface-etched Pt Schottky diodes fabricated on semipolar (112¯2)(112¯2) GaN films using photo-electrochemical wet etching. The surface-etched Pt Schottky diodes showed a rapid sensing response to 4% hydrogen, as well as a full recovery to their initial current level after removing the hydrogen from the ambient. They also demonstrated stable and reproducible current changes with a reasonable linearity in response to H2 concentrations of 0.5∼4% in increments of 0.5%. The hydrogen

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sensitivity of Pt Schottky diodes on semipolar (112¯2)(112¯2) GaN could therefore be improved by incorporating surface etching on the Schottky contact area using KOH solutions. This rough surface is expected to improve hydrogen detection sensitivity due to the presence of more available adsorption sites, resulting in effective variations of the Schottky barrier height. Room temperature observation of trapped exciton-polariton emission in GaN/AlGaN microcavities with air-gap/III-nitride distributed Bragg reflectors Institute of Industrial Science and ‡Institute for Nano Quantum Information Electronics, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8505, Japan ACS Photonics http://dx.doi.org/10.1021/acsphotonics.6b00003

We demonstrate trapped exciton-polariton emission at room temperature from non-polar GaN/AlGaN cavities sandwiched between air/AlGaN distributed Bragg reflectors. Nanoscale thickness fluctuations characteristic to the non-polar AlGaN cavity layer create deep potential traps, giving rise to a strong (in-plane) localization of exciton-polaritons. The observed quantized exciton-polariton states exhibit a large quantized energy of up to 6 meV, which benefits from the wide bandgap of III-nitrides. The experimental results are well explained by numerical simulations. III-nitride exciton-polaritons in such deep traps will be useful for practical exciton-polariton lasers with high degrees of coherence, and high-repetition rate Josephson oscillators with multi-component condensates. In situ asymmetric island sidewall growth of high-quality semipolar (11[2 with combining macron]2) GaN on m-plane sapphire Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices,, Department of Physics, Xiamen University, Xiamen 361005, China CrystEngComm http://dx.doi.org/10.1039/C6CE00878J

In situ asymmetric island sidewall growth (AISG) was developed to enhance Ga-face facet growth

and improve the crystalline quality of (11[2 with combining macron]2) GaN epilayers on m-plane sapphire substrates. In the early growth stage island shaping and sidewall faceting were distinct and controlled by growth design. Using in situ AISG, {0002} instead of {[1 with combining macron]103} sidewall facets were formed on the Ga-rich island surface, which eliminated formation of a {[1 with combining macron]103} phase during subsequent layer growth of semipolar GaN. Enhanced Ga-face sidewall facet growth led to +c regions overlapping −c regions, which reduced defect density. Pure semipolar (11[2 with combining macron]2) epilayers with a reduced surface striation density and a basal-plane stacking fault density of 8 × 103 cm−1 were obtained. The observation of a narrow EH2 peak and an intense E1(LO) peak in Raman spectra indicates that almost strain-free high-quality semipolar (11[2 with combining macron]2) GaN films were achieved. The photoluminescence emission intensity from the (11[2 with combining macron]2) GaN film prepared by in situ AISG was dominated by band-edge emission and enhanced ∼4 times more than that from conventional (11[2 with combining macron]2) GaN.

OTHER (fundamental, material, characterization, equipment)

Information selected by Agnès Trassoudaine (Université d'Auvergne)

and Yvon Cordier (CRHEA-CNRS)

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films Department of Electrical Engineering and Automation, Aalto University, P.O. Box 13500, FIN-00076 Aalto, Espoo, Finland Department of Micro- and Nanosciences, Aalto University, P.O. Box 13500, FIN-00076 Aalto, Espoo, Finland J. Vac. Sci. Technol. A http://dx.doi.org/10.1116/1.4953029

Plasma-enhanced atomic layer deposition was utilized to grow aluminum nitride (AlN) films on Si from trimethylaluminum and N2:H2 plasma at 200 °C. Thermal treatments were then applied on

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the films which caused changes in their chemical composition and nanostructure. These changes were observed to manifest in the refractive indices and densities of the films. The AlN films were identified to contain light element impurities, namely, H, C, and excess N due to nonideal precursor reactions. Oxygen contamination was also identified in the films. Many of the embedded impurities became volatile in the elevated annealing temperatures. Most notably, high amounts of H were observed to desorb from the AlN films. Furthermore, dinitrogen triple bonds were identified with infrared spectroscopy in the films. The triple bonds broke after annealing at 1000 °C for 1 h which likely caused enhanced hydrolysis of the films. The nanostructure of the films was identified to be amorphous in the as-deposited state and to become nanocrystalline after 1 h of annealing at 1000 °C. Characterization of capture cross sections of interface states in dielectric/III-nitride heterojunction structures Research Center for Integrated Quantum Electronics, Hokkaido University, Kita-13 Nishi-8, Kita-ku, 060-8628 Sapporo, Japan Surface Physics and Nanostructures Department, Institute of Physics-CND, Silesian University of Technology, Konarskiego 22B, 44-100 Gliwice, Poland J. Appl. Phys. http://dx.doi.org/10.1063/1.4952708

We performed, for the first time, quantitative characterization of electron capture cross sections σ of the interface states at dielectric/III-N heterojunction interfaces. We developed a new method, which is based on the photo-assisted capacitance-voltage measurements using photon energies below the semiconductor band gap. The analysis was carried out for AlGaN/GaN metal-insulator-semiconductor heterojunction (MISH) structures with Al 2O3, SiO2, or SiN films as insulator deposited on the AlGaN layers with Al content (x) varying over a wide range of values. Additionally, we also investigated an Al 2O3/InAlN/GaN MISH structure. Prior to insulator deposition, the AlGaN and InAlN surfaces were subjected to different treatments. We found that σ for all these structures lies in the range between

5×10−195×10−19 and 10−1610−16 cm2. Furthermore, we revealed that σ for dielectric/AlxGa1− xN interfaces increases with increasing x. We showed that both the multiphonon-emission and cascade processes can explain the obtained results. Site-controlled crystalline growth of InN on GaN substrate and its photoluminscence National Chiao Tung University, Taiwan Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_AT.2016.JTh2A.85

We report a site-controlled growth of InN on a GaN substrate. Crystalline InN micropillars were selectively grown from the hexagonal V-pits on GaN surface. The grown mechanism and photoluminescent property will be discussed. Terahertz Magnetospectroscopy Studies of an AlGaN/GaN Heterostructure The University of Manchester, United Kingdom Conference on Lasers and Electro-Optics http://dx.doi.org/10.1364/CLEO_SI.2016.SM3L.2

A laboratory based terahertz cyclotron resonance spectrometer is used to determine 2D electron gas parameters in a GaN/AlGaN heterotructure. The modified ASOPS system acquires ~100 terahertz-traces under a 14 ms long multi-Tesla magnetic field pulse. Structure and chemistry of aluminum predose layers in AlN epitaxy on (111) silicon Department of Materials Science and Engineering, University of California, Davis, USA Acta Materialia http://dx.doi.org/10.1016/j.actamat.2016.05.036

In this study, (111) silicon substrates were exposed to varied trimethylaluminum predoses and ammonia using metalorganic chemical vapor deposition and the resulting deposits were examined using AFM, SEM, TEM, STEM, EDXS, and XPS. Growth patches were observed with facets in the both the vertical and lateral directions. The width of these patches increased with increasing total volume of deposited aluminum. Their

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structure was found to be diamond cubic silicon with dilute concentrations of aluminum. Small, rounded AlN islands were observed on the surface of these patches which had electron diffraction patterns consistent with both strained wurtzite and zinc blende structures. A model is proposed in which silicon diffuses into liquid aluminum prior to ammonia exposure and the resulting liquid Al-Si alloy is converted into AlN and silicon upon nitridation. Effects of electronic and nuclear stopping power on disorder induced in GaN under swift heavy ion irradiation CIMAP, Normandie Universite ENSICAEN/CEA/CNRS, 6 Bd Maréchal Juin, 14050 Caen, France Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms http://dx.doi.org/10.1016/j.nimb.2016.05.024

Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm−1, 300 cm−1 and 670 cm−1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm−1 observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).

Formation of InN atomic-size wires by simple N adsorption on the In/Si(111)–(4 × 1) surface Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autónoma de México, Apartado Postal 14, Ensenada Baja California, Codigo Postal 22800, Mexico Applied Surface Science http://dx.doi.org/10.1016/j.apsusc.2016.05.145

We have carried out first principles total energy calculations to study the formation of InN atomic-size wires on the In/Si(111)–(4 × 1) surface. In its most favorable adsorption site, a single N atom forms InN arrangements. The deposit of 0.25 monolayers (MLs) of N atoms, result in the breaking of one of the original In chains and the formation of an InN atomic size wire. Increasing the coverage up to 0.5 ML of N atoms results in the formation of two of those wires. Calculated surface formation energies show that for N-poor conditions the most stable configuration is the original In/Si(111)–(4 × 1) surface with no N atoms. Increasing the N content, and in a reduced range of chemical potential, the formation of an InN wire is energetically favorable. Instead, from intermediate to N-rich conditions, two InN atomic wires are more stable. Projected density of states calculations have shown a trend to form covalent bonds between the Insingle bondp and Nsingle bondp orbitals in these stable models. Diffusion of oxygen in bulk GaN crystals at high temperature and at high pressure Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland Department of Physics, Ivan Franko National University of Lviv, Dragomanova 50, Lviv 79005, Ukraine Journal of Crystal Growth http://dx.doi.org/10.1016/j.jcrysgro.2016.05.037

Experimental studies of diffusion of oxygen in bulk wurtzite-type GaN crystals grown by Halide Vapor Phase Epitaxy (HVPE) are reported. Oxygen concentration profiles were studied in as-grown GaN crystals and also after annealing of crystals at temperatures up to 3400 K and pressures up to 9 GPa. Investigated crystals contained large conical defects i.e. pinholes of significantly higher oxygen concentration (NO=(2–4)×1019 cm−3) than that in the bulk matrix (NO<1×1017 cm−3). The pinholes

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were revealed by a photo-etching method in as-grown and annealed GaN samples. Confocal micro-Raman spectroscopy was applied to measure the profiles of free electron concentration, which directly corresponds to the concentration of oxygen impurity. Lateral scanning across the interfaces between pinholes and matrix in the as-grown HVPE GaN crystals showed sharp step-like carrier concentration profiles. Annealing at high temperature and high pressure resulted in the diffusion blurring of the profiles. Analysis of obtained data allowed for the first time for estimation of oxygen diffusion coefficients DO(T, P). The obtained values of DO(T, P) are anomalously small similarly to the values obtained by Harafuji et al. by molecular dynamic calculations for self-diffusion of nitrogen. Whereas oxygen and nitrogen are on the same sublattice it could explain the similarity of their diffusion coefficients. Valence band offsets of Sc x Ga1−x N/AlN and Sc x Ga1−x N/GaN heterojunctions Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK Journal of Physics D: Applied Physics http://dx.doi.org/10.1088/0022-3727/49/26/265110

The valence band offsets of Sc x Ga1−x N/AlN heterojunctions were measured by x-ray photoelectron spectroscopy (XPS) and were found to increase from 0.42 eV to 0.95 eV as the Sc content x increased from 0 to 0.15. The increase in valence band offset with increasing x is attributed to the corresponding increase in spontaneous polarization of the wurtzite structure. The Sc x Ga1−x N/AlN heterojunction is type I, similar to other III-nitride-based heterojunctions. The data also indicate that a type II staggered heterojunction, which can enhance spatial charge separation, could be formed if Sc x Ga1−x N is grown on GaN. An unambiguous identification of 2D electron gas features in the photoluminescence spectrum of AlGaN/GaN heterostructures Semiconductor Physics & Devices Lab., Raja Ramanna Centre for Advanced Technology, Indore, 452013, Madhya Pradesh, India

Homi Bhabha National Institute, Mumbai, 400094, India Journal of Physics D: Applied Physics http://dx.doi.org/10.1088/0022-3727/49/26/265107

A fast and non-destructive method for probing the true signatures of 2D electron gas (2DEG) states in AlGaN/GaN heterostructures is presented. Two broad features superimposed with interference oscillations are observed in the low temperature photoluminescence (PL) spectrum. The two features are identified as the ground and excited 2DEG states which are confirmed by comparing the PL spectra of as-grown and top barrier layer etched samples. Broad PL features disappear at a certain temperature along with the associated interference oscillations. Furthermore, the two broad PL features depicts specific temperature and excitation intensity dependencies which make them easily distinguishable from the bandedge excitonic or defect related PL features. The presence of strong interference oscillations associated with the 2DEG PL features is explained by considering the localized generation of PL signal at the AlGaN/GaN heterointerface. Finally, a large value of the polarization induced electric field of ~1.01 MV cm−1 is reported from PL measurements for AlGaN/GaN HEMT structures. It became possible only when the true identification of 2DEG features was made possible by the proposed method. Photoexcited carrier trapping and recombination at Fe centers in GaN Department of Materials and Nano Physics, KTH Royal Institute of Technology, Electrum 229, 16440 Kista, Sweden Materials Department, University of California, Santa Barbara, California 93106, USA Kyma Technologies Inc., 8829 Midway West Road, Raleigh, North Carolina 27617, USA Semiconductor Research Center, Wright State University, Dayton, Ohio 45435, USA Air Force Research Laboratory Sensors Directorate, Wright-Patterson AFB, Ohio 45433, USA Wyle Laboratories, Inc., 2601 Mission Point Blvd., Dayton, Ohio 45431, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4953219

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Fe doped GaN was studied by time-resolved photoluminescence (PL) spectroscopy. The shape of PL transients at different temperatures and excitation powers allowed discrimination between electron and hole capture to Fe3+ and Fe2+ centers, respectively. Analysis of the internal structure of Fe ions and intra-ion relaxation rates suggests that for high repetition rates of photoexciting laser pulses the electron and hole trapping takes place in the excited state rather than the ground state of Fe ions. Hence, the estimated electron and hole capture coefficients of 5.5 × 10−8 cm3/s and 1.8 × 10−8 cm3/s should be attributed to excited Fe3+ and Fe2+ states. The difference in electron capture rates determined for high (MHz) and low (Hz) (Fang et al., Appl. Phys. Lett. 107, 051901 (2015)) pulse repetition rates may be assigned to the different Fe states participating in the carrier capture. A weak temperature dependence of the electron trapping rate shows that the potential barrier for the multiphonon electron capture is small. A spectral feature observed at ∼420 nm is assigned to the radiative recombination of an electron in the ground Fe2+ state and a bound hole. Analysis of compositional uniformity in AlxGa1−xN thin films using atom probe tomography and electron microscopy Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, Pennsylvania 15213 J. Vac. Sci. Technol. A http://dx.doi.org/10.1116/1.4953410

Calculated frequency distributions of atom probe tomography reconstructions (∼80 nm field of view) of very thin Al xGa1− xN (0.18 ≤ x ≤ 0.51) films grown via metalorganic vapor phase epitaxy on both (0001) GaN/AlN/SiC and (0001) GaN/sapphire heterostructures revealed homogeneous concentrations of Al and chemically abrupt Al xGa1− xN/GaN interfaces. The results of scanning transmission electron microscopy and selected area diffraction corroborated these results and revealed that neither superlattice ordering nor phase separation was present at nanometer length scales.

Recombination-related properties of a-screw dislocations in GaN: A combined CL, EBIC, TEM study V.A. Fok Institute of Physics, St. Petersburg State University, Russia IRC for Nanotechnology, Research Park, St.-Petersburg State University, Russia AIP Conf. Proc. http://dx.doi.org/10.1063/1.4954345

Cathodoluminescence (CL), electron beam current (EBIC) and transmission electron microscopy (TEM) techniques have been applied to investigate recombination properties and structure of freshly introduced dislocations in low-ohmic GaN crystals. It was confirmed that the only a-screw dislocations exhibited an intense characteristic dislocation-related luminescence (DRL) which persisted up to room temperature and was red-shifted by about 0.3 eV with respect to the band gap energy not only in HVPE but also in MOCVD grown samples. EBIC contrast of the dislocations was found to be temperature independent indicating that the dislocation-related recombination level is situated below 200 meV with respect of conduction band minimum. With the increasing of the magnification of the dislocation TEM cross-sectional images they were found to disappear, probably, due to the recombination enhanced dislocation glide (REDG) under electron beam exposure which was immediately observed in CL investigations on a large scale. The stacking fault ribbon in the core of dissociated a-screw dislocation which form a quantum well for electrons was proposed to play an important role both in DRL spectrum formation and in REDG. Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN Institute of Applied Physics, Technische Universität Braunschweig, Mendelssohnstrasse 2, 38106 Braunschweig, Germany J. Appl. Phys. http://dx.doi.org/10.1063/1.4954289

The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy

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have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection high energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below TGrowth = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth. Overview of band-edge and defect related luminescence in aluminum nitride Physikalisches Institut, Georg-August Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2016.05.055

This review gives the reader an overview of the published results describing near band-edge as well as defect related luminescence in aluminum nitride, also presenting findings from theoretical reports investigating band-structure, intrinsic defects or foreign impurities. Especially in the case of defect related luminescences, the different points of view in the literature are outlined and compared to each other. To facilitate future reference for respective energy transfers, the various assignments to specific emission peaks are presented in neatly arranged tables. Additionally, involved theoretical simulations are summarized in a condensed manner to give a simple view to key features investigated in the particular reports, respectively.

Epitaxy and optical properties of InGaN/GaN multiple quantum wells on GaN hexagonal pyramids template Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, Jiangsu 210093, PR China College of Optoelectronics Engineering, Zaozhuang University, Zaozhuang 277160, PR China Institute of Opto-Electronics, Nanjing University & Yangzhou, Yangzhou 225009, PR China Materials Letters http://dx.doi.org/10.1016/j.matlet.2016.05.174

The InGaN/GaN multiple quantum wells (MQWs) with truncated pyramid structure have been successfully epitaxially grown on the GaN hexagonal pyramids template through a simple and low-cost etch-regrown process. GaN hexagonal pyramids template was contained by a convenient photo-assisted chemical (PAC) etching method. The truncated pyramids are composed of View the MathML source and View the MathML source semi-polar facets as well as (0001) polar facet. It was observed that the InGaN/GaN MQWs substantially emitted broad spectrum with multiple peaks by room temperature photoluminescence (PL). The cathodoluminescence of MQWs red-shifts as the location moves from bottom to top on the facets due to the indium diffusion mechanism. Study of GaN doping with carbon from propane in a wide range of MOVPE conditions Ioffe Institute, 26 Politekhnicheskaya, St. Petersburg 194021, Russian Federation Submicron Heterostructures for Microelectronics, Research & Engineering Center, RAS, 26 Politekhnicheskaya, St Petersburg 194021, Russian Federation Journal of Crystal Growth http://dx.doi.org/10.1016/j.jcrysgro.2016.06.002

Complex studies of intentional GaN carbon doping from propane during MOVPE were performed in a wide range of growth conditions. A strong dependence of carbon doping efficiency on growth rate and ammonia flow is revealed, while dependence of carbon doping efficiency on reactor pressure is small. Atomic force microscopy

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confirms the good quality of the GaN:C layers for doping levels as high as 2*1019 cm−3 grown with growth rate up to 45 μm/h. The dependence of carbon incorporation into GaN is proportional to the propane concentration to the power 3/2 in most growth regimes, but for very high growth rate a linear or sub-linear component of the dependence becomes prominent. Temperature-dependent stress in diamond-coated AlGaN/GaN heterostructures Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10, 162 00 Prague 6, Czech Republic Materials & Design http://dx.doi.org/10.1016/j.matdes.2016.06.006

In this study, we present a complex methodology for evaluation of the thermally induced stress in patterned diamond microstructures. The diamond strips (2 mm in width and 0.78 or 2.8 μm in thickness) were selectively grown on AlGaN/GaN heterostructures. The stress was evaluated from the Raman shift of the diamond peak position within the temperature range from 50 to 400 °C. The shift was measured at two positions, i.e. at center and edge of the strip. The methodology for stress evaluation is based on the appropriate temperature correction of measured Raman spectra. We observed that for temperature increase from 50 to 400 °C the difference between stresses evaluated at the center and edge of diamond strip (Δstress) decreases from 0.27 to 0.18 GPa and from 0.32 to 0.1 GPa for the thinner and thicker diamond films, respectively. Experimental data were compared with FEM simulations. The simulations fitted well to experimental data and confirmed that the stress difference between the center and edge of diamond strip was caused by thermal stress component. As the temperature approaches the value close to the diamond deposition condition (~ 700 °C), the stress becomes homogeneous and equal to the intrinsic stress induced after the diamond growth.

AlN interlayer to improve the epitaxial growth of SmN on GaN (0001) Centre de Recherche sur l’Hétéro-Épitaxie et ses Applications (CRHEA), Centre National de la Recherche Scientifique, Rue Bernard Gregory, 06560 Valbonne, France Journal of Crystal Growth http://dx.doi.org/10.1016/j.jcrysgro.2016.06.006

An in situ study of the epitaxial growth of SmN thin films on Ga-polar GaN (0001) templates by molecular beam epitaxy is reported. Using X-ray photoelectron spectroscopy we found that Ga segregates at the surface during the first stages of growth. We showed that the problem related to Ga surface segregation can be simply suppressed by growing a few monolayers of AlN before starting the SmN growth. This results in a significant improvement of the crystallinity of SmN thin films assessed by X-ray diffraction. Photoluminescence of gallium ion irradiated hexagonal and cubic GaN quantum dots Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum, Germany Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms http://dx.doi.org/10.1016/j.nimb.2016.06.004

We report on ion implantation into GaN QDs and investigate their radiation hardness. The experimental study is carried out by photoluminescence (PL) measurements on molecular beam epitaxy-grown GaN quantum dots after ion implantation. Both quantum dots grown in the hexagonal (H) and the cubic (C) crystal structure were subjected to gallium ions with an energy of 400 kV (H) and 75 kV (C) with fluences ranging from 5×1010 cm−2 to 1×1014 cm−2 (H) and to 1×1015 cm−2 (C), respectively. Low-temperature PL measurements reveal a PL quenching for which a quantitative model as a function of the ion fluence is developed. A high degradation resistance is concluded. A non-radiative trap with one main activation energy is found for all QD structures by temperature-dependent PL measurements. Further analysis of fluence-dependent PL energy shifts shows ion-

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induced intermixing and strain effects. Particular for the hexagonal quantum dots, a strong influence of the quantum confined Stark effect is present. Cross-sectional stress distribution in AlxGa1-xN heterostructure on Si(111) substrate characterized by ion beam layer removal method and precession electron diffraction Department of Materials Physics, Montanuniversität Leoben, Leoben, Austria Materials & Design http://dx.doi.org/10.1016/j.matdes.2016.06.001

A residual stress depth gradient is characterized in a 1.8 μm thick AlN/Al0.25Ga0.75N/GaN/Al0.22Ga0.78N heteroepitaxial structure grown using metallic-organic chemical vapour deposition on Si(111) substrate. The cross-sectional stress profile is evaluated with a step of 100 nm using ion beam layer removal (ILR) method based (i) on a sequential focused ion beam milling of a microcantilever, (ii) on an evaluation of a cantilever bending after every milling step and (iii) on a stress profile recalculation using finite element simulation. The profile shows tensile stress of ~ 1.5 GPa in AlN nucleation layer, stress changing from compressive to tensile in Al0.25Ga0.75N and GaN sublayers and relatively small stresses below 100 MPa in the top Al0.22Ga0.72N sublayer. The stress profile is qualitatively correlated with the results from precession electron diffraction which indicates approximately the same stress behavior. The cross-sectional stress magnitude and variation are interpreted by the mismatches of lattice constants and coefficients of thermal expansion as well as by growth mode changes during Al0.25Ga0.75N and GaN sublayer formation. The approach demonstrates the possibility to resolve nanoscale variation of residual stresses in heteroepitaxial structures using ILR method. Phonon properties and thermal conductivity of GaN nanofilm under prestress and surface/interface stress Department of Engineering Mechanics and Key Laboratory of Soft Machines and Smart Devices of

Zhejiang Province, Zhejiang University, Hangzhou 310027, Zhejiang, China Journal of Alloys and Compounds http://dx.doi.org/10.1016/j.jallcom.2016.05.314

This work investigates the effects of surface/interface stress and prestress fields on phonon thermal conductivity of wurtzite-GaN nanofilms theoretically. The elasticity model is applied to describe the phonon dispersion relations of spatially confined GaN nanofilms. The acoustoelastic effects and surface/interface stress effects are accounted for in calculating the phonon properties and thermal conductivity. Theoretical results show that the prestress and surface/interface stress can alter significantly the phonon properties such as the phonon dispersion relations, resulting in modification of thermal conductivity in GaN nanofilms. In addition, the prestress and surface/interface stress can change the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in controlling the thermal conductivity based on the strain/stress engineering in GaN nanostructures-based electronic devices. Polarization induced three-dimensional hole gas in compositionally graded In x Ga1− x N layer Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, U.S.A. R&TD Center, Tsukuba Plant, LED Materials Department, Mitsubishi Chemical Corporation, Ushiku, Ibaraki 300-1295, Japan Applied Physics Express http://dx.doi.org/10.7567/APEX.9.075502

A polarization-induced three-dimensional hole gas (3DHG) was demonstrated in undoped and compositionally graded In x Ga1− x N layers. All samples were grown on Ga-face bulk GaN substrates by metal organic chemical vapor deposition. A high hole concentration of 2.8 × 1018 cm−3 was obtained in a 100-nm-thick In x Ga1− x N layer where the indium composition was graded from x = 0 to x = 0.2. 3DHG density control by varying the indium composition and thickness

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of a compositionally graded In x Ga1− x N layer was also demonstrated. Vacancy-type defects in Mg-doped GaN grown by ammonia-based molecular beam epitaxy probed using a monoenergetic positron beam Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan J. Appl. Phys. http://dx.doi.org/10.1063/1.4954288

Vacancy-type defects in Mg-doped GaN were probed using a monoenergetic positron beam. GaN films with a thickness of 0.5–0.7 μm were grown on GaN/sapphire templates using ammonia-based molecular beam epitaxy and characterized by measuring Doppler broadening spectra. Although no vacancies were detected in samples with a Mg concentration [Mg] below 7 × 1019 cm−3, vacancy-type defects were introduced starting at above [Mg] = 1 × 1020 cm−3. The major defect species was identified as a complex between Ga vacancy (V Ga) and multiple nitrogen vacancies (V Ns). The introduction of vacancy complexes was found to correlate with a decrease in the net acceptor concentration, suggesting that the defect introduction is closely related to the carrier compensation. We also investigated Mg-doped GaN layers grown using In as the surfactant. The formation of vacancy complexes was suppressed in the subsurface region (≤80 nm). The observed depth distribution of defects was attributed to the thermal instability of the defects, which resulted in the introduction of vacancy complexes during the deposition process. Cross-stacked carbon nanotubes assisted self-separation of free-standing GaN substrates by hydride vapor phase epitaxy State Key Laboratory of Solid-State Lighting, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China Scientific Reports http://dx.doi.org/10.1038/srep28620

We report a novel method to fabricate high quality 2-inch freestanding GaN substrate grown on cross-stacked carbon nanotubes (CSCNTs)

coated sapphire by hydride vapor phase epitaxy (HVPE). As nanoscale masks, these CSCNTs can help weaken the interface connection and release the compressive stress by forming voids during fast coalescence and also block the propagation of threading dislocations (TDs). During the cool-down process, thermal stress-induced cracks are initiated at the CSCNTs interface with the help of air voids and propagated all over the films which leads to full self-separation of FS-GaN substrate. Raman and photoluminescence spectra further reveal the stress relief and crystalline improvement of GaN with CSCNTs. It is expected that the efficient, low cost and mass-producible technique may enable new applications for CNTs in nitride optoelectronic fields. Discovery of earth-abundant nitride semiconductors by computational screening and high-pressure synthesis Department of Materials Science and Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan Nature Communications http://dx.doi.org/10.1038/ncomms11962

Nitride semiconductors are attractive because they can be environmentally benign, comprised of abundant elements and possess favourable electronic properties. However, those currently commercialized are mostly limited to gallium nitride and its alloys, despite the rich composition space of nitrides. Here we report the screening of ternary zinc nitride semiconductors using first-principles calculations of electronic structure, stability and dopability. This approach identifies as-yet-unreported CaZn2N2 that has earth-abundant components, smaller carrier effective masses than gallium nitride and a tunable direct bandgap suited for light emission and harvesting. High-pressure synthesis realizes this phase, verifying the predicted crystal structure and band-edge red photoluminescence. In total, we propose 21 promising systems, including Ca2ZnN2, Ba2ZnN2 and Zn2PN3, which have not been reported as semiconductors previously. Given the variety in bandgaps of the identified compounds, the present study expands the potential suitability of nitride semiconductors for a broader range of

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electronic, optoelectronic and photovoltaic applications. Unintentionally doped high resistivity GaN layers with an InGaN interlayer grown by MOCVD School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China RSC Advances http://dx.doi.org/10.1039/C6RA10696J

High-resistivity GaN (HR-GaN) epilayers with an in situ annealed InGaN interlayer were grown by MOCVD technique. Hall-effect measurements show a background carrier concentration as low as 1.0 × 1012 cm−3 and a high sheet resistivity of 2.1 × 108 Ω per square. Combining the high-resolution X-ray diffraction, transmission electron microscopy and secondary ion mass spectroscopy characterization, the compensation mechanism through the carbon acceptors impurities induced by increased edge-type threading dislocations (TDs) was demonstrated. Additionally, few increase of the screw TDs density in the HR-GaN epilayers by introducing the annealed InGaN interlayer has been demonstrated, which is beneficial to the device reliability in AlGaN/GaN high electron mobility transistors. Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Rev. Sci. Instrum. http://dx.doi.org/10.1063/1.4954203

Micro-Raman thermography is one of the most popular techniques for measuring local temperature rise in gallium nitride (GaN) high electron mobility transistors with high spatial and temporal resolution. However, accurate temperature measurements based on changes in the Stokes peak positions of the GaN epitaxial layers require properly accounting for the stress and/or strain induced by the inverse piezoelectric effect. It is common practice to use the pinched OFF state as the unpowered reference for

temperature measurements because the vertical electric field in the GaN buffer that induces inverse piezoelectric stress/strain is relatively independent of the gate bias. Although this approach has yielded temperature measurements that agree with those derived from the Stokes/anti-Stokes ratio and thermal models, there has been significant difficulty in quantifying the mechanical state of the GaN buffer in the pinched OFF state from changes in the Raman spectra. In this paper, we review the experimental technique of micro-Raman thermography and derive expressions for the detailed dependence of the Raman peak positions on strain, stress, and electric field components in wurtzite GaN. We also use a combination of semiconductor device modeling and electro-mechanical modeling to predict the stress and strain induced by the inverse piezoelectric effect. Based on the insights gained from our electro-mechanical model and the best values of material properties in the literature, we analyze changes in the E2 high and A1 (LO) Raman peaks and demonstrate that there are major quantitative discrepancies between measured and modeled values of inverse piezoelectric stress and strain. We examine many of the hypotheses offered in the literature for these discrepancies but conclude that none of them satisfactorily resolves these discrepancies. Further research is needed to determine whether the electric field components could be affecting the phonon frequencies apart from the inverse piezoelectric effect in wurtzite GaN, which has been predicted theoretically in zinc blende gallium arsenide (GaAs).

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PRESS RELEASE Technical and economic information selected by Knowmade

OPTOELECTRONICS

Samsung launches line-up of LED components for automotive lighting, featuring CSP Semiconductor Today

Samsung Electronics Co Ltd of Seoul, Korea has launched Fx-CSP - a line-up of LED packages featuring chip-scale packaging (CSP) and flexible circuit board technology - for use in automotive lighting applications. “Our new Fx-CSP line-up will bring greater design flexibility and cost competitiveness to the automotive lighting industry,” claims Jacob Tarn, executive VP, LED business team, at Samsung Electronics. “We will continue to introduce innovative LED products and technologies, such as multi-chip array technology, that can play a key role in the growth of the automotive LED lighting industry,” he adds. The combination of chip-scale packaging and flexible circuit board technology together enables more compact chip sizing and a higher degree of reliability, says the firm. The use of a flexible circuit board also enables greater heat dissipation, which leads to lower resistance and brings about a greater degree of lumen-per-watt efficiency than using a ceramic board. Read more LED luminaire sales for horticultural applications to grow to $2.8bn by 2024 Semiconductor Today

The global market for light-emitting diode (LED) luminaires for horticultural applications is expected to grow to $2.8bn by 2024, according to the report 'LED Lighting for Horticultural Applications' from Navigant Research.

The next five years are expected to bring great opportunity for lighting companies as new indoor growing facilities are built and as new horticultural market entrants make decisions on available brands. Despite being more expensive than other technologies, LEDs are now the preferred lighting technology in an increasing number of facilities, because of advantages that can increase energy efficiency and crop yields, notes the report. Read more US DOE investing $10.5m in nine solid-state lighting R&D projects Semiconductor Today

Building on the new commitments to the Global Lighting Challenge announced in early June during the Clean Energy Ministerial, the US Department of Energy (DOE) is announcing funding for nine research and development projects that will support solid-state lighting (SSL) core technology research, product development, and manufacturing research and development. The projects aims to help to accelerate the development of high-quality light-emitting diode (LED) and organic light-emitting diode (OLED) lighting products. “Solid-state lighting research and development has contributed to more than $2.8bn in US energy cost savings over the past 15 years, and further improvements in the technology will increase those savings even more in the years to come,” says Energy Secretary Ernest Moniz. “By 2030, solid-state lighting could reduce national lighting electricity use by nearly half — which would equate to the total energy consumed by 24 million American homes today and could save American families and businesses $26bn annually,” he adds. Today's most advanced LED products are about 10 times more energy efficient than conventional incandescent lighting and last more than 25 times longer, notes the DOE.

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Department-funded R&D aims to foster technology breakthroughs to unlock new levels of SSL performance and energy savings. For example, DOE targets aim to increase the efficiency of existing LEDs by an additional 66%. LED lighting also offers new potential for advanced lighting control, including color tuning and intelligent, adaptive lighting. In total, the nine selected projects will receive more than $10.5m and will make a cost-share contribution for a total public-private investment of over $13.5m, as they help to further reduce the cost and improve the quality of SSL products:

Cree Inc (Durham, NC) — Developing a high-efficacy LED lighting fixture that has good color rendering as well as advanced features such as the ability to tune the color of the light;

Columbia University (New York, NY) — Developing improved quantum dots to increase the efficiency and lower the cost of LEDs;

GE Global Research (Niskayuna, NY) — Developing an efficient LED fixture that features interchangeable modules and allows for simplified manufacturing and customized performance specifications;

Iowa State University (Ames, IA) — Demonstrating a method to significantly increase the light output of white OLEDs by changing their internal features;

Lumenari, Inc. (Lexington, KY) — Developing a narrow-bandwidth red phosphor to improve the efficacy of phosphor-converted LEDs;

Lumileds (San Jose, CA) — Improving the design of an LED to make it more efficient by using a patterned sapphire substrate (PSS) flip-chip architecture;

North Carolina State University (Raleigh, NC) — Developing a way to get more light out of OLEDs using low-cost corrugated substrates;

Pennsylvania State University (State College, PA) — Developing a way to better understand and predict the occurrence of short circuits in OLED lighting panels in order to reduce failure rates; and

University of Michigan (Ann Arbor, MI) — Developing three innovative methods to harness the light within OLEDs.

This is the eleventh round of the department's investments in solid-state lighting core technology research and product development. Read more

ELECTRONICS

GaN-on-Si technologies: Let the games begin i-micronews

It is now common knowledge throughout the semiconductor industry: MACOM Technology Solutions Holdings, Inc. (MACOM), a supplier of high-performance analog RF, microwave, millimeter wave and photonic semiconductor products for diverse applications, is pursuing legal action against Infineon Technologies AG (Infineon), a provider of semiconductor solutions. The story is complex yet so predictable: Yole Développement (Yole) and its sister company KnowMade, both heavily involved in technology, marketing and IP analysis for the semiconductor industry, released a patent landscape analysis report two years ago dedicated to GaN-on-Si technologies. The GaN-on-Silicon Substrate Patent Investigation report highlights the on-going structuration of the market and the maturity of related patents. Behind such huge market potential, both partners had predicted possible litigation in the coming years due to an increasing number of players and limited number of key patents. With both acquisitions taking place within a 2-year period—International Rectifier (IR) by Infineon and Nitronex by MACOM—the game has become more complex, and today the industry wants to know: What happens now? Two years ago, Yole and KnowMade analysts expected GaN-on-Si to be widely adopted by power electronics and RF applications because of its lower cost and CMOS compatibility. The status of today’s market confirms this conclusion: “At Yole we are following GaN-on-Si technology and

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its existing and emerging applications daily,” says Dr. Hong Lin, Yole’s Technology & Market Analyst. “The global market for GaN RF applications reached US$298.5 million in 2015, with a significant CAGR for the coming years. At the same time, numerous developments are showing the potential of GaN-on-Si technology in RF products. And we believe that the GaN RF industry could be reshaped, with a strong impact at the supply chain level, if GaN-on-Si technology is in fact adopted. On the power-electronic applications side, GaN-on-Si has currently attained only a few million dollars; but we have also identified huge business opportunities and impressive activities in the GaN-on-Si patent landscape. With such strong growth, we expect the market to reach a few hundred million dollars at mid-term.” That is likely why the battle predicted in the KnowMade and Yole report is taking place today. Industrial companies are playing the game to penetrate the market and reinforce their market positions. The dispute between MACOM and Infineon is just one example; many may soon follow suit. MACOM acquired Nitronex in February 2014. This transaction provided MACOM with innovative GaN-on-Si technology process and materials for RF and other applications. At the end of March, the company announced an IP licensing program; IR and other companies were part of the game. Today, Nitronex patents are widely used within the power electronics and RF sectors. Within this context, MACOM could very well initiate many other legal actions. “When MACOM acquired Nitronex in June 2014, the company took control of the use of overall GaN-on-Si technology and potentially blocked targeted markets,” asserts Nicolas Baron, CEO of KnowMade. He adds, “Its strategy might extend beyond just the RF sector: The company probably expects to maintain an open path to the power electronics market with Nitronex GaN-on-Si patents. Today, with the legal procedure announced on April 26, MACOM wants to put an end to unacceptable activities from Infineon.” With the acquisition of IR, Infineon has a leading market position in the power-electronics sector. According to MACOM, the German company would gain some developments in the RF markets and, as a consequence, reduce MACOM’s rights in

the sector. “This legal action is clearly a strong message from MACOM to the GaN-on-Si community today,” confirms Yole and KnowMade analysts. The synergy between GaN-on-Si markets, RF and power electronics are undeniable today. Yole’s Business Unit Manager, Pierric Gueguen, explains, “GaN-on-Si technology has resulted in numerous assets for many applications, including RF and power electronics, and GaN-on-Si players have latched onto this potential. It is entirely natural for a bridge to form between the RF and power electronics markets. Under this scenario, RF companies are expanding their activities into the power electronics market. On the other side, power electronics companies are developing their product lines and offering RF solutions. This strategy is a good way to secure their business and ensure increasing revenues.” Dream or reality? Only the future will tell. Partners Yole and KnowMade are pursuing their investigation into GaN-on-Si technologies as well as into other power electronics and compound semiconductor technologies. All year long, Yole and KnowMade have been releasing serious value-added analyses of technology, markets and IP to provide a clear view of the industry landscape and evaluate the impact of disruptive technologies on markets. More information is available at i-micronews.com. Yole and KnowMade invite you to stay tuned and discover how the market for disruptive technologies evolves. Read more VisIC launches new generation of low-Rdson ALL-Switch 650V GaN devices usable with standard drivers Semiconductor Today

VisIC Technologies Ltd of Nes Ziona, Israel, a fabless developer of power conversion devices based on gallium nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) founded in 2010, has announced the availability of its new generation of ALL-Switch (Advanced Low Loss Switch) devices, comprising V22S65A (with an internal SiC diode) and V22N65A (without internal SiC diode).

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The new version of VisIC's ALL-Switch is said to significantly reduce the Miller effect, enabling readily available, standard drivers to be used in VisIC-based designs. The new devices also reduce the bill of materials required for specific applications. Effective in hard-switching topologies, the V22 series can be used for zero voltage switching or zero current switching topologies. It is claimed to have the lowest Rdson among either 650V GaN- or SiC-based MOSFET transistors, and can achieve extremely efficient power conversion with a slew rate exceeding 100V/nS. In addition, since the threshold voltage exceeds 5V, the devices work well in harsh EMI environments, adds the firm. VisIC has demonstrated what it claims is record with performance of its half-bridge demonstration board, achieving better than 99.3% peak efficiency at 200kHz in a hard-switched topology, providing 2.5kW output. Read more Is GaN Disruptive? Revisiting the Criteria SemiWiki

In March 2010 Efficient Power Conversion (EPC) proudly launched our GaN technology at the CIPS conference in Nuremberg, Germany. Parts and development kits were readily available off-the shelf and therefore designers could immediately get started with a new state-of-the-art semiconductor technology.

Figure 1: EPC2036 die photo. This family of devices was the first to break the price of MOSFETs with the same voltage and on-resistance.

At that time, we listed four key attributes we believed a new semiconductor technology needed in order to be really disruptive to the end markets. A lot has happened in the six years since. GaN has continued to ascend as the presumptive replacement for the aging power MOSFET, yet there are still a few design engineers and technical managers that remain skeptical. So let’s look again at these four key attributes and see where GaN stands in addressing them. The Four Requirements:

1. Does it enable significant new applications? 2. Is it easy to use? 3. Is it VERY cost effective to the user? 4. Is it reliable?

Does it enable significant new applications? GaN transistors and integrated circuits are significantly faster and smaller than the best silicon MOSFETs. Today, commercially available eGaN® FETs and ICs are 5 to 50 times better than the silicon state-of-the-art. This large jump in performance has led to several new applications that were not possible until the availability of GaN technology. But eGaN FETs, and in fact any GaN transistor from any of several manufacturers, are still several orders of magnitude away from GaN’s theoretical performance limits. There is a learning curve ahead that only widens the performance gap between GaN and silicon, and continues to enable new applications and transform entire end markets. Here are just a few examples: Transforming Space Power converters used in harsh environments, such as space, high-altitude flight, or high-reliability military applications must be resistant to damage or malfunctions caused by radiation. eGaN FETs today perform 40 times better electrically while being able to withstand 10 times the radiation compared with the aging Rad Hard power MOSFET. This enables entirely new architectures for satellite power and data transmission.

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Figure 2: eGaN FETs and ICs can withstand ten times more radiation than silicon devices, making them ideal for satellite systems.

Elon Musk, CEO of SpaceX, has set as his mission to reduce the cost of putting objects in space by a factor of 10. With eGaN technology applied to satellites we can reduce the size of the electronics, eliminate the shielding required, and greatly improve the performance of the data communications. This eliminates solar panels, makes the entire system smaller and lighter weight, and extends the life of the satellite. Reducing the weight by a factor of two is within our reach with today’s technology, whereas a factor of 10 reduction is possible as eGaN technology is used to produce entire systems on a single chip. Multiply the impact of SpaceX with eGaN technology and we will change the way we use space and accelerate the exploration (and possible colonization?) of our universe. Augmented Reality and Autonomous Vehicles LiDAR (Light Distancing and Ranging) uses high speed pulsed lasers to rapidly create a three dimensional image or map of a surrounding area. One of the earliest adopters of this technology was the “driverless” car. LiDAR is evolving quickly in both resolution, size, and cost and will soon start appearing in a variety of commercial drones, including the replacement of many existing sensors currently found on conventional vehicles.

Figure 3a: Autonomous cars depend on LiDAR systems powered by eGaN FETs and ICs.

Figure 3b: Many augmented reality systems use LiDAR to quickly create a digital image or the surroundings. GaN improves accuracy, speed and greatly reduces power usage.

LiDAR is the fastest and lowest-cost way to develop a 3D digital image and thus ideal for new applications such as augmented and merged reality systems.Projects are already underway to include “3D Awareness” in our cell phones. Imagine if phones could understand the space around us. We will be able to get directions in a new, more comprehensive way. An iPhone today can provide the location of the building you desire, but with LiDAR, 3-D mapping could guide you inside the building and straight to a specific office. Transforming the Use of Electricity Wires suck! Today, we need wires to supply power to our ever-growing collection of electrically-powered gadgets. For those gadgets that are so completely indispensable, we need to take them with us at all times, and they need batteries that must be recharged all-too-frequently.

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Figure 4: Wireless power will eventually eliminate power cords throughout the home.

Wireless power systems using eGaN technology are beginning to unload this wired burden by providing energy wirelessly to power and charge cell phones, tablets, and computers. By integrating thin transmission coils in furniture, the floor tiles and the walls of buildings and homes, the need for wall sockets will be eliminated altogether! This same wireless power technology can be used to charge electric vehicles when parked over a transmitting coil embedded in the floor of a garage, or even drone in mid-air. There are projects underway to embed wireless chargers at bus stops. Eventually, in a one-minute stop, a bus can get enough charge to drive a mile to the next bus stop. This could eliminate the need for most of the heavy batteries and overhead electrical systems that burden electric buses today. Transforming Medicine We are all getting older, and, as we age, we develop more opportunities for frailties and chronic health problems. Today there are major advances in fields such as implantable systems, diagnostic imaging, and prosthetics that are enabled by eGaN technology.

Figure 5: Diagnostic colonoscopy "pill".

Wireless power is already having an impact on implantable systems such as heart pumps. Beyond just artificial hearts, many other medical systems can also benefit. As Dr. Pramod Bonde of the University of Pittsburg Medical Center speculated, “[wireless power] can be leveraged to simplify sensor systems, to power medical implants and reduce electrical wiring in day-to-day care of the patients.” But it’s not just eGaN technology in wireless power that is transforming medicine. Imaging technology is also improving by leaps and bounds! The resolution of MRI machines is being enhanced through the development of smaller and more efficient sensing coils using eGaN FETs and ICs. Diagnostic colonoscopies are about to become a thing of the past due to today’s eGaN FETs that are enabling an entire x-ray system to be squeezed into an ingestible and disposable tablet. These types of non-invasive imaging breakthroughs significantly reduce the cost of health care through early warning and non-invasive diagnostics. As we integrate entire systems on a single eGaN chip, miniaturization and image resolution improves the standard of care while medical costs come down. Wireless Communications Envelope Tracking is a power supply technique that can double the energy efficiency of RF power amplifiers used to transmit all of our voice and data communications through satellites, base stations, and cell phones. Envelope tracking is accomplished by tracking the power demand precisely and providing the power to exactly fit the amplifier’s signal modulation needs. Today, RF power amplifiers operate at a fixed power level

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delivering maximum power whether or not the transmitter needs it. Excitingly enough, eGaN transistors were the first transistors capable of tracking power demands at the high data transmission rates used in 4G LTE network base stations! As we move to 5G formats the need for envelope tracking becomes absolute.

Figure 6: Without envelope tracking most of the power consumption in the 4G/LTE power amplifier is wasted.

Is it easy to use? At EPC we designed our GaN transistors (eGaN FETs) to be very similar in behavior to the aging power MOSFETs (except they deliver much, much more performance!), and therefore power systems engineers can use their design experience with minimal additional training. To assist design engineers up the learning curve, EPC has established itself as the leader in educating the industry about gallium nitride devices and their applications. EPC published the industry’s first GaN transistor textbook (in English and Chinese) – GaN Transistors for Efficient Power Conversion. The second edition was published in 2015 by J. Wiley and is available through Amazon as well as textbook retailers. More recently, we have published two application-focused handbooks to further assist power designers of DC-DC conversion and wireless power transfer systems in the use of GaN. EPC is working with more than 60 universities around the world in order to lay the groundwork for the next generation of highly skilled power system designers trained in getting the most out of GaN technology. Is it VERY cost effective? GaN transistors and integrated circuits from EPC are produced using processes similar to silicon power MOSFETs, have many fewer processing steps than MOSFETs, and more devices are

produced per manufacturing run because GaN devices are much smaller than their silicon counterparts. In addition, lower voltage (<500 V) GaN transistors do not require the costly packaging needed to protect their silicon predecessors. This packaging advantage alone can cut the cost of manufacture in half and, combined with high manufacturing yields and small device size, has resulted in the cost of a GaN transistor from EPC to be lower in cost than a comparable (but lower performance) silicon power MOSFET. Today the designer does not even need to take advantage of the higher performance of GaN to realize cost savings in their system! Is it reliable? To date, several manufacturers of GaN transistors have reported excellent results from in-house stress testing. In December 2015 EPC published its 7th reliability report including 7 million device hours under stress. In addition, for the first time, EPC published the results from tracking parts in the field for 17 billion hours over a six year period. GaN FETs, aided by the fact that they are chipscale, and therefore do not suffer from failure modes common to packaged semiconductors, achieved a remarkable 0.24 failures for every billion device hours. There is no doubt that eGaN FETs are suitable for any application in which MOSFETs are used.

Figure 9: eGaN FET reliability after 6 years and 17 billion hours in the field is proving better than the aging MOSFET.

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Summary Thus, the four requisite attributes for GaN to displace the silicon MOSFET have been achieved: switching speed, small size, competitive cost, and high reliability give the GaN transistor the “winning edge” to displace the silicon MOSFET in power conversion applications. Similar analysis shows that soon the same will be true for power ICs and analog integrated circuits created with GaN technology. Perhaps in 3-5 years the same will be true for digital integrated circuits. GaN is a relatively new technology and has just begun its journey up the learning curve! Read more Six Reasons to Rethink Power Semiconductor Packaging SemiWiki

In my 40 years’ experience in power semiconductors I have visited thousands of customers, big and small, on every continent except Antarctica. When the issue invariably turns to the packaging of the power semiconductor – transistor, diode, or integrated circuit – the requests for improvement fall into six categories:

1. Can you make the package smaller? 2. Can you reduce the package inductance? 3. Can you make the product with lower

conduction losses? 4. Can you make the package more thermally

efficient? 5. Can you sell the product at a lower price? 6. Can you make the package more reliable?

eGaN® FETs and integrated circuits from EPC have taken a very different approach to packaging power semiconductors – we have ditched the package altogether! Pretty radical. The reason for ditching the package in the first place was serendipitous. As a fledgling startup, no company specializing in power semiconductor packaging wanted to be bothered with small volumes and high up-front engineering costs. So we went with the idea of supplying our products in chipscale formats.

Figure 1 shows an EPC1001 transistor first introduced in March 2010. This device has a thin layer of gallium nitride (GaN) grown on top of a standard silicon substrate. Inside the GaN we fabricated a first-generation discrete transistor that performed 5 – 50 times better than the best silicon MOSFETs, depending upon the application. And, instead of a plastic molded package, we put solderable bars directly on the surface of the device. Flip this part over and it can be mounted it directly onto a PCB (See figure 2).

Figure 1: The EPC1001 was first introduced in March 2010 and began the chipscale packaging revolution.

Figure 2: Two EPC eGaN FETs are soldered to a PCB with the active area facing down. The blue back surface is silicon nitride on top of silicon. GaN-on-silicon has some amazing advantages over silicon power MOSFETs. In addition to much, much superior device performance, the thin layer of GaN in which the active devices are manufactured can be sealed under multiple layers of glass during the standard fabrication process. These layers of glass effectively protect the device from the environment, something silicon MOSFETs cannot do easily because the entire silicon-on-silicon structure is electrically active. The lateral GaN devices are only active on the surface attached to the PCB.

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When I was CEO of International Rectifier Corporation (now part of Infineon), we built about 1 billion MOSFETs every 6 weeks. When all the expenses were added up, the cost of the packaging was equal to the cost of making the silicon chip inside the package. The smaller the device, the higher the ratio of package-to-device cost. Cutting out the packaging therefore cut out half the cost as well as a lot of the logistics required in the assembly process. This significant cost reduction was a pretty good motivator to keep going with the chipscale packaging idea. GaN transistors are much smaller than their silicon counterparts. This size advantage translates into additional cost benefits to the GaN device maker, and it translates into additional cost benefits to the user. PCB real estate is very expensive. Smaller devices mean less real estate. In some cases, the smaller footprint and greater performance of GaN enables a new end product not possible with larger silicon parts. Figure 3 is my personal favorite example of the power of “small size.” In this figure is a miniaturized X-ray machine in a pill that you swallow. The result: the X-ray pill performs a colonoscopy without prior purging. The high-resolution images of the colon are wirelessly transmitted to a receiver worn as a patch on the patient’s back. The cost of the pill is low enough that it does not have to be recovered after use (Whew!). Can’t do it with silicon; just can’t.

Figure 3: This X-ray pill from Check Cap can do a full colonoscopy without prior purging. A high resolution image of the colon is beamed wirelessly to a receiver worn as a patch on the patient’s back.

Small has other advantages. Small devices can be located closer to other devices in a circuit. This reduces unwanted inductance. Stray or parasitic Inductance is the enemy of a power system in that it causes the circuit to react more slowly and “ring” with voltage and current oscillations. This ringing can damage devices in the circuit and cause unwanted noise that may need to be filtered out. Figure 4 shows the impact of just the inductance inside silicon MOSFET packages on the power losses in a common power supply. In this case, the internal package inductance causes the devices to turn on and off slower and therefore the transistor generates higher switching losses. The popular SO-8 package induces losses that amount to 80% of the total losses incurred in the device. Even the most efficient package – the DirectFET – doubles the losses in the device. The EPC2001 chipscale device has less than 20% losses added due to inductance in the traces on the PCB under the device. Lower losses, less heat, higher power conversion efficiency. Oh, and the chipscale package also doesn’t add any unwanted resistance to the device. Package resistance can add 20-50% to the resistance of a low voltage state-of-the-art silicon MOSFET. Pure loss.

Figure 4: Popular power packages such as the SO-8, LFPAK, and DirectFET add considerable parasitic inductance to a power conversion circuit. This inductance induces large losses in the transistor inside the package.

Many customers, when they see the tiny eGaN transistors or ICs, worry about their ability to remove the heat from the part. Power losses in the transistor generate heat. Thus, this heat must be removed or the device, and the entire system, may overheat. The best way to get rid of heat is

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not to generate it in the first place. In the above paragraphs we explained that GaN-on-silicon devices are much more efficient than silicon-based devices and therefore generate less power losses and less heat. However, an amazing attribute of a package-less device is that it is much more thermally efficient than a MOSFET in the best power package. Figure 5 is a comparison between eGaN FETs, double-sided QFNs, and DirectFETs. In the figure, the vertical axis is the thermal resistance from the device to the ambient and the horizontal axis is the device size. The lower the resistance the better, and eGaN FETs in chipscale “packages” are much better. It is not a surprise, because eliminating all barriers between the active device and the ambient environment gives heat the most direct path to the outside world.

Figure 5: Chipscale packages have lower thermal resistance than the most efficient silicon packages.

Size, inductance, conduction losses, thermal resistance, and cost – chipscale beats packages every time! What about reliability? Experienced users and producers of power semiconductors will all tell you that it is the package that causes the most reliability problems. Packaging induces high stress on the silicon device during the encapsulation processes. Multiple dissimilar materials are used in a package to create a protected and sealed environment, but these dissimilar materials tend to grind against each other and come apart during thermo-mechanical stress.

Over 6 years and 17 billion device hours, eGaN FETs and ICs from EPC have demonstrated an unprecedented record of reliability in the field. Whether it be in truck headlamps, on board autonomous vehicles, inside 4G/LTE base stations, or within DC-DC power supplies, eGaN FETs have demonstrated a total field failure rate of under 1 FIT (Failures every billion device hours). Figure 6 is a year-by-year record of eGaN FET field reliability.

Figure 6: Field reliability results for eGaN FETs. As of January 2016, EPC has documented over 17 billion hours in the field.

The six key attributes of a better package, size, inductance, resistance, thermal efficiency, cost, and reliability all point to the future of packaging for GaN FETs and ICs as being – package-less -- that is, no package at all! Read more RF power semiconductor market to grow at 15.4% CAGR, almost tripling from $10.57bn in 2015 to $31.26bn in 2022 Semiconductor Today

The RF power semiconductor market will grow from $10.57bn in 2015 to $31.26bn in 2022, rising at a compound annual growth rate (CAGR) of 15.4% between 2016 and 2022, forecasts the firm MarketsandMarkets. According to the report 'RF Power Semiconductor Market by Product, Material, Frequency, Application, and Geography - Global Forecast to 2022', manufacturers have seen increased shipments of devices for applications such as

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aerospace & defense, medical, consumer, automotive, telecommunications and data communications. RF power amplifiers to play a key role in the RF power semiconductor market RF power amplifiers held the largest share of the RF power semiconductor market in 2015 and - due to increasing adoption worldwide and driven by the growing preference for wireless connectivity - are expected to dominate the market between 2016 and 2022. Other devices such as RF duplexers and RF switches are also expected to see high growth. The use of power amplifiers is increasing with the growing demand for smartphones and the need for higher data rates in LTE (long-term evolution) and 5G in the near future. The transition to LTE requires significant investment as the core networks also need to change for upgrade of the wireless standard, which is also driving demand for RF power devices. Consumer sector largest, but aerospace & defense growing fastest Driven by the growing use of smartphones and demand for faster data rates (particularly LTE), consumer applications are expected to hold the largest market share by application, and to dominate the RF power semiconductor market between 2016 and 2022. However, aerospace & defense applications are expected to grow fastest during the forecast period due to increasing demand from defense equipment manufacturers for RF power semiconductor devices in avionics and radar systems. Growth in the production of defense equipment worldwide is due to increased investment in the defense sector, notes the report. APAC to hold largest market share and grow fastest The Asia-Pacific (APAC) is expected to hold the largest market share by geographic region, and to dominate the RF power semiconductor market between 2016 and 2022, presenting huge growth opportunities for companies operating worldwide

due to the increasing number of consumers using smartphones. The main driving factors for the APAC region's growth are its established electronics industry, the adoption of innovative technologies, and the low manufacturing and development costs in countries such as Taiwan, Malaysia and China. The APAC market is expected to grow at a high rate in consumer, telecom, datacom and medical sectors. The increasing number of players in the region is further expected to drive growth. The North America region was the second-largest market in 2015 and has a steady growth rate. Despite being a mature market, growth is highly sustainable because of the presence of a large number of manufacturers in the region, notes the report. Key players in the RF power semiconductor market are listed as Infineon Technologies AG (Germany), M/A-COM Technology Solutions Holdings Inc (USA), NXP Semiconductors N.V. (The Netherlands), Qorvo Inc (USA), Broadcom Ltd (USA), Toshiba Corp (Japan), Qualcomm Inc (USA), Skyworks Solutions Inc (USA), Mitsubishi Electric Corp (Japan), and Murata Manufacturing Co Ltd (Japan). The report cautions that the RF power semiconductor market is a highly fragmented market, which reduces the price margin of RF device suppliers. Also, the increase in cost of RF devices with performance improvement is another restraint. Read more RF GaN revenue growing at 17.5% CAAGR, more than doubling to $688.5m in 2020 Semiconductor Today

Growing adoption of gallium nitride (GaN) technology in RF applications - coupled with the widespread deployment of LTE base-stations in China - drove an increase in RF GaN revenue of nearly 50% in 2015, according to the Strategy Analytics Advanced Semiconductor Applications (ASA) service report 'RF GaN Market Update: 2015 – 2020'. The growth in the base-station segment pushed the commercial portion of the RF GaN

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revenue to more than 60% of the total in 2015, with base-station applications specifically comprising nearly 55%. “The performance advantages of GaN fit nicely with the requirements of new LTE base-station power amplifiers,” notes Eric Higham, a director of Strategy Analytics' Advanced Semiconductor Applications service. “Despite an anticipated decline in the base-station power market, we anticipate that GaN revenue will increase as more equipment manufacturers convert to the technology,” he adds. “As countries undertake new platform builds and retrofits, RF GaN revenue in defense applications will grow faster than the overall market, bringing it on par with commercial RF GaN revenue by 2020,” says Asif Anwar, service director, Advanced Defense Systems service. So, driven by emerging system requirements, RF GaN revenue in the defense sector will rise from nearly 38% of the total revenue in 2015 to just short of 50% in 2020. The continuing growth in base-station and defense applications collectively will drive RF GaN revenue to rise at a compound average annual growth rate (CAAGR) of 17.5%, more than doubling to nearly $688.5m in 2020, forecasts the report. Read more CoorsTek unveils enhanced GaN-on-Si epiwafers at ISPSD Semiconductor Today

In stand # 10 at the 28th IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD 2016) in Prague, Czech Republic(12-16 June), engineered ceramics supplier CoorsTek Inc of Golden, CO, USA is unveiling its enhanced gallium nitride on silicon (GaN-on-Si) epitaxial wafers. For the first time at this event, CoorsTek is displaying the integrated capabilities of CoorsTek and Covalent Materials (formerly Toshiba Ceramics, now CoorsTek KK), including:

GaN-on-Si epiwafers for power devices and integrated circuits (ICs); aluminum nitride (AlN) substrates for hybrid circuits; and engineered ceramic components for semiconductor processing equipment made from PureSiC CVD silicon carbide, PlasmaPure high-purity alumina, and other technical ceramics. “The latest CoorsTek gallium nitride-on-silicon technology helps customers achieve higher device manufacturing yields and breakdown voltages based on lower defect densities and leakage current,” says R&D manager Jun Komiyama PhD. “The shift from 150mm- to 200mm-diameter GaN-on-Si process is also improving the economics for power electronics in electric and hybrid automobiles, solar photovoltaic inverters, RF and microwave power, and more.” Read more NXP targets GaN transistors for electronic warfare i-micronews

Six new transistors meet needs for high performance while reducing size, weight, and power consumption. NXP Semiconductors has expanded its portfolio of broadband GaN RF power transistors for electronic warfare and battlefield radio applications. The expansion includes six new driver or final-stage amplifiers that have frequency coverage as broad as 1 to 3000MHz. The new GaN on SiC transistors are said to combine high power density, ruggedness, and very flat frequency response over wide bandwidths. All are input matched to optimise operating frequency range, and can withstand a VSWR greater than 20:1 with 3 dB overdrive without degradation. They are also part of NXP's Product Longevity Program. The transistors' broadband frequency coverage from HF to S-band allows them to cover virtually all frequencies used by radios or the lower-frequency sections of electronic systems. This reduces the number of RF power transistors required to build an amplifier with a specific RF

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output level, which decreases amplifier size and bill of materials, according to the company. The new transistors include:

MMRF5011N (28V) and MMRF5013N (50V): operate from 1 to 3000MHz with RF output power up to 12W CW, 15dB gain, and 60 percent efficiency, housed in an OM-270-8 over-molded plastic package.

MMRF5015NR5: operates from 1 to 2700 MHz with RF output power up to 125W CW, gain of 16dB, and efficiency of 64 percent, housed in an OM-270-2 over-molded plastic package

MMRF5019N: operates from 1 to 3000 MHz with RF output power up 25W CW, gain of 18 dB, and efficiency of 40 percent, housed in an OM-270-8 over-molded plastic package

MMRF5021H: operates from 1 to 2700 MHz with RF output power up to 250W CW, 16dB gain, and 58 percent efficiency, housed in a NI-780H-4L air-cavity ceramic package

MMRF5023N: operates from 1 to 2700 MHz with RF output power up to 63W CW, 16dB gain, and 60 percent efficiency, housed in an OM-270-2 over-molded plastic package

“Our customers want to reduce the size, weight, and power of military systems even at the device level,” said Paul Hart, executive vice president and general manager of NXP's RF Power business unit. “Our new GaN transistors meet these requirements and can provide improved ruggedness, broad operating bandwidth and high efficiency.” Read more Qorvo introduces new GaN-On-SiC Pas i-micronews

Qorvo has introduced three new GaN power amplifiers (PAs) that are said to achieve industry-leading power, power added efficiency (PAE) and gain. Qorvo's newest GaN PAs are optimised for use in military radar, communications and electronic warfare systems, and include the TGM2635-CP X-band 100W MMIC amplifier for satellite communications, data links and radar applications; the TGA2307-SM C-band 50W MMIC amplifier for radar applications, in low cost plastic packaging; and the TGA2963 20W MMIC amplifier for wideband communication platforms, radar

systems, electronic warfare and test instrumentation. The three new GaN solutions allow defence manufacturers to develop cost effective next-generation systems optimised for size, weight and power, according to the company. Roger Hall, general manager of Qorvo's Defence & Aerospace Products business unit, said: “Defence and commercial customers recognise Qorvo for world-class performance and the most reliable and robust GaN on SiC solutions in the industry. Qorvo's newest GaN PAs improve performance and reduce size and cost for defence radar, communications and EW systems by offering a combination of power, PAE and gain that is unmatched over their respective frequency bands.” The TGM2635-CP operates from 7.9-11GHz and provides 50dBm of saturated output power, with 22.5 dB of large signal gain and 35 percent PAE. Available in a pure copper-base, bolt-down package, the TGM2635-CP is said to offer superior thermal management for added system flexibility. The TGA2307-SM C-Band MMIC amplifier produces more than 47 dBm of saturated output power with a PAE greater than 44 percent and a large signal gain greater than 20dB. It is packaged in a small 6mm x 6mm plastic overmold package. The TGA2963 wideband MMIC amplifier operates from 6-18 GHz and provides more than 43dBm saturated output power. With PAE of more than 20 percent, the TGA2963 also has a large-signal gain of more than 20dB. Qorvo will feature the TGM2635-CP and other GaN products at IMS 2016, in San Francisco. Read more

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OTHER

BluGlass reports progress on Lumileds and Veeco collaborations; first iteration of HC Semitek collaboration begun Semiconductor Today

BluGlass Ltd of Silverwater, Australia – which was spun off from the III-nitride department of Macquarie University in 2005 to develop a low-temperature process using remote plasma chemical vapor deposition (RPCVD) to grow materials including gallium nitride (GaN) and indium gallium nitride (InGaN) on glass substrates – has reported progress in key areas critical to the completion of its evaluation agreements with three leading companies. Lumileds evaluation BluGlass' chief technology & operations officer Dr Ian Mann recently returned from visiting LED maker Lumileds of San Jose, CA, USA in the USA to review recent RPCVD data and plan the next iterations of experiments critical to the collaboration milestones. Veeco evaluation Samples were recently prepared by BluGlass and shipped to epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview, NY, USA. Veeco has compiled recent data for both the green light-emitting diode (LED) and high-electron-mobility transistor (HEMT) projects, with both returning progressive results. Technical and commercial discussions with Veeco are ongoing. HC SemiTek evaluation Collaborative development work announced in April with LED epitaxy and chip maker HC SemiTek Corp of Wuhan, China (which supplies full-color ultra-high-brightness LED products throughout China) has now begun. The firms are exploring RPCVD's advantages for both green LEDs and aluminium nitride (AlN) to use in high-brightness

LEDs. A planned set of experiments has been agreed for both projects. The 4” sapphire wafers have now arrived in Silverwater, and deposition of the RPCVD AlN films has begun. These will be shipped to HC SemiTek to fabricate into LEDs for testing. BluGlass has also just received the LED wafers for the green LED development, and this RPCVD work is beginning this week. Uniformity and scaling project The RPCVD chamber upgrade to improve RPCVD deposition uniformity is well underway, with the first upgraded system expected to be operational in July. The upgrade of the second, larger RPCVD system will be determined by the progress on industry evaluations (to ensure minimal interruption to ongoing projects with partners). Other applications and interest BluGlass says that it continues to receive interest from major industry participants looking at novel ways of exploiting RPCVD, and discussions are ongoing under confidentiality agreements. Read more Veeco wins first MBE R&D system order from Chinese university Semiconductor Today

Epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview, NY, USA has received the first order from a Chinese customer for its GENxplor R&D molecular beam epitaxy (MBE) system. Nanjing University is scheduled to receive the system in second-quarter 2016. The GENxplor system is said to be the top-selling MBE system worldwide since its introduction in August 2013. Read more

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GANEX | Newsletter No. 42 - III-N Technology 52

Kyma and Quora partner on GaN material development CompoundSemi

Kyma Technologies of Raleigh, North Carolina USA, and Quora Technology have announced a strategic partnership to develop and commercialize GaN substrate materials. Kyma’s GaN materials products include GaN templates and free-standing GaN substrates. Quora Technology is a new privately held Silicon Valley fabless technology startup that is currently commercializing its unique QST™ substrate technology. Kyma and Quora will collaborate to demonstrate that Kyma’s high growth rate GaN processes can be used to realize a low defect GaN on QST™ template. Quora says that it engineered its QST substrate technology to alleviate stress from epi layers and to be fully diameter scalable (6-inch, 8-inch, 12-inch and beyond). This diameter scalability allows deposition of tens of microns of high quality and low dislocation density GaN on 6-inch or larger diameter substrates. According to Quora, major GaN device manufacturers have validated the performance results of its QST™ substrate solution in LED, power, and RF applications. Kyma confirmed that they can fabricate uncracked, low defect density (<108cm-2) 6-inch diameter GaN on QST™ templates that feature smoother surface morphology, up to 40% narrower x-ray diffraction (XRD) linewidths, and much lower bow than for similar structures grown on sapphire. Notably, low bow and other wafer shape factors are important for achieving high yielding and advanced device fabrication. GaN cracking or entire wafer breakage is one of the major obstacles which limits achievable economies of scale. The companies point out that they could potentially extend the GaN on QST™ template to full GaN boule manufacturing. Quora Technology president and CEO Cem Basceri commented, “This special class of material will hopefully improve the existing device processes,

designs, and performances, and also unlock new applications.” Kyma president and CEO Keith Evans commented, “By combining Kyma’s advanced and high gowth rate GaN technology with Quora’s QST™ technology, we have the potential to help device manufacturers to accelerate their roadmaps for making higher performance devices at lower cost.” Read more Microfluidic cooling may prevent the demise of Moore's Law i-micronews

Micro-drops of water channeled through the chip silicon looks like a promising way to keep chips cool and increase their performance. Existing technology's inability to keep microchips cool is fast becoming the number one reason why Moore's Law may soon meet its demise. In the ongoing need for digital speed, scientists and engineers are working hard to squeeze more transistors and support circuitry onto an already-crowded piece of silicon. However, as complex as that seems, it pales in comparison to the problem of heat buildup. “Right now, we're limited in the power we can put into microchips,” says John Ditri, principal investigator at Lockheed Martin in this press release. “One of the biggest challenges is managing the heat. If you can manage the heat, you can use fewer chips, and that means using less material, which results in cost savings as well as reduced system size and weight. If you manage the heat and use the same number of chips, you'll get even greater performance in your system.” Resistance to the flow of electrons through silicon causes the heat, and packing so many transistors in such a small space creates enough heat to destroy components. One way to eliminate heat buildup is to reduce the flow of electrons by using photonics at the chip level. However, photonic technology is not without its set of problems.

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GANEX | Newsletter No. 42 - III-N Technology 53

Microfluidic cooling might be the answer To seek out other solutions, the Defense Advanced Research Projects Agency (DARPA) has initiated a program called ICECool Applications (Intra/Interchip Enhanced Cooling). “ICECool is exploring disruptive thermal technologies that will mitigate thermal limitations on the operation of military electronic systems while significantly reducing the size, weight, and power consumption,” explains the GSA website FedBizOpps.gov. What is unique about this method of cooling is the push to use a combination of intra- and/or inter-chip microfluidic cooling and on-chip thermal interconnects. The DARPA ICECool Application announcement notes, “Such miniature intra- and/or inter-chip passages (see right) may take the form of axial micro-channels, radial passages, and/or cross-flow passages, and may involve micro-pores and manifolded structures to distribute and re-direct liquid flow, including in the form of localized liquid jets, in the most favorable manner to meet the specified heat flux and heat density metrics.” Using the above technology, engineers at Lockheed Martin have experimentally demonstrated how on-chip cooling is a significant improvement. “Phase I of the ICECool program verified the effectiveness of Lockheed's embedded microfluidic cooling approach by showing a four-times reduction in thermal resistance while cooling a thermal demonstration die dissipating 1 kW/cm2 die-level heat flux with

multiple local 30 kW/cm2 hot spots,” mentions the Lockheed Martin press release. In phase II of the Lockheed Martin project, the engineers focused on RF amplifiers. The press release continues, “Utilizing its ICECool technology, the team has been able to demonstrate greater than six times increase in RF output power from a given amplifier while still running cooler than its conventionally cooled counterpart.”

MicroCooling 1 - Image: DARPA.

Moving to production Confident of the technology, Lockheed Martin is already designing and building a functional microfluidic cooled transmit antenna. Lockheed Martin is also collaborating with Qorvo to integrate its thermal solution with Qorvo's high-performance GaN process. The authors of the research paper DARPA's Intra/Interchip Enhanced Cooling (ICECool) Program suggest ICECool Applications will produce a paradigm shift in the thermal management of electronic systems. “ICECool Apps performers will define and demonstrate intra-chip and inter-chip thermal management approaches that are tailored to specific applications and this approach will be consistent with the materials sets, fabrication processes, and operating environment of the intended application.” If this microfluidic technology is as successful as scientists and engineers suggest, it seems Moore's Law does have a fighting chance. Read more

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GANEX | Newsletter No. 42 - III-N Technology 54

PATENT APPLICATION

More than 210 new patent applications were published between 2016-06-02 and 2016-07-01.

Patent Applicants Number of new patent applications

NGK Insulators 5

Infineon 5

Seoul Viosys 4

Sino Nitride Semiconductor 4

Toyoda Gosei 4

Dowa Electronics 4

Intel 4 Other patent applicants: 38th Research Institute China Electronics Technology, Aledia, Anhui Sanan Optoelectronics Technology, Asahi Kasei E-Materials, Avogy, Bae Systems, Beijing NMC, Changzhou Optics Photoelectric, China Bright Photoelectricity, CNRS, Cree, Dalian Dehao Photoelectric Technology, Denso, Disco, Electronics & Telecommunications Research Institute (ETRI), Enraytek Optoelectronics, Episil Technologies, Foshan Guoxing Semiconductor Technology, Freescale Semiconductor, Fuji Electric, Fujitsu, Georgia Technology, Guangdong Quantum Wafer Optoelectronic Technology, Guangdong Real Faith Semiconductor, Guangdong University Of Science & Technology, Hangzhou Dianzi University, Hangzhou Silan Azure, HC Semitek, Hebei University Of Technology, Huazhong University Of Science & Technology, Iljin Led, Imec, Indian Institute Of Technology Bombay, Institute Of Semiconductors, Intermolecular, Jiangnan University, Jiangsu Broadwave Electronics Technology, Katholieke Universiteit Leuven - Ku Leuven, Korea Advanced Institute Of Science & Technology (KAIST), Lattice Power, LG Innotek, Lockheed, Mitsubishi Chemical, Mitsubishi Electric, National Taiwan University, Nichia, No 55 Institute Of China Electronics Science & Technology, Northrop Grumman Systems, Osaka University, Panasonic, Peugeot Citroen Automobiles, Playnitride, Renesas Electronics, Samsung Electronics, Sensor Electronic Technology, Seoul Semiconductor, Shandong Tide China Light Photoelectron, Sharp, Shineon Technology, Silan, Sixpoint Materials, Sony, Sumitomo Electric Device Innovations, Sumitomo Electric Industries, Sun Yat Sen University, Sunedison Semiconductor, Sungrow Power Supply, Taiyuan University Of Technology, Tianjin San An Optoelectronics, Tokuyama, Toshiba, Transphorm, Tsinghua University, Universite Lille 1 Sciences & Technologies, University Beijing, University Libanaise, University Of Chiba University, Wenzhou University, Xi An University Of Technology, Xiamen Changelight, Xiangneng Hualei Optoelectronic Corppration, Xidian University, Yan Min, Yancheng Institute Of Technology, Yuanrong Photoelectric Technology, Zhejiang Inteled Optoeletronic Technology …

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GANEX | Newsletter No. 42 - III-N Technology 55

New patent applications selected by Knowmade Integrated circuit die having reduced defect group III-nitride layer and methods associated therewith Publ. Nb: WO2016099494, WO2016099491 Patent Applicant: Intel (US)

Embodiments of the present disclosure are directed towards an integrated circuit (IC) die. In embodiments, an IC die may include a semiconductor substrate, a group III-Nitride or II-VI wurtzite layer disposed over the semiconductor substrate, and a plurality of buffer structures at least partially embedded in the group III-Nitride or II-VI wurtzite layer. In some embodiments, each of the plurality of buffer structures may include a central member disposed over the semiconductor substrate, a lower lateral member disposed over the semiconductor substrate and extending laterally away from the central member, and an upper lateral member disposed over the central member and extending laterally from the central member in an opposite direction from the lower lateral member. The plurality of buffer structures may be positioned in a staggered arrangement to terminate defects of the group III-Nitride or II-VI wurtzite layer. Other embodiments may be described and/or claimed. Read more

Light-emitting element and method for manufacturing same Publ. Nb: WO2016093257 Patent Applicant: Marubun, Riken, Tokyo Ohka Kogyo, Toshiba Machine, Ulvac

A semiconductor light-emitting element with a reflective film disposed on a front surface (side) of a GaN substrate and with a photonic crystal periodic structure disposed on a rear surface (side) of the GaN substrate, the photonic crystal periodic structure being such that the design wavelength λV in vacuum, a period a as a periodic structure parameter, and a radius R satisfy the Bragg condition, wherein, in a range of R/a of 0.18 to 0.40, a TM light photonic band structure has two photonic bandgaps within the fourth photonic band. Read more

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GANEX | Newsletter No. 42 - III-N Technology 56

Recessed ohmic contacts in a III-N device Publ. Nb: US2016172455, WO2016100225 Patent Applicant: Transphorm (US)

A device includes a III-N layer having an upper side and a lower side, the lower side being opposite the upper side, and at least one conductive contact on the upper side of the III-N layer, the conductive contact extending into the III-N layer. The conductive contact comprises a top side facing away from the lower side of the III-N layer, and a bottom side facing towards the lower side of the III-N layer. The bottom side includes a first end and a second end opposite the first end, a first side rising from the first end to an intermediate point closer to the top side than the first end, and a second side falling from the intermediate point to the second end further from the top side than the intermediate point. Read more

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