Download - Gallium Nitride

Gallium NitrideGallium Nitride

Presented by

Rakesh Sohal

Supervision

Prof. Dieter Schmeißer

Research & Development

OutlineOutline

•Introduction•GaN - Physics•Crystal Growth MOVPE MBE•Substrates & Buffer layers•Recent Advances•Applications

GaN - Research & Development

Why GaN ?Why GaN ?

Semiconductor with Direct and Wide Bandgap•Optoelectronics Devices•Blue & Blue/green light emitters•Transistors withstand extreme heat and•High frequencies and power levels•More efficient amplifiers at base stations•Si-only 10% power used and 90% wasted as heat


GaN PhysicsGaN Physics

a

Crystal Structure

Zince BlendeWurtzite


GaN PhysicsGaN PhysicsEnergy band Structure


GaN comparisonGaN comparison

Silicon cannot provide the power-bandwidth product for military applications


GaN-Crystal GrowthGaN-Crystal Growth

First epilayer by vapour transport - Murusk and Tietjen (1969) Growth rate - 0.5µm/min. High background n-type carrier concentrations ~1019 cm-3

Modern Technique - MOVPE by Nakamura Key aspect : downward subflow of He and N2

Claim - Improves the interaction of the reactant gases with the substrate

Shortcomings High Substrate temperature Thermal mismatch strain & defects

MOVPE Approach


GaN-Crystal GrowthGaN-Crystal GrowthMBE Approach

N - supplied by µ-wave plasma excitation provided by compact ECR Limited N-flux lower growth rate(GR) ~ 500Å/hr.

GR can be increased by higher power Degraded Material Quality


GaN-Crystal GrowthGaN-Crystal GrowthSubstrates for Epigrowth

Baule Growth efforts are ongoingTill date - not possible

The only Option - Heteroepitaxy

The most Stringent Issue/Barrier



650nm650nm

650nm

650nm

650nm

AlN

BN

MgO3C-SiC

6H-SiC

AlN

BN

GaNGaN

InN

Sapphire

Lattice Constant / Å

Ban

d ga

p / e

V 4.5

5.5

3.5

2.5

1.5

6.5

2 2.5 3 3.5 4 4.5 5 5.5

ZnOHexagonalCubic

Thermal & lattice mismatch - Strain and Defects



Thermal & lattice mismatch - Strain and Defects



GaN-Crystal GrowthGaN-Crystal GrowthInterfacial buffer layer

AlN GaN

- Akashaki - Nakamura

Large lattice and thermal mismatch

Strained and sometime cracked layers

GaN-AdvancesGaN-Advances

Three major hurdles has been cleared

• Heteroepitaxy - via buffer layer• Control of n (Si) & p(Mg)-type doping• Reduction in dislocation density

Residual e-concentrations - --- due to N-vacancies(earlier) Van de Walle showed - energy required for Nv too high--- due to O incorporation


GaN-AdvancesGaN-AdvancesUse for patterned SiO2

Robert F. Davis, Proceedings of the IEEE, Vol. 90, No. 6, 2002


Comparison - bulbs & LEDsComparison - bulbs & LEDsGaN - Research & Development

New two flow MOCVDNew two flow MOCVDNakamura‘s Method


Pioneer of Nakamura Pioneer of Nakamura • 1989-Started III-V nitride research.• 1990-Develops new ‘two-flow’ MOCVD equipment for growth of

high quality single crystal GaN layers.• 1992-begins to grow InGaN single crystal layers for the production

of double heterostructures.• 1993-Succeeded in developing a blue LED with a luminous

intensity as high as 2cd using III-V nitride materials.• 1995-Developed high-brightness SQW structure blue/green LEDs

with a luminous intensity of 2 cd and 10 cd, and developed a violet laser diode using III-V nitride materials for the first time.

• 1996-The first current infection III-V nitride based LDs were fabricated.

• 1996-Announces the first CW blue GaN based injection laser at room temperature.


The thickness of the GaN buffer layer was varied between 100Å and 1200Å

The substrate was heated to 1050oC in a stream of hydrogen

The substrate temperature was elevated to between 1000oC and 1030oC to grow the GaN

film.

The substrate temperature was lowered to between 450oC and 600oC to grow the GaN

buffer layer.

The total thickness of the GaN film was about 4 m,and the growth time was 60 min.

Steps to grow crystalline GaNSteps to grow crystalline GaNNakamura‘s Method


Buffer layer thicknessBuffer layer thickness

The value of the FWHM is almost constant between 200Å and 1200Å thickness.The optimum thickness of the GaN buffer layer was around 200Å


GAN - PotentialGAN - PotentialGaN - Research & Development

• Large scale displays (large outdoor television screens)

• Smaller full-color flat panel display screens

(inside trains or subway stations)

• Full-color scanners

• Full-color photocopying machines

• Full-color FAX machines

• Traffic lights

• LED white lamps

ApplicationsApplicationsGaN - Research & Development

ApplicationsApplications

2 inch dia blue LED wafer on GaN-on-sapphire


Thanks for

your attention!
