Simulation of HEMT slide
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Transcript of Simulation of HEMT slide
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I. Introduction
II.Objective
III.Literature Review
IV.Methodology
V.Future DevelopmentVI.Gantt Chart
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High electron mobility transistor(HEMT) is a three
terminal device consisting of a junction/channel between 2
different band-gap materials (heterojunction) instead of a
doped region (MOSFET).
HEMT is one type of FET with excellent high frequencycharacteristics.
Operation principle of HEMT is based on metal
semiconductor field effect transistor MESFET.
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HEMT is also known as
MODFET(Modulation-doped FET)TEGFET(Two-dimensional Electron Gas FET)
SDHT(Selectively Doped heterostructure Transistor)
HFET(Heterojunction FET).
Figure 1 Schematic Draw of HEMT device[1]
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The current between drain and source is controlled by the
space charge which is changing by control the voltage to the
gate contact (Behave like a switch).
The current between drain and source is flowing through
the two dimensional conducting channel (2DEG) which
created by electrons.
The 2DEG channel is formed below the hetero-interface of
two different band-gap material as in the case of
AlGaN/GaN material and AlGaAs/GaAs material.
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Two dimensional electron gas is a couple of nanometer
thick thin layer for all the electrons gathered to minimize
their energy. It is also known as a conducting channel
where allows free electrons travel from source to drain.
At heterostructure junction, the Fermi level must be
continuous over the heterostructure since the two different
band gap materials are in contact.
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In order fulfill the requirement of Fermi level, the energy
band will be bend and an energy valley or potential well willbe formed.
According to Charles Kittel Introduction to solid state
physics, the potential well is very thin, electron prefer todiffuse sideways instead of up and down because otherwise
they would have to move out the well into a less preferable
energy state.
Figure 2 Conduction band of an n-doped AlGaAs and semi-insulating GaAs Junction[2]
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High Electron Mobility Transistor is a promising
candidate for microwave power amplification such asmobile satelite communication systems because HEMT has
lower noise and better performance at high frequencies.
As compared to MESFET, HEMT has higher trans-conductance due to the close confinement of channel to the
gate and high mobility of the carriers without presence of
ionized impurity scattering.
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As compared to Heterojunction bipolar transistor (HBT),
HBTs able to operate a higher current and power densityhowever, device dimension critical for HBT speed are not
planar.
Figure 3 Performance Comparison, Weakness and strength of MESFET,HEMT and HBT[4]
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To simulate characteristics of high electron mobility
transistor using Sentaurus.
To simulate and study the fabrication process of the
device structure.
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Technology Computer Aided Design (TCAD) is
using physics based computer for simulating
semiconductor processing and device operation to
design , analyze and optimize semiconductor
devices.[5]
This physics based approach is represent available of
physical knowledge of semiconductor processing and
devices in terms of computer models.
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The advantages of TCAD:
Less time consuming when developing and
characterizing a novel structures.
Easy for understanding of how a device work well as
they can be utilized in order to reproduce or predict a
trend.
Simulation reduce the cost of a device studying without
using real devices.
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Sentaurus TCAD is the software suite consists of many
different modules that are used in different situation tosimulate your desired devices, invented by Synopsys Inc.
For this final year project , there are 3 modules are used
instead of 4 modules.1. Sentaurus Workbench(SWB)
2. Sentaurus Device(SDevice)
3. Sentaurus Structure Editor(SDE)
4. Inspect/Techplot
Sentaurus Work Bench(SWB) is primary graphical font
that integrates Sentaurus simulation program into single
environment. The graphical user interface is used to design,
organize and run simulation.
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Ligament is a generic interface for TCAD processsimulations. Ligament consist of 2 editor :
Ligament Flow Editor ->To create and edit process
flows.
Ligament Layout Editor->To create and edit layouts.
Techplot is a plotting software with 2D and 3D
visualization for visualizing data from simulations and
experiments.11
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Figure 4 Conventional Epitaxial Structure of a basic AlGaAs/GaAs HEMT[5]
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Substrate
Buffer Layer
Buffer
Layer 2
ChannelLayer
Spacer Layer
Delta dopinglayer
Donor Layer
Cap Layer Metallization
Passivation
Gateformation
Figure 5 Flow Chart of Fabricating pHEMT in Sentaurus
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Figure 6 Table of parameters for deposition process of pHEMT in Sentaurus
Layer Material Deposit
Thickness
Annealing
Temperature
Time of
Annealing
Buffer Layer GaAs 20nm 200c 10 sec
Buffer Layer AlGaAs 4nm 1050c 10 sec
ChannelLayer InGaAs 12nm 1050c 10 sec
Spacer Layer AlGaAs 4nm 1050c 10 sec
Delta doping
Layer
Silicon, Si 5nm 1050c 10 sec
Donor Layer N+ AlGaAs 40nm 1050c 10 secCap Layer N+ GaAs 4nm 1050c 10 sec
Passivation
Layer
Silicon Nitride
Si3N4
10nm 1050c 10 sec
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Si3N4 Passivation Layer
Nickel Contact
Figure 8 Design and Structure of my AlGaAs/InGaAs/GaAs HEMT
AlGaAs Buffer Layer
InGaAs Channel
AlGaAs Spacer LayerSilicon Delta Doped Layer
n+AlGaAs Donor layer
GaAs Cap Layer
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In order to achieve higher output power density , high
electron mobility transistor (HEMT) need a high currentdensity and high sheet charge concentration.
The breakdown voltage is an important parameter to
determine the classification of power devices.
The higher breakdown voltage can be biased at higher
drain voltage so drain efficiency, voltage gain and power
added efficiency will increased.
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There are several approach in order to increase the
breakdown voltage for HEMT proposed by MauriceH.Francombe Frontiers of thin film technology.
Planar doping AlGaAs layer (Donor Layer).
Low Temperature grown GaAs Buffer layer.
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Substrate: Semi-insulating GaAs
According to thesis of Dr.Noor Muhammand Memon,he mentioned GaAs has attractive features at high
frequencies compared to silicon.
The conduction band electrons in GaAs is six timeshigher mobility and twice the peak drift velocity as that
of silicon. This lead to low parasitic resistance, large
transconductance and shorter transit time.
The larger band-gap in GaAs allow working in a
higher temperatures so it is important for small
geometry power devices.
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Buffer Layer: Unintentionally doped GaAs
Actis et al 1995,stated the low temperature grown GaAs asbuffer layer can increase the breakdown voltage and reduce
the threading dislocation between channel and substrates.
Channel Layer: Unintentionally doped InGaAs
Based on Smith et al 1989, InGaAs helps maintaining a
high breakdown voltage and InGaAs has good balance
between its high mobility and manageable band gap.
Based on Roberto Menozzi and his team 1998,varying Al
mole fraction x into AlGaAs can widen the band gap but
they also investigated the parasitic effect (DX center) after
increasing x more than 0.2.
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So to avoiding AlGaAs is presence of a deep level defect
(DX center) which trap electron and weaken the HEMToperation, thin layer of InGaAs will be used to form a
pseudomorphic HEMT due to large conduction band
discontinuity between InGaAs/AlGaAs can be achieved.
Spacer Layer: AlGaAs
Spacer layer is used to increase the mobility of electron in
two dimensional electron gas channel. AlGaAs layercontains a low energy barrier for electron so It can maximize
the high electron mobility in channel.
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Passivation Layer: Silicon Nitride, Si3N4
Passivation Layer is used to keep unwanted element away
from channel.
Silicon Nitride is industry standard material as a source of
passivation layer due to its has high dielectric constant.
Ohmic Contact layer: Nickel
Nickel is often actual substrate contact because it has best
sticking properties. In order to achieve low contact
resistance, alloyed metal contact play an important role foroptimum device performance.(Kezia Cheng)
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The future development to enhance the HEMTs
structure and characteristic:
T-gate /Mushroom gate
Alloyed Ohmic Contact
Partially Oxidized pHEMTS
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[1] Peter Javorka, Fabrication and Characterization ofAlGaN/GaN High
electron mobility Transistor,2004.
[2] Andres Lundskog, Characterization of advanceAlGaN HHEMT
structures,2007.
[3]Otto Berger, GaAs MESFET, HEMT and HBT Competition With
Advanced Si RF technologies Mantech 1999.
[4]L. Aucoin, Chapter IV. HEMTs and PHEMTs.
[5]TCAD Sentaurus Tool Training Manual Book, Synopsys 2011.[6] Maurice H.Francombe , Frontiers of thin film technology, 2001.
[7] Dr Noor Muhammad Memom, Modeling Techniques of Submicron GaAs
MESFETs and HEMTs ,2008.
[8] Actis et al 1995
[9] Smith et al, Milimeter-wave Power Operation of AlGaAs/InGaAs/GaAs
Quatum Well MISFET, 1989.[10]Roberto Menozzi, Hot Electron and DX centerInsensivitivity of
Al0.25Ga0.75As/GaAs HFETs Designed For Microwave Power Applications ,
1998.
[11]Kezia Cheng, Effect ofOhmic Metal on Electrochemical Etching Of GaAs in
pHEMT Manufacturing .
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