simulation of hemt slide

7/23/2019 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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simulation of hemt slide

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