Transcript High Electron Mobility Transistors

HIGH ELECTRON MOBILITY TRANSISTORS
Abstract: HEMT is a field effect transistor incorporating a
junction between two materials with different band gaps
as the channel. We will discuss different types of HEMTs
and their Applications.
Presented by:
Sujana Korrapati,
Sai Divya Anne
Date: 04/28/2014
OUTLINE

Introduction

GaN HEMT structure and operation principles

Design rules for AlGaN/GaN HEMT

InP HEMT

Comparison of GaN HEMT with GaAs HEMT

Applications in Technology

Summary
INTRODUCTION

Transistors are used in electronic devices
e.g. switch, amplifiers, oscillators


To satisfy the growing demands of

High Power

High Speed

High Efficiency communications
Conventional HEMTs use a AlGaAs/GaAs
AlGaN/GaN
BASIC GAN HEMT STRUCTURE
Source: http://www.eetimes.com/document.asp?doc_id=1272514
GALLIUM NITRATE


High electron density(Polarization effects)
Adequate for high power amplifiers High
Breakdown voltage

Large heat capacity

Necessary to growth in a wafer of another material

Molecular Beam Epitaxy

Metal Organic Vapor Beam Epitaxy
SUBSTRATE MATERIAL

Sapphire

Most used material, cheap, good quality commercial
wafers.



Poor thermal conductivity.
Silicon Carbide

Low lattice mismatch.

High thermal capacity.
Silicon

Most common semiconductor.

Acceptable thermal conductivity.
OPERATION PRINCIPLES (POLARIZATION)
AlGaN/GaN HEMTs transistor don’t need doping
to obtain a high electron density.
Spontaneous polarization.
+
Piezoelectronic polarization.
=
1013 (cm2/Vs) carrier concentration
ENEGRY BAND DIAGRAM OF GAN/ALGAN HEMT
•HEMTs utilize heterojunction
between two semiconducting
materials to confine electrons to
a triangular quantum well.
•Conduction band edge EC
and Fermi level EF determine
the electron density in the
2DEG
Source:http://research.pbsci.ucsc.edu/chemistry/li/
research.html
HETEROJUNCTION
Heterojunction: 2 layers
•Highly doped layer
with grand gap
•Non-doped layer
with small gap
DESIGN RULES FOR GAN/ALGAN HEMTS:
MATERIALS PERSPECTIVE

Thickness of the Barrier Layer

Al composition of the barrier layer
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Nucleation and Buffer layer

Substrate for epitaxial growth
DESIGN RULES FOR GAN/ALGAN HEMTS:
FABRICATION PERSPECTIVE

Gate footprint, cross-sectional area and width controls
the frequency response

Gate drain spacing as well as gate footprint
determines the breakdown voltage

Geometry of the device also plays a role
DC CHARACTERISTICS OF GAN/ALGAN HEMTS
INP HEMT
Source: http://www.mwe.ee.ethz.ch/en/about-mwe-group/research/vision-andaim/high-electron-mobility-transistors-hemt.html
ADVANTAGES OF INP BASED HFETS

Lower noise

Higher cutoff frequency

Higher gain

Operating voltage below 3 V
COMPARISON OF GAN HEMT WITH GAAS HEMT
Φ
B
AlGa
N
GaN
c
d
σcomp
+v
e
σsurf
Ec
∆E
EF
σB
AlGaA
s donor
layer
GaAs buffer
2 DEG
AlGaAs
spacer
AlGaN/GaN HEMT
AlGaAs/GaAs HEMT
HEMT APPLICATIONS

A Monolithic HEMT Passive Switch for PhasedArray Applications

High Power and High Efficiency GaN-HEMT for
Microwave Communication Applications
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Highly efficient high power InP HEMT amplifiers for
high frequency applications

Highly Uniform InAlAs–InGaAs HEMT Technology
for High-Speed Optical Communication System ICs
A MONOLITHIC HEMT PASSIVE SWITCH FOR
PHASED- ARRAY APPLICATIONS
A 0.2 x 200 ,um2 HEMT
device is used as a series
passive FET switch
HIGH POWER AND HIGH EFFICIENCY GAN-HEMT
FOR MICROWAVE COMMUNICATION APPLICATIONS
In the typical mobile communication band of more than 2GHz, the RF
signal loss through the Cds and Rs becomes significant. Thus, the
minimization of Cds is effective in the high efficiency amplification.
INALAS–INGAAS HEMT TECHNOLOGY FOR HIGHSPEED OPTICAL COMMUNICATION SYSTEM ICS

Uniformity of the transistors is required to fabricate
high-speed ICs

ICs with more than 1000 transistors were fabricated
using Y-shaped gate technology and operated at 40 Gb/s
SUMMARY & CONCLUSIONS

HEMT transistor are widely used in electronic
application

AlGaN/GaN structure looks promising

AlGaN/GaN HEMT grown on Si substrate not
only reduces the production cost but also
prepares for the possible combination of GaN
devices and Si technology
REFERENCES
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&
arnumber=536950
 http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&
arnumber=5877127
 http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&
arnumber=1219481
 “Characterization of advanced AlGaN HEMT
structures” Anders Lundskog.
 http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&
arnumber=877122

FIVE KEY POINTS ABOUT HEMT

3 contacts:
Source and drain  ohmic contacts.
Gate Schottky barrier

Conventional HEMTs use a AlGaAs/GaAs AlGaN/GaN

High electron density (Polarization effects)

The HEMT-HBT monolithic microwave integrated circuit (MMIC)
is fabricated using selective molecular beam epitaxy (MBE)

InAlAs-InGaAs HEMT grown on InP substrate promises excellent
gain and noise performance for amplifier applications
QUESTIONS ??