HIGH ELECTRON MOBILITY TRANSISTORS

Presented by: Date: 04/28/2014

Sujana Korrapati,

Sai Divya Anne

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.

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

Source:http://research.pbsci.ucsc.edu/chemistry/li/research.html

•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

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

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-and-aim/high-electron-mobility-transistors-hemt.html

ADVANTAGES OF INP BASED HFETS

Lower noise

Higher cutoff frequency

Higher gain

Operating voltage below 3 V

AlGaAs donorlayer

GaAs buffer

AlGaAs spacer

AlGaAs/GaAs HEMT

ΦB

EF

∆Ec

AlGaN

GaN

d

Ec

AlGaN/GaN HEMT

2 DEG

σsurf

σBσcomp

+ve

COMPARISON OF GAN HEMT WITH GAAS HEMT

HEMT APPLICATIONS

A Monolithic HEMT Passive Switch for Phased-

Array Applications

High Power and High Efficiency GaN-HEMT for

Microwave Communication Applications

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 HIGH-SPEED 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 ??