(High Electron Mobility Transistor)A REVOLUTION FOR HIGH SPEED DEVICES

CONTENTS FLOW

• LIMITATIONS OF CONVENTIONAL TRANSISTORS

• HEMT INTRODUCTION

• HETEROJUNCTION REQUIREMENT

• BAND STRUCTURE AND BAND BENDING

• HOW THEY WORK??

• SWITCHING IN HEMT

• APPLICATIONS

• CONCLUSIONS

LIMITATIONS OF CONVENTIONAL TRANSISTORS

• Short channel effects

• Gate leakage current

• Gate power dissipation

• Ionizing Impurities

• Lattice and impurities scattering

• Less mobility

• Less transconductance

HEMT STRUCTURE

AlGaAs-GaAs HEMT band diagrams

HETERO JUNCTION REQUIREMENT

•Two dissimilar semiconductor having different band energies.

•Lattice match between them.

AlGaAs/GaAs have excellent match.

FORMATION OF NOTCH

SWITCHING IN HEMT

HEMT STRUCTURE

2-D ELECTRON GAS

HIGH ELECTRON MOBILITY TRANSISTORS (HEMT)

• High speed device

• Referred to as heterojunction field effect transistors.

• Two layer of different semiconductor with different band gap energies.

2-D ELECTRON

GAS

LESS ELECRON

COLLISION

LESS NOISE+HIGH

MOBILITY

APPLICATIONS

Originally for high speed applications• High power/ high temperature microwave applications• Power amplifiers• Oscillators• Cell Phones• Radar• Most MMIC’s radio frequency • Compatible for nano devices

CONCLUSIONS

• Free carrier concentration increase without significant dopantimpurities.

• Reduced ionised impurity scattering hence higher mobility.

• Good electron confinement within 2 Dimensional Electron Gas (2DEG).

• Fantastic mobility. 2,50,000cm2/Vsec at 77K and 20,00,000cm2/Vsec at 4K. APROX 200-300 times more than conentional transistors.

• Its two main features are low noise and high frequency capability.

• A heterojunction is two layers different semiconductors with different band gap energies.

• The 2-D electron gas is essential to the low noise feature.

• AlGaAs and GaAs are the most common materials for heterojunction.