HEMTs (High Electron Mobility Transistors) are transistors that use a heterojunction between two semiconductor materials with different band gap energies to confine electrons in a 2D gas layer. This results in much higher electron mobility than conventional transistors, allowing HEMTs to operate at higher speeds with lower noise. Key features include a heterojunction interface that forms a potential well trapping electrons, reducing scattering and increasing mobility. Initial applications were in high-speed microwave devices, and HEMTs are now widely used in cell phones and other wireless technologies.

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

2. CONTENTS FLOW
• LIMITATIONS OF CONVENTIONAL TRANSISTORS
• HEMT INTRODUCTION
• HETEROJUNCTION REQUIREMENT
• BAND STRUCTURE AND BAND BENDING
• HOW THEY WORK??
• SWITCHING IN HEMT
• APPLICATIONS
• CONCLUSIONS

3. LIMITATIONS OF CONVENTIONAL
TRANSISTORS
• Short channel effects
• Gate leakage current
• Gate power dissipation
• Ionizing Impurities
• Lattice and impurities scattering
• Less mobility
• Less transconductance

5. HEMT STRUCTURE

6. AlGaAs-GaAs HEMT band diagrams

7. HETERO JUNCTION REQUIREMENT
•Two dissimilar semiconductor having
different band energies.
•Lattice match between them.
AlGaAs/GaAs have excellent match.

8. FORMATION OF NOTCH

10. SWITCHING IN HEMT

11. HEMT STRUCTURE

12. 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

13. 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

14. CONCLUSIONS
• Free carrier concentration increase without significant dopant
impurities.
• 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.