(High Electron Mobility Transistor)
A REVOLUTION FOR HIGH SPEED DEVICES
•SCHOOL OF MATERIAL SCIENCE
•LIMITATIONS OF CONVENTIONAL
•BAND STRUCTURE AND BAND BENDING
•HOW THEY WORK??
•SWITCHING IN HEMT
• 1960 GaN small crystals was made.
• 1980 Takashi Mimura, Fujitsu laboratories
designed the features of the first HEMT.
• 1985 HEMT was announced the lowest
• 1994 the first AlGaN/GaN HEMT was
• After 2010 it is widely used for high speed
•Short channel effects
•Gate leakage current
•Gate power dissipation
•Lattice and impurities scattering
HIGH ELECTRON MOBILITY TRANSISTORS (HEMT)
•High speed device
•Referred to as heterojunction field effect transistors.
•Two layer of different semiconductor with different band gap
•Two disimmilar semiconductor having
different band energies.
•Lattice match between them.
Alx Ga(1-x)As/GaAs have excellent match.
Electron affinities qc1 for GaAs and qc2 AlxGa1-xAs
Results so far: EC1 and EC2 band-bending:
Keeping the electron affinities correct resulted in a triangular quantum well in EC
(for this heterojunction combination):
In this region: a triangular
quantum well has developed
in the conduct
We have got electron which
have got a high mobility, put a
contact between two ends.
If we apply a vltage between
them the electron gets
Electrons locked up here can be used up by
Originally for high speed applications
•High power/ high temperature microwave
•Most MMIC’s radio frequency
•Comaptible for nano devices
• Fantastic mobility. 2,50,000cm2/Vsec at 77K and
20,00,000cm2/Vsec at 4K. APROX 200-300 times more than
•Its two main features are low noise and high frequency
•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