Transcript SeminarPresentations\HEMTAmirAbdurahimRev1x

High electron mobility
transistors (HEMT)
AMIR ABDURAHIM
EE4611
04/11/2016
Introduction
•
Is a FET
•
Uses Hetero-junction instead of PN junction
•
Uses high mobility materials (GaAs/AlGaAs, GaN/AlGaN,
III-V)
•
Small gate-to-channel separation to keep capacitance
and drift time to minimum
Introduction (continue)
 Optimum
performance at 30– 300GHZ
 Often
used in high gain, low noise
applications
 Works
best under high temperature (269c)
 GaN
HEMT works best for high power
applications due to its high band gap
 InP
is super low noise transistor. Fastest
transistor in the world (Cut off at 500GHZ)
Potential Applications

Satellite communication

Wireless communication

TV signals

Cellphones

Radars

radio astronomy
Before HEMT (GaAs MESFET)

GaAs MESFET

Used in high frequency
applications

GaAs preferred due to its high
carrier mobility

Si was replaced by GaAs

Was used in application such as
RF amplifiers
GaAs MESFET

GaAs semiconducting layer has to be doped to
ensure that the electrons are mobile

This created a problem of electrons collision with
impurities

The collision degraded the high mobility of GaAs
HEMT
GaAs/AlGaAs
 Hetero-juction: junction
between two materials with
2 different band gap
 forms a two dimensional
electron gas (2-deg) along
the GaAs
 Conduction Channel along
GaAs

HEMT
HEMT (energy band interface)



Electrons trapped in
the quantum well due
to band gap
difference
It can accumulate up
to 10^12/cm^2 in a
thin layer of <900nm
No depletion since
AlGaAs is fully
depleted under
normal condition
HEMT (energy band interface)

Creation of quantum well
Summary and Conclusion

HEMT uses Hetero-junction instead of PN junction

Used in high bandwidth, low noise and high power
applications

Small gate-to-channel separation to keep capacitance and
drift time to minimum

Electrons accumulate in the conduction channel as 2
dimensional electron gas (2-DEG)

HEMT has the ability to locate a large electron density in a thin
layer (<900nm)

High electron mobility and maximum electron velocity in
GaAs makes more applicable than MESFET
Work cited

Pal, Gyan Prakash, and Anuj Kumar Shrivastav. "International
Journal of Scientific and Engineering Research." International
Journal of Scientific Research Engineering &Technology
(IJSRET) (2012): 43+. Web. 08 Apr. 2016.

Poole, Ian. "HEMT, High Electron Mobility Transistor Tutorial." What Is a
HEMT. Adrio Communications Ltd. Web. 08 Apr. 2016.

Poole, Ian. "GaAs FET MESFET Tutorial." MESFET / GaAs FET| MEtal
Semiconductor FET / Gallium Arsenide. Adrio Communications Ltd.
Web. 08 Apr. 2016.

Zhaojun Liu, Tongde Huang, Qiang Li, Xing Lu, and Xinbo Zou
Synthesis Lectures on Emerging Engineering
Technologies 2016 2:3, 1-73
Five concepts

HEMT is a Field transistor

HEMT uses Hetero-junction rather than PN
junction

Small gate-to-channel separation to keep
capacitance and drift time to minimum

HEMT used for high gain and low noise
applications

Works best under high temperature