Design, Simulation and Modeling of AlGaN/GaN High Electron Mobility Transistors

dehisceforkElectronics - Devices

Nov 2, 2013 (3 years and 11 months ago)

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Design, Simulation and Modeling of AlGaN/GaN High Electron Mobility Transistors

Nitin Goyal

and Tor A. Fjeldly

Norwegian University of Science and Technology

AlGaN/GaN high electron mobility transistors (HEMTs) are emerging as promising candidates for
radio
-
frequency (RF)/microwave power amplifiers and high temperature electronics

for hostile environments
,
due to
the unique capabilities of achieving high breakdown voltage, high current density, high cut
-
off frequencies,
highly linear characteristics and

high operating temperatures.

T
his can be attributed to the e
xcellent physical
properties of

a
h
igh band gap (more than 3.4 eV)
,
a
high spontaneous and piezoelectric polarization
,

and
a
high
critical field for breakdown of these nitrid
e based heterostructures.
Due to
the
lattice mismatch between AlGaN
and GaN,
the
AlGaN layer is pseudo
-
morphically grown on the GaN substrate and strain
-
induced piezoelectric
polarization present in
the
AlGaN layer

is much higher than that in

traditional I
II
-
V semiconductors. Due to this,
a positive
fixed

sheet charge is present at the AlGaN/GaN interface and an equal and opposite negative sheet
charge (2DEG) is present at the top AlGaN surface.

It has been shown that distributed surface donor states
presen
t at the top AlGaN layer are the main source of
the two
-
dimensional
gas (2DEG)
in the quantum well
at
the AlGaN/GaN interface.

As part of
the EU project COMON (
Compact modeling framework
)
, we have
developed a physics based charge model for
the
AlGaN/GaN he
terostructures. An analytical model for bare
surface barrier height

(SBH)

was also developed using the same theoretical formulation. Strain relaxation in
AlGaN at higher thicknesses and their corresponding effects on the resultant
SBH and 2DEG is also show
n.

The
p
roposed a
nalytical model
s are

in good agreement with reported experimental data

as indicated in the figures
below.



Figure. 1 Structure of AlGaN/GaN
HEMT




Figure.
2

Numerical Simulation of
AlGaN/GaN

h
eterostructure showing
different
sub bands.


Figure.
3

Band Diagram of
AlGaN/GaN
heterostructure with low
density surface donor states and 2DEG



Figure.
4

Normalized residual strain as
function of AlGaN barrier layer
thickness





Figure.
5

Modeled 2DEG

charge
density

and

c
omparison with
experimental data
.



Figure.
6


Modeled SBH including
strain relaxation and comparison with
experimental data
.