Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency
The mm-wave as well as noise properties of IMPATT diodes for the D-band are efficiently determined, with 4H-SiC and wurtzite type GaN as base materials, using advanced computer simulation techniques developed by the authors. The breakdown voltage (180 V) and efficiency (14.7%) is higher in case of 4...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2011
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| Цитувати: | Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency / P.R. Tripathy, M. Mukherjee, S.P. Pati // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 2. — С. 137-144. — Бібліогр.: 26 назв. — англ. |
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irk-123456789-1177152017-05-27T03:02:51Z Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency Tripathy, P.R. Mukherjee, M. Pati, S.P. The mm-wave as well as noise properties of IMPATT diodes for the D-band are efficiently determined, with 4H-SiC and wurtzite type GaN as base materials, using advanced computer simulation techniques developed by the authors. The breakdown voltage (180 V) and efficiency (14.7%) is higher in case of 4H-SiC as compared to wz GaN based diode having the breakdown voltage (153 V) and efficiency (13.7%). The study indicates that 4H-SiC IMPATT diode is capable of generating high RF power density of about 8.383×10¹⁰ W/m² as compared to GaN IMPATT diode that is capable to develop the power density 6.847×10¹⁰ W/m² for the same frequency of operation. It is also observed that wz-GaN exhibits better noise behavior 7.42×10⁻¹⁵ V²·s than SiC (5.16×10⁻¹⁵ V² ·s) for IMPATT operation at 140 GHz. A tradeoff between the power output and noise from the device reveals that wz-GaN would be a suitable base material for high power application of IMPATT diode with moderate noise. 2011 Article Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency / P.R. Tripathy, M. Mukherjee, S.P. Pati // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 2. — С. 137-144. — Бібліогр.: 26 назв. — англ. 1560-8034 PACS 73.50.Td, 85.30.Kk http://dspace.nbuv.gov.ua/handle/123456789/117715 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
The mm-wave as well as noise properties of IMPATT diodes for the D-band are efficiently determined, with 4H-SiC and wurtzite type GaN as base materials, using advanced computer simulation techniques developed by the authors. The breakdown voltage (180 V) and efficiency (14.7%) is higher in case of 4H-SiC as compared to wz GaN based diode having the breakdown voltage (153 V) and efficiency (13.7%). The study indicates that 4H-SiC IMPATT diode is capable of generating high RF power density of about 8.383×10¹⁰ W/m² as compared to GaN IMPATT diode that is capable to develop the power density 6.847×10¹⁰ W/m² for the same frequency of operation. It is also observed that wz-GaN exhibits better noise behavior 7.42×10⁻¹⁵ V²·s than SiC (5.16×10⁻¹⁵ V² ·s) for IMPATT operation at 140 GHz. A tradeoff between the power output and noise from the device reveals that wz-GaN would be a suitable base material for high power application of IMPATT diode with moderate noise. |
| format |
Article |
| author |
Tripathy, P.R. Mukherjee, M. Pati, S.P. |
| spellingShingle |
Tripathy, P.R. Mukherjee, M. Pati, S.P. Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Tripathy, P.R. Mukherjee, M. Pati, S.P. |
| author_sort |
Tripathy, P.R. |
| title |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency |
| title_short |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency |
| title_full |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency |
| title_fullStr |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency |
| title_full_unstemmed |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency |
| title_sort |
dynamic properties and avalanche noise analysis of 4h-sic over wz-gan based impatts at mm-wave window frequency |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2011 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/117715 |
| citation_txt |
Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency / P.R. Tripathy, M. Mukherjee, S.P. Pati // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 2. — С. 137-144. — Бібліогр.: 26 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT tripathypr dynamicpropertiesandavalanchenoiseanalysisof4hsicoverwzganbasedimpattsatmmwavewindowfrequency AT mukherjeem dynamicpropertiesandavalanchenoiseanalysisof4hsicoverwzganbasedimpattsatmmwavewindowfrequency AT patisp dynamicpropertiesandavalanchenoiseanalysisof4hsicoverwzganbasedimpattsatmmwavewindowfrequency |
| first_indexed |
2025-07-08T12:40:43Z |
| last_indexed |
2025-07-08T12:40:43Z |
| _version_ |
1837082548755234816 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
PACS 73.50.Td, 85.30.Kk
Dynamic properties and avalanche noise analysis of 4H-SiC
over wz-GaN based IMPATTs at mm-wave window frequency
P.R. Tripathy1, Moumita Mukherjee2 and S.P. Pati3
1Purushottam Institute of Engineering & Technology, Rourkela, Odisha, India
2CMSDS, Institute of Radio Physics & Electronics, University of Calcutta
1, Girish Vidyaratna Lane, Kolkata 700009, West Bengal, India
3National Institute of Science & Technology, Berhampur, Odisha, India
1,3School of Physics, Sambalpur University, Sambalpur, Odisha, India
E-mail: pravashrt76@yahoo.co.in, mm_drdo@yahoo.com, prof_sppati@yahoo.co.in
Abstract. The mm-wave as well as noise properties of IMPATT diodes for the D-band
are efficiently determined, with 4H-SiC and wurtzite type GaN as base materials, using
advanced computer simulation techniques developed by the authors. The breakdown
voltage (180 V) and efficiency (14.7%) is higher in case of 4H-SiC as compared to wz-
GaN based diode having the breakdown voltage (153 V) and efficiency (13.7%). The
study indicates that 4H-SiC IMPATT diode is capable of generating high RF power
density of about 8.383×1010 W/m2 as compared to GaN IMPATT diode that is capable to
develop the power density 6.847×1010 W/m2 for the same frequency of operation. It is
also observed that wz-GaN exhibits better noise behavior 7.42×10-16 V2·s than SiC
(5.16×10-15 V2·s) for IMPATT operation at 140 GHz. A tradeoff between the power
output and noise from the device reveals that wz-GaN would be a suitable base material
for high power application of IMPATT diode with moderate noise.
Keywords: avalanche noise, gallium nitride, IMPATT, RF power, silicon carbide, mm-
wave window frequency.
Manuscript received 15.06.10; accepted for publication 16.03.11; published online 30.06.11.
1. Introduction
IMPATT diodes has been identified as a premier class of
semiconductor devices suitable for stable RF power
generation, used for present day e-communication
systems with the added advantage that any form of p-n
junction fabricated from any semiconductor material,
can exhibit IMPATT action based on combined physical
phenomena of both transit time and avalanche phase
delay. Studies on new materials are being carried out by
several groups spreading over the globe to enhance the
RF power/efficiency and reduce the avalanche noise in
this class of devices even at far mm-wave frequencies. In
recent years, wide band gap materials like SiC and GaN,
with their superior electronic properties, are studied for
IMPATT action and the characteristics include high
breakdown voltages, ability to sustain large electric
fields, high temperature and high power applications as
compared to the conventional narrow band gap Si-based
IMPATT diode. The important and most attractive
material for high power device applications is GaN and
some of the various polytypes of SiC. In both these
materials, the breakdown electric field strengths are
expected to be about four times larger than
corresponding values of narrow band gap material like
Si or GaAs [1]. In addition, the other properties of GaN
like wide energy band gap, high carrier saturation
velocity and relatively small dielectric constants make
them suitable for high power, high frequency amplifiers.
GaN is emerging as an important semiconductor
material for many diverse optoelectronics and
electronics device applications [2, 3]. The wide direct
band gap of GaN is particularly useful in short
wavelength optoelectronic device applications. GaN is
mostly grown in the wurtzite phase [4]. The 4H
polytype, however, is considered as more appropriate for
fabricating 4H-SiC IMPATT diodes due to higher and
nearly isotropic electron mobility [5, 6]. Many reports
suggest that IMPATT diodes based on these materials
(GaN and 4H-SiC) are soon likely to find their place in
modern communication systems. Thus, it has motivated
the authors to undertake a comparative study on the
7
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
137
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
performance of IMPATT diodes based on these
materials. The purpose of this work is to characterize the
performances of the double drift IMPATT diodes with
SiC and GaN as base materials, for application in D-
band. The simulation method has been made sensible by
incorporating most recently reported material parameters
data for SiC and GaN [7, 8]. The mm-wave as well as
noise properties of IMPATT diodes in D-band are
efficiently computed, with 4H-SiC and wz-GaN as base
materials, using our computer simulation scheme. The
results are quite helpful in determining the best suited
material for IMPATT operation at 140 GHz.
2. Computer simulation method
The three-stage computer simulation method consists of
DC analysis, small signal analysis and noise analysis.
The equations involved in these analyses are nonlinear in
nature, and thus their solution involves complexity. So,
we have first considered the diode to be consisting of
small space points. The diode active layer width is
divided into several number of space points with a space
step of 0.1 nm. Fig. 1 represents the schematic structure
of a double drift IMPATT diode.
2.1. DC analysis
The DC analysis is done by solving simultaneously three
non-linear device equations, namely: Poisson’s equation,
the carrier continuity equation and the space charge
equation using a double iterative field extremism
initiated using DC simulation program [9]. The DC
electric field profiles, carrier current profiles, breakdown
voltage, etc., are obtained from this analysis. The
ionization rates of electrons and holes for both these
materials have been taken from the recent experimental
reports for 4H-SiC [10] and wz-GaN [11, 12],
respectively. The computer method framed for DC
analysis is initiated from the location of the field
maximum point E0 at x = x0 within the p-n junction,
where 0=
∂
∂
x
E , the value of the field maximum E0 and
its location x0 are suitably chosen for the diode, and then
it is used to obtain the value of the mobile space charge
ϕ(x0) at the starting point. Then the Poisson equation and
the carrier continuity equations are solved
simultaneously through the numerical approach [9].
Iterations over E0 and x0 are carried out till boundary
conditions are satisfied at both edges of the depletion
layer. The space step width is taken to be very small, i.e.
of the order of 0.1 nm. The numerical solution is
progressed from the point x = x0 and moving first
towards the right side of the field maximum till the field
boundary condition, in carrier current and electric field
is satisfied at x = xR. Thus, the DC field and carrier
current distribution profiles for a particular IMPATT
diode operating at a given current density are obtained
from the final solution of E0 and x0. The method
described above gives the avalanche breakdown
characteristics of the IMPATT diode. The depletion
layer width of the diode is obtained as W = |xL| + |xR|.
The avalanche layer width xA can be determined from
the condition |P(x)| = 0.95, i.e. 95% growth of carrier
current. The drift zone width is then obtained from the
expression (W – xA). The voltage drop across different
zones, i.e. breakdown voltage (VB) and avalanche
voltage drop (VA) are determined by integrating the
electric field over the respective zone layer. The drift
voltage drop is then taken as VD = VB – VA. The
qualitative value of diode efficiency ( ) can be obtained
from the expression
η
∏=η BVVD / . The DC electric
field profiles, carrier current profiles, breakdown
voltage, etc., are obtained from this analysis. We have
considered a one dimensional model with doping
distributions of the form n+-n-p-p+. The data obtained
from the DC analysis are used as input for the high
frequency analysis of the diode.
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Fig. 1. Active layer of a double drift IMPATT diode.
2.2. Small signal analysis
The high frequency analysis of the diode is carried out
using the small signal simulation method developed by
our group [13]. The small signal model takes into
account the contribution from each space point and
effectively determines the device parameters such as
negative conductance (–G), susceptance (B) and
negative resistance (–ZR) of the diode. The variations of
these values with frequency are also computed using the
double iterative computer program [12]. In the high
frequency analysis, it is possible to find out the spatial
variation of negative resistance (R) and reactance (X) in
the depletion layer, which would provide a clear idea
regarding the intensity of microwave oscillation along
different regions of the diode. The unperturbed diode
impedance Z0 (without considering the diffusion current)
138
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
is separated into its real and imaginary components (i.e.
Z0 = R0 + iX0) to obtain the second order non-linear
implicit differential equation in small signal resistance
(R0) and reactance (X0) as
( )
( ) ,22
2
002
2
00
2
0
2
εα
α
=
ωα
−
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
−
ω
+
+
∂
∂ω
−
∂
∂
α−α+
∂
∂ −
X
v
RxH
v
x
X
v
r
x
R
x
R
pn
(1)
( )
( ) ,2
2
2002
2
00
2
0
2
ε
ω
−=
ωα
+
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
−
ω
+
+
∂
∂ω
−
∂
∂
α−α+
∂
∂ −
v
R
v
XxH
v
x
R
v
r
x
X
x
X
pn
(2)
with
( ) ( ) ( )[ ] ( ) .2
x
E
E
xgxg
Ev
qr
Ev
jxH m
npTpTn ∂
∂
α−α
∂
∂
+′+
∂
∂
ε
+
∂
α∂
ε
= +
Finally, the small signal diode resistance (R) and
reactance (X) due to drift, diffusion and tunnel currents
are obtained from the expression including a
perturbation part
∑+=
k
kRRR 0 and . (3) ∑+=
k
kXXX 0
The integrated values of resistance and reactance
give ZR and ZX , if using the relation,
∫=
W
R dxxRZ
0
)( and . (4) ∫=
W
x dxxXZ
0
)(
Using the values of ZR and ZX , the diode
conductance (G), susceptance (B) and the quality factor
(Q) are calculated via the relations
22
xR
R
ZZ
Z
G
+
= ,
22
xR
x
ZZ
Z
B
+
−
= and
G
BQ −= . (5)
The series positive resistance (RS) of any device
which is one of the important limiting factors
responsible for limiting power output and device
efficiency can also be determined. The expected RF
power delivery from the diode can be computed using
the relation
PRF = (VRF)2 |Gp| × A/2. (6)
The power density PA is taken as PRF/A, where A is
the area of cross section of the device. VRF can be
approximated as VB/2 for 50% modulation. Gp is the
device negative conductance at the peak frequency [14].
2.3. Small signal noise analysis
The fundamental avalanching process involved in the
IMPATT diode operation leads to sufficient avalanche
noise generation in the device. So, noise is an important
aspect of the present study and the noise characteristics
of the diode structure are also computed using the
generalized noise simulation program [15]. The noise
characteristics like mean square noise voltage per
bandwidth (〈V2〉 / Δf ) and noise measure (NM) of the
device are computed from this analysis. The noise
generation rate of individual sources can be calculated
by using the equation:
γN(x′) = n(x′)αn(x′)vn(x′) + p(x′)αp(x′)vp(x′). (7)
The exact values of n, p, αn and αp are determined
from a static analysis of the diode under avalanche
breakdown condition, which also gives the distribution
of electric field and the carrier concentration along the
depletion layer of the diode [16].
The noise sources αn(x′) are located at x′ in the
avalanche region gives rise to noise electric fields (x, x′)
at every point in the depletion region of the diode. The
noise electric field (e(x, x′) = eR(x, x′) + i eX(x, x′))
contribution from each space point is calculated using a
double iterative simulation program [8], which solves
the following two second-order differential equations for
the real eR(x, x′) and imaginary eX(x, x′) parts of the noise
electric field at each space point subject to the boundary
conditions:
( )
ε
γ
=
ωα
−⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
ω
+
+
∂
∂ω
−
∂
∂
α−α+
∂
∂
+
−
v
qre
v
eH
v
x
e
v
r
x
e
x
e
N
XR
XR
pn
R
22
2
2
2
2
2
(8)
and
( )
.02
2
2
2
2
2
=
ωα
+⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
ω
+
+
∂
∂ω
−
∂
∂
α−α+
∂
∂ −
RX
RX
pn
X
e
v
eH
v
x
e
v
r
x
e
x
e
(9)
First, the noise generation source is assumed to be
located at the left-hand edge of the active zone at ix′ ,
where i = 1. Iterations over initial chosen values of eR
and eX in the left-hand edge of the diode depletion layer
are carried out till the boundary conditions are satisfied
at the right-hand edge. The profiles of noise field eR and
eX can be obtained from the final solution of equations
(8) and (9). The method is repeated to obtain the
integrated noise voltage and noise-field profile due to
noise source successively located at x = x′ + n ∂x′, where
n = 1, 2, 3,…, 1000. Thus, the noise generation profile
along the length of the depletion layer can be determined
separately for noise sources located in various space
points of the active zone. The integrated values of
eR(x, x′) and eX(x, x′) over x give the real and imaginary
parts of the terminal voltage VR(x′) and VX(x′) due to
noise generating source at x′ and are obtained as
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
139
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
( ) ∫ ′=′
W
RR dxxxexV
0
),( and . (10) ( ) ∫ ′=′
W
XX dxxxexV
0
),(
The noise source is then shifted to ixx ′= for
i = 2, 3,…, n and VR(x′), VX(x′) are determined for
individual noise sources. These values of VR(x′) and
VX(x′) are then integrated for noise sources considered
along the entire depletion zone.
So and . (11) ( )∫ ′′=
W
RR xdxVV
0
( )∫ ′′=
W
XX xdxVV
0
These final values of VR and VX are taken to
calculate the integrated noise parameters.
Now the diode transfer impedance (ZT) can be
computed taking the values of the terminal voltage from
the equation (10). The transfer impedance of the diode is
defined as the ratio of open circuit incremental voltage
to the injected current at x′. Taking the injected current
in x′ as xdAxqdI NN ′′γ= )( , A being the area of cross
section, one can obtain the real and imaginary parts of
the transfer impedance using the relations
xdAxq
xVxZ
N
R
TR ′′γ
′
=′
)(
)()( and
xdAxq
xVxZ
N
X
TX ′′γ
′
=′
)(
)()( . (12)
The transfer impedance is determined from the
relation
22 )()(),( xZxZxZ TXTRT ′+′=ω′ . (13)
Considering xdAq N ′γ as a shot current fluctuation
due to avalanching process and using the theory of shot
noise, one can write the mean square deviation for the
current as
fdIqId NN Δ= 22 . (14)
Using the expression for diode transfer impedance
from the equation (13) and mean square fluctuation of
current from the equation (14), one can compute the
mean square noise voltage from the relation
∫ ′γω′Δ= xdAqxZfqV NT
22 |),(|2
∫ ′ω′γ=
Δ
⇒ xdxZAq
f
V
TN
22
2
|),(|2 . (15)
From the knowledge of the mean square noise
voltage, the noise measure (NM) of the diode can be
computed from the expression
)(4
NM
2
RZKT
fV
−
Δ
= , (16)
where K is the Boltzmann constant, T is the junction
temperature (taken to be 473 K) and –ZR is the total
negative diode resistance.
3. Results and discussion
3.1. Comparison of GaN and SiC-based IMPATTs:
simulation results
The results obtained from the computer simulation for
IMPATT diodes, with 4H-SiC and wz-GaN as base
materials, are presented in this section. The breakdown
voltage (VB) for 4H-SiC IMPATT diode is found to be
180 V and that for GaN IMPATT diode is 153 V. The
breakdown electric field has been computed to be
5.33×108 V/m for wz-GaN as compared to 7.30×108 V/m
for 4H-SiC based IMPATT diode. High breakdown field
results in a high breakdown voltage. It is worth to
mention here that these values of the breakdown voltage
are approximately 10-12 times higher than the
corresponding values of the breakdown voltage for Si
IMPATT diodes designed to operate at the same
frequency (13.3 V for 140 GHz). Since the breakdown
voltage is indicative of input power of the device, 4H-
SiC and wz-GaN are promising IMPATT diode
materials for high-power operation.
Material and physical parameters of both these
materials, i.e. 4H-SiC and wz-GaN, are presented in
Table 1. The other device properties like device negative
conductance, expected power density, mean square noise
voltage per bandwidth, etc., at 140 GHz are presented in
Table 2. Fig. 2 shows the electric field profile for both
materials (4H-SiC and wz-GaN) based DD IMPATTs.
The variation of the negative conductance with
frequency for 4H-SiC and GaN IMPATT diodes are
plotted in Fig. 3. The variation of the power density
versus frequency is also plotted in Fig. 4. The negative
conductance for both 4H-SiC and wz-GaN diodes peaks
at around 140 GHz which can be regarded as an
optimum frequency of operation of the diodes. The
negative resistance contribution at any space step, which
is the ratio of ac voltage (eac) to ac current(iac), can be
computed from the final computer run as the magnitude
of R0 in the corresponding space step. It is seen that the
negative resistance profile along depletion zone is of
double peak nature with one peak remaining in each of
the drift region. The peak of negative resistance together
with its spread along the active zones indicates
contribution of negative resistance by individual space
step. However, in case of both the diodes, the avalanche
zones produce positive RF resistance. The magnitude of
the peak for the negative resistance profile is higher in
4H-SiC diode than that for wz-GaN diode. This leads to
higher RF power generation from 4H-SiC device. These
facts are reflected from Table 2 and Fig. 4, which
indicates that 4H-SiC DDR shows high power density
and, thus, 4H-SiC may have an advantage for being
chosen as a base material for IMPATT diodes.
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
In order to make a comparison, the authors have
also studied the properties of silicon IMPATT DDR for
the same frequency of 140 GHz. The power density from
silicon diode remains only around 3.274×109 W/m2,
which is nearly lower by a factor of around 25 than its
SiC and GaN counterparts. However, wz-GaN has the
140
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
advantage of producing low noise as compared to 4H-
SiC for IMPATT operation at 140 GHz. This can be
inferred from Fig. 5 where the authors have plotted the
variation of mean square noise voltage per band width
versus frequency for IMPATT diodes based on these two
materials. This graph shows the transition frequency
where the plots show peak. However, the mean noise
square voltage at around 140 GHz is lower for GaN
diode. The noise measure has been presented in Fig. 6
for both materials also reflect the same fact. Basing on a
tradeoff between the power output and noise from the
device, it reveals that wz-GaN would be a suitable base
material for high power application of IMPATT diodes
with moderate noise.
Table 1. Material parameters of 4H-SiC and wz-GaN.
Parameter 4H-SiC wz-GaN
Band gap, Eg (eV) 3.26 3.45
Dielectric constant, εr 10.1 9.0
Critical electric field, Ec (×107
V/m) 35.0 30.0
Thermal conductivity, θ (W/m·K) 500.0 225.0
Electron mobility, μe (cm2/v·s) 1140 1600
Hole mobility, μh (cm2/v·s) 50 28
Saturated electron drift velocity,
vsat (×105 m/s) 2.0 2.5
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Table 2. mm-wave and noise properties of IMPATT diodes
with 4H-SiC and wz-GaN as base materials, designed for
operation at 140 GHz.
Parameter 4H-SiC wz-GaN
Break down voltage (VB) B 180 153
Efficiency (η) (%) 14.7 13.7
Negative conductance, –G
(S/m2) 2.07×107 2.34×107
Power density (W/m2) 8.383×1010 6.847×1010
〈V2〉/Δf (V2s) 5.16×10-15 7.42×10-16
Noise measure (dB) 36.1 31.8
-0.6 -0.4 -0.2 0 0.2 0.4 0.6
0
0.5
1
1.5
2
2.5
3
3.5
4
E
le
ct
ric
fi
el
d
E
(1
0
8 V
/m
)
Distance X in (um)
4H-SiC
Wz-Gan
Fig. 2. Electric field profiles for 4H-SiC and wz-GaN DD
IMPATT.
Fig. 3. Variation of the negative conductance with frequency
for 4H-SiC and GaN IMPATT diodes.
Fig. 4. Variation of the power density with frequency for 4H-
SiC and GaN IMPATT diodes.
Fig. 5. Variation of the mean square noise voltage per
bandwidth with frequency for 4H-SiC and GaN IMPATT
diodes.
141
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
Fig. 6. Noise measure versus frequency for wz-GaN and 4H-
SiC DDRs.
3.2. Fabrication issue related to GaN and SiC-based
IMPATT diodes
The computer simulation results show the importance
and superiority of both the wide band gap material (4H-
SiC and wz-GaN) for high-power source at mm-wave
regime. Special efforts have been taken for the material
growth, doping and device processing, oscillator
performance, characterization of the device by taking the
SiC and GaN as base material for fabrication of the
diode [17, 18]. Due to the lack of experimental data on
wide band gap semiconductor mm-wave devices,
simulation results could not be compared. However, the
authors have proposed the practical issues related to the
fabrication of GaN and SiC IMPATT devices. GaN p-n
junction can be obtained by using the molecular beam
epitaxy (MBE). In order to form an p-n junction, first,
the MBE growth process can be carried out using Si
donor impurity to form the n-type layer of GaN on an n+
substrate, and after that, a p+-type cap layer can be
grown on the n-layer by the MBE process by doping
high concentration of Mg impurity. In order to activate
p-type conductivity, high-temperature post-growth
anneal in a nitrogen atmosphere may be required.
Because Mg requires large energy for ionization, in
general, it is difficult to obtain heavily doped p+-type
GaN with Mg. Beryllium (Be) may be used to achieve
p+-type GaN because the ionization energy of Be is low
(∼60 meV). Recently, Pastor et al. [19] assessed the
crystal damage of Be+-implanted GaN by UV Raman
scattering and found a correlation between implantation
dose and the extent of lattice damage caused to the
target.
A SiC IMPATT device can be fabricated on the
epiwafer by following the process steps briefly described
below [20].
Growth of p+ 4H-SiC layer
In order to assist p-type ohmic contact formation, the p+
4H-SiC layer can be grown on the top of n-type film by
Al2+ ion implantation. The post-implantation annealing
may be performed at a very high temperature in an argon
atmosphere.
Formation of low-resistive p+ and n+ contacts
Power dissipation of IMPATT devices strongly depends
on the contact resistance. The samples may be cleaned by
a “piranha” solution. After rinsing in DI water, the
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Fig. 7. Experimental arrangement for realization of SiC and GaN IMPATT diodes for D-band.
142
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
samples may be dipped in dilute hydrofluoric acid
solution and dried for nearly fifteen minutes. Through the
lithographic process, windows can be opened inside the
oxide layer. Using lithography and liftoff techniques,
contact metals (Al/Ti/Al) can then be deposited in the
oxide windows by an electron beam evaporator. In order
to obtain ohmic contacts, the samples may be annealed for
3 to 5 min in a rapid thermal anneal (RTA) furnace in
nitrogen atmosphere at around 950 °C. The post-
deposition annealing at high temperature is generally
preferred to reduce the specific contact resistance. For an
n+-type contact, an Ni layer of 200-nm thickness may be
evaporated on the backside (n+-side) of the wafer,
followed by the RTA treatment for 3 min at 950 °C [21].
The choice of the metallic composition is based on the
formation of Ni2Si alloy. As mentioned in several
publications [22], the higher the concentration of Ni2Si in
contacts is, the lower the specific contact resistance is.
The specific contact resistance can be determined from
transmission line measurement (TLM) data. Several
experimental attempts have been taken for the develop-
ment of SiC material for device fabrication [23-25].
Experimental verification of mm-wave properties
of IMPATT diodes can be done by the arrangement
shown in Fig. 7 [26].
4. Conclusion
A detailed comparative analysis of both 4H-SiC and wz-
GaN-based IMPATT devices in the millimeter-wave
range has been reported by studying the DC, small signal
and avalanche noise analysis through the simulation
technique developed by the authors. It may be concluded
that both 4H-SiC and GaN are potential materials for
high power IMPATT application. The wide gap
associated with a high breakdown voltage in both cases
with tolerance to the high operating current density
would help in possible realization of high RF power.
Both 4H-SiC and GaN diodes may yield a RF power 25-
30 times higher than its Si counterpart. It is observed
that for high-power operation the 4H-SiC is a suitable
base material for IMPATT diode, whereas GaN is a
better material than SiC for high power operation with
moderate noise. To the best of authors’ knowledge this is
the first report on the comparative analysis of mm-wave
characteristics and avalanche noise analysis of SiC and
GaN IMPATTs at an important window frequency of
140 GHz. This study will be useful for practical
realization of high-power, low noise IMPATT in the
mm-wave region.
Acknowledgement
Moumita Mukherjee is grateful to Defence Research and
Development Organisation, Ministry of Defence, Govt.
of India for providing her ‘Senior Research Fellowship’
to carry out this research work.
References
1. V.V. Buniatyan and V.M. Aroutiounian, Wide gap
semiconductor microwave devices // J. Phys. D:
Appl. Phys., 40 (20), p. 6355-6385 (2007).
2. M.S. Shur, GaN based transistors for high power
applications // Solid-State Electron., 42(12),
p. 2131-2138 (1998).
3. U.K. Mishra, Y. Wu, B.P. Kellar, S. Kelar,
S.P. Baars Den, GaN microwave electronics //
IEEE Trans. Microwave Theory Technique MTT-
46, p. 756-761 (1999).
4. S.J. Peatron, J.C. Zolper, R.J. Shul and F. Ren,
GaN: processing, defects, and devices // J. Appl.
Phys. 86, p. 1-78 (1999).
5. J.B. Casady and R.W. Johnson, Status of silicon
carbide as a wide-bandgap semiconductor for high-
temperature applications: a review // Solid-State
Electron., 39(10), p. 1409-1422 (1996).
6. P.G. Neudeck, Progress in silicon carbide
semiconductor electronics technology // J.
Electron. Mater., 24 (4), p. 283-288 (1995).
7. W.S. Loh, B.K. Ng, J.S. Ng, Stanislav I. Soloviev,
Ho-young Cha, Peter M. Sandvik, C. Mark Johnson
and John P.R. David, Impact ionization coefficients
in 4H-SiC // IEEE Trans. Electron. Devices, 55(8),
p. 1984-1990 (2008).
8. A. Reklaitis and L. Reggiani, Monte Carlo study of
hot-carrier transport in bulk wurtzite GaN and
modeling of a near-terahertz impact avalanche
transit time diode // J. Appl. Phys., 95(12), p. 7925-
7935 (2004).
9. P.R. Tripathy, A.K. Panda and S.P. Pati,
Comparison between the DC and microwave
performance of wurtzite phase and zinc-blende
phase GaN-based IMPATTs // Proc. XV Intern.
Workshop on Physics of Semiconductor Devices
(IWPSD-2009), p. 525-528 (2009).
10. Electronic Archive: New Semiconductor Materials,
Characteristics and Properties. [Online]. Available:
http://www.ioffe.rssi.ru/SVA/NSM/Semicond/SiC
11. I.H. Oguzman, E. Belloti, K.F. Brennan, J. Kolnik,
R. Wang, P.P. Buden, Theory of hole initiated
impact ionization in bulk zinc blende and wurtzite
GaN // J. Appl. Phys., 81(2), p. 7827-7836 (1997).
12. Electronic Archive: New Semiconductor Materials,
Characteristics and Properties. [Online]. Available:
http://www.ioffe.rssi.ru/SVA/NSM/Semicond/GaN
13. S.K. Dash and S.P. Pati, Effect of optical radiation
on millimeter-wave characteristics and avalanche
noise generation in double-drift IMPATT diodes
based on opto-sensitive semiconductors //
Microwave and Optical Technology Letter, 33(4),
p. 295-300 (2002).
14. H. Eisele and G.I. Haddad, Microwave
Semiconductor Device Physics, S.M. Sze Ed.
Willey, New York, 1997, p. 343.
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
143
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 2. P. 137-144.
15. A.K. Panda, D. Pavlidis, and E. Alekseev, Noise
characteristics of GaN-based IMPATTs // IEEE
Trans. Electron Devices, 48, p. 1473-1475 (2001).
16. A. Reklaitis and L. Reggiani, Monte Carlo
investigation of current voltage and avalanche
noise in GaN double-drift impact diodes // J. Appl.
Phys., 97, 043709 (2005).
17. K. Vassilevski, K. Zekentes, G. Constantidis,
A. Strel’chuck, Fabrication and electrical
characterization of 4H-SiC p+-n-n+ diodes with low
differential resistance // Solid-State Electron., 44,
p. 1173-1177 (2000).
18. S.J. Pearton, C.B. Vartuli, J.C. Zolper, C. Yuan,
and R.A. Stall, Ion implantation doping and
isolation of GaN // Appl. Phys. Lett., 67(10),
p. 1435-1437 (1995).
19. D. Pastor, J. Ibáñez, R. Cuscó, L. Artús,
G. González-Diaz, and E. Calleja, Crystal damage
assessment of Be+-implanted GaN by UV Raman
scattering // Semicond. Sci. Technol., 22(2), p. 70-
73 (2007).
20. M. Mukherjee, N. Mazumder and S.K. Roy,
Photosensitivity analysis of gallium nitride and
silicon carbide terahertz IMPATT oscillators:
Comparison of theoretical reliability and study on
experimental feasibility // IEEE Trans. Device and
Materials Reliability, 8, p. 608-620 (2008).
21. R. Konishi, R. Yasokuchi, O. Nakatsuka, Y. Koide,
M. Moriyama, and M. Murakami, Development of
Ni/Al and Ni/Ti/Al ohmic contact materials for p-
type 4H-SiC // Mater. Sci. Eng. B, 98 (3), p. 286-
293 (2003).
22. C.H. Carter Jr., V.F. Tsvetkov, R.C. Glass,
D. Henshall, M. Brady, S.G. Muller, O. Kordina,
K. Irvine, J.A. Edmond, H.-S. Kong, R. Singh,
S.T. Allen, J.W. Palmour, Progress in SiC: from
material growth to commercial device development
// Mater. Sci. Eng., B61-2, p. 1-8 (1999).
23. R.R. Siergiej, R.C. Clarke, S. Sriram, A.K. Agar-
wal, R.J. Bojko, A.W. Morse, V. Balakrishna,
M.F. MacMillan, A.A. Burk Jr., C.D. Brandt,
Advances in SiC materials and devices: an
industrial point of view // Mater. Sci. Eng. B61-2,
p. 9-17 (1999).
24. R. Madar, Silicon carbide in contention // Nature,
430, p. 1009-1012, Aug. 26 (2004).
25. L. Yuan, J.A. Cooper Jr, M.R. Melloch and
K.J. Webb, Experimental determination of a SiC
IMPATT oscillator // IEEE Electron Device Lett.,
22(6), p. 266 (2001).
26. M. Mukherjee, N. Mazumder and A. Dasgupta,
Simulation experiment on optical modulation of
4H-SiC millimeter-wave high power IMPATT
oscillator // J. Europ. Microwave Association
(EuMA Publishing – UK), 4, p. 276-282 (2008).
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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