Internati
o
nal
Journal of Ele
c
trical
and Computer
Engineering
(IJE
CE)
Vol.
5, No. 6, Decem
ber
2015, pp. 1347~
1
353
I
S
SN
: 208
8-8
7
0
8
1
347
Jo
urn
a
l
h
o
me
pa
ge
: h
ttp
://iaesjo
u
r
na
l.com/
o
n
lin
e/ind
e
x.ph
p
/
IJECE
Ohmic Cont
act Charact
eri
zation
Using I
m
age P
r
ocessin
g
B. N. Shashikala*,
B
.
S.
Nagabhushana**
* M.G.R. Univer
sity
, Ch
ennai, In
dia
** BMS Colleg
e
of Eng
i
neering
,
Bengaluru
Article Info
A
B
STRAC
T
Article histo
r
y:
Received Apr 3, 2015
Rev
i
sed
Ju
l 7
,
2
015
Accepte
d
J
u
l 28, 2015
The
Ti/Al
/
Ni/A
u film
s deposit
e
d
b
y
electron b
eam evapor
ation
on n
ty
pe
GaN was
dem
o
ns
trated
as
a s
u
ita
ble s
o
lution for
l
o
w res
i
s
tive and
therm
a
l
l
y
stable
contact to
n-ty
pe G
a
N. The
surface morpholog
y
of Ti/Al/Ni/Au an
d
Ti/Al con
t
ac
ts
were s
t
udied
as
a func
tion of the
annealing process conditions
using image pro
cessing techniqu
es.
Th
e algorith
m was implemented usin
g
the M
A
TLAB s
o
ftware. Us
ing t
h
e algori
t
hm
m
a
de, the
area o
c
c
upied b
y
the
pores and
porosity
in
the ohmic c
ontact structures
were obtained
.
Keyword:
GaN
Ohm
i
c contact
Po
ro
sity
Surface m
o
rphology
Copyright ©
201
5 Institut
e
o
f
Ad
vanced
Engin
eer
ing and S
c
i
e
nce.
All rights re
se
rve
d
.
Co
rresp
ond
i
ng
Autho
r
:
B
.
N. Sha
s
hi
kal
a
,
Depa
rt
m
e
nt
of
El
ect
roni
cs
an
d C
o
m
m
uni
cati
on
En
gi
nee
r
i
n
g,
Sid
d
a
g
a
n
g
a
In
stitu
te o
f
Techno
log
y
,
B
.
H. R
o
a
d
,
Tu
m
a
kur
u,
I
ndi
a.
Em
a
il: sh
ash
i
kala.b
n@red
i
ffmail.co
m
1.
INTRODUCTION
Cu
rren
t pro
g
ress in
th
e GaN
d
e
v
i
ces
requ
ires h
i
gh
qu
ality o
h
m
ic co
n
t
acts. Oh
m
i
c co
n
t
acts wh
ich
have
l
o
w resi
s
t
ance an
d a
g
o
od
su
rface
m
o
rp
h
o
l
o
gy
are
r
e
qui
red
f
o
r t
h
e
de
vel
o
pm
ent
of
hi
g
h
t
e
m
p
erat
ure,
h
i
gh
p
o
w
e
r
and
h
i
gh
f
r
e
q
u
e
ncy electr
o
n
i
c
dev
i
ces [1
],
[
5
].
A
f
e
w
attem
p
ts to
ach
i
ev
e
good
o
h
m
ic co
n
t
acts on
GaNep
ilayers su
ch
as Ti, Ti/Al,
Ti/Al
/
Cu
/Au, Ti/Al
/
Pt/Au
,
Ti/A
l/Ti/Au
,
Ti/Al/Pd
/
Au
, Ti/Al/Mo
/
Au,
Ti/Al/Re/Au, e
t
c. have
bee
n
report
e
d
[6]-[14]recently. L
o
w resista
n
ce oh
m
i
c contacts to Ga
N are
of great
im
portance
,
be
cause it woul
d lead to the
im
provem
ent
of device perform
ance.
The
surface of the
ohm
ic
contact s
h
ould be rea
d
y to
make an electrical connec
tion
b
y
w
i
r
e
i
n
th
e bon
d
i
ng
pro
cess.
Th
e
kno
w
l
ed
ge
ab
ou
t th
e ch
emical co
m
p
o
s
itio
n
of an
oh
mic co
n
t
act will b
e
v
e
ry u
s
efu
l
to
pred
ict th
e
metallu
rg
ical b
e
h
a
vi
or
ofbond i
n
terfa
ce betwee
n t
h
e
wire
and t
h
e s
u
rface
of th
e
ohm
i
c contact.
Alum
inum
(Al) a
n
d gold (Au) wi
res
are com
m
onl
y
use
d
i
n
t
h
e bo
ndi
ng
pr
ocess
.
In
vest
i
g
at
i
o
ns
of o
h
m
i
c cont
act
s on Ga
Nepi
l
a
y
e
rs have i
n
di
cat
ed
that the form
ation of TiN at the interface may be im
por
tant for ohm
i
c contact form
ation due to its low work
fun
c
tion
and
t
h
e form
atio
n
o
f
n
itrog
en
v
acancies in
th
e
Ga
N bel
o
w the c
ontact layer
by a reaction of
Ti with
GaN
.
T
h
e
use
of
Ti
/
A
l
i
n
st
ea
d
of
Ti
dec
r
eas
es t
h
e c
ont
act
resi
st
i
v
i
t
y
fu
rt
her
by
fo
rm
i
ng Al
N
at
t
h
e i
n
t
e
rfac
e
in
add
itio
n to
TiN.
In this work, the surf
ace morphol
ogy of
Ti/Al and Ti/Al/Ni/Au
ohm
ic contacts to n-GaN
were
exam
ined with the use
of SEM. SE
M im
a
g
es were used to
stu
d
y
th
e
t
h
in
film
o
f
T
i/Al and
Ti/Al/Ni/Au
co
n
t
acts t
o
n
-
GaN layer
u
s
i
n
g im
ag
e p
r
o
c
essin
g
techn
i
qu
es. In
t
h
is
p
a
p
e
r v
a
riou
s filters
Disk
, Gaussian,
Mo
tio
n,
Av
erag
e,
un
sh
arp
,
M
e
d
i
an
, Max, M
i
n
and
Ad
ap
ti
ve W
i
ener filters
were u
s
ed
to
rem
o
v
e
n
o
i
se fro
m
ohm
ic contact im
ages and a
l
so com
p
are results with
est
i
m
a
tion of Pea
k
Signal Nois
e Ratio (PSNR). The
alg
o
rith
m
u
s
ed
in
th
is wo
rk
was im
p
l
e
m
en
ted
u
s
i
n
g
the MATLAB s
o
ftware
. Usi
ng t
h
e algorithm
,
the area
occupied by t
h
e pores
and
porosity in th
e
ohmic contact structureswe
re
obtained.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
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088
-87
08
IJECE
Vol. 5, No. 6, D
ecem
ber
2015 :
1347 –
1353
1
348
2.
IMA
G
E
P
R
O
C
ESSI
NG
TECH
N
IQ
UES ON OH
MI
C CO
NTA
C
T
Figure 1 s
h
ows the bloc
k
diagra
m
for
finding
porosity on ohm
ic
contact surface Sca
n
ning Elect
ron
Microsc
ope
(SEM) im
ages.
Im
age acquisit
i
on is
done
usin
g SEM. Seco
nd
step
is pr
epr
o
cessing
,
w
h
ich
in
vo
lv
es d
e
no
isin
g,
d
e
bris
rem
o
v
a
l, rem
o
v
a
l o
f
sa
lt and pep
p
e
r
no
ises.
Sin
ce
po
ro
sity is b
a
sed on
min
u
t
e
p
o
res
of
n
a
no
sizes on
su
rface, on
e
h
a
s to
carefu
lly select filters.
Figure 1.
Bloc
k diag
ram
for finding porosity
on Oh
m
i
c contact surface SE
M im
ages
Filter is a technique that disc
rim
i
nates accordi
ng to
one or
m
o
re attribute
s
at its input,
what
passes
th
ro
ugh
it. Fo
r ex
am
p
l
e, co
lo
r filters ab
so
rb lig
h
t
at
certai
n
wav
e
leng
th
s. It p
a
sses signals with
freq
u
en
cy
com
pone
nt
s i
n
som
e
bands and at
t
e
n
u
at
e si
gnal
s
i
n
ot
her
fre
que
ncy
ba
n
d
s. T
h
ese t
ech
ni
q
u
es use
ope
rat
i
o
n
s
lik
e con
v
o
l
u
tion
an
d correlati
o
n
.
Co
rrelatio
n
is
an
o
p
e
ratio
n wh
ich
i
n
vo
lv
es filterin
g
a m
a
sk
o
v
er an
im
ag
e. Th
e Correlatio
n
op
erat
or
◊
o
f
filter
w(p
,
q
)
of im
ag
e o
f
size (m
x
n
)
with
an
im
ag
e I(p
,
q
)
is g
i
v
e
n b
y
[1
5
]
:
w
p,
q
◊I
p,
q
∑∑
w
s,
t
I
p
s
,
qt
(
1
)
Whe
r
e a
m
is amask
ov
er an imag
e, w(p
,
q
)
i
s
a
filter
o
f
size (m
,n
),
I(p
,
q)-i
m
a
g
e
.
Co
nvo
lu
tion
is al
m
o
st sa
me
as co
rrelation
b
u
t
th
e m
a
sk
reflected
abo
u
t
b
o
t
h
ax
es. Mask
is ro
tated
b
y18
0
o
. Conv
olu
tio
n
op
erat
o
r
*
of filter
w(p
,
q
)
of size m
x
n
with
im
ag
e f(p
,
q
)
is g
i
v
e
n b
y
:
w
p,
q
∗I
p,
q
∑∑
w
s,
t
I
p
s
,
q
t
(
2
)
Co
nvo
lu
tion
is u
s
ed
in
tim
e
d
o
m
ain
filtering
wh
er
eas m
u
ltip
licatio
n
is used
in frequ
e
ncy d
o
m
ain
filterin
g
.
Sp
atial filters con
s
id
er im
ag
e as a g
r
i
d
of
p
i
x
e
ls. It d
i
rectly
man
i
pu
lates p
i
xels in
an
im
ag
e. The
val
u
es
of
nei
g
h
b
o
r
ho
o
d
pi
xel
s
are i
m
port
a
nt
here
. Thi
s
uses
con
v
o
l
u
t
i
o
n.
Thi
s
cha
n
ges
p
i
xel
s
i
n
t
h
e re
g
i
on
o
f
in
terest
b
y
its neig
hb
or p
i
x
e
l valu
es.
Th
er
e are th
ree typ
e
s
o
f
sp
atial filters
u
s
ed
.
1)
Li
nea
r
2
)
No
n lin
ear
3
)
Ad
ap
tiv
e.
2.1. Perform
a
nce
Me
as
ures
2.
1.
1. Me
an S
quare
E
rror
(
M
SE
)
Th
e MSE
d
e
no
tes th
e co
llectiv
e s
qua
re
d
errorbetwee
n
t
h
e com
p
resse
d and the
ori
g
inal im
age,
whe
r
eas PS
NR
den
o
t
e
s an a
m
ount
oft
h
e
hi
ghe
st
err
o
r. T
h
e l
o
wer t
h
e
va
l
u
e of M
S
E
,
t
h
e l
e
sser t
h
e err
o
r
.
To
com
put
e t
h
e
P
S
NR
, t
h
e
bl
oc
k
fi
rst
c
o
m
put
es t
h
e m
ean-sq
u
a
r
ed
er
ro
r
usi
n
g
t
h
e s
ubse
q
uent
eq
uat
i
on:
MSE
∑∑
I
i,
j
K
i
,
j
(
3
)
Whe
r
e m
and n are t
h
e
num
ber
of
rows
and c
o
lu
m
n
s in
t
h
e i
n
pu
t im
ag
es, resp
ectiv
ely.
2.
1.
2. Pea
k
Si
gn
al
-t
o
-
N
o
i
s
e Ra
ti
o
(P
SN
R)
PSNR is th
e evalu
a
tio
n
stan
d
a
rd
o
f
t
h
e reconstru
c
te
d
im
ag
e q
u
a
lity, and
is
an
im
p
o
r
tan
t
featu
r
e. Th
e
sm
a
ll v
a
lu
e of
PSNR m
ean
s t
h
at im
ag
e is p
o
o
r
qu
ality. PSNR is
d
e
fi
n
e
d
as fo
llo
w [16
-
18
]:
Evaluation Warning : The document was created with Spire.PDF for Python.
I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Oh
mi
c C
ont
act
ch
ar
act
e
ri
zat
i
o
n
Usi
n
g
I
m
ag
e Proce
ssi
n
g
(
B
. N
.
S
h
a
s
hi
k
a
l
a
)
1
349
PSNR
1
0.
log
(
4
)
Wh
ere 255
is
m
a
x
i
m
u
m
p
o
ssib
l
e v
a
lu
e t
h
at can
b
e
attain
ed
b
y
th
e imag
e sig
n
a
l.
Id
eally it is
in
fin
ite.
Practically it is
in
th
e rang
e
o
f
25
to 40
d
B
.
3.
E
X
PERI
MEN
T
AL WO
RK
The e
xpe
ri
m
e
nt
al
proce
d
ure
o
f
t
h
i
s
wo
r
k
co
nsi
s
t
s
o
f
t
h
ree
im
port
a
nt
st
e
p
s:
t
h
e fa
bri
cat
i
o
n
o
f
ohm
i
c
co
n
t
act stru
ctur
es, th
e ch
ar
acter
izatio
n
o
f
th
e str
u
ctur
es
u
s
ing
th
e SEM and an
alysis o
f
th
e i
m
ag
es th
r
ough
the
extraction
of the m
o
re accurate
m
o
rphology
of the st
ruct
ure
s
.
3.
1. Fa
bri
c
ati
o
n Proce
dure
A do
pe
d n-t
y
p
e
(N
D
+
a
p
pr
o
x
i
m
at
ely
3x
10
18
cm
-3
by
Hal
l
m
easurem
ent
)
G
a
N l
a
y
e
r
of
5µ
m
grow
n
by
M
O
C
V
D
on
c-
pl
ane
sap
p
h
i
r
e
sub
s
t
r
at
e
was
use
d
f
o
r t
h
e e
x
peri
m
e
nt
. Pri
o
r
t
o
m
e
t
a
l
dep
o
s
i
t
i
on, a
sam
p
l
e
wa
s
cleaned in t
r
ichloroet
h
ylene
(TCE) to
de
grease and
t
h
e
n
treated usi
n
g acetone
for
furt
her cleaning.
The
sam
p
le was th
en
i
m
m
e
rsed
in
isop
ro
p
y
l alco
ho
l (IPA) fo
r
co
m
p
lete re
m
o
v
a
l o
f
o
r
g
a
n
i
c so
lv
en
ts. Th
e sa
m
p
le
was t
h
en
wel
l
ri
nse
d
i
n
dei
o
n
i
zed w
a
t
e
r
(D
I
)
a
n
d
rea
d
y
fo
r
rem
oval
o
f
i
o
ni
c c
ont
am
i
n
ant
s
a
n
d
nat
i
ve
oxi
de.
Th
e sam
p
le was th
en immersed
in an equ
a
lly p
r
op
ortio
n
e
d
so
lu
tion
o
f
dilu
te HCl in
deio
n
i
zed water. After
t
h
i
s
t
r
eat
m
e
nt
fo
r
5 m
i
nut
es,
t
h
e sam
p
l
e
w
a
s ri
n
s
ed
agai
n i
n
D
I
wat
e
r
an
d
bl
o
w
dri
e
d
usi
n
g
N
2
gas. Th
e
electron beam (e-beam
) evaporator was e
v
acu
at
e
d
t
o
a base press
u
r
e
of ab
out
5
x
1
0
-6
m
b
ar p
r
io
r to
d
e
po
sition
.
Th
e co
m
p
osite
m
e
tal
layers
were Ti/Al(2
0
n
m
/1
0
0
n
m
) and
Ti/
A
l/Ni/Au
(2
0
n
m
/
100nm
/20
n
m
/
100
nm
). Al
l
t
h
e
m
e
t
a
l
s
were
dep
o
si
t
e
d by
el
ect
ro
n
b
e
am
evapo
r
at
i
on at
5
0
ºC
. Th
e
m
e
t
a
l
co
n
t
acts were fab
r
icated
with
stan
d
a
rd
ph
o
t
olith
o
g
raph
ic tech
n
i
q
u
e
with
a p
o
s
itiv
e
ph
o
t
oresist. Th
e m
e
t
a
l lift
of
f wa
s f
o
l
l
o
w
e
d by
a
ra
pi
d t
h
erm
a
l
anneal
(R
TA
) i
n
a
N
2
a
m
b
i
en
t. Th
e
Ti/Al o
h
m
ic co
n
t
act sam
p
les wer
e
anneale
d
at 600ºC, 700ºC,
800ºC and 90
0ºC
in an RTA furnace for 1 m
i
n in a N
2
a
m
b
i
e
n
t. Th
e Ti/Al/Ni/Au
ohm
ic
metalliz
ation sam
p
les
were anneale
d
at 750ºC,
800ºC, 850ºC, and
900ºC in
an R
T
A furnace for 1
m
i
n
in
a N
2
am
bient. The influe
nc
e of the a
n
nealing
process
on
the surface m
o
rphology of
Ti
/Al and Ti/Al/
Ni/Au
ohm
ic contacts
to
GaN we
re e
x
am
ined with the
use
of a SE
M.
3.
2.
An
al
ysi
s
o
f
SE
M Im
a
g
es
Usi
n
g Im
a
g
e
Processi
n
g
T
e
chni
ques
SEM
im
age i
s
save
d as JPEG
form
at
. Lat
e
r im
age i
s
i
nput
i
n
t
o
M
A
TL
AB
envi
ro
nm
ent
usi
ng i
m
read
fun
c
tion
.
Im
ag
es are co
nv
ert
e
d
in
to
grayscale fo
r th
re
shold
i
n
g
. Vari
o
u
s filterin
g
techn
i
qu
es were used
to
select pre
p
roce
ssing m
e
thod s
u
itable for t
h
es
e im
ages. PS
NR is used to m
easure
the
perform
ance of di
ffere
n
t
filterin
g
techn
i
q
u
e
s. Th
e
d
i
fferen
t
filtering
tech
n
i
qu
es
were app
lied
on
8
i
m
ag
es o
f
Ti/
A
l an
d
Ti/Al/
Ni/A
u
materials, whe
r
e four im
ages of eac
h m
a
terial were ta
ke
n
at
di
ffe
rent
t
e
m
p
erat
ure.B
a
s
e
d o
n
m
e
t
r
i
c
, t
h
e be
st
su
itab
l
e filtering
techn
i
qu
e
was d
eci
d
e
d.
4.
RESULTS
A
N
D
DI
SC
US
S
I
ON
Typ
i
cal I
-
V
ch
ar
acter
istics sh
own
in
Fi
gu
re 2
co
rr
espond
to
Ti/A
l contacts an
n
ealed at d
i
f
f
e
r
e
n
t
t
e
m
p
erat
ures:
a
s
-de
p
osi
t
e
d,
6
0
0
°C
,
7
0
0
°C
,
8
0
0
°C
a
n
d
90
0°C
.
Fi
gu
re
2.
I
-
V
c
h
aract
eri
s
t
i
c
s
o
f
Ti
(
2
0
nm
)/
Al(1
0
0
nm
) cont
a
c
t
s
o
n
n-
GaN
a
s
de
p
o
si
t
e
d a
n
d a
f
t
e
r a
nne
al
i
n
g
at
di
ffe
re
nt
t
e
m
p
erat
ure
s
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
IJECE
Vol. 5, No. 6, D
ecem
ber
2015 :
1347 –
1353
1
350
Fi
gu
re
3.
I
-
V
charact
e
r
i
s
t
i
c
s of
Ti
(
2
0
nm
)/Al
(
1
00
nm
)/
Ni
(2
0
nm
)/
Au
(
1
0
0
nm
) co
nt
act
s o
n
n-
GaN
a
s
deposited and
after a
nne
aling at differe
n
t te
m
p
eratures
Typical I-V c
h
aracteristics
shown
in Figu
r
e
3
co
rr
espo
nd
t
o
T
i/Al/Ni/Au contacts annealed a
t
di
ffe
re
nt
t
e
m
p
erat
ure
s
:
as-
d
e
posi
t
e
d,
75
0°
C
,
8
0
0
°
C
,
85
0°C
a
n
d
9
0
0
°
C
. It
i
s
s
h
o
w
n t
h
at
t
h
e Ti
/
A
l
a
n
d
Ti/Al/Ni/Au
co
n
t
acts i
n
Figure
2
and
Fi
g
u
re 3
,
resp
ectiv
ely
exh
i
b
it
o
h
m
ic in
th
eir as d
e
po
sited
con
d
ition
.
It is
n
o
t
eworth
y th
at th
e Ti/Al/Ni/
Au
con
t
acts sho
w
b
e
tter elect
rical p
r
o
p
e
rties th
an
th
e Ti/Al
co
n
t
acts.
All o
f
the
contacts
showed
ohm
ic cha
r
acteristics aft
e
r a
nnealin
g. The
dec
r
eas
e in t
h
e c
ont
act resistance
with
increasinga
nne
a
ling tem
p
erature is
believe
d to
be from
an
increase
in t
h
erm
a
l interd
iffusion at the int
e
rface
b
e
tween
t
h
e
d
e
p
o
s
ited
m
e
tals
an
d GaN. Th
e
resistiv
ity
o
f
bo
th
t
h
e
Ti/Al an
d Ti/Al/Ni/Au
con
t
acts d
e
creases
after ann
ealing. Th
e po
ssib
l
e
cau
se fo
r decrease in
th
e resistiv
ity
is d
u
e
to
th
e form
at
io
n
o
f
a TiN layer o
n
the
GaN surfa
ce a
n
d ass
o
ciated
with its
growt
h
, an ex
ce
ss
of
N
vacancies
ne
ar the
TiN-Ga
N inte
rface.
The s
p
ecific c
ontact re
sistance was
det
e
rm
i
n
ed
fr
om
pl
ot
s of t
h
e m
easure
d
re
si
st
ance
vers
us t
h
e
spacing
betwe
e
n the CTLM
pads. Meas
ure
m
ents showe
d
that the speci
fic
contact re
sistances
of Ti/Al
after
anneal
(
6
00 t
o
90
0°C
)
va
ri
ed
i
n
t
h
e ra
nge
of
2x
1
0
-4
to
8x
10
-4
Ω
cm
2
. Ot
her resea
r
ch
gr
o
up
has al
so
o
b
s
erve
d
sim
ilar specific contact resistances
fo
r Ti/Al
contact [19].
The lowest s
p
e
c
ific contact re
sistance was
obtaine
d
at
60
0°C
.
T
h
e
vari
at
i
o
n i
n
t
h
e
co
nt
act
resi
st
a
n
ce
wi
t
h
i
n
cre
a
si
ng
an
neal
i
n
g t
e
m
p
erat
ure
i
s
bel
i
e
ve
d t
o
b
e
fr
om
an
in
crease i
n
th
erm
a
l in
terd
iffu
sion
at
t
h
e i
n
t
e
rface
bet
w
e
e
n t
h
e
de
p
o
si
t
e
d m
e
t
a
l
s
and
GaN
.
M
eas
ure
m
ent
s
showe
d
that the specific cont
act resi
stance ofTi/Al/Ni/Au
ohm
i
c contact a
f
ter
an
neal
(
7
5
0
°C
t
o
90
0°C
)
vari
e
d
in
th
e r
a
ng
e
of
2
x10
-5
to 8x1
0
-5
Ω
cm
2
. O
t
her
resea
r
ch
g
r
o
u
p
s
ha
ve al
s
o
observe
d
si
milar specific
contact
resistan
ces for
Ti/Al/Ni/Au
co
n
t
act
[19
]
-[2
1
]
. It
is
no
teworth
y
th
at the Ti/Al/Ni/Au co
n
t
act sh
ow b
e
tter
electrical properties than
th
e
Ti/Al con
t
acts.
Fi
gu
re
4 s
h
ow
s t
h
e t
o
p
vi
ew
SEM
i
m
ages of
su
rface
m
o
rph
o
l
o
gy
of t
h
e
Ti
/
A
l
o
h
m
i
c cont
act
a
f
t
e
r
annealing
at va
rious tem
p
eratures
600
ºC, 700
ºC, 800
ºC
and
9
0
0
º
C
fo
r
60s. Figur
e
5
sh
ow
s the top
v
i
ew
SEM
im
ages of surface m
o
rphology of
the T
i/Al/Ni/Au ohmic contact a
f
te
r therm
a
l a
nnealing at various
te
m
p
eratures
for 60s. An i
n
crease i
n
a
n
nealing tem
p
erature
res
u
lted in t
h
e
decre
a
se in t
h
e
de
nsity of
ag
g
l
o
m
erates
an
d
lead
s to
metal
in
terd
iffu
sion
an
d
all
o
yin
g
.
Th
is wo
rk
aim
s
to
p
r
esent the
structural
ch
aracterizatio
n
of th
e
oh
m
i
c
co
n
t
act
o
n
t
h
e
n
-
GaN b
a
se
d
on
th
e
filterin
g
t
ech
n
i
q
u
e
s app
l
ied
to
SEM imag
es.
Th
e sam
p
le i
m
ag
es stu
d
i
ed in
th
is p
a
p
e
r are of the sa
me
m
a
gnification (5000).
Variou
s im
ag
e filterin
g
techniques
suc
h
as
Dis
k
,
Ga
ussian
,
Mo
tion
,
A
v
er
ag
e
,
Un
s
h
a
r
p,
Me
d
i
an
,
Ma
x
,
Min a
nd Ad
a
p
tiv
e
W
i
en
e
r
in
sp
atial filterin
g
were
im
pl
em
ent
e
d usi
n
g
M
A
TLAB
pl
at
fo
rm
. PSNR
i
s
used t
o
m
easure t
h
e
per
f
o
r
m
a
nce of
d
i
fferen
t
filterin
g
techn
i
q
u
e
s. Th
e filtering
tech
n
i
qu
es
were app
lied
on
8
i
m
ag
es o
f
Ti/Alan
d
Ti/Al/Ni/Au
materials.Th
e p
e
rform
a
n
ce of all th
ese i
m
ag
e filteri
ng
tech
n
i
q
u
e
s are an
alyzed
fo
r a set o
f
Ti/Al and
Ti/Al/Ni/Au
ohm
i
c contact images and
res
u
lts are
present
e
d in Ta
ble 1 a
n
d 2,
respectively.
4
.
1
.
Metrics Va
lues
fo
r Spatia
l Filters
Tabl
e 1
sh
o
w
s
t
h
e va
ri
at
i
on
o
f
PS
NR
o
f
Ti
/
A
l
o
h
m
i
c cont
act
vers
us a
n
n
eal
i
ng t
e
m
p
erat
ure f
o
r
Dis
k
,
Gau
s
sian
, Mo
ti
o
n
, Av
erag
e, Un
sharp
,
Med
i
an
, Max
,
Min
an
d
Ad
ap
tiv
e
Wien
er in
sp
atial filterin
g
techniques
.
Peak
s at 600
ºC
an
d
8
0
0
º
C
o
f
Ti/Al o
h
m
ic c
o
n
t
act rep
r
esent
m
o
re n
o
i
se is filtered
in
th
e
i
m
ag
e an
d
has
h
i
gh
PSNR.
Valleys at 700ºC a
nd
900ºC re
present less noise is
filtered in the im
age and
have
low PS
NR. T
h
e size
o
f
t
h
e
k
e
rn
el
filter an
d co
effi
cien
ts are
fix
e
d
an
d ca
nno
t be ad
ap
ted
t
o
a
g
i
v
e
n
im
ag
e in Gau
ssian, Motio
n,
Av
erag
e
and
Med
i
an
filters.
An
ad
ap
tiv
e W
i
en
er p
r
o
v
i
des
a ro
bu
st so
l
u
tio
n th
at is ad
ap
tab
l
e to
t
h
e v
a
rying
n
o
i
se lev
e
ls
o
f
th
ese i
m
ag
es. Ad
ap
tiv
e
W
i
en
er
g
i
v
e
s
b
e
tter PSNR th
an
oth
e
r filtering
tech
n
i
q
u
e
s fo
r
Ti/Al
ohm
ic contact.
The
highest PSNR a
n
d lowest specifi
c c
o
nta
c
t resistance
was obtaine
d
at
600
ºC.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Oh
mi
c C
ont
act
ch
ar
act
e
ri
zat
i
o
n
Usi
n
g
I
m
ag
e Proce
ssi
n
g
(
B
. N
.
S
h
a
s
hi
k
a
l
a
)
1
351
(a)
T=
60
0ºC
(b
)
T=70
0ºC
(c)
T=800
ºC
(d
)
T=90
0ºC
Fi
gu
re
4.
SEM
im
ages o
f
t
h
e
ohm
i
c
cont
act
Ti
/
A
l
af
ter t
h
ermal annealing
at vari
ous
temperat
ures
for 60s
(a) T=7
5
0
ºC
(b
) T=
8
0
0
º
C
(c) T=8
5
0
ºC
(d
) T=
9
0
0
º
C
Fig
u
re
5
.
SEM
i
m
ag
es of t
h
eo
h
m
ic co
n
t
act
Ti/Al/Ni/A
u a
f
ter therm
a
l annealing at
vari
ous tem
p
erature
s
for
60s
Table 1. PSNR
for Ti/Al
ohm
i
c
contact
T
e
m
p
er
a
t
ur
e
(°C)
Disk Gaussian
Motion
Av
erage
Unsharp
Median
Max
Min
Adaptive
Wiener
600
26.
50
27.
65
27.
04
26.
61
16.
55
27.
15
19.
35
20.
75
27.
25
700
20.
28
21.
30
20.
94
20.
41
15.
20
20.
57
13.
22
14.
96
21.
70
800
24.
44
26.
22
25.
37
24.
85
19.
29
26.
07
17.
64
18.
85
26.
02
900
23.
96
24.
69
24.
33
24.
09
17.
39
24.
03
16.
89
18.
03
24.
97
Tab
l
e 2
.
PSNR
fo
r Ti/Al/Ni/Au
o
h
m
ic
co
n
t
act
T
e
m
p
er
a
t
ur
e
(°C)
Disk
Gaussian Motion Average
Unsh
ar
p M
e
dian
M
a
x
M
i
n
AdaptiveW
iener
750
23.
70
25.
07
24.
56
23.
97
15.
33
24.
33
16.
72
18.
03
24.
87
800
25.
50
26.
94
26.
75
26.
05
18.
11
27.
38
18.
47
19.
89
27.
99
850
25.
27
26.
56
26.
16
25.
54
16.
72
25.
42
18.
39
19.
21
26.
35
900
25.
30
27.
75
26.
19
25.
88
16.
82
25.
86
18.
41
19.
81
26.
84
The
grai
ns a
g
gl
om
erat
i
on a
ppea
r
e
d
at
7
5
0
ºC
in Ti/Al/Ni/Au oh
m
i
c
co
n
t
act.
As t
h
e ann
ealin
g
tem
p
erature
was increase
d
from
750ºC to
900ºC in steps
of
50ºC, the a
ggl
om
erates
m
i
grated
on t
h
e surface
and c
o
alesce
nce into larger
aggl
om
erates. Thus, th
e t
h
ermal annealing proce
ss si
gni
ficantly changes the
m
o
rp
ho
log
y
o
f
th
e o
h
m
ic co
n
t
act an
d
in
flu
e
n
ces th
e ch
em
i
cal co
m
p
o
s
ition
of th
e surface o
f
bo
th
Ti/Al and
Ti
/
A
l
/
N
i
/
A
u c
ont
act
s.
Ta
bl
e
2 s
h
ows
t
h
e
va
ri
at
i
on
of
PS
N
R
of
Ti
/
A
l
/
N
i
/
A
u
o
h
m
i
c cont
act
s ver
s
us
an
n
eal
i
n
g
te
m
p
erature
for
D
i
sk
, G
a
u
s
s
i
a
n
,
Mo
tion
,
Av
e
r
ag
e
,
Un
sh
ar
p,
Me
d
i
an
,
Ma
x
,
Min
an
d
A
d
ap
tiv
e
W
i
en
e
r
in
sp
atial filterin
g
tech
n
i
q
u
es.
Peak
s at
80
0ºC an
d 900
ºC
o
f
Ti
/A
l/Ni/Au ohmic
contact represent
m
o
re noi
se
is
filtered
in
th
e
i
m
ag
e an
d
h
a
s h
i
g
h
PSNR
. Valleys at 7
5
0
ºC an
d
8
5
0
º
C
represen
t less n
o
i
se is filtered
in
th
e
im
age and ha
ve low PSNR.
A
d
ap
tiv
e
W
i
en
e
r
gi
ves
bet
t
e
r
PSNR
t
h
a
n
ot
her e
dge
det
e
c
t
i
on f
o
r Ti
/
A
l
/
Ni
/
A
u
ohm
ic contact. The
highest
PSNR a
n
d low
specific c
ontact re
sistance were
ob
tain
ed
at
80
0
ºC for
Ti/Al/Ni/Au
oh
m
i
c
co
n
t
act.
A
d
ap
tiv
e
W
i
en
e
r
g
i
v
e
s b
e
tter PSNR
fo
r Ti/
A
l/Ni/A
u ohmic contact tha
n
Ti/Al
ohm
i
c
cont
act
.
As shown in Figure 4 and 5,
th
e surface oftheohm
ic contacts gets
quite rough due to
many groove
s
produce
d
on t
h
e surface afte
r annealin
g at high tem
p
erature
.
A
rough s
u
rface of
ohm
ic contact is bad for
reliab
ility an
d
stab
ility. Th
e ro
ugh
n
e
ss is d
u
e to
th
e Al ex
istin
g
in
th
e oh
mic co
n
t
act sch
e
mes, wh
ich
d
o
es n
o
t
react com
p
letely and is s
u
bj
ec
t to m
e
lting at t
h
ese
high a
n
ne
aling tem
p
eratures
.
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I
S
SN
:
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08
IJECE
Vol. 5, No. 6, D
ecem
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2015 :
1347 –
1353
1
352
4.2. De
terminati
on of
OHMIC
Contact
P
o
rosity on n-GaN
Us
ing Image
Pr
ocessing Method
The s
u
rface st
udy
of
Ti/Al a
nd
Ti/Al/Ni/Au film
s depo
sited by
electron beam
evaporat
ion on
n
type
GaN
were cha
r
acterized by e
m
ploying SE
M. SEM im
ag
es
of t
h
e ohm
i
c contacts
were use
d
to
determine the
porosity. The
surface m
o
rpho
logy of Ti/Al/Ni/Au a
nd T
i/Al contacts
were st
udie
d
as a function
of t
h
e
an
n
ealing
p
r
o
c
ess co
nd
itio
ns u
s
ing
im
ag
e p
r
o
cessing
techniq
u
e
s. Th
en
v
a
riou
s seg
m
en
tatio
n
techn
i
qu
es were
use
d
to distinguish pore
s
on the s
u
rface im
a
g
e.
Tabl
e 3. Perce
n
t
a
ge o
f
whi
t
e
and
bl
ac
k po
re
s
o
n
Ti
/
A
l
o
h
m
i
c
cont
act
Te
m
p
e
r
ature (°C)
White
Black
600
81.
06
18.
94
700
78.
81
21.
19
800
72.
02
27.
98
900
60.
37
39.
63
Tabl
e 4. Perce
n
t
a
ge o
f
whi
t
e
and
bl
ac
k po
re
s
o
n
Ti
/
A
l
/
N
i
/
Au
o
h
m
i
c
cont
act
Te
m
p
e
r
ature (°C)
White
Black
750
69.
70
30.
30
800
73.
96
26.
04
850
62.
03
37.
97
900
70.
00
30.
00
Por
o
si
t
y
i
s
def
i
ned a
s
t
h
e
f
r
a
c
t
i
on
of
t
h
e
b
u
l
k sam
p
l
e
area
A t
h
at
i
s
not
occu
pi
ed
by
so
l
i
d
m
a
tt
er. If
the area
of the
solids is denot
e
d by
A
s
, and t
h
e pore area as
A
p
= A
- A
s,
then
poro
s
ity = (A
p
/A
).
Th
e po
res ar
e
in black a
nd t
h
e surface
of t
h
e thin
film
is
in white.
T
h
e
analysis of the binarize
d image is base
d on the
digitalization of
eac
h pore of the
th
in film
surface
followe
d
by the m
easur
em
ent of t
h
e
pore a
r
ea.
T
h
e
m
a
jor
effects of annealin
g
pro
c
ess are to
p
r
o
m
o
t
e recrystalliza
tio
n
lead
ing
to
g
r
ain
g
r
owth
an
d
g
r
ain
bou
nd
ary
passi
vat
i
o
n.
T
h
e e
ffect
of
an
neal
i
n
g
u
n
d
er
di
ffe
re
nt
t
e
m
p
er
atu
r
e on th
e
d
i
str
i
bu
tio
n
of these
thi
n
films
pore
s
and t
h
e pe
rcen
t
a
ge p
o
r
o
si
t
y
of t
h
e
w
h
i
t
e
and
bl
ack
po
res
are as sh
ow
n
i
n
t
h
e Tabl
e
3
and
4 f
o
r Ti
/
A
l
an
d
Ti/Al/Ni/Au ohm
i
c contacts, respectively.
T
h
e porosity of
white areas
on
the surface of Ti/Al film
decreases
as the annealing tem
p
erature
increases a
n
d the blac
k ar
eas
increases as t
h
e annealing te
m
p
erature increases.
The porosity of white areas
on the s
u
rface of Ti/Al/Ni/Au
film
is highe
st a
t
800°C anneal
ing tem
p
erature and
the porosity of the black a
r
ea
s is
lowest at 800°C. T
h
e pr
oportion of porosity on the
s
u
rface of
ohm
i
c c
ontact
varies
with a
n
nealing tem
p
erature
b
eca
use t
h
e a
nneali
n
g
works
on rec
r
ysta
llized grai
ns
of the t
h
in
film
s so
the white areas
are less a
n
d
which
re
prese
n
ts
the s
u
rface
of the
ohm
ic co
ntact. On the
ot
her
ha
nd, the
black
areas a
r
egrowi
ng which re
pre
s
ent
pores, cra
c
ks,
and
defect
s on t
h
e s
u
rfac
e of the
ohm
i
c
contact.
5.
CO
NCL
USI
O
N
Ti/Al and
Ti/
A
l/Ni/Au oh
m
i
c con
t
acts were
d
e
po
s
ited on
n-type
Ga
N and a
n
nealed at va
rious
te
m
p
eratures
for 60s
ha
ve
been c
o
m
p
ared
in term
s of s
p
ecific contact
resistance
a
n
d surface
m
o
rphology.
The
va
ri
at
i
ons
o
f
P
S
NR
o
f
Ti
/
A
l
an
d Ti
/
A
l
/
N
i
/
A
u
ohm
i
c
co
nt
act
s ve
r
s
us a
n
neal
i
n
g
t
e
m
p
erat
ure
f
o
r
Di
sk,
Gau
s
sian
, Mo
ti
o
n
,
Av
erag
e,
Un
sh
arp, Med
i
an
, Max
,
Mi
n
an
d Ad
ap
tiv
e
W
i
en
er in sp
at
ial filterin
g
tech
n
i
q
u
e
s
w
e
r
e
stud
ied.
Gaus
sian
an
d
A
d
ap
tiv
e W
i
en
e
r
g
i
v
e
s
b
e
tter PSNR for Ti/
A
l and Ti/Al/Ni/Au oh
m
i
c co
n
t
acts.
A
d
ap
tiv
e
W
i
ene
r
g
i
v
e
s
b
e
tter PSNR fo
r Ti/Al/Ni/Au
oh
m
i
c
co
n
t
act th
an
Ti
/Al o
h
m
ic co
n
t
act. Th
e p
r
op
ortion
of
porosity on the surface of
Ti/Al
and Ti/Al/Ni/Au
films decreases as
th
e annealing t
e
m
p
erature inc
r
eases
because the annealing
works on the re
cr
ysta
llized grains of the thin fil
m
s. Thus Ti/Al/Ni
/
Au ohm
i
c contacts
m
a
y
be p
r
efe
r
r
e
d
fo
r
hi
g
h
t
e
m
p
erat
ure a
n
d
hi
gh
p
o
w
er
de
vi
ces o
n
Ga
N.
ACKNOWLE
DGE
M
ENT
The a
u
t
h
ors
w
oul
d l
i
k
e t
o
t
h
ank t
h
e
pr
ofes
sors
an
d staff
me
m
b
ers of t
h
e Center
of E
x
cellence i
n
Nan
o
el
ect
r
oni
c
s
(C
E
N
)
f
o
r t
h
ei
r s
u
pp
ort
d
u
ri
ng t
h
e
fab
r
i
cat
i
on
pr
ocess
.
The e
x
peri
m
e
nt
s i
n
t
h
i
s
pap
e
r we
re
carried
ou
t at Ind
i
an
In
stitu
t
e
o
f
Tech
no
log
y
Bo
m
b
ay a
n
d
Ind
i
an
In
st
itu
te o
f
Scien
c
e Ban
g
a
lore un
d
e
r the
Indian Na
noelectronics Users
Program
.
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I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Oh
mi
c C
ont
act
ch
ar
act
e
ri
zat
i
o
n
Usi
n
g
I
m
ag
e Proce
ssi
n
g
(
B
. N
.
S
h
a
s
hi
k
a
l
a
)
1
353
REFERE
NC
ES
[1]
S. Sundeep and Dr. G. Madhusu
dhan Ra
o, “Modelling
and Anal
ysis of Custo
m
Power Devices fo
r Im
prove Powe
r
Qualit
y,
”
Intern
ational Journal of
Electr
ical and
Computer Eng
i
neering
, Vol. 1,
No. 1, pp. 43-48, 2011.
[2]
S.
M.
Ma
ha
ei,
M.
Ta
ra
fda
r
Ha
gh,
a
nd K. Zar
e
,
“Modelling FACTS Devices in
P
o
wer S
y
s
t
em
S
t
ate
Es
tim
atio
n
,
”
International Jo
urnal of
Electr
ical and Computer Engin
eering
, V
o
l. 2
,
No
. 1
,
pp
.
57-67, 2012
.
[3]
Subramaniam Arulkumaran,
et
al
.
,
“
R
ecord-
l
o
w
contact red
i
s
t
ance for InAlN/
AlN/GaN high
ele
c
tron m
obili
t
y
transistors on Si
with non-gold
metal,”
Japan
ese Journal
of Applied
Physics
, Vol. 5
4
, pp
. 04-12
, 20
15.
[4]
X. Zhang, A. Saxler, P. Kung, M.
Razeghi
, D. W
a
lker, and J. Xu, “
A
lGaN
Ultraviol
e
t photoco
nductors grown
on
Sapphire,”
Applied Ph
ysics Letters
, Vol. 68
, No.
15, pp
. 2100-21
01, 1996
.
[5]
R
.
S
t
a
l
l
,
S
.
L
i
a
n
g
,
Y
.
L
u
,
C
.
J
o
s
e
p
h
,
I
.
F
e
r
g
u
s
o
n
,
C
.
A
.
T
r
a
n
,
R
.
F
.
K
a
r
l
icek
,
an
d Z.
C. F
e
ng
, “
G
aN and AlGa
N
m
e
tal-Sem
i
cond
uctor-m
et
al Pho
t
odetectors,”
M
a
terials Scien
c
e and Engin
eering,
Vol. 50
, N
o
. 1, pp. 311-3
14,
1997.
[6]
N. A. Papani
col
a
ou, M. V.
Ra
o
,
J. Mitter
e
der
,
an
d W
.
T. Anderso
n
, “
Re
li
able
Ti
/
A
l and Ti
/Al/Ni/
Au contac
ts to n
-
ty
p
e
GaN
formed b
y
vacuum an
nealing,”
Journa
l of Vacuum
Science
&
Technology B
, Vol. 19
, pp
. 261-267
, 2001
.
[7]
M
.
E
.
L
i
n
,
Z
.
M
a
,
F
.
Y
.
H
u
a
n
g
,
Z
.
F
.
F
a
n
,
L
.
H
.
A
l
l
e
n, and H. Morkoc, “Low r
e
sist
ance ohmic contacts on wide
band-gap G
a
N,”
Appl. Ph
ys. Letters
, Vol. 64, No. 8, pp. 1003-100
5, 1994
.
[8]
Cong W
a
ng and Nam
-
Young
Kim
,
“
E
lectri
cal
charac
ter
i
za
tion
and nanoscale
surface m
o
rpholog
y
of optim
iz
e
d
Ti/Al/
Ta/Au
oh
m
i
c cont
ac
t for
AlGaN/GaN HEMT,
”
Nanosca
le Research
Letter
s,
Vol. 7, No. 1
,
pp. 107
, 2012
.
[9]
V. Rajagopal R
e
dd
y
and
C. K. Rame
sh, “Lo
w
-resistance oh
mic contacts
to
n-ty
pe GaN u
s
ing Ti/Al/Re/Au
m
u
ltila
ye
r sch
e
m
e
,”
Journal of
Optoelectronics
and Advan
ced
M
a
terials
, Vol. 6
,
No. 1, pp. 177-1
82, 2004
.
[10]
H. C.
Le
e,
J. W
.
Bae,
and
G. Y.
Yeom
, “
T
herm
al
l
y
Stabl
e
Ti/Al
/
W
/Au Multila
ye
r Ohm
i
c Conta
c
t
s
on n-t
y
pe
Ga
N,”
Journal of the
K
o
rean
Phys
i
c
al
S
o
cie
t
y
, Vol. 51
,
No. 3, pp. 1046-
1049, 2007
.
[11]
Deepak S
e
lv
ana
t
han, F
i
tih M
.
Mohammed, Asrat Tesfay
es
us
,
and Iles
anm
i
Ades
ida, “
C
om
pa
rative
stud
y
of
Ti/Al/Mo/Au
, Mo/Al/Mo/Au, and
V/Al/Mo/A
u
ohm
ic
contacts to AlGaN/G
a
N heterostructures,”
Journal of
Vacuum Scien
c
e
&
Technology B
, Vol. 22
, No. 5,
pp. 2409-2416
,
2004.
[12]
L. Dobos, B. Pecz,
L. To
th, Zs.
J. Horvath, Z. E. Horvat
h, A. Toth, E. Horvath, B.
Beaumont, and Z. Bougrioua,
“
M
etal con
t
a
c
t
t
o
n-GaN,”
Applied Surface S
c
ien
c
e
, Vol. 253, pp. 655-661, 2006.
[13]
Liu Y,
et al
.,
“
M
echanis
m
s
of Ohm
i
c Contact
F
o
rm
ation and
carri
er Tr
ans
port of Low T
e
m
p
eratur
e Annea
l
e
d
Hf/Al/Ta on In
0.
8
Al
0.82
N/GaN-on-Si,
”
ECS Journ
a
l of Solid Sta
t
e
Scien
ce and Technology
, Vol. 4,
No. 2. pp. 30-35
,
2015.
[14]
Su Jin Kim,
Tae Yang Nam,
and
Tae G
e
un Kim, “Low-Resistance Nona
llo
y
e
d Ti/Al Ohmic Contacts on N-Face
n-
T
y
p
e
GaN
via
a
n
P
l
as
m
a
Tr
eatm
e
nt,
”
I
EEE
E
l
ec
t
r
on Devic
e
L
e
tte
r
s
, Vol. 32
, No.
2, pp
. 149-151
,
2011.
[15]
R. C. Gonzalez
and R. C
.
W
oods, Digitsl Image P
r
ocessing, 3
rd
edition, 2008.
[16]
Z. Wang
, A. C. Bovik, H. R
.
Sheikh,
a
nd
E
.
P.
Si
monc
e
l
li
, “Ima
ge
qua
li
ty
asse
ss
me
nt
from e
rror vi
si
bi
l
ity
to
struc
t
ural simila
rity
,”
I
EEET
rans.
Image
Process.,
Vol. 13, No. 4
,
pp. 600–612
, 20
04.
[17]
H. R. Sheikh an
d A. C. Bovik, “Ima
ge information and visu
al qu
ality
,
”
IEEE Trans. Image Process.
, V
o
l. 15
, N
o
.
2
,
pp. 430–444
, 20
06.
[18]
Zhou Wang, Alan C. Bovik, “A
Universal Image Quality
Index
,
”
IEEE Signa
l Processing L
e
tters
,
Vol. 9, No. 3, pp
.
81-84, 2000
.
[19]
N. A. Papani
col
a
ou, M. V. R
a
o,
J. Mitter
e
der
,
an
d W
.
T. Anderso
n
, “
R
eliab
l
e
Ti/
A
l and Ti
/Al/Ni/
Au ohm
ic conta
c
ts
to n-ty
pe GaN f
o
rmed b
y
vauu
m annealing
,
”
Journal of Vacuu
m
Science
&
Te
chnology B
, Vol. 19, No. 1, pp
.
261-
67, 2001
.
[20]
Z.
X.
Qin,
Z.
Z. Chen,
Y.
Z.
Tong,
X.
M.
Ding, X.
D.
Hu
, T. J.
Yu, and G. Y. Z
h
ang, “
S
tud
y
of
Ti/Au, T
i/Al/Au
,
and T
i/Al/Ni
/
Au ohm
ic
contacts to n-GaN,”
Applied Ph
ysics
A
, Vol. 78
, pp
. 729-7
31, 2004
.
[21]
B.
Ja
c
obs, M.
C. J.
C.
M. Kra
m
er,
E.
J.
Geluk,
and F.
Karouta
,
“
O
ptim
isation of
the T
i/Al/Ni
/
Au
ohm
ic cont
act
o
n
AlGaN/GaN FET structures,”
Jo
urnal of Crysta
l
Growth
, Vol. 24
1, pp
. 15-18
, 20
02.
Evaluation Warning : The document was created with Spire.PDF for Python.