Acky Uyeda School of Information Science JAIST Ishikawa Japan Ohmic contacts on diamond semiconductor devices tueeedajaistacjp TTI2013Italy 30 th Jul2013 Collaboration ID: 580632
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Slide1
Tack
Acky
Uyeda
School of Information Science,JAIST, Ishikawa, Japan.
Ohmic contacts on diamond semi-conductor devices
tueeeda@jaist.ac.jp
TTI2013@Italy, 30
th
Jul.2013 Slide2
Collaboration
with Kenya/
Eldoret
Group Prof. N.W.
Makau, Prof. G.O. Amolo,
and Mr. I. MotochiSlide3
Background
New Generation
Semi-conductors
Power
semi-conductors
Diamond semi-conductor!(
c.f,, Si for processors etc.)
AC/DC conversion, High frequency signal processing, etc.
(
SiC
,
GaN
,
Diamond
; wide-gap)
Si,
GaAs
,
InP
Frequency
Power
GaN
SiC
Diamond
→High Power, High Freq.,
→Easy to chilled due
to
heat conductivitySlide4
How to fabricate
Ohmic Contact
Required Properties
・
Ohmic
barrier・Difficult to be peeled.
Motivation
Except
Si
,
the process NOT established.
Preventing
Schottky
junction
(bring about rectification)
For new semi-conductors, ...
Try & Error such as scratching surfaces..Slide5
Which kind of metal used?
S
urface termination for dangling bonds
- Tighten the bonding between Electrode & Slab.
What is clarified
Au, Ta, Ti, ...
Diamond
metal
- Introducing carrier to make N/P semi-conductorSlide6
Project Here
By using
DFT/
QMC,
・
Robustness against peeling・Ohmic property
Our Conclusion so far
Ta
with
Oxygen
-termination gives
d
eepest cohesion with
Ohmic
property.
→ Surface Cohesive energies.
→ DOS between Gap.
DOS of Diamond bulkSlide7
Cohesive Energy
x =
Ti
,
V
, Ta
, and Au, Pd
Oxygen
,
Hydrogen
or
Without
＜
Slab
＞
＜
Parent Surface
＞
Diamond
metal
metal
metal
＜
Atom
＞
DiamondSlide8
Method
DFT study
QUANTUM ESPRESSO
(PW basis)
・
XC
functionals
; PBE or LDA
・
Pseudo Potentials;
UltraSoft
&
NormConserving
(NC)
(Trail-Needs)
・
Structure Optimization; by PBE (both
Ultrasoft
, NC) Slide9
・
DFT
・
PBE
・ultra-soft
pseudo potential
・variable cell relaxed
Results
Dotted lines ;
Motochi's
previous work
(predicting V as best)
→ Present results predict Ta is best.Slide10
Results
Motochi's
previous work ;
V is best
Present results ;
Ta is best
.
cutt
off energy
37
[
Ry
] →
90
[
Ry
]
k-point
4x4x1
→
14x14x1 Slide11
・
DFT
・
LDA
・Ultra-soft
pseudo potential
Results
From now,
sticking to Ta & V
cases.
LDA doesn't change the trend.Slide12
In-gap state
Ta
with
Oxygen
termination
Valenve
bondSlide13
・
DFT
・
Norm Conserving
pseudo potential
Results
・
PBE
NC-
pp
evaluation also predict Ta as best.Slide14
Results
V
; 3s
(2
) 3p(6) 3d(3)4s(2)
Ta ; 5s(2) 5p(6)
5d
(3)6s(2)
Ta without semi-core elec.
Now the evaluation using the same core-size in progress...
But we expect Ta will get more cohesive energy
NC-
pp
evaluation also predict Ta as best.
We note that..
.
Different core sizes for V and Ta for NC-PP.
N.B.) similar elec.
config
. for V and Ta.
(
≒ not changing the conclusion)Slide15
Results
"CASINO"
DMC calculations
<Ta> w/o
term'd
H-
term'd
O-
term'd
221 -3.6878(4) -3.6499(4)
-3.7898(4)
441 -3.8571(4)
-
3.6124(4)
(
in_Progress
)
<V>
221 -0.34532(3) -0.3131(2) -0.36244(6)
441 -0.3808(5) -0.3023(6)
(in_Progress
)
system size
Cohesion energies in
hartree
.
<Ta> w/o term'd H-term'd O-term'd
221 -0.48060 -0.66995 -0.61163441 -0.58996 -0.85234 -0.81761<V>
221 -0.22537 -0.28249 -0.24647441 -0.35067 -0.39617 -0.36941
DFT calculation(NC PP)Slide16
Results
"CASINO"
DMC calculations
<Ta> w/o
term'd
H-
term'd
O-
term'd
z
221 -3.6878(4) -3.6499(4)
-3.7898(4)
<V>
221 -0.34532(3)
-
0.3131(2)
-
0.36244(6)
system size
Cohesion energies in
hartree
.
<Ta> w/o term'd H-
term'd O-term'd
221 -0.48060 -0.66995 -0.61163
<V>221 -0.22537 -0.28249 -0.24647
DFT calculation(NC PP)Slide17
Results
Cohesion energies in
hartree
.
c
oh_E(hta221)= -68.09176 - ( -58.06663 + 2*(-3.18760)) = -3.64993coh_E(hta221)=
-68.16341 - ( -58.04167 + 2*(-4.82057)) = -0.48060
coh_E
(ota221
)=
-98.92987 - ( -88.76489 + 2*(
-3.18760
)) = -3.78978
coh_E
(ota221
)=
-99.12718
- ( -
88.81609 + 2*(-4.82057)) = -0.66995coh_E(xta221)= -66.82612 - ( -56.76308 + 2*(-3.18760)) = -3.68784coh_E(xta221)= -67.02145 - ( -56.76868
+ 2
*(-4.82057)) = -0.61163
Comparing DFT and QMC
QMC cohesion data
DFT cohesion data