1 金金金金金金金 Novel Metal-Insulator-Sem iconductor Photodetector •金金金金 金金金 金金 : •金金 金金金 : •金金金金金金金金金金金金
Jan 24, 2016
1
金氧半光偵測器
Novel Metal-Insulator-Semiconductor Photodetector
•指導教授:劉致為 博士•學生:郭平昇•台灣大學電子工程學研究所
2
Outline
• Introduction• LPD Oxynitride• Recessed Oxynitride Dots on Self-assembled Ge
Quantum Dots• Ge/Si Quantum Dot MOS Photodetectors for Opti
cal Communication• MIS Ge/Si Quantum Dot Infrared Photodetectors
(QDIP) (intraband transition)• A Dual-polarity Operable MOS Photodetector with
Pt Gate (interband transition)• Summary
3
Introduction• The electro-optical products may be one of the
killer applications in the future Si market.• The worldwide revenue of the optical semicon
ductor is ~5 % (~7 B) of the total semiconductor revenue (~140 B) 2002.
(Note RF: 4.7 B, MEMS : 4.6 B)
• The ITRS has predicted that the incorporation of optoelectronic components into CMOS-compatible process is needed to achieve System-on-a-Chip.
• CMOS optoelectronics: OE Devices fabricated by CMOS available technology
4
Introduction
• Si-based CMOS optoelectronics
- low cost, high reliability, VLSI compatible
Electrical PartsOptical Parts
5
0.0 0.2 0.4 0.6 0.8 1.00.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
strained SiGe
relaxed SiGe
Ge mole fraction
E n
e r
g y
( e
V )
2.42.22
1.8
1.6
1.4
1.2
1
w a v e l e n
g t h
( m )
0.0 0.2 0.4 0.6 0.8 1.010-2
10-1
100
101
102
103
strained SiGe
1550 nm
1300 nm
820 nm
Abs
orpt
ion
Len
gth
( m
)
Ge mole fraction
Introduction
• Ge mole fraction cut-off wavelength absorption length
6
0.90 0.95 1.00 1.05 1.10 1.15 1.20
Inte
nsity
(arb
itrar
y un
it)
Wavelength (m)
1.18m
NMOS detector response
• Al gate• Zero bias• Cut-off wavelength
= 1.18m• Ecutoff = 1.05 eV <
Ebandgap
• Phonon-assistant absorption (65 meV)
7
LPD Oxynitride
H2SiF6 3.09 mol/l
H2SiF6 2 mol/l
SiO2 Saturated H2SiF6
SiO2:xH2O
LPD SiON Coated Si
Heat Treatment
NH4OH
P-Si Substrate
O O O
Si Si SiO Si OO
O O
Si SiO Si SiO Si O
O O
O
N
H H
N
F
OH
N F
N
N
F
N
H
N
H
O
Si
O
Si
+ H2O
O
H H
LPD SiON
dehydration
Si SiO
O
O
O
O
H H
SiOx SiOx SiOx SiOx SiOxNative oxide
P-Si substrate
N
H H
O H
F
N
Process flow of LPD oxynitride. The proposed LPD-SiON mechanism.
8
-3 -2 -1 0 1 2 31E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
substrate
LPD oxide
Al
Cur
rent
(A)
Voltage (V)
SiO2 1nm SiON 0.3M NH4OH 1nm SiON 0.5M NH4OH 1nm
Al
traps
P - Si
3.1 e.V
4.7 e.V
P - Si
Al
traps
dominant
Accumulation region Inversion region
• The LPD-SiON has a lower current than the LPD-SiO2.
9
Recessed Oxynitride Dots on Self-assembled G
e Quantum Dots
oxide dot
Ge dot
20 nm
(a) Oxynitride (b) Oxide
10
Tensile Strain :
GeSi spacer
GeSi spacer
GeSi cap
SiO2/SiON
p-type Si substrate
Si buffer layer ~ 50nm
~100nm ~2nm
~6nm
•The tensile strain can enhance the oxynitride deposition rate on the strained Si on SiGe 20% buffers.
•The Si cap area above the Ge dots has a tensile strain, and the Si cap area on Ge wetting layers is strain free.
11
O:N = 16:7 at the interface
SIMS profile of Oxynitride
Recess the top Ge dot
12
Dot Height
• The LPD-SiON has a higher deposition rate as compared to the LPD-
SiO2, and the deposition rate increases as ammonia concentration
increases.
• Under the same wetting layer thickness, the LPD-SiON dots still yield
a higher dot height.
13
AFM Morphologic :
Quantum Dot
AFM surface image and Cross- section morphology of LPD oxynitride (1M NH4OH) with 15 nm wetting layer thickness.
AFM surface image and Cross- section morphology of LPD oxide with 15 nm wetting layer thickness.
14
Quantum Ring
Depostion time : (a) 12 min (b) 20 min.
• The tensile strain area can have preferential oxide deposition. • The LPD-SiO2 deposited on quantum ring sample acts just like the stalactite.
15
Ge Quantum Dots
• 5 ~ 20 layer self-assembled Ge quantum dots prepared by UHVCVD under SK growth mode.
p-Si substrate
Si buffer layer 50 nm
Active region (x layers)
Wetting layer2 nm
Si spacer50 nm
Ge DotSi cap 3 nm
16
LPD vs. RTO (700 oC)
• Devices with LPD oxide have higher efficiency.
1300 nm 1550 nm
RTO oxideLPD oxide
Effic
ien
cy (
a.u
.)
17
Device Operation
• I-V curves at 820 nm (device area = 3x10-4 cm2)
-2 -1 0 1 2 3
5-layer QD device10-12
10-9
10-6
10-3
1.5 mW 1.0 mW 0.5 mW dark current
C
u r
r e
n t
( A
)
Voltage ( V )
18
Al
traps
hv
quantum dot
wetting layer
dark currentphotocurrent
Device Operation
• Carriers can tunnel through oxide via the assistance of multiple traps.
19
Results and Discussion
0.0 0.5 1.0 1.5 2.0
10-11
10-8
10-5
10-2
D
ark
Cu
rren
t (A
)
| Vg | ( V )
Multi-layer Si0.8
Ge0.2
Ge 5-layer Quantum dot Si
• Dark current of all 4 devices.• The dark current of 5-layer QD device 0.06 mA/cm2
20
820 nm
• Efficiency of 5-layer Ge QD device 20%
0.4 0.6 0.8 1.0 1.2 1.4 1.6
100
101
102
Vg = 2 V
Ge 5-layer Quantum dot S i Multi-layer Si
0.8Ge
0.2
Power ( m W )
Res
po
nsi
vity
( m
A/W
)
10-3
10-2
10-1
820 nm Extern
al Qu
antu
m E
fficiency
21
1300 nm
• Efficiency : 5-layer Ge QD (0.16 mA/W) > multi-layer Si0.8Ge0.2 (0.04 mA/W)
0.4 0.6 0.8 1.0 1.2 1.4 1.6
10-2
100
1021300 nm
Ge 5-layer Quantum dot Multi-layer Si
0.8Ge
0.2
Vg = 2 V
Res
po
nsi
vity
( m
A/W
)
Power ( mW )
10-7
10-3
10-5
10-1
Extern
al Qu
antu
m E
fficiency
22
1550 nm
• Only Ge and 5-layer Ge QD detectors have response.
0.4 0.6 0.8 1.0 1.2 1.4 1.6
10-3
10-1
101
1031550 nm
Ge 5-layer Quantum dot
Vg = 2 V
Power ( mW )
Res
pons
ivity
( m
A/W
)
10-3
10-5
10-7
10-1
External Q
uantum E
fficiency
23
Optimized QD Structure
• Optimize number of periods and Si spacer layer thickness.
• Number of periods 5, 10, 20 periods
• Si spacer thickness 20 nm, 50 nm
24
High Efficiency at 850 nm
• 20 - period QDs, 50 nm spacers• High responsivity at 850 nm 0.6 A/W
-2 -1 0 1 2 310-8
1x10-5
10-2
101
850 nm
Cu
rren
t D
ensi
ty (
A/c
m2 )
Gate Voltage ( V )
1 mW 0.5 mW 0.25 mW Dark
0.2 0.4 0.6 0.8 1.010-2
100
102
Res
po
nsi
vity
( m
A /
W )
Light Intensity ( mW )
@ 3 V 850 nm 1310 nm 1550 nm
25
Discussion
• Quantum dot periods Responsivity • Si spacer thickness
dark current ↓ ( x 10-3 )
• For 20-period QDs, 50 nm spacers
- High responsivity 0.6 A/W at 850 nm
- Low dark current 0.3 mA/cm2
26
MOS Ge/Si QDIP ( intraband transition) • Quantum dot infrared photodetector (QDIP)
=> low dark current, high operation temperature and normal incident detection
• Applications => military, medical, astronomical and many others.
• The MOS structure with tunneling insulator can make the Ge/Si QDIP
=> small dark current
compatible with Si ULSI process
27
Device Fabrication
Si substrate
Si buffer layer 50 nm
Ge wetting layer (quantum well)
Ge quantum dot
Si spacer layer 50 nm
Si cap layer 3 nm
oxideAl
20 nm
• Grown by UHVCVD• The base width and height of the Ge dots are ~100 nm and
6~7 nm, respectively. The Ge dot density is ~1010 cm-2
28
• Dark current is limited by minority generation rate (from Dit and bulk traps).
• The confined holes have transitions under infrared exposures.
Device Fabrication
Al
Infrared
Darkcurrent
SiO2
E1
E2
Wetting layerQD
29
Discussion
• PL spectrum => QD barrier 0.3~0.4 eV
0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15
Wetting layersignals
barrier ~ 0.3 eV Si
SiTO
Ge QD signals
20 K
Inte
nsit
y (
A. U
.)
Photon energy ( eV )
30
Device Performance
0.0 0.5 1.0 1.5 2.0 2.5 3.0
77 K
200 K
300 K
10-9
10-6
10-3
100
C
urr
en
t D
en
sit
y (
A / c
m2 )
Gate Voltage ( V )
Oxide Oxynitride
• Smaller dark current duo to lower Dit
31
2 3 4 5 6 7 8 9 10
0.00
0.01
0.02
0.03
0.04
0.05
0.06
QD
QW
140 K
120 K
100 K
80 K
60 K
40 K
20 K
R
esp
on
siv
ity
( m
A / W
)
Wavelength ( m )
OxynitrideV
g = 5 V
• The operating temperature reaches 140 K for 3~10μm detection. Device Performance
32
Device Performance
• 2~3 μm response up to 200 K
• large response at short wavelength => interband transition
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.00.000
0.002
0.004
0.006
0.008
0.010
200 K
160 K
120 K
100 K
60 K
20 K
OxynitrideV
g = 5 V
Wavelength ( m )
Resp
on
siv
ity
( m
A / W
)
33
Device Performance
20 40 60 80 100 120 140 160 180 200107
108
109
1010
1011
Temperature ( K )
D* (
cm
Hz1
/2 / W
)
6.8 m
2.7 m
Oxynitride V
g = 1 V
Vg = 5 V
• Peak Detectivity @ 100 K ~ 1010 cmHz0.5/W
34
Device Performance
• The normalized detectivity D* is defined as:
• A is the detector area, Δf is the equivalent bandwidth of the electronic system, and NEP = in/R is the noise equivalent power. The in is current noise and R is the responsivity.
• The current noise is limited by the dark current and can be approximated as the shot noise (2eIdΔf)1/2, where Id is the measured dark current.
Ri
fA
NEP
fAD
n /*
35
A Dual-polarity Operable MOS Photodetector with Pt Gate (interband transition)
-10 -8 -6 -4 -2 0 2 410-10
10-8
10-6
1x10-4
10-2 Pt gate
Die Area 3E-4 cm2
p-Si substrate
Si buffer layer 50 nm
Ge wetting layer
Ge quantum dot
Si spacer layer 60 nm
Si cap layer 100 nm
Ge quantum dot device Si device
Gat
e C
urr
ent
(A)
Gate Voltage ( V )
Pt
3.1 eV
4.5 eV
4.3 eV
4.6 eV
(a)
dominate
3.1 eV
4.6 eV
Pt
4.3 eV
4.5 eV
(b)
•The quantum dot device has lower current as compared to the Si device both in accumulation and inversion region due to hole blocking effect.
36
-10 -8 -6 -4 -2 0 2 410-11
1x10-8
1x10-5
1x10-2
Pt gate has photo-response
Die Area 3E-4 cm2
photo current
dark current
850 nmIntensity = 1 mW
Gat
e C
urr
ent
( A
)
Gate Voltage ( V )
Al Device Pt Device
• The Q.D device with Pt gate has photo-response under accumulation region due to Pt has larger workfunction 5.3 e.V ( high electron barrier = 4.3 eV ). Al has lower barrier : 3.1 eV.
Photo I-V
37
-10 -8 -6 -4 -2 0 2 41E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
Pt P-Si
Pt quantum dot
Al P-Si
Al quantum dot
LPD-SiO2 25A
Cu
rren
t (A
)
Voltage (V)
Al P-Si Al QD100-60 Pt P-Si Pt QD100-60
•For Al gate device, quantum dot has higher inversion current than Si due to Ge dot has a smaller bandgap.
•There is a inverse trend for Pt gate device due to hole blocking effect.
Pt & Al
Pt
3.1 eV
4.5 eV
4.3 eV
5.7 eV
3.1 eV
Al
4.6 eV
38
Low Temperature photo I-V of Ge quantum dot device
Pt
3.1 eV
4.5 eV
4.3 eV
4.6 eV
(a)
dominate
3.1 eV
4.6 eV
Pt
4.3 eV
4.5 eV
(b)
-14 -12 -10 -8 -6 -4 -2 0 2 41E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
100 K
photo current
dark current
Cu
rrre
nt
(A)
Voltage (V)
Photo generated
electron current in depletion regionNo depletion
region, low photo current
Extra electron current from Pt gate
39
100 150 200 250 3001E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
Die area 1.5E-3 cm2
Pt
+ 3V
P-Si quantum dot
Dar
k C
urr
ent
(A)
Temperature (K)
Hole blocking at low temperature
Pt
3.1 eV
4.5 eV
4.3 eV
4.6 eV
dominate
• Hole blocking effect is more severer at low temperature.
40
Conclusion• The tensile strain on the Si cap above self-assemble
d quantum dots can probably enhance the etching rate of Si and have a preferential oxynitride deposition on the Ge dots during LPD process.
• Due to the N atoms passivation of the interface states, the device with oxynitride yields a lower dark current as compared to oxide device.
• The MOS Ge/Si QDIPs for 2 ~ 10 μm using hole inter-valance subband transitions are successfully demonstrated. The maximum operating temperature is 140 K for 3 ~10 μm and is up to 200 K for 2 ~ 3 μm detection with LPD oxynitride.
41
• The MOS Ge quantum dot devices can have high responsivity (0.6 A/W at 850 nm) and low dark current. • Oxide is grown by LPD and Ge quantum
dot structures are prepared by UHVCVD. • MOS Ge quantum dot devices Si spacer thickness dark current↓( x10-3 )• The NMOS Ge quantum dot photodetector with Pt gate can be operated in both inversion and accumulation regions. The valence bandoffset in Si/Ge heterojunction can confined the hole and form a energy barrier to block the hole current.
Conclusion