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Reviewing SiC photo-sensing devices
Manuela Vieira Manuel Vieira Paula Louro Miguel Fernandes Alessandro Fantoni João Costa Victor Silva Manuel Barata
Lisbon 1
The Eighth International Conference on Sensor Device Technologies and Applications SENSORDEVICES 2017
September 10 - 14, 2017 - Rome, Italy
NOBEL in Physics 2009
TWO REVOLUTIONARY OPTICAL TECHNOLOGIES
“The Nobel Prize in Physics 2009 honors three scientists, who have played important roles in shaping the modern information technology, with one half to Charles K. Kao and with Willard S. Boyle and George E. Smith sharing the other half.”
Charles K. Kao Willard S. Boyle
George E. Smith
1. W.S. Boyle and G.E. Smith, Bell Systems Technical Journal 49 (1970) 587; G.F. Amelio, M.F. Tompsett and G.E. Smith, ibid. 49 (1970) 593. 2. J.R. Janesick: Scientific Charge-Coupled Devices (SPIE Press, 2001).
1. J. Hecht, “City of light. The story of fiber optics”, Oxford University Press (1999). 2. K.C. Kao and G.A. Hockham, “Dielectric-Fibre Surface Waveguides for optical frequencies” Proc. IEEE, 113, 1151 (1966).
Useful reading
Apparently the first still remaining photograph was produced by J.N. Niépce in 1826 using a camera obscura with an 8 hour exposure time.
W.H.F. Talbot invented in 1841, light sensitive papers containing silver salts for first obtaining a negative image and there after, through contact copying with another light sensitive paper, a positive image. In 1888 the Eastman Kodak box camera for roll film appeared on the market.
Charge-Coupled Devices
G. Lippman was awarded the 1908 Nobel Prize in Physics for his color photographic process based on interference effects. Traditional color films consist of three light sensitive emulsions with different sensitivities for light: top layer for blue, middle layer for green, and bottom layer for red. Film capture full color at every point in the image.
Kodak developed the Bayer filter mosaic pattern used for CCD image sensors (1975), only after the groundbreaking CCD invention (1970) W.S. Boyle and G.E. Smith.
The CCD digital image sensors were only capable of recording just one color at each point in the captured image instead of the full range of colors at each location.
Full color image sensors
p+hg
Ec
E v
w
i n+i n+
Pinc
Pinc
JdlJdif
Jdif
Jdl
++
+
--
-
p+hg
Ec
E v
w
i n+i n+
Pinc
Pinc
JdlJdif
Jdif
Jdl
++
+
--
-
p+hg
Ec
E v
Ec
E v
w
i n+i n+
Pinc
Pinc
JdlJdif
Jdif
Jdl
++
+
--
-
All of these devices use essentially the same light sensing mechanism. Photons penetrating a depletion region generate electron-hole pairs. These carriers are swept away by the electric field across the depletion region and generate a small transverse photocurrent.
p_-Si
Clock
Potential well
SiO2
+V -V
One color at each point in the captured image
Full range of colors at each location
#1 #2a #2b
Device Architecture
•Produced by PECVD •The thickness of the front photodiode are optimized for blue collection and red transmittance •The thickness of the back photodiode was adjusted to achieve high collection in the red spectral range
ITO
G
lass
p
i’(a-S
iC:H
)
i (a
-Si:H
)
n
p
n
ITO
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,410
24
1x1025
1x1026
400 nm 580 nm
450 nm 615 nm
470 nm 650 nm
550 nm
Genera
tion (
m-3s
-1)
Position (m)
Both front and back diodes act as optical filters confining, respectively, the blue and the red optical carriers, while the green ones are absorbed across both.
Fro
nt
Back
Light-to-dark sensitivity (Homo- vs Hetero-structures)
400 450 500 550 600 650 700 750 8000,0
0,2
0,4
0,6
0,8
1,0
L=2 mWcm
-2
L=1 mWcm
-2
L=0#M007192
RN
Wavelenghth (nm)
400 450 500 550 600 650 700 750 8000,0
0,2
0,4
0,6
0,8
1,0
L=2 mWcm
-2
L=1 mWcm
-2
L=0#M007192
RN
Wavelenghth (nm)
400 450 500 550 600 650 700 750 8000,0
0,2
0,4
0,6
0,8
1,0
L=4 mWcm
-2
L=0
#M006291
RN
Wavelength (nm)
400 450 500 550 600 650 700 750 8000,0
0,2
0,4
0,6
0,8
1,0
L=4 mWcm
-2
L=0
#M006291
RN
Wavelength (nm)
Homostructure: • light bias independent • no light-to-dark sensitivity
Heterostructure
•light bias dependent.
• light-to-dark sensitivity
GlassITO
P
i-Si:H (1000 nm)
nITO
GlassITO
P
i-Si:H (1000 nm)
nITO
s d D E s d / s ph
Single
films ( W-1 cm -1 ) (eV)
p-Si:H 8.2 10 -7 0.499 7.3
p-SiC:H 2.5 10 -9 0.649 4.5
i-Si:H 7.6 10 -11 0.739 7.1 10
4
n-Si:H 7.8 10 -7 0.426 1.2
n-SiC:H 1.9 10 -12 0.834 21
GlassITO
P
i-Si:H (1000 nm)
nITO
GlassITO
P
i-Si:H (1000 nm)
nITO
Light-to-dark sensitivity
400 450 500 550 600 650 700 750 8000.00
0.05
0.10
0.15
0.20
#1(L=0)
#1b(L=0)
#1a(L=0)
Sen
siti
vit
y (
A/W
)
Wavelength (nm)
0,0 1,0 2,0 3,0 4,0 5,0 6,0
i ac
(L)/
i ac(0
)
L (mWcm
-2)
0,0
0,2
0,4
0,6
0,8
1,0
#1a
#1
#1b
#1 (2mWcm-2
)
#1a(2mWcm-2)
#1b(2mWcm-2)
The light-to-dark ratio depends strongly on the carbon concentration of the doped layers.
p
i
n
a-SiC:H a-Si:H
When highly resistive a-SiC:H doped layers are used its higher optical gap when compared with the active layer are responsible by charge accumulation at the illuminated interfaces which blocks the carrier collection under illumination. Those insulator-like layers prevent excess signal charge from blooming to the nearby dark regions avoiding the image smearing.
-0,6
-0,4
-0,2
0,0
0,2
0,4
0,6
0,10,2
0,30,4
0,50,6
0,00,2
0,40,6
0,81,0
Pote
ntial (V
)
Position (m)
Voltage (V
)
-0,6
-0,4
-0,2
0,0
0,2
0,4
0,6
0,10,2
0,30,4
0,50,6
0,00,2
0,40,6
0,81,0
Pote
ntial (V
)
Position (m)
Voltage (V
)
p
n
p
i
n
Scanner
i p
i
n
0 10 20 30 40 50 600,0
0,5
1,0
1,5
2,0
2,5
3,0
Dark DarkIlluminated
Bias (V)
i ac (
nA
)
Position (a.u)
Laser Scanned Photodiode Technique
Imagem
iac
• The LSP utilizes light modulated depletion layers as detector and a laser beam for readout.
Heterostructure
•light-to-dark sensitivity
M. Vieira, M. Fernandes, J. Martins, P. Louro, R. Schwarz, and M. Schubert, “Laser Scanned p-i-n Photodiode (LSP) for image detection” IEEE Sensor Journal, 1, no.2 pp. 158-167
ITO p
i
n ITO
Laser Scanned Photodiode Image Sensor (LSP)
Matrix intensity
Xm,n =-(Im,n- Sm,n)
Glass
A large cell detector where the image is scanned by sequentially detecting scene information at discrete XY coordinates.
p(a-SiC:H)/i(a-Si:H)/n(a-SiC:H)
Characteristics
•No pixels •p-i-n structure and two contacts •Integrated read-write system. •In time image processing.
p-i-n p-i-n
Laser Scanned Photodiode Color Sensor (CLSP)
•p-i-n B&W LSP image sensors were produced and tested.
•The tandem structure takes advantage on the radiation wavelength selectivity due to the different light penetration depth inside the a-Si:H and a-SiC:H
Large area color image sensors with improved response.
M. Vieira, P. Louro, M. Fernandes, and A. Fantoni “Optical confinement in a Double Colour Laser Scanned Photodiode (D/CLSP)” Sensor and Actuators A 114/2-3 (2004), pp. 219-223
400 500 600 700 800
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35Front cell
ITO/pi´(a-SiC:H)n/ITO/pi(a-Si:H)n/ITO
Ph
oto
cu
rre
nt
(a
)
Wavelength (nm)
0.0
0.5
1.0
1.5
2.0-5V
+1V
-10 -8 -6 -4 -2 0 20.0
0.1
0.2
0.3
0.4
0.5
Photo
curr
ent (
A)
Front cell
ITO/pi´(a-SiC:H)n/ITO/pi(a-Si:H)n/ITO
Photo
curr
ent (
A)
Voltage (V)
650 nm
550 nm
450 nm
600 nm
500 nm
-1.2
-0.8
-0.4
0.0
0.4
Back cell
Optical filter
Front diode –Cuts the red
Back diode –Cuts the blue
Back cell
400 500 600 700 800
0.0
0.1
0.2
0.3 NC10 p-i'(a-SiC:H)-n-p-i(a-Si:H)-n
75 Hz
Ph
oto
cu
rre
nt
(A
)
Wavelength (nm)
-10 V
-5 V
0 V
+3 V
Spectral response
Voltage controlled spectral response.
•As the applied voltage changes from forward to reverse the blue/green spectral collection is enlarged while the red one remains constant
Full colour recognition
450 500 550 600 650
Front diode
Optical image
a-SiC:H
a-Si:H
V1
V2
Electronic image
V=V1+V2
02
2,2
)(ln
I
IVIVV Tlight
02
02,2
)(ln
I
IVIVV Tdark
02
2,2 ln
I
IVIVV Tlight
02
02,2 ln
I
IVIVV Tdark •Color rejection
•Image recognition
0201
21lnII
IIIIVV T
CLSP take advantage of the fact that red, green, and blue light penetrate silicon to different depths forming an image sensor that captures full color at every point in the captured image without the need of pixels.
-0.5
0.0
0.5
1.0
1.5
5
10
15
2025
3035
40
510
1520
25
Ph
oto
cu
rren
t (m
A)
X position
Y positi
on
-6V
-6 -5 -4 -3 -2 -1 0 1 2
-8x10-8
-6x10-8
-4x10-8
-2x10-8
0
b)
a)
S=650 nm
NC#5 (pin/pin)
whithout
optical bias
L=550 nm
L=650 nm
L=450 nm
Photo
curr
ent (A
)
Voltage (V)
Color recognition
Self reverse bias effect
M. Vieira, M. Fernandes, P. Louro, C. Mendes, R. Schwarz, Y. Vigranenko “OSIP Optical signal and image processing device optimized for optical read-out” Sensor and Actuators A: Physical, 120 (2005) pp. 88-93
55
55
55
400 450 500 550 600 650 700 750 8000,0
0,2
0,3
0,5
0,7
0,8
1,0
L=0.1 mWcm
-2
L=0
Heterostructure
p-i-n-p-i-n
RN
Wavelength (nm)
Optical amplification
0.0 1.0 2.0 3.0 4.0 5.00.0
0.5
1.0
1.5
2.0
2.5
3.0Red channel
Ph
oto
cu
rre
nt (a
.u.)
Time (ms)
V=-8V
no bias,
L=650 nm
L=470 nm
L=470 nm
V=+1V
no bias
L=650 nm
L=524 nm
L=470 nm
0.0 1.0 2.0 3.0 4.0 5.00.0
0.5
1.0
1.5
2.0
2.5
3.0
V=+1V
no bias
L=650 nm
L=524 nm
L=470 nm
V=-8V
no bias,
L=650 nm
L=470 nm
L=470 nm
Green channel P
ho
tocu
rren
t (a
.u.)
Time (ms)
B
C
D
E
F
G
H
I
0.0 1.0 2.0 3.0 4.0 5.00.0
0.5
1.0
1.5
2.0
2.5
3.0
V=+1VV=-8V
no bias
L=650 nm
L=524 nm
L=470 nm
no bias,
L=650 nm
L=470 nm
L=470 nm
Blue channel
Ph
oto
cu
rre
nt (a
.u.)
Time (ms)
B
C
D
E
F
G
H
I
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
Self reverse bias effect
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6-4x10
5
-3x105
-2x105
-1x105
0
1x105
-6V
+2V
NC#5
L=650 nm
Ele
ctr
ical field
(V
/m)
Position (m)
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-2,0x105
-1,5x105
-1,0x105
-5,0x104
0,0
5,0x104
1,0x105
L=550 nm
+2V
-6V
NC#5
Ele
ctr
ical field
(V
/m)
Position (m)
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-2,0x105
-1,5x105
-1,0x105
-5,0x104
0,0
5,0x104
1,0x105
+2V
-6 V
NC#5
L=450 nm
Ele
ctr
ical field
(V
/m)
Position (m)
When an external electrical bias is applied, it mainly influences the field distribution within the less photo excited sub-cell.
Blue bias amplifies the red and the green channels and reduces the blue. Red bias reduces the red and green channels and amplifies de blue. Green bias reduces the green channel keeping the others almost constant.
Front
diode
Back
diode
-
Substrate InOx
p (a-SiC:H)
n (a-SiC:H)
i (a-SiC:H)
200 nm
p (a-SiC:H)
i (a-Si:H)
1000 nm
n (a-SiC:H)
n (a-SiC:H) InOx
B R G
B
R
G
V
Wavelength Division Multiplexing
Wavelength Division Demultiplexing
•The tandem structure takes advantage of the radiation wavelength selectivity due to the different light penetration depth inside the a-Si:H and a-SiC:H
Divison Wavelength Multiplexing Device (WDM)
M. Vieira, P. Louro, M. Fernandes, M.A. Vieira, A. Fantoni and M. Barata, “Large area a-SiC:H WDM devices for signal multiplexing and demultiplexing in the visible spectrum”, Thin Solid Films 517 (2009), pp. 6435-6439. DOI:10.1016/j.tsf.2009.02.096
Bias sensitive WDM device
V
0.0 1.0 2.0 3.0 4.0 5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
V=+1V
V=-8V
G
BR
B (-8V)
R(-8V)
G(-8)
B(+1)
R(+1)
G(+1)
Led R
Led G
Led B
Ph
oto
cu
rre
nt (
A)
Time (ms)
R+G+B R&G&B
soma
+1V
-8V
###
###
###
###
###
###
###
###
###
Optical amplification under negative bias. !!!!!
•High: all the channels ON •Low: all the channels OFF. •The signal due to the mixture of two input channels (R&B, R&G, G&B) are higher than only one (R, G, B).
Under negative applied voltages, the multiplexed signal keeps the memory of the single input channels.
0.0 1.0 2.0 3.0 4.0 5.00.0
0.2
0.4
0.6
0.8
Photo
curr
ent(
A
)
Time (ms)
0.0 1.0 2.0 3.0 4.0 5.00.0
0.2
0.4
0.6
0.8
Time (ms)
0,0 1,0 2,0 3,0 4,0 5,00,0
0,2
0,4
0,6
0,8
1,0
1,2
&0
&B
&B
0&
0
B
R&G
R&G G
GR R
0&0 R / GR / GR&G
t=Tt=0
00110011
01010010
00111100
V=+1
V=-8V
Green
Blue
Red
E
F
B
C
D
Photo
curr
ent(uA
)
Time (ms)
R&G
R&G R
/G
R/G
G/R
G/R
0/B
0/B
R&G
R&G R
/G
R/G
G/R
G/R
0/B
0/B
X
X X X X X
B
B
0&0&0
WDM – Recovery of the input channels
Using this simple algorithm the independent red, green and blue bit sequences can be decoded as: R[00111100], G[00110011] and B[01010010].
ELECTRICAL MODEL
I2
15u
I
I II
C2
1000p
I
0
Q1 V
Q2
I
I1
15u
C1
2500p
I3
10u
I4
8u
I
I2
15u
I
I II
C2
1000p
I
0
Q1 V
Q2
I
I1
15u
C1
2500p
I3
10u
I4
8u
I
Negatively biased The p-n internal junction is forward-biased
Positively biased The p-n internal junction is reverse-biased
M A Vieira, M. Vieira, M. Fernandes, A. Fantoni, P. Louro, M. Barata, Amorphous and Polycrystalline Thin-Film Silicon Science and Technology — 2009, MRS Proceedings Volume 1153, A08-03
Q1
Q2 i
n
n
p
i
n
n
p
i
n
n
p
i
n
n
p
i
n
n
p
i
n
n
p
i
n
n
p
i
n
n
p
p
i
n
p
p
i
n
p
p
i
n
p
p
i ’
n
p
p
i
n
p
p
i
n
p
p
i
n
p
p
i
n
p
p
i ’
n
p
I1
I2
I3
I4
0 1 2 3 4-20
-10
0
10
20
30
I(C2)
I(C1)
I4
I2
I(+1)
I(-5V)I1
I3,
Blue
Red
Green1
I(-5)
Green2
C1
C2
I(0)
Curr
ent (
A)
Time (ms)
-4 -3 -2 -1 0 1 2 3 4-6
-5
-4
-3
-2
-1
0
1
2
3
4
V(Q1)
V(Q2)
I3,I4
I2
I1
B
C
D
E
F
G
H
I
J
K
L
M
V (
Q1;Q
2)
V
Time (ms)
B
C
D
E
1221 )()( CtiCti CC -
dt
dvCtiC
2,1
2,12,1 )(
Current&Voltage (SPICE simulation)
Blue the emiter-base of Q1 becomes optically forward biased and C2 is rapidly charged in inverse polarity of C1
Red changes, in the opposite way.
Green the current is the balance between the blue- and the red-like contributions
I4
Q2
I1 1
I2
Q1
C2 R2 R1 (V)
C1 I3
I(C1)
I(C2)
V(Q1)
V(Q2)
I4
Q2
I1 1
I2
Q1
C2 R2 R1 (V)
C1 I3
NUMERICAL SIMULATION
ac equivalent
electrical circuit
MATLAB as a programming environment and the four order Runge-Kutta method to solve the state equations
)(1
1
)(111
11
2,1
2
12,1
222121
11112,1ti
c
ctv
crcrcr
crcr
dt
dv
--
-
tvr
ti 2,1
2
10
0.0 1.0 2.0 3.0 4.0 5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5 i(R
1=10MW,R
2=5kW)
i(R1=1kW,R
2=5kW)
I1=0.32
I2=1.1
I3=1.1
I4=0.82
C1/C
2=2.5
V=+1V
V=-8V
C
I -8V
IR
IGR
IGB
IB
I(+1=
Ph
oto
cu
rre
nt
(A
)
Time (ms)
0.000 0.001 0.002 0.003 0.004 0.005
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
B
C
0.0 1.0 2.0 3.0 4.0 5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5 i(OFF)
R1=10MW
R2=5kW
i(ON)
I1=0.32
I2=1.21
I3=0.54
I4=0.82
C1/C
2=2.5
=0
=73mWcm-2
=554 nm
C
I -8V
IR
IGR
IGB
IB
Ion
dif
Ph
oto
cu
rre
nt (
A)
Time (ms)
0.000 0.001 0.002 0.003 0.004 0.005
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
iOFF
-iON
B
C
D
I2
15u
I
I II
C2
1000p
I
0
Q1 V
Q2
I
I1
15u
C1
2500p
I3
10u
I4
8u
I
I2
15u
I
I II
C2
1000p
I
0
Q1 V
Q2
I
I1
15u
C1
2500p
I3
10u
I4
8u
I
THEORETICAL MODEL
1221 )()( CtiCti CC -
Negatively biased
Positively biased
M A Vieira, M. Vieira, M. Fernandes, A. Fantoni, P. Louro, M. Barata, Amorphous and Polycrystalline Thin-Film Silicon Science and Technology — 2009, MRS Proceedings Volume 1153, A08-03
400 450 500 550 600 650 700 750 8000.00
0.05
0.10
0.15
0.20
#1
#1b
#1a
L =0
#1
L =2mWcm
-2
#1a#1b
Sen
siti
vit
y (
A/W
)
Wavelength (nm)
CONCLUSIONS Single and stack a-SiC:H pin devices were compared under different
optical and electrical bias conditions and readout techniques.
400 500 600 700 8000.0
0.1
0.2
0.3
0.4 pi(a-SiC:H)n/pi(a-Si:H)n
-10 V
+3 V
Ph
oto
cu
rre
nt (
a)
Wavelength (nm)
B
B
B
B
B
B
B
B
B
B
B
B
B
B
GlassITO
P
i-Si:H (1000 nm)
nITO
GlassITO
P
i-Si:H (1000 nm)
nITO
GlassITO
P
i’-SiC:H (200 nm)
#2a
nP
i-Si:H (1000 nm)
nITO
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
LSP
WDM
Readout techniques
0.0 1.0 2.0 3.0 4.0 5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
R+G+B
B[10101010]
G[10011001]
R[01111000]
V=+1V
V=-8V R&G&B
G
BR
B (-8V)
R(-8V)
G(-8)
B(+1)
R(+1)
G(+1)
Led R
Led G
Led B
soma
+1V
-8V
Ph
oto
cu
rre
nt
(A
)
Time (ms)
CONCLUSIONS If a light scan with a fixed wavelength is
used to readout the generated carriers it can recognize a color pattern projected on it, acting as a color and image sensor.
-6 -5 -4 -3 -2 -1 0 1 2
-8x10-8
-6x10-8
-4x10-8
-2x10-8
0
b)
a)
S=650 nm
(pin/pin)
whithout
optical bias
L=550 nm
L=650 nm
L=450 nm
Photo
curr
ent (A
)
Voltage (V)
If the photocurrent generated by different monochromatic pulsed channels or their combination is readout directly, the information is multiplexed or demultiplexed.
When triggered by light with appropriated wavelengths, it can amplify or suppress the generated photocurrent working as an optical amplifier.
0.0 0.3 0.5 0.8 1.0 1.30.0
0.5
1.0
1.5
2.0
Dark
V=+1V V=-8V
L=0
RL
=626nm
GL
=524nm
BL
=470nm
S=626 nm
Photo
curr
ent (
)A
Time (ms)
B
D
E
F
C
G
H
I
Three integrated transducers in one single photodetector
TEAM Manuela Vieira Alessandro Fantoni Paula Louro Miguel Fernandes Yuri Vygranenko João Costa Manuel Barata Manuel A. Vieira António Maçarico João Martins Vitor Fialho Donatello Brida Victor Silva Reinhard Schwarz Manfred Niehus
A group of experienced and young researchers covering the areas of materials and devices processing; materials and devices characterization and optimization, well supported by the physics modelling of the devices and the corresponding software for information extraction
Thanks for your attention
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