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Quantum Imaging - UMBC
Part IV
Single-photon measurement device for “ghost” imaging
- Fabrication of individual addressable 2-D APD arrays
MOCVD Laboratories
Reactor I
Cleanroom
Reactor II
Cleanroom
Reasons To Select APD for Photon
Counting
• Possible to achieve large arrays with good
uniformity.
• Possible to obtain good photon counting
performance at TE cooler chilled
temperatures.
• Infrastructure for commercialization exists.
Remote Sensing - Imaging Lidar
Prof. Ray Hoff, UMBC, NASA JCET Center
Range Finder, and 3-D Lidar (APD Arrays)
Applications
Principles of Chemical Detection
with Lasers
DIfferential SCattering/DIfferential Absorption Lidar
(DISC/DIAL)
IR LASER
TRANSMITTER
AND RECEIVER
•
•
•
•
... .
.
. ..
Rapidly tuned laser emits 2 or more wavelengths that penetrate cloud
Light is differentially absorbed/scattered upon transmission as well as reflection
Light reflects off of topographic/aerosol/rain targets & detected at receiver
Agents identified since each has a unique absorption/scattering spectrum
16x16 Arrays
64x64 Arrays
Key Requirements for Photon Counting (PC)
1. Low Dark Counts:
Dark current is caused by surface leakage, tunneling, defects assisted tunneling.
Can be reduced by decrease the electrical field in the active (absorption) region.
2. High Gain and High Differential Gain
High gain can be obtained with high bias voltage. However, with high bias, a
high dark current will also be produced. High differential gain relies on high
rising slope of APD (dG/dV). An ideal PC APD will have a straight angle I-V
curve, which can be achieved with better device designs.
3. Designing and Fabricating Materials with Reduced AfterPulse Dark Current (AFDC) Amplitude and Duration
AFDC comes from traps in the avalanche regions and trapped carriers in the
hetero-interface. Interstitial Zn atoms created during the diffusion processes are
source of traps and can be activated and converted to substitutional dopants by
appropriate annealing procedures. More steps of InGaAsP quaternary layers
(1.1Q, 1.2Q, 1.3Q, 1.5Q, ..etc.) can added to the InP/InGaAs interface to reduce
hole trapping.
Etched-Mesa APD Arrays
0.00001
0
0.000001
1E-07
1E-08
1E-09
1E-10
5
10
15
20
25
30
35
Etch-Mesa Surface Leakage
Current Studies
With H2SO4 treatment
Annealing with 300°C
Polyimide passivation
H2SO4 surface treatment can reduce the surface leakage
current, However, after add in polyimide passivation the
surface leakage current increases.
Guard-Ring
Mesa
Mesa vs. Guard-Ring
• Mesa structure APDs are the
current state-of-the-art
• Potential issues with mesa
APDS for space applications:
– Short lifetime from early
breakdown
– Dark current increases over
time
• We are focusing on guard-ring
designs to address the above
issues
Reliability of Guard-Ring
APDS
-6
Dark current at M~10 (A)
10
Mesa APDs*
-7
10
-8
10
Goddard/AdTech guard ring APDs
-9
10
0
10
1
10
2
10
3
10
4
10
5
10
Time (hour)
Aging test condition: 200oC/I=100A Testing method: measure dark current
at M~10 periodically * S. Tanaka et al on OFC 2003
Fabricated Avalanche Photodiode Structure
Guard Ring Type High Stability and
High Reliability APDs
P doping
InP P+
InP N
InGaAs (NID)
Absorption
InP N
Buffer
InP N+
Substrate
Optimize Design To Achieve High Differential
Gain and Low Dark Current
InGaAs contact
Guard
Ring
p-Metal contact
AR coating
Passivation
P InP
Guard
Ring
n- InP
d1
n-InP
-
n InGaAsP
d2
-
n InGaAs
+
n InP Buffer
n+-InP Substrate
n-Metal contact
Changing the avalanche
region thickness, d1, the
charging layer Doping
and thickness d2 will
greatly affect the APD
characteristics
Lower dark current and
high diff gain can be
achieved
Reducing Tunneling Leakage Current
Reducing the distance between the punch through
voltage and the breakdown voltage will help to reduce
the voltage drop falling on the small bandgap
absorption region
Vp
0
10000
-200
1000
Dark current
10
100
Gain
Electrical Field (kV/cm)
Gain
-300
10
1
-400
1
-500
-600
0
0.1
0.1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Front (micrometer)
BreakdownDistant
fieldfrom(V/cm)
for InP is around
5e5 (handbook series on semiconductor
parameters); and for InGaAs is 2e5.
Dark Current (nA)
100
-100
10
20
30
Voltage (V)
40
50
VB
Summary of Calculated Results
d1=400 nm
d1=200 nm
3 Different APDs at Room Temperature
C urrent (A) low Vb APD @ 29 7.6 K
C urrent (A) ne w APD @ 294 .6 K
C urrent (A) old APD @ 297 .1 K
Room Temp
-6
10
10-10
-12
10
Voltage (V)
50
40
30
20
10
0
10-14
-10
Current (A)
10-8
3 Different APDs at 200 Degree K
C urrent (A) low Vb APD
C urrent (A) ne w APD
C urrent (A) old APD
200 k
10-9
10-11
10-13
Voltage (V)
40
30
20
10
0
10-15
-10
Current (A)
10-7
3 Different APDs at 150 Degree K
Current (A) low Vb APD
Current (A) ne w APD
Current (A) old APD
150 k
-9
10
10-11
10-13
-15
Voltage (V)
35
30
25
20
15
10
5
0
10
-5
Current (A)
10-7
Dark Current I-V Characteristics
Changing with Temperature
Dark Current variation with Temperature
* The dark current is
reduced
• The gain is increased
• A sharp rising gain with
the bias voltage will
help to choose good
operating points.
-7
10
-9
10
-11
10
-13
10
Current (A) @ 294 K
Current (A) @ 260 K
Current (A) @ 230 K
Current (A) @ 200 K
Current (A) @ 140 K
-15
10
-17
10
-10
0
10
20
Voltage (V)
30
40
50
4x4 Photon Counting APD Arrays and
Their I-V Characteristics
1.0E-05
Dark Current (A)
1.0E-06
1.0E-07
1.0E-08
1.0E-09
1.0E-10
1.0E-11
1.0E-12
0
10
20
30
Voltage (v)
40
50
APD Capacitance and
Modulation Bandwidth
10
1.8
Long metal pad
Short metal pad
1.4
3dB Bandwidth (GHz)
Capacitance (pF)
1.6
1.2
1
0.8
0.6
0.4
1
0.2
0.1
0
0
10
20
30
Voltage (V)
40
50
1
10
Gain
100
Photon Counting Testing
Setup
Photon Counting Set Up
Photon Counting Operations I
CAPD
R// 1
Current
Source
Determined by the avalanche process
and is not sensitive to ext. Circuits
Determined by T= R// *CAPD
R// 2
Photon Counting Pulse
Amplitude Statistics
IDC=0.005 µA,
Vac=4.0 V
IDC=0.007 µA,
Vac=4.0 V
16x16 Arrays
64x64 Arrays