Download QLID Presentation Holmes

Near-infrared (NIR) Single Photon
Counting Detectors (SPADs)
Chong Hu, Minggou Liu, Joe C.
Campbell & Archie Holmes
ECE Department
University of Virginia
Outline
Introduction to Single Photon Counting
Detectors (SPADs)
Current States of near-infrared SPADs
Summary and Future Goals
Mature
PMT
Novel
APD
Superconductors
2000 V
• High gain
• Low dark current
• Low noise
• Low quantum efficiency
• Large, bulky
• Expensive
• High voltage
• Fragile
• Ambient light catastrophic
t
• Electron & Hole avalanche
multiplication
• Good efficiency
• Acceptable dark
counts
• Afterpulsing
• Hotspot Generation
and Resistive Barrier
• High efficiency
• Low dark counts
• No afterpulsing
• T < 1K!!
Geiger mode - APD functions as a switch
Analog
Digital
Responsivity
Dark current
Single photon detection
efficiency
Probability of dark count
Geiger-mode operation
Single photon input
Concept of excess noise does not apply!
APD output
Discriminator
level
on
Linear
mode
Geiger
mode
Digital comparator output
Current
time
time
off
time
Vbr
Voltage
Photon absorbed
Successful
single photon but insufficient
gain – missed
detection
count
Dark count –
from dark
current
Linear
on
Geiger
mode
mode
on
Linear
Geiger
quench
mode
mode
avalanche
Current
off
off
arm
Vdc + DV
V
Voltage
br
Performance Parameters
Single photon input
 Photon detection efficiency
(PDE)
 The probability that a single
incident photon initiates a
current pulse that registers in
a digital counter
 Dark count Rate
(DCR)/Probability (DCP)
 The probability that a count
is triggered by dark current
instead of incident photons
APD output
time
Discriminator
level
Digital comparator output
time
time
Photon absorbed
Successful
single photon but insufficient
gain – missed
detection
count
Dark count –
from dark
current
Photon Detection Efficiency
hPDE = hexternal x hcollection x Pavalanche
Breakdown Probability
1.0
0.8
InP: 1110 nm
0.6
0.4
0.2
0.0
0.0
0.1
0.2
0.3
DV/Vbr
InGaAsP
InGaAs
1.06, 1.3 mm
1.55 mm
40mm-diameter In0.53Ga0.47As/InP
10-5
220K
230K
240K
250K
260K
270K
280K
290K
300K
Dark current (A)
10-6
10-7
10-8
10-9
-10
300K Photocurrent
Dark current
10
10-11
10-12
-30
-35
-40
-45
-50
-55
Reverse Bias (V)
Dark current
• 0.18nA at 95% of Vbr at 297K
• 0.15pA at 95% of Vbr at 200K
Good enough?
-60
1.06 μm SPADs: DCR vs. PDE
 InGaAsP absorber lower generation-recombination dark current
 DCR approaching Si SPAD DCR with greatly increased PDE
 Si SPADs have PDE < 2% at 1.06 μm
105
Dark Count Rate (Hz)
300K
*
104
273K – 295K
259 K
250 K
103
237 K
80 μm dia. InGaAsP SPAD
1-ns gated operation
500 kHz repetition rate
0.1 photon/pulse
AP probability < 10-4 per gate
102
101
0%
10%
20%
30%
Photon Detection Efficiency
40%
50%
Dark Count Probability versus Photon
Detection Efficiency
-2
10-5
InGaAs/InP, 300K
1550 nm (2007)
10
220K
230K
240K
250K
260K
270K
280K
290K
300K
10-6
Dark current (A)
Dark Count Probability
10
-3
10-7
10-8
10-9
300K_photo
10-10
10-11
10-12
10
-4
10
-5
-30
InGaAs/InP (2007)
268K
240K
200K
10
-6
10
-7
215K
0
5
10
15
20
25
30
35
40
45
Single Photon Detection Efficiency (%)
50
-35
-40
-45
-50
Reverse Bias (V)
-55
-60
Linear
on
Geiger
mode
mode
on
Linear
Geiger
quench
mode
mode
avalanche
Current
off
off
arm
Vdc + DV
V
Voltage
br
Quenching Techniques
Vb +VEx
Quenching circuit
– Quench avalanche current
– Reset the device
RL=300k
h
• Passive Quenching
Cs
– Quenched by discharging
capacitance
– Slow recharge
• Active Quenching
– Raise the anode voltage
– Quick recharge
Comparator
Rs=50
Vb +VEx
Vq>VEX
Quench
Vq driver
h
• Gated Quenching
Comparator
Rs
Afterpulsing
Number of trapped carriers
Biasing scheme
1E+8
1E+8
1E+7
Released carriers 1E+6
from traps
1E+5
1E+4
Dark Count Rate (Hz)
Initial avalanche
Dark Count Rate (Hz)
6 V overbias
6 V overbias 220K
1E+3
200K
175K
150K
1E+7
22
20
17
15
1E+6
1E+5
1E+4
1E+3
1
1
10
100
10
100
Hold-off Hold-off
Time (μs)
Time (μs)
1000
Reduction of Afterpulsing: Decreasing
Charge Flow
Passive quenching
RL=100k
h
Cs
Comparator
Rs=50
Excess voltage (V)
3.5
1.0
Released carriers
carriers from
Released
fromtraps
traps
3.0
0.8
Passive
quench with
Passive quench

100k100k
2.5
2.0
1.5
Passive
quench
PQAR
10M 
1.0
0.5
0.0
0
The total charges flowing
through device:
Q=(Cs+Cd)Vex
Cd: device capacitance
Cs: stray capacitance
100
200
300 400
Time (ns)
Time (ns)
500
600
0.6
0.4
0.2
0.0
700
Carrier emission rate (a.u.)
Vb +VEx
Passive Quenching with Active Reset
V +V
(PQAR)
b
ex
Rs =50 Ω
10nF
Amplifier
A
Trigger in
10MΩ
Transistor
Pulse
Generator
Excess voltage (V)
Output
3.5
1.0
Released carriers from traps
3.0
0.8
Conventional
passive quench
100k
2.5
0.6
2.0
1.5
1.0
PQAR
passive quench
10M 
0.5
0.4
PQAR
active reset
0.2
0.0
0
100
200
300
400
Time (ns)
500
600
0.0
700
Carrier emission rate (a.u.)
Counter
PQAR at 230K
1.E+07
50
Vex=2.6V
Vex=2.0V
Vex=1.6V
40
Hold-off = 15ms
60
30
20
10
0
1.E-01
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04
CW laser power (fW)
Photon count rate (#/s)
Measured counts x 1000 (/s)
70
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Photon flux (#/s)
Voltage on device
Compare with gated mode results
34ms
15ms
Nd
 Rd  Pb
1  N d  holdoff
Nt
TotalCR 
 ( Rd    QE )  Pb
1  N t  hold off
DCR 
PCR  TotalCR  DCR   PDE
Dark count probability (/ns)
1.E+02
10-4
Dark count rate (kHz)
Vb
Vex=2.6V
Vex=2.0V
Vex=1.6V
NEP ~ 10-16 W/Hz1/2
-5
10
1.E+01
230K
240K gated mode
-6
10
1.E+00
10
15
20
25
30
PDE (% )
35
40
45
16
Gated Quenching of a SPAD
VDC
AC pulse
Rload
AC pulse
width
Comparator
h
Excess bias
(V ex )
Rs=50
Total bias
on APD
Vbr
V dc
Time
Laser
pulse
Time
Avalanche
pulse
Time
Avalanche pulse
due to incident photon
Missed photon
(false negative)
Photon Detection Efficiency
Avalanche pulse
due to dark carriers
(false positive)

Dark Count Rate
Gated-PQAR
Rs=50Ω
Compared to PQAR
Amplifier
A
Cac
Counter
• Suppressed dark counts by
gated bias
• Reduced complexity
Cag
10MΩ
Vgate
• Array operation: recharge
together, quench separately
Vbias
The transistor can be HBT monolithically integrated on the SPAD, and
the its gate/base input can be shared over the whole array.
Gated Quenching and Gated PQAR
Dark Count Rate (kHz)
10
8
6
4
220K
200K
180K
220K
200K
180K
2
1
0
5
10
gated-quenching
gated-PQAR
15
20
25
30
Photon Detection Efficiency (%)
35
Dark Count Probability
Gated Quenching and Gated PQAR
220K, Vex = 5.6%
200K, Vex = 6.0%
180K, Vex = 6.2%
220K, Vex = 5.6%
200K, Vex = 6.0%
180K, Vex = 6.2%
-3
10
gated-quenching
gated-PQAR
-4
10
-5
10
0.01
0.1
1
Repetition Rate (MHz)
10
Conclusions
Performance of Geiger-mode APDs is
improving rapidly
Acceptable detection efficiencies and dark count
probability levels
Getting a better control over the afterpulsing
problem
Future Goals
Move closer to quantum limited detection
Dark Current  0
Quantum Efficiency  100%
Read Noise  0
Move to longer wavelengths
Do photon number resolving
High QE Structure
Type-II Quantum Wells (QWs)
Formed between materials with staggered band line-ups
 Electrons and holes are confined in adjoining layers
 Spatially indirect absorption and emission
 Smaller effective bandgap for long-wavelength operation
GaAs0.5Sb0.5
ΔEc=0.236eV
0.79eV
CB
0.49eV ≈ 2.5 μm
VB
ΔEv=0.247eV
Ga0.47In0.53As
0.77eV
x
E
Where we are now (pin devices)
Rogalski, A., Progress in Quant. Elec., 27(2-3), pp 59 (2003)
-2 V bias
(200K)
-2 V bias
(RT)
Gated-PQAR for Synchronized Detection
Gated Quench
photon
photon
photon
AC
Gated-PQAR
photon
Vgate
Vdiode
output
• Comparable circuit
complexity
• Wider AC pulses: easier to
generate and synchronize
output
Vbias
Compared to gated quench
photon
photon
• Uniform output pulse shape,
good for photon-numberresolution with multiplexing
Transistor on: low
resistance for fast reset
Transistor off: high
resistance for fast passive
quench
26
Questions??
Simulated Breakdown Probabilities
J. P. R. David, University of Sheffield
Breakdown Probability
1.0
0.8
InP
AlInAs
0.6
0.4
InAlAs 190nm PbrE
InP 190nm PbrH
InAlAs 1110nm PbrE
InP 1110nm PbrH
0.2
Decreasing thickness:
0.2 mm, 0.5 mm, 1.0 mm
0.0
0.0
0.1
DV/Vbr
0.2
0.3
• 4 x 4 Subarray – uniform single-photon
response
10-4
10-5
Dark Current (A)
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
-46
-48
-50
Reverse Bias (V)
-52
160
Dark Count Rate (kHz)
• 20 x 20 Array – 98% yield
140
120
100
80
60
40
20
0
1.5
2.0
2.5
3.0 3.5 4.0
Excess bias (%)
4.5
5.0
5.5
Afterpulsing Probability vs. Total Charge
AC pulse
Delay
1ms
Period
Laser
pulse
Afterpulsing probability
1
Duration
Magnitude
0.8
0.6
0.4
0.2
0
0
20
40
60
80
Total charge (pC)
100
30
Total Charge Flow
total charge (pC)
10
36x reduction
1
gated-quench with 2 ns gates
PQAR with 0.23 pF of total capacitance
0.1
0
1
2
3
4
5
6
excess bias (V)
7
8
9
normalized
afterpulsing probability
1000
100
100
10
1
gated-quench with 2ns gates
PQAR with 0.23 pF of total capacitance
0
1
2
3
4
5
6
7
8
excess bias (V)
31
9
“Effective Excess Noise Factor”
Effective excess noise factor  1 
 2 (peak signal)
 peak signal  2
2
 11.6mV 
1
 1.0004

 572mV 
32
Pixel Level Monolithic Integration
of Active Switching Elements
• Reduced parasitics
Rs =50 
Counter
• Faster quenching
• Reduced afterpulsing
• Increased transmission and
Active
switching
element
Vbias
sampling rates
• Packaging advantages