Near-infrared (NIR) Single Photon Counting Detectors (SPADs)

Chong Hu, Minggou Liu, Joe C. Campbell & Archie Holmes

ECE DepartmentUniversity of Virginia

Outline

Introduction to Single Photon Counting Detectors (SPADs)

Current States of near-infrared SPADs

Summary and Future Goals

Mature Novel

PMT

• High gain• Low dark current• Low noise• Low quantum efficiency• Large, bulky• Expensive• High voltage • Fragile• Ambient light catastrophic

2000 V

APD

t

• Electron & Hole avalanche multiplication

• Good efficiency• Acceptable dark counts• Afterpulsing

Superconductors

• Hotspot Generation and Resistive Barrier

• High efficiency• Low dark counts• No afterpulsing• T < 1K!!

Geiger mode - APD functions as a switchAnalog DigitalResponsivity Single photon detection

efficiencyDark current Probability of dark count

Concept of excess noise does not apply!

Current

Voltage

Current

Linearmode

Geigermode

Vbr

on

off

Current

Voltage

Current

Linearmode

Geigermode

Vbr

on

off

timetime

timetime

time

Single photon input

APD output

Discriminatorlevel

Digital comparator output

Successfulsingle photondetection

Photon absorbed but insufficient gain – missed count

Dark count – from dark current

Geiger-mode operation

Current

Voltage

Current

Linear

mode

Geiger

mode

Vbr

on

off

Current

Voltage

Current

Linear

mode

Geiger

mode

Vbr

on

avalanche

off

quench

armVdc + V

Performance Parameters 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

timetime

timetime

time

Single photon input

APD output

Discriminatorlevel

Digital comparator output

Successfulsingle photondetection

Photon absorbed but insufficient gain – missed count

Dark count – from dark current

Photon Detection EfficiencyPDE = external x collection x Pavalanche

V/Vbr

0.0 0.1 0.2 0.3

Bre

ak

do

wn

Pro

ba

bili

ty

0.0

0.2

0.4

0.6

0.8

1.0

InP: 1110 nm

InGaAsP 1.06, 1.3 m

InGaAs 1.55 m

Dark current• 0.18nA at 95% of Vbr at 297K• 0.15pA at 95% of Vbr at 200KGood enough?

40m-diameter In0.53Ga0.47As/InP

Reverse Bias (V)-60-55-50-45-40-35-30

Dar

k cu

rren

t (A

)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5220K 230K 240K 250K 260K 270K 280K 290K 300K

300K Photocurrent

Dark current

1.06 μm SPADs: DCR vs. PDE InGaAsP absorber lower generation-recombination dark currentDCR approaching Si SPAD DCR with greatly increased PDE

Si SPADs have PDE < 2% at 1.06 μm

101

102

103

104

0% 10% 20% 30% 40% 50%Photon Detection Efficiency

Dar

k Co

unt R

ate

(Hz)

237 K

259 K

250 K

80 μm dia. InGaAsP SPAD 1-ns gated operation500 kHz repetition rate0.1 photon/pulseAP probability < 10-4 per gate

105

273K – 295K

**300K

0 5 10 15 20 25 30 35 40 45 5010 -7

10 -6

10 -5

10 -4

10 -3

10 -2

Dar

k Co

unt P

roba

bilit

y

Single Photon Detection Efficiency (%)

InGaAs/InP, 300K1550 nm (2007)

InGaAs/InP (2007)

Dark Count Probability versus Photon Dark Count Probability versus Photon Detection EfficiencyDetection Efficiency

200K

240K

Reverse Bias (V)-60-55-50-45-40-35-30

Dar

k cu

rren

t (A

)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5220K 230K 240K 250K 260K 270K 280K 290K 300K 300K_photo

215K

268K

Current

Voltage

Current

Linear

mode

Geiger

mode

Vbr

on

off

Current

Voltage

Current

Linear

mode

Geiger

mode

Vbr

on

avalanche

off

quench

armVdc + V

Quenching Techniques

Quenching circuit– Quench avalanche current– Reset the device

• Passive Quenching– Quenched by discharging

capacitance– Slow recharge

• Active Quenching– Raise the anode voltage– Quick recharge

• Gated Quenching

hh

RRLL=300k=300k

RRss=50=50

VVbb ++VVExEx

Comparator

Cs

hh

RRLL=300k=300k

RRss=50=50

VVbb ++VVExEx

RRLL=300k=300k

RRss=50=50

VVbb ++VVExEx

Comparator

Cs

hh

RRss

VVbb ++VVExEx

Comparator

VVqq

Quenchdriverhh

RRss

VVbb ++VVExEx

Comparator

VVqq

Quenchdriver

Vq>VEX

Afterpulsing

Initial avalanche Released carriers from traps

Number of trapped carriers

1E+3

1E+4

1E+5

1E+6

1E+7

1E+8

1 10 100 1000Hold-off Time (μs)

220K200K

175K150K

6 V overbias

1E+3

1E+4

1E+5

1E+6

1E+7

1E+8

1 10 100 1000

Dar

k C

ou

nt

Rat

e (H

z)

Biasing scheme

Reduction of Afterpulsing: Decreasing Charge Flow

hh

RRLL=100k=100k

RRss=50=50

VVbb ++VVExEx

Comparator

Cs

hh

RRLL=100k=100k

RRss=50=50

VVbb ++VVExEx

RRLL=100k=100k

RRss=50=50

VVbb ++VVExEx

Comparator

Cs

The total charges flowing through device:Q=(Cs+Cd)Vex

Cd: device capacitanceCs: stray capacitance

Passive quenching

Time (ns)0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.2

0.4

0.6

0.8

1.0

Passive quench with 100k

PQAR

Released carriers from traps

Passive quench with 100k

PQAR

Released carriers from traps

Time (ns)

0 100 200 300 400 500 600 700

Exc

ess

vo

lta

ge

(V

)0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Ca

rrie

r em

iss

ion

ra

te (

a.u

.)

0.0

0.2

0.4

0.6

0.8

1.0

Passive quench 100k

Released carriers from traps

Passive quench 10M

Passive Quenching with Active Reset (PQAR)

Time (ns)

0 100 200 300 400 500 600 7000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Car

rier

em

issi

on

rat

e (a

.u.)

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500 600 700

Exc

ess

volt

age

(V)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.2

0.4

0.6

0.8

1.0

Conventional passive quench

100k

PQARactive reset

Released carriers from traps

PQARpassive quench

10M

10MΩ

Vb+Vex

10nFRs =50 Ω Amplifier

Trigger in

Transistor

PulseGenerator

Counter

A

Output

10MΩ

Vb+Vex

10nFRs =50 Ω Amplifier

Trigger in

Transistor

PulseGenerator

Counter

A

OutputOutputOutput

16

0

10

20

30

40

50

60

70

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04CW laser power (fW)

Me

as

ure

d c

ou

nts

x 1

00

0 (

/s)

Vex=2.6V

Vex=2.0V

Vex=1.6V

PQAR at 230K

bdoffholdd

d PRN

NDCR

1

( )1

td b

t hold off

NTotalCR R QE P

N

PCR TotalCR DCR PDE

Hold-off = 15s

1.E+00

1.E+01

1.E+02

10 15 20 25 30 35 40 45PDE (%)

230K240K gated mode

10-4

10-5

10-6

Dar

k co

unt

prob

abili

ty (

/ns)

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Photon flux (#/s)

Ph

oto

n c

ou

nt

rate

(#

/s)

Vex=2.6V

Vex=2.0V

Vex=1.6V

34s 15sVb

Voltage on device Compare with gated mode results

NEP ~ 10-16 W/Hz1/2

Gated Quenching of a SPAD

hh

RRloadload

RRss=50=50

VVDCDC

Comparator

AC pulse

hh

RRloadload

RRss=50=50

VVDCDC

RRloadload

RRss=50=50

VVDCDC

Comparator

AC pulse

Dark Count RatePhoton Detection Efficiency

Laser pulse

Total bias on APD

Avalanchepulse

Avalanche pulse due to dark carriers

(false positive)

Avalanche pulse due to incident photon

Missed photon

Excess bias(V ex)

AC pulse width

Time

V dc

Vbr

Time

Time

(false negative)

Gated-PQAR

10MΩ

Cag

Cac

Vbias

Rs=50ΩAmplifier

A Counter

Vgate

Compared to PQAR

• Suppressed dark counts by gated bias

• Reduced complexity

• Array operation: recharge together, quench separately

The transistor can be HBT monolithically integrated on the SPAD, and the its gate/base input can be shared over the whole array.

0 5 10 15 20 25 30 351

2

4

6

8

10

Dar

k C

oun

t R

ate

(kH

z)

Photon Detection Efficiency (%)

220K 200K 180K 220K 200K 180K gated-quenching

gated-PQAR

Gated Quenching and Gated PQARGated Quenching and Gated PQAR

Gated Quenching and Gated PQARGated Quenching and Gated PQAR

0.01 0.1 1 1010

-5

10-4

10-3

Dar

k C

oun

t P

rob

abil

ity

Repetition Rate (MHz)

220K, Vex = 5.6%

200K, Vex = 6.0%

180K, Vex = 6.2%

220K, Vex = 5.6%

200K, Vex = 6.0%

180K, Vex = 6.2%

gated-quenchinggated-PQAR

Conclusions

Performance of Geiger-mode APDs is improving rapidlyAcceptable detection efficiencies and dark count

probability levelsGetting a better control over the afterpulsing

problem

Future Goals

Move closer to quantum limited detectionDark Current 0Quantum 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

CB

VB

GaAs0.5Sb0.5

0.79eV

Ga0.47In0.53As0.77eV

ΔEc=0.236eV

ΔEv=0.247eV

0.49eV ≈ 2.5 μm

E

x

Where we are now (pin devices)

Rogalski, A., Progress in Quant. Elec., 27(2-3), pp 59 (2003)

-2 V bias(RT)

-2 V bias(200K)

26

AC

output

photon photon photon

Gated Quench

output

photon photon photon

Gated-PQAR

Vgate

Vbias

Transistor off: high resistance for fast passive quench

Transistor on: low resistance for fast reset

Vdiode

Compared to gated quench

• Comparable circuit complexity

• Wider AC pulses: easier to generate and synchronize

• Uniform output pulse shape, good for photon-number-resolution with multiplexing

Gated-PQAR for Synchronized DetectionGated-PQAR for Synchronized Detection

Questions??

Simulated Breakdown ProbabilitiesSimulated Breakdown Probabilities

V/Vbr

0.0 0.1 0.2 0.3

Bre

akd

ow

n P

rob

abili

ty

0.0

0.2

0.4

0.6

0.8

1.0

InAlAs 190nm PbrE InP 190nm PbrHInAlAs 1110nm PbrE InP 1110nm PbrH

J. P. R. David, University of SheffieldJ. P. R. David, University of Sheffield

InP

AlInAs

Decreasing thickness: 0.2 m, 0.5 m, 1.0 m

Excess bias (%)

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Dar

k C

ou

nt

Rat

e (k

Hz)

0

20

40

60

80

100

120

140

160

Reverse Bias (V)-52-50-48-46

Dar

k C

urr

ent

(A)

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

• 4 x 4 Subarray – uniform single-photon response

• 20 x 20 Array – 98% yield

Afterpulsing Probability vs. Total Charge

30

AC pulse

Laser pulse

Delay1s

Period

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

Total charge (pC)

Aft

erp

uls

ing

pro

ba

bili

ty Duration

Magnitude

31

Total Charge Flow

0 1 2 3 4 5 6 7 8 9

1

10

100

1000

no

rma

lize

da

fte

rpu

lsin

g p

rob

ab

ilit

yexcess bias (V)

gated-quench with 2ns gates PQAR with 0.23 pF of total capacitance

0 1 2 3 4 5 6 7 8 90.1

1

10

100

tota

l c

ha

rge

(p

C)

excess bias (V)

gated-quench with 2 ns gates PQAR with 0.23 pF of total capacitance

36x reduction

0 1 2 3 4 5 6 7 8 90.1

1

10

100

tota

l c

ha

rge

(p

C)

excess bias (V)

gated-quench with 2 ns gates PQAR with 0.23 pF of total capacitance

36x reduction

32

“Effective Excess Noise Factor”

2

2

2

(peak signal)Effective excess noise factor 1

peak signal

11.6 1 1.0004

572

mV

mV

Pixel Level Monolithic Integration of Active Switching Elements

• Reduced parasitics

• Faster quenching

• Reduced afterpulsing

• Increased transmission and

sampling rates

• Packaging advantages

Vbias

Rs =50

Counter

Vbias

Rs =50

Counter

Active switching element