HgCdTe avalanche photodiodes development at CEA/Leti-Minatec

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1

2007

Detectors for Astronomy Workshop 2009 - HgCdTe e-APDs at CEA/LETI - Johan Rothman

HgCdTe avalanche photodiodes development at CEA/Leti-MinatecJohan Rothman

CEA: L. Mollard, S. Bisotto

Sofradir: X. Lefoule, F. Pistone

2009



2

2007


Outline

HgCdTe e-APD development in FranceWhy HgCdTe e-APDs?

PerformanceApplications

HgCdTe e-APDs for photon-countingFocal plane array resultsHgCdTe e-APD road map at LETI-

Minatec and SofradirConclusion/perspectives



3

2007


HgCdTe e-APD development in France

CEA/LETI E-APD technology

and design Epitaxy, µ-tech.

E-APD physics and test Response time Multiplication process

(gain, noise) Sensitivity limits

ROIC design EO FPA test

Sofradir ROIC design EO FPA test E-APD FPA

industrialisation Fab etc..

ONERA E-APD physics

Multiplication process (gain, noise)

EO FPA test

Astro-physics labs LAOG ( Grenoble) and

LAM (Marseille) Adaptiv optics, fringe

tracking Photon-counting imaging

e-APDs

Detector lab and fab

System labs



4

2007


The photodiode: an ideal light detector?

High timing resolutionQE100% i.e. no loss of informationHigh Sensitivity

Dark currents can be lower than 1 electron/sLimited by proximity-electronics (PE) noise

Can be reduced by amplified photo detection!

M

M x Photo-current

PE noise



5

2007


APDs Advantages vs. Photo-multipliers or amplified-CCD

High Quantum efficiency 100% All detection-modes are possible

Photon-counting Real time measurement of the flux f(t) at high speed Integration (standard imaging operation) Non-linear geiger mode (avalanche breakdown)

Small and fast Compatible with imaging and telecom applications

…but furious (other than HgCdTe-APDs…) Multiplication of both electrons and holes in Si and III-V

material APDs Gain is strongly dependent on junction profile High

dispersion (not good for imaging) Strong degradation of the SNR: F=SNRSNL/SNRout>2-5 at

M>10 Response time is slowed down at high gain Limited

gain- Band-Width product < 340GHz (Intel record, Nature Photonics, 3, 2008)

After pulsing probability >0 (photon counting) Dead time (photon counting)

dtttint

t



6

2007


Exclusive electron multiplication in HgCdTe APDs

Exponential gain without avalanche break down (Beck,DRS, 2001) Exclusive electron multiplication

Felectric~1-1.2 (DRS, SELEX, LETI, BAE, TELEDYNE) Response time independent of gain GBW>16THz (LETI) Low gain dispersion Noise equivalent input counts Neq_in< 10 000 e/s (LETI, DRS)

Stable up to M>5000 (LETI APD Record, 2006)PLUS all the standard properties of HgCdTe

High quantum efficiency (close to 100% internal QE) Detect wavelengths from visible to IR (with QE~100%)Low operating temperatures due to small Eg

1.0

10.0

100.0

1000.0

10000.0

-14.0 -13.0 -12.0 -11.0 -10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0

Bias (V)

Ga

inG

ain

M=

I/I C

C

HgCdTe e-APDc=5µm, T=80K



7

2007


A new horizon of applications from visible to IR wavelengths with MCT e-APDs :(M>1000, F~1, Neq_in<10 000 e/s)

Photon counting Quantum optics

Physics, astronomy, quantum cryptography Imaging in Astronomy, biomedical applications, high-energy physics

Astronomy : higher order correlation functions! Real-time measurements

Telecommunications Time resolved Raman and Fluorescence spectroscopy, Doppler effect

Environmental surveillance, element recognition Real-time dynamics observations

Integration (Imaging FPAs) Active laser assisted imaging

Long range identification, safe planetary landing (NASA), bio-medical (fluorescence imaging), observation through semi transparent surfaces

Passive amplified imaging Low flux applications ; hyper spectral imaging, wave front

detection for astronomy, high dynamic range The geiger modes is not (yet) possible due to the absence

of avalanche break-down threshold

dtttint

t

This talk (1)

This talk (2)



8

2007


Performance optimization of HgCdTe e-APDs?

MW (c=4.2-5µm) e-APD performances:M>100, F=1.2, Ieq_in~10000 e/s, tresp~2 ns, Top<100K

Application Photon countingM, F ok

Passive amplified imagingM, F, tresp ok

Critical parameter

1. Reduce tresp : <100 psReduce Ieq_in : <1000 e/s(Operability)

1. Reduce Ieq_in :

< 1000 e/s2. Increase Top

(Operability)

This talk E-APD gain (F~1) for photon countingResponse time limits (jitter)

Impact of xCd:

Gain, F, dark current(Diodes and FPAs)



9

2007


Photon counting

Counter : Direct pixel digitalization Read-out noise supression High dynamic range (>16 bit) High frame-rate Dark-current thresholding

Timer :Estimation of the time of arrival of the photons 3D imaging Quantum optics and imaging

higher order photon correlation functions



10

2007


0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 100 200 300 400 500 600 700 800 900

Output counts

pro

ba

bil

ity

de

ns

ity

Exclusive electron multiplication for Linear mode proportional photon counting

Low F Proportional photon counting Distinguish the number of photons that arrives simultaneously in the

depletion layer (not possible in GM-APDs) Reduce after-pulsing effects 0% (GM –APDs ~10%)

High order temporal correlation function A new window for astronomy !

No quenching high repetition rates >GHz is possible (GM-APDs ~ 10MHz)

1 photon2 photons

Output count probability distribution for <M>=300 and F=1.04



11

2007


0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 100 200 300 400 500 600 700 800 900

Output counts

pro

ba

bil

ity

de

ns

ity

Exclusive electron multiplication for Linear mode proportional photon counting

Low F Proportional photon counting Reduce after-pulsing effects (GM –APDs ~10%) No quenching high repition rate >GHz is possible (GM-APDs ~

10MHz) Low F Discrimination of non-amplified dark current Low DCR

Depends on the distribution of the dark current generation Homogeneous distribution <M>dark=52 for Mdiff=300

1 photon2 photons

Output count probability distribution for <M>=300 and F=1.04

Distributed dark-current generation p i n

DC generation

diffdiff

diff

gencontdark MM

MM

11

ln__

<M>dark



12

2007


Response time optimization in APDs

n-

n+

p

Depletion layer = mutliplication region

E

Collection of minority electrons Diffusion ~ 1-5 ns1

Drift (xCd gradient) Vd of e in p type HgCdTe 50-100 ps jitter3

Transit time of e and h Vd(E) : th=10-50ps GBW limit ~20THz (MW)1,2

RC charge evacuation ~ 10-50 ps Ultimate photon counting timing resolution <100ps!

Collection of minority electrons

Transit time of e and h

RC charge evacuation

1. G. Perrais et al. JEM, 37, 20082. G. Perrais et al. JEM, 38, 20093. J. Rothman et al. to be published, JEM, 40 (2010)

Response time jitter limits the timing precision



13

2007


CTIA coupled one-shot TOF+R imaging (3D) Pulse detection in C10 (1)

Sample time sweep TOF (2) Switch to integrate the total light pulse in C20 (3)

+

-

Vth

C3D

Track & Hold

Vref

C2D

Lock

Time base(analog voltage ramp)

+

-

OTAN1

N2 N3

Iin

Return intensity

T.O.F.

Pixel outputs :

RESET

Precharge

"Advanced pixel design for infrared 3D LADAR imaging"F. Guellec, SPIE DSS, 6940-84

First move towards photon counting (2008): Active 3D Imaging 4x10 test FPA, 40µm pitch

Sequential and spatial TOF<2ns over 4x10 pixels range resolution < 30 cm

320x256, 30µm pitch array under test today Objectives: TOF<2 ns and read noise < 2 e-

Vsub<0V

(1)

(2)

(3)

0

1

2

3

4

0 25 50 75 100 125 150 175 200 225 250 275

laser pulse delay (ns)

T.O

.F. N

oise

(ns

)

TOF noise measured with a flux of 560/e per pixel, at M=100 variable delay, T=80K

First 3D event driven pixel



14

2007


Gain performance in e-APDs (xCd)

c=5.3 µm

LPE

c=4.2 µm

LPE

c=3.3 µm

MBE

c=2.9 µm

MBE

c=2.9 µm

MBE, larger depletion layer

Exponential gain exclusive electron multiplication at M>600 for c=2.9 µm (T=80K) Hole multiplication is still negliable up to high gains at high xcd c=2.9µm is compatible with high operating temperature active laser

imaging (Isat~20pA in VHg doped MCT at T=200K) Gain is dependent on junction geometry also at c=2.9µm



15

2007


Excess noise factor in c=2.9µm e-APD (T=80 K)

M=10

M=600

M=60

qIinoise 2

FqIMinoise 2

M=1

Noise factor F~1 for c=2.9 µm MCT e-APD up to M=600 Noise is √F higher than the shot-noise

Consistent with a high stability of the exclusive electron multiplication at high xCd

Absence of 1/f noise !



16

2007


0.01

0.1

1

10

100

1000

3.0 3.5 4.0 4.5 5.0 5.5

Cut-off wavelength (µm)

Ieq_

in -

Icc

(fA

)

e-APD sensitivity :Equivalent input dark current M=100, T=80K: FqM

iI FOV

ineq 2

20

_ 2

Icc=0, A1, ZFIcc=0, A2, ZFIcc, A1, RFIcc, A2, RF

Ieq_in =200-500 fA at M=100 for c=5.3 µm Strong reduction for shorter c Ieq_in~ fA

(10 ke/s) Needs Low noise ROIC to measure at M<100 or c<4µm

M<300

Test array diode

Measurements

without

ROIC

M=380

ROIC needed



17

2007


M

2D identification :

Cactive=30fF (0.3Me, 90 e rms noise)

Passive thermal surveillance

Cpassive=120fF (1.2Me, 150 e rms noise)Specification Expected value Complianc

e

Max frame rate 450 Hz (10MHz, 4 outputs)

C

Linearity >99.7% from 0% to 90% of ROIC

Well-fill

C

Mini Integration time / gating

100 nsec C

Blooming No parasitic effect

C

Max diode reverse bias 7 V C

320x256 30µm pitch MCT bi-mode e-APD FPASuccess of DEFIR in 2009 (collaboration with Sofradir)

MW e-APD, c=5.3µm à 80K

TIA

3:rd demonstration of large format e-APD FPA for 2D imaging

Selex (2004) , DRS (2006), both with gain operability of 99%



18

2007


1.0

10.0

100.0

1000.0

-9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0

Bias (V)

Gai

n

Test array gain

FPA average gain

<M>=14.1/<M>=7.7%Op50%=99.84%

320x256 30µm pitch MCT bi-mode e-APD FPA Gain measurements

f/2, 5VTest array / FPA gain

An identical gain is measured in test-arrays and FPAs Record high 99.8% operability QE>70% FPA compatible low gain dispersion (<10%) up to 7V reverse bias

Gain dispersion is dominated by the EPL ripple Reduced dispersion by using MBE or reduced ripple EPL

Excess noise factor Fmax=1.4 (consistent with similar test diodes) Excess noise factor operability <F>+/-100%=99.7% up to M=70!



19

2007


320x256 MW HgCdTe e-APD c=5.4 µm, T=80 K(Narrow multiplication layer tunneling)

Bias M Ieq_in (A) Iobs (A) <M>dark <M>cont_gen

2.5 5 5.0E-15 4.0E-14 3.13 2.50

3.5 10 1.0E-14 7.5E-13 1.33 3.90

4.5 25 7.0E-14 7.0E-11 0.63 7.45

Flux (BB at T=290K)

FOV=0° +Photon leakage

Zero flux

Ieq_in 3.5V, M=10, C1=120fF, tint=40ms

Ieq_in=10 fA (60 ke/s)

4.5V, M=25, C1=120fF, tint=300µs

Ieq_in=70 fA (420 ke/s)

<M>dark<< <M>cont_gen. for M>10: Dark current can be suppressed using photon counting thresholding

p i n

DC generation

dark

ineqdiffdark I

IMM _

2



20

2007


320x256 30µm pitch c=3.3µm T=80K

Flux (BB at T=290K)

Zero flux

6 V, M=6 (M/M=2.3%), C1=30fF, tint=2 s

Ieq_in=95 aA (590 e/s)

Gain ~test array gain <Mdark>=2.6 ~ <M>cont_gen=2.7

continuos GR in the junction at low gain p i n

DC generation

M=6



21

2007


0.01

0.1

1

10

100

1000

3.0 3.5 4.0 4.5 5.0 5.5

Cut-off wavelength (µm)

Ieq_

in -

Icc

(fA

)

e-APD sensitivity :Equivalent input dark current M=100, T=80K: FqM

iI FOV

ineq 2

20

_ 2

Icc=0, A1, ZFIcc=0, A2, ZFIcc, A1, RFIcc, A2, RF

Reduction is lower than M=100 trend line Evaluation of parameter space is under way

xCd, gain, LPE, MBE hetero-structure APDs

M=380

MSW-FPA=6 (590 e-/s)

MMW-FPA=10

Late news data (14/10/2009):

M=24 (12 e-/s) at 10.5V



22

2007


LETI/Sofradir HgCdTe e-APD Road-map

Exclusive electron multiplication HgCdTe APDs

2009 2010 2011

Q2

2D Active/passive FPA

320x256, p30µm

Q3

3D Active FPA

320x256, p30µm

Wavefront/Fringe tracking

320x256, > 1.5kFPS,

noise < 2 e-

photon counting

Single element

Photon counting array

Format to be defined

Q4

Real time BW>GHz

Single element

Q3

2D TOF imaging

320x256, p30µm

Optimizing HgCdTe e-APDs Operability >99.9%, low dark noise (10 e-/s), speed (<100ps)

Develop dedicated proximity electronics to address a maximum of applications (RON < 1 e-)



23

2007


Conclusions/Perspectives MCT e-APDs

F~1 at M>600 for c=2.9 µm to 5.4 µm at T=80K Linear mode photon counting

Proportional counting (detect 1, 2.. photons) Discriminate non-amplified dark currents

Low DCR Timing precision below 100 ps No after pulsing is expected

ROIC (CMOS)-design is the key to harnest the potential of MCT e-APDs 2D active imaging array

Neq_in<12 e-/s in c=2.9 µm array at M=25 enables wave front sensing

3D AI array under testing : timing precision~1ns (15cm) 2010

Low noise-high speed wave front sensor Neq_in < 1 e-/s at M>10 Single element photon counting

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HgCdTe avalanche photodiodes development at CEA/Leti-Minatec

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