ELECTRON- AND HOLE- AVALANCHE HgCdTe PHOTODIODE ARRAYS FOR ASTRONOMY Donald N. B. Hall Institute for Astronomy University of Hawaii

ELECTRON- AND HOLE- AVALANCHE

HgCdTe PHOTODIODE ARRAYS FOR ASTRONOMY

Donald N. B. Hall

Institute for AstronomyUniversity of Hawaii

OUTLINE• WHY APDs?• CONVENTIONAL APD’S e.g. Si, Ge & GaAs.• WHY Hg:Cd:Te – the PERFECT INFRARED

(and VISIBLE) APD MATERIAL?• e-APD and h-APD CHARACTERISTICS of

Hg:Cd:Te.• STATUS of the NASA FUNDED

UH/GSFC/TELEDYNE Hg:Cd:Te APD PROGRAM.

• UH TEST and CHARACTERIZATION.• FUTURE DEVELOPMENTS.

WHY APDs?• THE HAWAII-2RG ARRAYS DEVELOPED FOR

JAMES WEBB APPROACH THE IDEAL DETECTOR IN ALL BUT ONE RESPECT – READ NOISE!

• DUE TO BASIC PHYSICS OF CMOS, READ NOISE HAS IMPROVED LITTLE SINCE HUBBLE NICMOS – TECHNOLOGY LARGELY FROZEN IN TIME FOR 20 YEARS.

• READ NOISE LIMITS LOW BACKGROUND AND/OR HIGH SPEED APPLICATIONS

• Hg:Cd:Te APDs HOLD PROMISE OF THE SOLUTION.

EXAMPLES

• HIGH SPEED – MODEST FORMAT, RELAXED DARK CURRENT:- Wave-front Sensing- Fringe Tracking

• HIGH SENSITIVITY – LARGE FORMAT, DEMANDING DARK CURRENT:- High Resolution Spectroscopy- Low Background Space

• BOTH – ALSO HIGH TIME RESOLUTION:- Time Resolved Spectroscopy- Quantum Astrophysics

CONVENTIONAL APDs e.g. Si, Ge & GaAs

• IN CONVENTIONAL APD MATERIALS (e.g. Si, Ge and GaAs) BOTH ELECTRONS AND HOLES AVALANCHE (IN OPPOSITE DIRECTIONS).

• THIS SPREADS THE STATISTICAL AVALANCHE GAIN PRODUCING EXCESS NOISE.

• McINTYRE (1968) DEFINED THE EXCESS NOISE FACTOR:

F = (S / B)IN / (S / B)OUT

• THE THEORETICAL LIMIT FOR “F” IN THE CASE WHERE BOTH ELECTRONS AND HOLES AVALANCHE IS 2 BUT IT IS OFTEN >>2.

• THIS DUAL AVALANCHING ALSO SIGNIFICANTLY STRETCHES OUT RESPONSE TIME.

• BEST CONVENTIONAL APDs REACH F VALUES ~ 2

McINTYRE MODEL • PHOTO-IONIZATION INITIATES

AVALANCHING BY BOTH ELECTRONS AND HOLES.

• COLLISIONS FULLY REDISTRIBUTE BOTH ELECTRONS AND HOLES BEFORE REACHING IONIZING ENERGY.

• EXCESS NOISE AND PULSE BLURRING INHERRENT IN PROCESS.

• RULES OUT “NOISELESS” (F = 1) PHOTON COUNTING IN LINEAR MODE.

• PHOTON COUNTING ONLY IN GEIGER MODE WITH LIMITED DUTY CYCLE, AFTER-PULSES AND REQUIREMENT FOR QUENCHING.

Hg:Cd:Te AVALANCHE CHARACTERISTICS

• IT IS WELL KNOWN THAT BY VARYING THE “x” FRACTION OF Hg(1-x):Cd(x):Te, THE CUT-OFF WAVELENGTH λc CAN BE VARIED OVER THE RANGE λc < 1.3 μm TO λc > 15 μm.

• OVER THIS RANGE THERE ARE ALSO DRAMATIC CHANGES IN THE AVALANCHE PROPERTIES OF THE CRYSTAL LATTICE.

• THE NEXT CHART SHOWS LOG10 GAIN vs BAND-GAP (eV) FOR LAYERS FROM LETI, BAE, TIS & DRS, ALL @ 77K & 6V REVERSE BIAS

e- & h- APD REGIMES OF HgCdTe

Figure 5: The distinct e-APD and h-APD regimes of HgCdTe cross over at Eg ~ 0.65 eV (λco ~ 1.9 μm). At lower band-gaps the e-APD gain increases exponentially

with decreasing bandgap - material for four manufacturers shows remarkably

consistent results. To higher bandgap the ratio k = αh / αe asymptotically approaches pure h-APD at Eg = 0.938 eV – the ideal SAM layer.

e-APD GAIN - SUMMARY

235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2

F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

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F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+0


F/5

T=80K

T=120K

T=160K


F/5

T=80K

T=120K


F/5

T=80K235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2

F/5


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n

T=200K

AVALANCH PROPERTIES of HgCdTe

• HOLE ACCELERATION IS VERY LOW – HIGH EFFECTIVE MASS – SLOWER.

• e- ACCELERATION IS VERY HIGH - PHONON SCATTERING LOW – VERY FAST.

• HOLE IONIZATION IS VERY LOW EXCEPT FOR 0.938 eV RESONANCE

• e- IONIZATION IS VERY HIGH• THUS FOR EB < 0.6 eV (λC > 2 μm) ONLY

e- AVALANCHE (k = 0)

HgCdTe as an e-APD

• AVALANCHE GAIN INCREASES EXPONENTIALLY WITH BIAS & DECREASING EB.

• e- TRAJECTORIES ARE BALLISTIC BETWEEN IONIZING COLLISIONS.

• DETEMINISTIC SO NO EXCESS NOISE – F ~ 1.• VERY FAST PULSE - GAIN BANDWIDTH > 1THZ.• THERE IS NO GEIGER BREAKDOWN AND SO NO

GEIGER MODE OPERATION.• HOWEVER NOISELESS (F ~ 1) PHOTON COUNTING

IS POSSIBLE IN THE LINEAR (PROPORTIONAL) MODE TO GAIN ~ 104.

• FOR ASTRONOMY, THE PRIMARY CHALLENGE IS TO REDUCE DARK CURRENT.

APDs in MBE HgCdTe

• DEPOSITION BY MBE ALLOWS A SEPARATE ABSORPTION-MULTIPLICATION (SAM) STRUCTURE.

• A-LAYER GRADED INTO M-LAYER• TO AVOID PHOTOIONIZATION IN THE M-

LAYER, λC FOR THE A-LAYER MUST BE LONGER THAN λC FOR THE M-LAYER.

• MISMATCH IN CRYSTAL LATTICE PROPERTIES MAY LIMIT THE DIFFERENCE BETWEEN THE TWO λCs.

BAND-GAP TRADE-OFF0.25 eV (λc ~ 4.5 μm) vs 0.5 eV (2.6 μm)

• 0.25 eV M-LAYER HAS HIGH GAIN (>5,000 @ 12.5 V) WITH MATURE PROCESSING TECHNOLOGY.

• BUT VERY SUSCEPTIBLE TO THERMAL BACKGROUND.

• 0.5 eV M-LAYER HAS MUCH LOWER GAIN BUT OFFSET BY MUCH LOWER BACKGROUND.

• 0.5 eV DARK CURRENT NOT DRAMATICALLY LOWER DUE TO TRAP INDUCED TUNNELING CURRENT.

• OPTIMUM M-LAYER BANDGAP?

J. ROTHMAN SUMMARY

EMPIRICAL MODEL for e-APD GAIN

• BECK (2001, 2002) DETERMINED THAT THE e-APD GAIN M VARIES WITH V AS:

M = 2 (V – VTH)/(VTH/2)

• VTH ~ 6.8 Eg FOR ALL COMPOSITIONS:

0.2 < x < 0.5• “DEAD VOLTAGE” MODEL OF e-APD

GAIN IN HgCdTe• FIGURE FOR VTH = 5 Eg AND ά = 1

M KINCH_JEM_V37N9P1453_2008 page 1454 Fig. 2

M KINCH_JEM_V37N9P1453_2008 page 1454 Fig.1.(a)

M KINCH, EAPDs, page 122, Fig. 7.13

e-APD DEVELOPMENT• DEFIR (Design and Future of the IR)

INITIATIVE BRINGS TOGETHER SOFRADIR’S R&D WITH CEA-Leti.

• MCT e-APD RESEARCH TOWARD INDUSTRIALIZATION.

• PASSIVE AMPLIFIED IMAGING (PAI) & 3-D LADAR.

• DRS DALLAS (WITH SELEX) - PAI & 3-D LADAR PLUS ASTRONOMY.

• RAYTHEON - PAI & 3-D LADAR (PLUS ASTRONOMY?).

• BAE R&D. • TIS – ASTRONOMY.

e-APDs by CEA LETI, DRS, BAE & TIS

Company Process Geometry Use

CEA-LETI LPE & MBE

Plane

(Width)

MWIR PAI

1.5μm LADAR

DRS MBE Cylinder MWIR PAI

1.5μm LADAR

BAE LPE Plane MWIR PAI

TIS MBE Plane PHOTON COUNTING

e-APD ARCHITECTURE - DEFIR

caption

e-APD ARCHITECTURE - DSL

caption

THREE COMPLIMENTARY TIS APPROACHES

e-APD GAIN - SUMMARY


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11


F/5

T=80K

T=120K

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1E+3

1E+2

1E+1

1E+0


F/5

T=80K

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F/5

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F/5


F/5


F/5

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T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n

T=200K

DEFIR F VALUES (J. ROTHMAN)

e-APD GAIN σ - DRS

caption

e-APD GAIN σ - DRS

caption

e-APD GAIN σ - DEFIR

caption

e-APD GAIN (CUM) - DEFIR

caption

e-APD GAIN vs TEMP - SUMMARY

e-APD GAIN vs TEMP - DEFIR

caption

e-APD GNDC - DEFIR

caption

e-APD GNDC vs TEMP - DEFIR

caption

e-APD PULSE PROFILE - DEFIR

caption

e-APD PULSE RISE TIME - DEFIR

caption

e-APD PULSE DECAY TIME - DEFIR

h-APD APPLICATIONS TO ASTRONOMY

• 0.938 eV (λc ~ 1.32 μm) M-LAYER COMPATIBLE WITH A-LAYER INSENSITIVE TO ROOM TEMPERATUREBACKGROUND.

• ATTRACTIVE FOR HST-LIKE MISSIONS & GROUND BASED APPLICATIONS.

• SUBSTRATE REMOVAL FOR VISIBLE APPLICATIONS.

• CHALLENGES ARE DARK CURRENT & ACHIEVING F ~ 1.

• h-APD AVLANCHE PULSE ~ 10X SLOWER.

h-APD DEVELOPMENT

• RAYTHEON (RVS, HRL & RMS) HAS DEMONSTRATED SWIR (1.55 μm) e-APD BASED LADAR OPERATING AT 300K.

• THEY REPORT NO EXCESS NOISE TO GAINS >100, NEP < 1nW & GHZ BANDWIDTH.

• CZT => 6” Si WAFER PROCESSING.

PERFORMANCE OF 90 RANDOMLY SELECTED APDs - RAYTHEON

Jack et al, Proc of SPIE V6542, P65421A (2007)

GOALS OF THE UH/GSFC/TELEDYNE Hg:Cd:Te APD PROGRAM

• THREE YEAR PROGRAM FUNDED PRIMARILY BY NASA “RESEARCH OPPORTUNITIES IN SPACE AND EARTH SCIENCES” INITIATIVE - SUPPLEMENTAL FUNDING BY GSFC.

• WILL UTILIZE TELEDYNE’S BROAD EXPERIENCE IN MBE Hg:Cd:Te PROCESSING TO PRODUCE APDs OPTIMIZED FOR ASTRONOMY.

• UH WILL MODIFY TEST FACILITIES DEVELOPED FOR THE JWST PROGRAM TO CHARACTERIZE ARRAYS IN PHOTON COUNTING MODE.

APPROACH

• SIMILAR MASKS FOR e-APD & h-APD HgCdTe INCLUDE:- PROCESS EVALUATION CHIPS (PECs).- FOUR 256 x 256 @ 18 μm PITCH SUB-ARRAYS- TWO “TADPOLES”

• SCREEN AND INITIAL EVALUATION OF LAYERS USING PECs.

• CHARACTERIZE PHOTON COUNTING WITH SUB-ARRAYS BONDED TO CORNER OF H1RG, READ OUT WITH SIDECAR ASIC.

• “TADPOLES” FOR HIGH SPEED (QUANTUM ASTROPHYSICS AND LADAR).

• GOAL IS LOW DARK WITH F ~ 1.

KSPEC MODIFICATIONSCONCEPTUAL “TADPOLE” LAYOUT

Diodes in the 64um-500um range aligned along two parallel lines

HAWAII - 2RGHAWAII - 2RG2002

2048 x 2048 pixels29 million FETs0.25 µm CMOS

18 µm pixel size

HAWAII - 1RGHAWAII - 1RG2001

1024 x 1024 pixels7.5 million FETs0.25 µm CMOS

18 µm pixel size

UH-TIS HAWAII Heritage

1024 x 1024 pixels3.4 million FETs

0.8 µm CMOS18 µm pixel size

HAWAII - 1HAWAII - 11994

2048 x 2048 pixels13 million FETs0.8 µm CMOS

18 µm pixel size

1998HAWAII - 2HAWAII - 2HAWAII - 1RHAWAII - 1R

2000

WFC 3

1024 x 1024 pixels3.4 million FETs

0.5 µm CMOS18 µm pixel size

4096 x 4096110 million FETs0.25 µm CMOS

10 µm pixel size

2006

On-chip butting Reference pixels Guide mode & read/reset opt.

Stitching

HAWAII-HAWAII-4RG-104RG-10

4096 x 4096110 million FETs

0.25 / 0.18 µm CMOS15 µm pixel size

2011 (proposed) HAWAII-HAWAII-4RG-154RG-15

15µm pixels

Smaller pixels, Improved performance, Scalable resolution

SIDECAR SIDECAR ASICASIC 2003

Control chip for H1RG, H2RG and

H4RG-10/15

UH 2.5um, UH 5.0um, and STScI 5.0um MeasurementsDark Current Logarithmic

0.001

0.010

0.100

1.000

10.000

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135

Temperature (K)

SC

A A

vera

ge

Dar

k C

urr

ent

(e- /s

ec, p

ixel

)

UH 2.5um

UH 5.0um

STScI 5.0um

DARK CURRENT vs TEMPERATURE FOR 2.5 AND 5 UM MATERIAL

CURRENT STATUS

• FIRST RUN OF n-on-p e-APDs HAD POOR DIODE CHARACTERISTICS.

• ATTRIBUTED TO PROBLEMS WITH SURFACE PASSIVATION.

• IN 2009 CONDUCTED AN EXTENSIVE INVESTIGATION OF SURFACE PASSIVATION.

• READY TO PROCEED WITH 2ND RUN.• FIRST RUN OF p-on-n h-APDs UNDERWAY.• TESTING IN NOVEMBER.• EVALUATION OF h-APD GAIN of TIS

HERITAGE 0.73 eV (λco ~ 1.7 μm) p-on-n PEC

h-APD GAIN of TIS HERITAGE 0.73 eV (λco ~ 1.7 μm) p-on-n PEC

• STANDARD 0.73 eV (λco ~ 1.7 μm) p-on-n PEC.

• NO APD OPTIMIZATION OR SAM – ALL SAME MATERIAL.

• GAIN & BANDGAP CONSISTENT WITH h-APD AVALANCHING.

• PLAN TO EVALUATE IN H1RG.• PRESENT h-APD RUN CONSISTS OF

THIS MATERIAL FOR A-LAYER WITH 0.938 eV M-LAYER.

h-APD GAIN of TIS HERITAGE 0.73 eV (λco ~ 1.7 μm). p-on-n PEC

Figure 3: Measured gain vs. reverse bias voltage for TIS heritage 0.73 eV p-on-n material (λco ~ 1.7 μm).

KSPEC UPGRADE - CURRENT STATUS

• COMPLETELY SEALED, ULTRA LOW BACKGROUND TEST FACILITY.

• ILLUMINATION BY IR LEDs.• REFERENCE DETECTORS.• HIGH GEOMETRIC ATTENUATION TO < 1

PHOTON per PIXEL per FRAME READ• FIBER FEED OPTION FOR LASER PULSE

MEASUREMENTS.• UP TO H2-RG.• < + 1 mK TEMPERATURE CONTROL OVER

30K to 200K RANGE.

KSPEC MODIFICATIONS

Sphere Assembly

Detector Module

Cryo ASIC

KSPEC X-SECTION

ASIC

DETECTOR

APERATURE

LEDS

PHOTON COUNTING WITH H1RG

• HYBRIDIZE 256 x 256 SUB-ARRAY TO OUTPUTS 0 – 3 IN CORNER OF H1-RG.

• SIDECAR ASIC READS @ 10 Mpxl/SEC.

• 50 – 60 RMS e- CDS READ NOISE.

• FRAME RATES:

SUB-ARRAY

#

PIXEL

FRA

μ-sec

ME

KHz

64 x 256 16,384 1,638 0.675

64 x 64 4,096 409.6 2.5

32 x 32 1,024 102.4 10

16 x 16 256 25.6 40

8 x 8 64 6.4 160

4 x 4 16 1.6 625

A LOOK INTO THE CRYSTAL BALL

• DISCRETE APDs FOR INTENSITY INTERFEROMETRY, ADAPTIVE OPTICS & FRINGE TRACKING IN 1 -2 YEARS.

• MODEST ARRAYS - H-1/4RG @ 10 KHz FRAME RATE WITH ONE ASIC.

• H-2RG, H-4RG-15 FOR LOW BACK-GROUND SPECTROSCOPY & SPACE.

• SPECIALIZED READOUTS – TIME TAGGING PHOTONS.

CURRENT STATUS

• END

A

• B

e-APD GAIN - DEFIR

caption

e-APD GAIN - DSL

caption

e-APD GAIN – TIS 2004

e-APD GAIN - BAE

caption


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2

F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+0


F/5

T=80K

T=120K

T=160K


F/5

T=80K

T=120K


F/5


F/5


F/5

T=80K

T=120K

T=160K

1E+3

1E+2

1E+1

1E+00 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Gai

n

T=200K

Documents

ELECTRON- AND HOLE- AVALANCHE HgCdTe PHOTODIODE ARRAYS FOR ASTRONOMY Donald N. B. Hall Institute for Astronomy University of Hawaii