electron- and hole- avalanche hgcdte photodiode arrays for astronomy donald n. b. hall institute for...
TRANSCRIPT
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
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)
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
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+0
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
T=160K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
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
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?
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
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 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
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)
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
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+0
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
T=160K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
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
T=200K
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.
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.
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.
e-APD GAIN - BAE
caption
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
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)
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
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+0
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
T=160K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K
T=120K
235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
T=80K235-Gʎco = 4.54µm at 80KElements 32, 44, 85 Area = 250x250 µm2
F/5
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
T=200K