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ALCPG, UT-ArlingtonJanuary 10th 2003
Preliminary Investigations of Preliminary Investigations of Geiger-mode Avalanche Photodiodes Geiger-mode Avalanche Photodiodes
for use in HEP Detectorsfor use in HEP Detectors
David Warner, Robert J. Wilson Department of PhysicsColorado State University
R.J.Wilson, Colorado State University
OutlineOutline
Motivation
Avalanche Photodiodes
Characteristics
R&D Plans
Conclusions
R.J.Wilson, Colorado State University
MotivationMotivation
Scintillating fiber, or WLS readout of scintillator strips basic component of several existing detectors (MINOS, CMS-HCAL)
Standard photodetector – photomultiplier tubes, great devices but…– “Expensive” (including electronics etc.),
– Bulky, magnetic field sensitive…
For the next generation would like a photon detector to be:– Cheaper
– Compact? Low mass? Magnetic field insensitive? Radiation hard?
Future experiments– BaBar upgrade - endcap?
– Future e+e- Linear Collider? LHC?
– Nuclear physics? Space-based (NASA)?
R.J.Wilson, Colorado State University
Silicon Avalanche Photodiodes (APD)Silicon Avalanche Photodiodes (APD)
Solid state detector with internal gain. Avalanche multiplication
– initiated by electron-hole free carriers, thermally or optically generated within the APD
– accelerated in the high electric field at the APD junction.
Proportional Mode – bias voltage below the breakdown voltage, low gain
– avalanche photocurrent is proportional to the photon flux and the gain
Geiger Mode– bias voltage higher than the breakdown voltage, gain up to 108 from single carrier
– avalanche triggered either by single photon generated carriers or thermally generated carriers
– signal is not proportional to the incident photon flux.
– high detection efficiency of single carriers single photon counter
– to quench Geiger mode avalanche bias has to be decreased below the breakdown voltage
R.J.Wilson, Colorado State University
UV Enhanced Avalanche PhotodiodesUV Enhanced Avalanche Photodiodes
Development by Stefan Vasile et al, Radiation Monitoring Devices, Inc. Cambridge, Massachusetts, USA. (Now at aPeak, Newton, Mass.)
Small Business Innovative Research (SBIR) award motivated by an imaging Cerenkov device application (focusing DIRC). c. 1996/97-98
Design and fabrication of silicon micro-APD (APD) pixels– 20-180 µm pixels, single photon sensitivity in the 200-600 nm wavelength range.
– Q.E.= 59% at 254 nm (arsenic doping, thermal annealing)
– very high gain > 108
– Geiger mode APD array with integrated readout designed but process/funding problems.
blue-infrared UV-blue
R.J.Wilson, Colorado State University
Geiger Avalanche CharacteristicsGeiger Avalanche Characteristics
Thermal carriers trigger avalanche– dark count rate decreased using small APD
space charge region generation volume
Compatible with 5 volt logic– strong noise rate dependence
Temperature dependence factor 3 decrease for 25°C to 0°C factor 20 decrease for 25°C to -25°C
Size dependence– roughly linear with effective avalanche
region area– at room temp. predict few kHz for 100 m,
100 kHz for 500 m
Characteristics measured on a small number of samples
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5
Pulse Amplitude (V)
Cou
nts
/ sec
45V
44V
RMD Inc.
20 m diameter pixel, room temp.
R.J.Wilson, Colorado State University
Photon Detection EfficiencyPhoton Detection Efficiency
RMD Inc. RMD Inc.
R.J.Wilson, Colorado State University
R.J.Wilson, Colorado State University
Prototype Prototype APD ArrayAPD Array
• APD active area is 150 m x 150 m on 300 m pitch
• Compatible with CMOS process potential for low cost large-scale production
• 70% photon collection efficiency with fused silica micro-mirrors (for f-DIRC)
• Fabrication attempt failed 1998/99. RMD claims to have solved the problems
but no funds for a fabrication run.
RMD Inc.
R.J.Wilson, Colorado State University
Uses a large volume of cheap co-extruded scintillator bars (8m x 4cm x 1cm) with a single 1.2mmØ Y11-175 multiclad WLS fiber epoxied in extruded groove
WLS fiber is coupled to a long clear fiber and readout with a pixelated pmt
~3-4 pe/fiber at ~3.7 m including connections and pmt QE Several production facilities still operational
MINOS Scintillation SystemMINOS Scintillation System
Source: BaBar IFR Upgrade Status Report III
R.J.Wilson, Colorado State University
Short (3.7m vrs 8m) version of MINOS system with Time to the get the second coordinate
Replace the pmt with (low gain) APD : 4X higher QE Increase number of fibers to 4 : ~2X more light Increase scintillator thickness to ~2cm : ~1.5X more light Project ~ 50-60 pe at 3.7m for min. ion.
BaBar Modifications (SLAC/CalTech)BaBar Modifications (SLAC/CalTech)
Source: BaBar IFR Upgrade Status Report III
R.J.Wilson, Colorado State University
CSU+SLAC Commissioned R&D at aPeakCSU+SLAC Commissioned R&D at aPeak
P.o. placed December 2002 3.1. Package GPD pixels
– Wire bonding; – Breadboard passive quenching circuitry and GPD pixels.
3.2. Reliability evaluation – Bias several pixels at 1.1V above breakdown for 1,000 hours, document
changes in dark count rate, and failure modes, if any.
3.3. GPD performance evaluation – dark count rate vs. T–40 to 30 °C – recovery time vs. pixel area: determine if one microsecond recovery time can
be achieved with passive quenching– Gain vs. Temp. and bias Voltage– Detection Efficiency @ Room Temp.
3.4. Optical interface fabrication and assembly– Fab. and evaluate 4x1 beam couplers using GRIN and/or tapered fibers
3.5. Test GPD in Cosmic Ray Setup
R.J.Wilson, Colorado State University
50 m diameter GPD layoutProprietary. Do not distribute.
R.J.Wilson, Colorado State University
Recovery Time with Passive Quenching.Recovery Time with Passive Quenching.
1 x 10 m GPD
Simple electronics -limiting resistor 10 s quench time
475 mV
10 s
R.J.Wilson, Colorado State University
Recovery Time - Active QuenchingRecovery Time - Active Quenching
Design 1:
Design 2:
Trade off pulse amplitude with pulse width (quench the avalanche sooner)
1 s
0.5 s
2.75 V
325 mV
R.J.Wilson, Colorado State University
Active Quenching - New DesignActive Quenching - New Design
Preliminary
Design 3:
1.2 V
100 ns
R.J.Wilson, Colorado State University
Temperature DependenceTemperature Dependence
R.J.Wilson, Colorado State University
0.00
0.05
0.10
0.15
0.20
0.25
0.30
12 12.2 12.4 12.6 12.8 13Bias Voltage, Vr (V)
-43-32
-30-24
-20-13
29
23
T (°C)
Preliminary
Detection EfficiencyDetection Efficiency
Nominal operating voltage
0 200 400 600 800 1000120014001600Dark Count Rate (Hz)
-43
-20 223
T (°C)
10 m gAPD 550 nm, 150 ns laser, 10 kHz Avg. ~7 photons/pulse DE = (Illuminated Rate - Dark Rate)/10 kHzDE
Preliminary
R.J.Wilson, Colorado State University
Optical coupling to small diameter pixelsOptical coupling to small diameter pixels
Couple 4 x 1.2 mm WLS fibers to 4 x 1mm glass fibers Draw 4 glass fiber into single fiber, various exit diameters Investigate light transmission efficiency
aA
Dd
Concentration Factor, CF =
Area of input aperture (A) / Area of photodetector (a)
Coupler Transmission Factor, TF =
Intensity at input aperture / Intensity at output aperture
R.J.Wilson, Colorado State University
Optical couplers – area reductionOptical couplers – area reduction4x1 Coupler Yield
(input aperture = 2.697 mm)
0.01
0.10
1.00
1 10 100
Concentration Factor
Yie
ld
w/concentratorcoupler exit aperture = 1mmcoupler exit aperture=0.8 mmcoupler exit aperture = 0.6 mm
GPD
GPD
Single Cone Concentrator Yield
0.01
0.10
1.00
1 10 100
Concentration Factor
Yie
ld
w/concentratorw/o concentrator
GPD
Benefit from tapered fibers compared to ratio of areas is not dramatic 50-200% Preliminary measurements at aPeak are in general agreement with the model We expect to get samples at CSU soon
ratio of areas
Concentration Factor, CF Concentration Factor, CF
Tra
nsm
issi
on F
acto
r
R.J.Wilson, Colorado State University
Test Setup at CSUTest Setup at CSU
Portable dark box
Initial Tests
Cosmics rays Calibrated with well-understood
PMT at CSU Measure efficiency with
gAPD+couplers
R.J.Wilson, Colorado State University
gAPD Progress SummarygAPD Progress Summary
SLAC+CSU initiated a p.o. to jumpstart further gAPD work at aPeak.
New design from aPeak claims to be a more reliable process than the old one.
Detection efficiency in 10 micron pixels 15% at room temp., 25% at –40°C
(~kHz dark count rate).
Only modest dark count reduction with lower temperature; expected to be better in
next batch.
Active quenching circuitry provides 1s-0.1s pulse widths, no additional deadtime.
Successful fabrication of 4x1 tapered couplers – complexity trade-off unclear.
50 m diameter gAPDs breakdown; occurs predominantly at the surface. Due to
suspected design sensitivity to humidity.
New run, with better control of the surface breakdown is being fabricated. Added
backup design to layout. Larger, 150 m devices by early February, 2003.
R.J.Wilson, Colorado State University
Motivation for Geiger-mode APDs - RecapMotivation for Geiger-mode APDs - Recap
High gain (~109), > 1 volt pulses– Minimizes required electronics
Good detection efficiency in WLS range (>20%? At 550 nm)– Efficient for low light output from WLS fibers
Low supply voltage requirements (~10-40V)– Simplifies wiring harness
Minimal cooling requirements– Simplifies mechanical plant
CMOS process– “simple”– on-chip integration of readout -> cost-savings
R.J.Wilson, Colorado State University
Next StepsNext Steps
Many unanswered questions. Need to get the devices in our own lab!
Assisting aPeak with SBIR proposal.
CSU proposal to DoE Advanced Detector R&D.
Hope to provide a real HEP demonstration of utility for broad range of fiber applications.
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