# Presentation: 146535

## Preliminary Investigations of Geiger-mode Avalanche Photodiodes for use in HEP Detectors

***David Warner, ***_***Robert J. Wilson***_*** ***
***Department of Physics***
***Colorado State University***

- R.J.Wilson, Colorado State University

## Outline

**Motivation**
**Avalanche Photodiodes**
**Characteristics**
**R&D Plans**
**Conclusions**

- R.J.Wilson, Colorado State University

## Motivation

- 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)

- 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 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 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**

*RMD Inc.*

- 20 m diameter  pixel,
- room temp.

- R.J.Wilson, Colorado State University

## Photon Detection Efficiency

*RMD Inc.*

*RMD Inc.*

- R.J.Wilson, Colorado State University

## Slide 8

- R.J.Wilson, Colorado State University

## Prototype APD 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

**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 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.

**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)

- Source: BaBar IFR Upgrade Status Report III

- R.J.Wilson, Colorado State University

## CSU+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 layout

- Proprietary. Do not distribute.

- R.J.Wilson, Colorado State University

## 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 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 Design

**Preliminary**

- Design 3:

- 1.2 V

- 100 ns

- R.J.Wilson, Colorado State University

## Temperature Dependence

- R.J.Wilson, Colorado State University

## T (°C)

- -43

- -32

- -30

- -24

- -20

- -13

- 2

- 9

- 23

- T (°C)

**Preliminary**

- Detection Efficiency

- Nominal operating voltage

- -43

- -20

-    2

- 23

- T (°C)

- 10 m  gAPD
- 550 nm, 150 ns laser, 10 kHz
- Avg. ~7 photons/pulse
- DE = (Illuminated Rate - Dark Rate)/10 kHz

**DE**

**Preliminary**

- R.J.Wilson, Colorado State University

## Optical 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

- D

- d

- 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 reduction

- 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

- Transmission Factor

- R.J.Wilson, Colorado State University

## Test 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 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 1********s-0.1********s 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 - 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 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. **

- R.J.Wilson, Colorado State University