# Presentation: 732142

## 
Progress in Using Cold Avalanche Photodiodes as Single Photon Detectors

J.Swain ,Y.Musienko*, S.Reucroft

Northeastern University, Boston

                     With thanks to A.Dorokhov, A.Glauser, C.Regenfus
(Physik-Institut der Universitat Zurich)

*on leave from INR (Moscow)

**Progress in Using Cold Avalanche Photodiodes as Single Photon Detectors**
_***J.Swain***_*** ,Y.Musienko*, S.Reucroft***
- Northeastern University, Boston
-                      With thanks to ***A.Dorokhov, A.Glauser, C.Regenfus***
- (Physik-Institut der Universitat Zurich)
- *on leave from INR (Moscow)

## Motivation 

- New Hamamatsu APD’s developed for CMS and optimized for radiation hardness can operate at M~3000 (T=300K). Since we have them anyway...
- Can they operate at high gains at low temperatures (~100K)?
- Low temperature -> low dark current -> low noise count ?
- What will be the efficiency for single photon counting, with APD operating in a linear mode?

## Where they came from: CMS

**PbWO****4**** crystal**

## Hamamatsu APDs used in this study

**Summary of APD parameters**

- APD`s designed for the CMS ECAL

## Gain

## Quantum Efficiency

## Capacitance

## Set-up

-  APD was inside evacuated metallic box inside a dewar
-  It was connected via ~60 cm cable to a preamplifier (Canberra-2003BT), followed by TENELEC TC-205A shaper (3s shaping time)
-  APD was illuminated with the blue (470nm) LED through a gray filter
-  Currents were measured using a Keithley-487 source-meter
-   Amplitude spectra were measured with the LeCroy LT342L DSO
-  LeCroy 623B discriminator and 250 MHz scaler were used for signal counting

## Gain at different temperatures

## Dark Current (room temperature)

- What is the dependence of dark current on the temperature?

## APD irradiated with neutrons (~1013 n/cm2)

## Dark current vs. temperature

- Ibulk~T**2** *Exp(-0.47eV/kT)

## Dark current vs. temperature

- Ibulk~T**2** *Exp(-0.47eV/kT)

## Excess Noise Factor

- Does it depend on the temperature? Shape of the gain curve can give some indication.

## High capacitance APD

- Full depletion at 80V

## Voltage coefficient of the gain

- Shape of the gain curve does not depend on the temperature: ionization coefficients for holes and electrons depend on the temperature, but their ratio (k-factor) remains constant!

## Light and noise counting rate

- Electronic noise was 430 el. rms at =3 s

## Single electron spectrum

- Theory: R.J.McIntyre, IEEE Trans. Electron Devices, vol. ED-19, p.703, June 1972

## Photoelectron detection efficiency

- Gain of the APD was measured at high LED current, then current was significantly reduced to achieve low photon rate (~26 kHz). At M=8000 Iill=34 pA (~4.3 fA primary photocurrent)

## Summary

- At T~100K new Hamamatsu  APD’s operate at M~104,
- k-factor does not depend on temperature (110K<T<295K)
- 25% photoelectron detection efficiency was measured with 1150 el. electronics threshold, APD operated in linear mode (M~8000)
- This correspond to ~20% single photon counting efficiency for 470nm light
- Noise count <0.1 Hz was measured at 2500 el. Threshold (T=108 K), while efficiency of photoelectron counting was ~20%
- Results are in agreement with McIntyre calculations
- Reducing electronic noise and k-factor, single photon counting efficiency can be significantly improved, while keeping noise count at very low level