Silicon Photomultiplier Development at GRAPES-3 K.C.Ravindran T.I.F.R, OOTY WAPP 2010 Worshop On behalf of GRAPES-3 Collaboration

2 September 2008 at CERN Problem with HPD for CMS, HO Testing CPTA & IRST diodes First batch (50 samples) 3 mm 2, Hamamatsu SiPM Characterisation VME and Keitley voltage source/ Pico ammeter mid at GRAPES-3 Few pieces characterised at GRAPES-3 Results reproduced Comparison with PMT, ETL9807B CMS Project

Photodetector Convert an optical signal to electrical signal : Photo detectors made of semiconductor material absorb incident photons and produces electrons If electric field is imposed on photo detector an electric current (photo current) is produced (photo diode) Basic requirements of a photo detector : Sensitivity at the required wavelength Efficient conversion of photons to electrons Fast response Low noise Sufficient area to couple the optical signal High reliability Low cost 3

4 Photo Multiplier Tubes  RCA first commercially produced PMTs in 1936  Single photons can be detected with PMTs (gain 10 5 to 10 7 )  High price, Bulky shape, Sensitivity to magnetic fields PIN photodiodes (No internal gain)  Used in CLEO, L3, BELLE, BABAR, GLAST  Noise in subsequent amplifier  Hundreds of photons Avalanche photodiodes (APDs)  Have internal gain ~ 100  ~20 photons are needed for a detectable signal  The excessive noise, the fluctuations of the avalanche multiplication limits the useful range of operation  CMS is one of the big experiment that uses APDs Gieger-APDs can detect single photons (gain 10 5 to 10 6 ) o They have been developed during the past decade Photodetectors

Principle of operation of APD and SiPM 5 Digital information Silicon Photo Mutipler (SiPM) OR Multi Pixel Photon Counter (MPPC) If V BR is constant Gain is constant

6 GAPD : Problems Dark counts : Typical 5 MHz at 0.5 pe threshold and 1 MHz at 1.5 pe threshold at 25 °C (Thermal noise) for MPPC S P(X), area 3mmX3mm After pulsing Carrier trapping and delayed release causes afterpulses during a period of several microseconds Optical Cross talk: Hot-Carrier Luminescence: 10 5 carriers in an avalanche breakdown emit in average 3 photons with an energy higher than 1.14 eV. A. Lacaita et al, IEEE TED (1993)

7 Features of MPPC S P(X) Photon Detection Efficiency (PDE) The photon detection efficiency (PDE) is the product of quantum efficiency of the active area (QE), a geometric factor ( g, ratio of sensitive to total area) and the probability that an incoming photon triggers a breakdown (P trigger ) PDE = QE · g · P trigger Hamamatsu, Multi Pixel Photon Counter - SiPM

8 Specifications of MPPC S P(X)

9 IV characteristics at different Temperatures Current (A) Voltage (V)

Temperature Vs Breakdown voltage 10 Positive temperature coefficient 50.5mV per degree C

11 Signal Generator SiPM Green LED qADC VME CrateComputer Data Pedestal & LED Calibration Setup LED Pulse Width=20 nsec Logic OR Pedestal Trigger  V8011 VME Crate  V2718, VME Crate controller with PCI interface and optical connectivity  V792, 32 channel QDC, 12 bit, Resolution 100fC/count  Supports ~ 4KHz trigger rate in block read with 1 QDC module Amp X 25 Trigger Gate=125 ns

12 Pedestal Distribution Single Photon resolution (σ/μ) is 33.4 %

13 Low LED Distribution Single Photon resolution (σ/μ) is 30.4 %

Pedestal distribution at different Bias Voltages 14 Bias =70V Bias =71.8V Bias =71.5VBias =71.2V Bias =70.9VBias =70.6V Bias =70.3V Bias =72.1V BLUE – PIN diode distribution and RED Pedestal distribution

LED, ADC distribution at different Bias Voltages 15 Bias =70VBias =70.3V Bias =70.6VBias =70.9V Bias =71.2VBias =71.5V Bias =71.8VBias =72.1V

Summary 16

17 Comparison of MPPC & ETL 9807B PMT Peak gain for PMT = 590 ch PMT s.p.e gain = 56 ch Number of Photo electrons detected by the PMT = 590/ 56 = 10.5 Peak gain for SiPM = 581 ch SiPm s.p.e gain = 22 ch Number of photo electrons = 26.4 The number of photo electrons detected by Si-PM is ~ 2.5 times that of ETL 9807 PMT PDE of Si-PM is ~ 40 % and Quantum efficiency for PMT, 9807 B is 15 to 20 % Amplifier X25 SiPM PMT LIGHT TIGHT BOX HT QDC BIAS QDC

18 Photon yield with SiPM Green Fibers SiPMVME PC Ped. Peak = 90.3 Single p.e.= 17.4 p.e. at peak = 44 p.e. at mean ~ 50 Trigger by MUONS with paddles Scintillator Size 25x25x1 cm 3

19 Problems & Possible solutions using MPCC Thermal Noise of the order of 5MHz at 0.5 photon level –Cooling Optical cross talk –More Effective Optical isolation between Pixels After pulsing –Improve quality of Fabrication Temperature sensitivity to V BR –Monitor Temperature OR Leakage current and adjust V-Bias Small Area for optical fiber coupling –More R&D

20 Conclusion Promising device to replace PMTs Advantages : – Small size – Low voltage operation – High PDE Challenges : –Temperature dependence –Sensitivity to Bias Voltage & Narrow Voltage operating window –Thermal noise, Optical cross talk, After pulsing

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SiPM Vertical Structure Conduct : Al Resistor: Poly-Si P+ N+ SiO 2 Epitaxy layer: boron doping 300~500nm 1~2um Trench: fill Polyimide Contact: Al * Each micropixel is isolated by trench * Resister is formed by Poly silicon. * P+ region of pn junction is a small size than n+ region to reduce leakage current