Recent Development and Study of Silicon Solid State Photomultiplier (MRS Avalanche Photodetector) Valeri Saveliev University of Obninsk, Russia Vienna Conference on Instrumentation Vienna, 20 February 2004 Feb 20, 2004 V.Saveliev 1
Technology, Development and Study of SiPM Obninsk State University of Atomic Energy, Obninsk, Russia Center of Perspective Technology and Apparatus, Moscow, Russia Feb 20, 2004 V.Saveliev 2
History of Metal-Resistor-Semiconductor Structures for Photon Detection Middle of 1985 At Research Laboratory of Moscow Radio Devices Enterprise is studied the Prof. Yu.Yusipov. Stationary Avalanche Multiplication of Photocurrent in Metal-Conducting Dielectric-Semiconductor Structures. 1989 The Photodetectors on this Principle where developed: Feb 20, 2004 V.Saveliev 3
History of Metal-Resistor-Semiconductor Structures (Photodetectors) End of 1992 First Tests for Physics Application ( red light ): Feb 20, 2004 V.Saveliev 4
Geiger Mode Operation for Single Photon and Low Photons Flux Detecting Si Avalanche Detector can operated in Geiger mode, The Gain of Geiger mode in Si Avalanche Detector is in order of 10 5-10 6, it is enough for Single Photoelectron Detection, If the Dark Rate of an avalanche pulses are triggered by bulk thermal carrier is low. The value of the dark rate is therefore a significant parameter of Si Avalanche Detector for photon-counting mode. (Dark rate is frequency of pulses on output of sensor with value of GM, correspondent single photoelectron). The operational conditions: Usually the avalanche process should quench, suppression of the avalanche process by addition effort actually by temporary lowering the bias voltage below breakdown voltage. Necessary of suppression of dark rate. Creating Structure with Possibility of detection of low photons flux in proportional mode. Feb 20, 2004 V.Saveliev 5
Si-SSPM Design and Operation Combination of large number of Si Avalanche Detectors with Geiger Mode operation( microcells ) with integrated quenching mechanism Microcell Photons Top Semitransparent Contact + antireflection coating Resistive Layer (SiC) Avalanche cells microcells Drift area Bulk Si material ( p+ ) Back Contact Quenching Mechanism for SiPM is passive resistive network on base High Technology Resistive Layer 10 3-10 4 microcells/mm 2, are Identical and Independent, Geiger mode operation, Output Q = S G i Sum of Identical Signals from Different Microcells, Dynamic Range of Proportional Mode of Photons Flux Measurements = N cells. Feb 20, 2004 V.Saveliev 6
Quenching Mechanism of MRS-APD Quenching Mechanism of SiPM is based on passive resistive network on base high technology ( SiC, Si 3 N 4 ion-plasma evaporation process): A characteristic feature of the Metal-Resistor-Semiconductor (MRS) Structures is negative feedback, which displays itself as follows: An avalanche creating process leads to increase the current trough the resistive layer and to a charge accumulation on the SiC-Si interface This is gives result in a constant redistribution of the potential in the microcell - increase the electric field of opposite direction appears, which screens the initial electric field and suppressed the avalanche process. The negative feedback has a local nature due to very low tangential conductivity of the resistive layer. Self stabilization of the avalanche process is responsible for gently sloping current voltage characteristics and allows producing multielement structures with small dispersion of multiplication factors of individual cells fed by a common voltage supply Feb 20, 2004 V.Saveliev 7
Detection Efficiency and Dark Rate of MRS_APD (Single photon detection) Detection Efficiency or Probability of Detection is product of the Geometry Efficiency ( technology ) Quantum Efficiency ( wave dependent ) Probability that the photoelectron will trigger an avalanche (bias voltage dependent) Dark Rate (Background Signals) Probability that the bulk thermal electron will trigger an avalanche (bias voltage dependent), and amplitude is value of single photon signal. The tradeoff is between Single Photon Detection Efficiency and Dark Rate: while a large bias voltage will increase the detection efficiency, so will it increase the background rate. Feb 20, 2004 V.Saveliev 8
Detection Efficiency of Si-SSPM Geometry Efficiency technology topology gives the limitation of Geometrical Efficiency ~ 0.6 Quantum efficiency of L opz η= (1 R) (1 e α L opz ) α koefficient of absorption, α=α(λ); R - reflection coefficient The Depletion Region is ~ 5 mkm, don t necessary to use the High Resistivity Si (p-type 2 Ohmcm) Geiger Process Triggering Probability that the photoelectron will trigger an avalanche - a Reach-Through Structure has a highest triggering probability. Feb 20, 2004 V.Saveliev 9
Basic Properties of MRS-Si-SSPM Operation Principle of Microcells: Geiger Mode Operation Single Photon Detecting Mode ( Probability to get second photon in the same microcell is very small) Operation Principle of Si-SSPM: Proportional Mode for the Photon Flux Sensitive Area 1x1 mm 2, Photon Detection Efficiency ( Green range ) 34% Number of microcells ( Dynamic Range ) 2x10 3, Amplification Gain (4-10) x 10 5, Recovery Time (measured) 100 ns, Bias Voltage 50 V, Feb 20, 2004 V.Saveliev 10
Performance of Si-SSPM (Efficiency) Quantum Efficiency of a recent APD from HAMAMATSU Photonic Drift Area 40 µm, Gain 100 Quantum Efficiency of Si PhotoMultiplier QE x Geometry Efficiency Drift Area 5 mkm, Gain 10 6 Feb 20, 2004 V.Saveliev 11
Performance of Si-SSPM (Timing) Si-SSPM is very fast photodetector a c 1 µs 100 ns 2 mv 50 mv b 10 ns d 50 ns 20 mv 100 mv a. Signal of Si-SSPM coupling with Sc fiber, b. Dark signal (electronic gain = 40), c. Signal from gained low flux light and dark signal d. Two delay large photon flux signal ( Recovery Time definition 100 ns) Feb 20, 2004 V.Saveliev 12
Spectrum of low flux from LED Low Photons Flux Performance Dark Rate is on the level 400 khz Independent Method of Self-Calibration of the SiPM Feb 20, 2004 V.Saveliev 13
Performance of SiPM Temperature dependence of SiMP is very significant: Most significant improvement is that as in any semiconductor the thermal generation of electron-hole pairs will decrease with decreasing temperature as the probability for exitation of an electron across the band gap, As the increasing the gain, for Geiger Mode it is increasing the time response Feb 20, 2004 V.Saveliev 14
Application for Scintillation Detection (Calorimetry) Signal from cosmic triggered by external scintillation counters system Tile: Bicron BC404 50x50x5 mm3 WLS: 1/4 loops of WLS fiber Kuraray Y11 1mm diameter Feb 20, 2004 V.Saveliev 15
Application TESLA Hadron Calorimeter Si-SSPM is can detect the MIP signal without any front-end electronics up to 20 m length of connection to Readout, Si-SSPM is easy coupled with Scintillation cells directly to WLS, Volume of Si-SSPM is such small that will not affect the Hermisity Performance of Calorimeter System. Optimal design of Scintillation cells (2x2 cm) for Digital Hadron Calorimeter Sc. cell 4 SiPM module WLS Feb 20, 2004 V.Saveliev 16
Application Positron Emission Tomography (PET) Si-SSPM is very promising photodetector for PET. The size is well fit to the space structure of PET photodetector Matrices of Sc. of size 2X2 mm. Efficiency is good enough The extremely Fast timing can give the addition factor for high quality of data. Work in progress Feb 20, 2004 V.Saveliev 17
UV Enhanced and Single Photon Mode The UV radiation in the spectral region 200-400 nm gets absorbed completely in the top 2 mkm of the Si layer. To increase UV response it is therefore essential to avoid dead layer formation on the surface due to heavy dopant diffusion required for ohmic contacts. The inversion layer diodes have no dead layer and hence their UV response is much better than p-n junction type photodiodes, UV response at the particular wavelength λ can be improved by groving an SiO2 layer on the Si surface with the thickness equal to λ/4 or any odd multiple of it, where the l is type wavelength of light in the SiO 2. Since the SiO 2 does not absorb UV light, it is good AR coating as well a passivation layer. Feb 20, 2004 V.Saveliev 18
UV Enhanced and Single Photon Counting Mode Horizontal Structure of SiPM Depleted Area is significantly less (reducing the Dark Rate), Sensitive area is covered only SiO2 antireflection layer, Geometrical Efficiency could be increase. Feb 20, 2004 V.Saveliev 19
Summary The technology of SiPM exist, recent test on the beams and TESLA hadron calorimeter prototype shown stable results. Si-SSPM already well fit to the requirements of TESLA Tile Hadron Calorimeter System with high magnetic field, including possibility of calibration of tiles with MIP, Si-SSPM fits to the Positron Emission Tomography requirements, Next step of Development of the SiPM is realization of Single Photon Counting Mode and Enhance the UV sensitivity. Feb 20, 2004 V.Saveliev 20