Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Novel type of avalanche photodetector with Geiger mode operation
Introduction
The silicon avalanche photodetector with Geiger mode operation—silicon photomultiplier (SiPM) is a combination of microcell semiconductor structure with integrated quenching mechanizm and common electrode structure. The silicon avalanche microcells with very low noise currents are operated in the Geiger mode, in which the bias voltage is above the diode breakdown voltage. In this mode, any electron event in the sensitive area will produce a very large current flow with amplification gain of up to 106. In this case single photon counting mode can be realized, in that, single photon events can be detected from the minimum count rate allowed by the background noise count.
All microcells are identical, independent and operated in single photon counting mode. The common electrode structure and quenching mechanism based on a specially resistive material technology gives the possibility to act as proportional detector for the measurement of low intensity photon flux. The output signal is defined as sum of the Geiger mode signals of microcells triggered by initial flux of photons.
The typical density of microcells, can be produced, is 1000–5000 per mm2 and the total number of microcells on the tested photodetector with sensitive area 1 mm2 is 2000. This is define by the dynamic range of the photodetector.
The noise conditions of the SiPM is defined by dark count rate, as in Geiger mode operation a single thermally generated electron or hole can initiate an avalanche, leading to an electrical pulse that is indistinguishable from a single photon detection. This gives the main limitation of increasing the sensitive area of SiPM operated in single photon counting mode, but it is not so significant for low photon flux measurement, Nphot>5.
Section snippets
Structure of the SiPM
The structure of the silicon photomultiplier is a combination of large number of avalanche microcells on a single substrate and with common quenching mechanism (resistive layer) and common electrodes [1].
Structure of avalanche microcell
The schematic structure of avalanche microcell of SiPM is shown Fig. 1 and presents a well-known “reach through avalanche structure” [2].
A reach-through avalanche microcell is an avalanche structure n+−p−π−p+, where π represents very slight p-type doping. The n+ side is thin and it is this side
Applications: SiPM for tile Hadron calorimeter of TESLA
We have studied the possibility of a tile scintillator and a WLS fiber readout with an Si Photomultiplier, for the Tesla Hadron Tile Calorimeter [3]. The plastic scintillation tile with a wavelength shifter (WLS) readout has become widely used in modern calorimeter systems, because of the need to readout a very large number of tiles in the small space available and in conditions with a high magnetic field up to 4 T.
In order to demonstrate the feasibility of TESLA hadron calorimeter, calibration
Conclusion
The design and technology of production of novel type of Silicon avalanche photodetectors with Geiger mode operation (SiPM) exists and latest test measurements have shown stable results.
SiPM characteristics are already fit well to the requirements of the operation in the TESLA hadron sctintillation tile calorimeter system with strong magnetic field and includes the possibility of calibration with mip signal.
Novel types of the avalanche photodetectors could be interesting for applications in
Acknowledgements
This work was supported by INTAS project 00-00679.
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