Reduction of optical crosstalk in silicon photomultipliers

The Silicon Photomultiplier (SiPM) is a novel device for low level light detection in various applications, for example scintillator- and fiber readout.1;2 The SiPM is insensitive to magnetic fields and has a high photon detection effciency. Current devices have a high optical crosstalk probability, which causes a significant increase of the excess noise factor.3 It may replace traditional Photo Multiplier Tubes (PMT) when the optical crosstalk is reduced to a lower level of below 10%. Depending on the quantity of hot electrons in the Geiger discharge approximately three to fifty secondary photons (in average three photons per 105 avalanche electrons4) with a wavelength range from 450nm to 1600nm are emitted from the excited cell in all directions.5 Some of those secondary photons cause the discharge of the neighboring cell.6;7 The different mechanism of optical crosstalk are categorized as direct and indirect crosstalk. To reduce direct crosstalk an optical barrier has to be implemented between the single micro cells.8 Thus, we have investigated different technological concepts with regard to the trench shape, the trench etching process as well as the trench fill material.