Effect of SSPM surface coating on light collection efficiency and optical crosstalk for scintillation detection

As part of a project to develop a complete stochastic model of the solid state photomultiplier (SSPM), we simulated the effects of a reflective layer in the non-active region which reflects photons back into the crystal for a second chance at detection. The scintillation photon collection efficiency of the proposed device is greater than that predicted by the scintillation yield and the ratio of active area. The added reflectivity also increases external optical crosstalk from hot carrier emissions and the collection efficiency for these photons was simulated to be of the same order as the scintillation photon collection efficiency. As a function of excess bias, the rate of hot carrier emissions will rise more rapidly than the photon detection efficiency (PDE), setting a practical upper limit on the applied bias. Due to spectral mismatch between detection and avalanche emission, a blue-sensitive SSPM will be largely transparent to its own emissions. The spatial dependence of externally reflected hot carrier emissions was determined to be approximately uniform.