Characterization of SiPM Avalanche Triggering Probabilities

Silicon photo-multipliers (SiPMs) are detectors sensitive to single photons that are used to detect scintillation and Cherenkov light in a variety of physics and medical-imaging applications. SiPMs measure single photons by amplifying the photo-generated carriers (electrons or holes) via a Geiger-mode avalanche. The photon detection efficiency (PDE) is the combined probability that a photon is absorbed in the active volume of the device with a subsequently triggered avalanche. Absorption and avalanche triggering probabilities are correlated since the latter probability depends on where the photon is absorbed. In this article, we introduce a physics-motivated parameterization of the avalanche triggering probability that describes the PDE of a SiPM as a function of its reverse bias voltage, at different wavelengths. This parameterization is based on the fact that in p-on-n SiPMs, the induced avalanches are electron-driven in the ultraviolet (UV) range, while they become increasingly hole-driven toward the infrared range. The model has been successfully applied to characterize two Hamamatsu multi-pixel photon counters (MPPCs) and one Fondazione-Bruno-Kessler (FBK) SiPM, and it can be extended to other SiPMs. Furthermore, this model provides key insight into the electric field structure within SiPMs, which can explain the limitation of the existing devices and be used to optimize the performance of the future SiPMs.