Defects studies towards more-radiation-tolerant Silicon Photomultipliers

Silicon photomultipliers (SiPMs) are single-photon sensitive large-area detectors widely used in many applications. Among them, they are used in several radiation-harsh applications, like high-energy physics and experiments in space, where they receive a significant radiation dose. The effect of ionizing and non-ionizing radiation dose on their performance is very interesting for those applications.We irradiated several Silicon Photomultipliers with protons and X-ray. We investigated the noise increment and directly compared per performance worsening on several SiPM technologies produced sat FBK (Trento, Italy). We also characterized the temperature dependence of the noise down to cryogenic levels, extracting the activation energy. We investigated in depth the defects created by protons within the microcells of the SiPMs, with emission microscopy measurements. We also investigated the effect of ionizing-energy-loss in the SiPM microcells, showing a relevant effect of charge accumulation in the dielectrics and in the trenches. Some technologies demonstrated a worse radiation tolerance with an internal modification of electric fields that increases the primary noise and afterpulsing. This have been directly confirmed with a dedicated irradiation campaign comparing SiPMs with different materials inside the deep trenches between microcells.All these considerations are useful to develop new SiPM technologies that are more radiation hard, both in terms of bulk damage and ionizing-energy-loss effects.