Effects of Proton Radiation on Noise Performance in Solid-State Photomultipliers

Solid-state photomultiplier (SSPM) devices are a viable alternative to photomultiplier tubes for nuclear and space radiation detection and science instruments. Noise terms such as dark noise, cross talk, after-pulsing, and their radiation sensitivity directly affect the photodetector performance for harsh environment applications. This paper presents the results from proton radiation-hardness tests conducted for two sets of SSPMs designed and fabricated in two different commercial complementary metal oxide silicon (CMOS) processes: 0.18-μm and 0.8 μm. Following proton exposures to the SSPMs at 100 krad, 500 krad and 1 Mrad, the measured proton induced dark noise at unity gain is higher in 0.18-μm SSPMs, but the dark current in Geiger mode is higher in 0.8 μm devices. The results and analysis suggest a higher proton-induced surface/sidewall dark current than bulk dark current in 0.18-μm samples. The proton induced bulk defect densities are similar between 0.18-μm and 0.8 μm SSPMs. Reasonable excess noise measurement results were obtained in 0.18-μm SSPM samples, and inter-pixel cross talk and after-pulsing remain statistically unchanged after proton exposure. The radiation insensitivity of after-pulsing noise suggests that shallow trap density responsible for after-pulsing is not significantly affected by proton irradiations in these CMOS high gain photodetectors.