Reliability investigations of 850 nm silicon photodiodes under proton irradiation for space applications

This paper deals with the robustness of silicon photodiodes under proton irradiation for space applications. Our interest is focused on the impact on darkness current and noise equivalent power (NEP), which corresponds to the smaller optical signal detectable by photodiodes. The photodiodes studied were selected for their very small NEP (2 × 10^?14 W/Hz^1/2) and darkness current (50 pA at ?10 mV). Proton irradiations at 60, 100 and 150 MeV energies with fluences ranging from 10¹⁰ to 10¹¹ protons/cm² have been conducted. After irradiation, the darkness current and the NEP at 870 nm of photodiodes dramatically, respectively, increase of about 10,000% and 1000% requiring to estimate the critical dose which can be tolerated by the photodiode before reaching failure criteria and to accurately calculate the minimal shield thickness embedded around the system. Lifetime distributions are also computed in operating conditions using an electrical model based on the decrease of carriers lifetimes caused by formation of defects during irradiation.