Effects of High Fluence Particle Irradiation on Germanium-on-Silicon Photodiodes

Waveguide-Integrated germanium-on-silicon (Ge-on-Si) photodiodes (PDs) are integral components in silicon photonics (SiPh) and understanding their radiation tolerance is important for applications that intend to use SiPh in harsh radiation environments. Here we report the results of high fluence particle irradiation tests on Ge-on-Si PDs. The PD samples are irradiated using neutrons and protons, with fluences reaching up to <inline-formula> <tex-math notation="LaTeX">$\mathrm {3 \times 10^{16}~n / \text {cm} ^{2} }$ </tex-math></inline-formula> (23 MeV) and <inline-formula> <tex-math notation="LaTeX">$\mathrm {4.1 \times 10^{16}~p / \text {cm} ^{2} }$ </tex-math></inline-formula> (24 GeV), respectively. Throughout the neutron irradiation, changes in PD responsivity and dark current are monitored, while the capacitance and current-voltage-characteristics are measured during the proton irradiation test. The results reveal only minimal losses in responsivity, along with moderate increases in dark current and capacitance. These observed changes could impose limitations on applications that demand high bandwidth in extreme radiation environment. However, it is worth noting that for example high-energy physics experiments, which represent some of the most extreme radiation environments, do not necessarily require exceptionally high receiver bandwidths. Consequently, our findings demonstrate excellent radiation tolerance that fulfills the requirements of next-generation high-energy physics experiments.