Displacement Damage and Ionization Effects on Waveguide-Integrated Germanium-Silicon p-i-n Photodiodes

On-chip germanium-silicon (Ge-Si) photodiodes are critical elements in advancing the inclusion of silicon photonics in integrated circuit design. Understanding their radiation tolerance is essential for use in instrumentation that is operated in harsh environments, where the benefits of photonic integrated circuits (PICs) on performance and compactness are increasingly advantageous. Effects of contact configuration and geometry on waveguide-integrated Ge-Si photodiodes under 1.8-MeV proton and 10-keV X-ray irradiation are studied. Modest operating dark current increases up to 35 nA or 4.25 dB resulting from nonradiative defect center generation and ionization-induced traps. Radiation sensitivities are compared to thermal effects on performance, supporting the relative robustness of Ge-Si photodiodes to radiation. Annealing testing is performed to evaluate interface trap stability due to total ionizing dose (TID), which is dependent on the specific design of the photodiode. The increases in photodiode noise floors are modest overall but are important to design strategies for space and accelerator environments, especially as performance requirements and circuit complexity of integrated photonic technologies increase.