Total Ionizing Dose Effects in 70-GHz Bandwidth Photodiodes in a SiGe Integrated Photonics Platform

Silicon waveguide (WG) integrated p-i-n germanium photodiodes (PDs) from a monolithic electronic–photonic integrated circuit technology were exposed to ionizing radiation from a 10-keV X-ray source to investigate total ionizing dose effects. Existing work on radiation effects in PDs, which is almost entirely based on normal-incidence PDs (rather than WG-integrated PDs), is reviewed to provide context and a framework for understanding the measurement results. Back-end-of-line considerations suggest the enhancement of the ionizing dose due to high- $Z$ materials near the PD. PD performance was characterized in terms of dark current, S-parameters, dc photocurrent response, and optical-to-electrical conversion frequency response, shortly before and after irradiation. No significant degradation was observed, indicating that these devices may be suitable for applications in harsh radiation environments.