The Effect of Gamma Radiation Exposure on Active Silicon Photonic Device Performance Metrics

In this paper, we test Si vertical-junction disk modulators and waveguide-integrated Ge p-i-n photodiodes (PDs) to see how the key performance metrics are affected by
⁶⁰
Co gamma radiation (total ionizing dose), a common proxy for simulating a mix of high-energy ion particle flux. It is found that reverse bias dark current increases significantly for both devices after 1-Mrad(Si) exposure. As the bandwidth of the Si disk modulator decreases by 6.5% after 1-Mrad(Si) dose, the bandwidth of the Ge p-i-n PD appears to be unaffected. The increased sensitivity of the Si disk modulator bandwidth to gamma radiation is hypothesized to be caused by a decrease in the carrier concentration of the junction with a resulting increase in the p-n junction RC time constant. The Ge p-i-n PD is relatively insensitive to the surface effects, because the absorption happens away from the SiO
₂
-Ge interface and the gamma radiation has a minimal effect on carrier mobility.