Effects of High Fluence Neutron Irradiation on Silicon Photonics Ring Modulators

In this work, silicon photonic ring modulators were irradiated with 23 MeV neutrons to a maximum fluence of 4 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> n/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. Ring modulators with varying design parameters were exposed to different neutron fluxes at different temperatures. However, only the differences in pn-junction doping levels resulted in observable differences in radiation response, with higher doping concentrations leading to better performance. The most significant observation in the IV characteristics is the reduction in forward threshold voltage, which restricts the modulation voltage range in a radiation environment. In the optical domain, changes were measured in resonance wavelength, modulation efficiency, and transmission penalty. While shifts in resonance wavelength can be compensated with built-in micro-heaters, degradation in modulation efficiency and transmission penalty must be accounted for in the link power budget. At the highest tested fluences, high-doping ring modulators degraded only by approximately 1 dB, while low-doping ring modulators degraded by around 3 dB to 4 dB. Modest recovery was observed in resonance wavelength shifts when modulators were kept at 100 °C or above, but no recovery was measured in other optical parameters. The observed changes in performance indicate that high-doping ring modulators have excellent tolerance to displacement damage, meeting the requirements of next-generation high-energy physics experiments.