High-speed, zero-biased silicon-germanium photodetector

We report high-speed performance for a photodetector operating at zero bias—with zero dark current and zero DC electrical power dissipation. Photocurrent generation is achieved through phonon-assisted absorption in a silicon microring resonator embedded with silicon-germanium, resulting in a responsivity of 0.35 and 0.043 A/W at wavelengths around 1180 and 1270 nm, respectively. We measure a 3 dB bandwidth of 14 GHz, the fastest reported to date for a zero-biased ring-resonant photodetector and which represents a 7× improvement with respect to previous work. We explore the source of such improvement through TCAD simulations and conclude that the optimization of the doping profile significantly decreases the effective carrier lifetime by limiting the impact of the photogenerated carriers drifting into the outer circumference of the resonator, with a low electric field. Using experimental data, we also extract both the free carrier and the phonon-assisted silicon-germanium absorption coefficient, showing good agreement with literature data. High-speed operation at temperatures up to 150 °C is also demonstrated.