Reliability Characterization and Modelling of High Speed Ge Photodetectors

Understanding the origin and protocols to induce performance degradations of silicon photonics high speed photodetector represent a major issue for the qualification of the reliability of these devices. Using advanced characterization technics, it is shown that the dark current, the photonic current and the cut-off frequency of the photodiode can be degraded during voltage stress of 106 s, which could ultimately induce some significant device performance drift and failure. An explanation of these degradations is presented based on both electrical characterization and device modelling. The observed degradations of both dark current and responsivity can indeed be modeled by a single carrier lifetime degradation, attributed to an increase of the surface recombination rate, impacting an unexpected large contribution of carrier diffusion in the photocurrent. The results obtained with this model are experimentally confirmed by extracting the activation energy of the dark current, before and after stress. The improved physical understanding of the degradation is expected to lead to shorter test protocols for silicon photonics devices.