TRANSIENT-RESPONSE OF HIGH-SPEED P-I-N PHOTODIODES INCLUDING DIFFUSION EFFECTS

In top-illuminated, vertical p-i-n photodiodes where one or more of th e interfaces is a homojunction, significant absorption can take place outside the high-field i-region, leading to diffusion currents which c an have a significantly slower response than currents due to absorptio n in the i region. In this paper, we derive the transient response of a p-i-n photodiode (including the effects of diffusion currents) for p hotogeneration in thin p, i and n regions, for the cases of analog, im pulse and step optical inputs. An exact solution is obtained, which ma y be used to optimize the speed and responsivity of these photodiodes, and in simulation studies. Design strategies to improve the performan ce of these devices are discussed.