MODELING OF ULTRAFAST METAL-SEMICONDUCTOR METAL PHOTODETECTORS

We have simulated the transient response of metal-semiconductor-metal (MSM) photodetectors to an optical impulse, using a two-dimensional (2-D) drift-diffusion model that incorporates deep traps and appropriate boundary conditions. We incorporate the external circuit using a method originally developed to describe photoconductors in transmission lines. Initially a one-dimensional (1-D) simulation is used to verify our model comparing our results to previous 1-D calculations and experimental results for GaAs MSM detectors. Then a full 2-D analysis is used to predict the performance of a novel MSM wave-guide photodetector whose structure incorporates a Si-Si0.5Ge0.5 strained-layer superlattice. We show that this device can have a response as fast as 50 ps, although pulse pile-up due to slow diffusion of carriers may be a problem at high duty cycles.