Monte Carlo simulation of the fundamental photodetector response on sub-picosecond time scales

The fundamental response of transit time photodetectors with picosecond response times has been analyzed through Monte Carlo simulation of MSM photodiodes. The fundamental response was found to consist of three components: a fast initial peak due to velocity overshoot in the /spl Gamma/ valley electrons, a slow secondary steady state electron response, and a slow steady state hole response. The relative magnitude of the two electron responses was found to be extremely sensitive to the device length, the electric field, and the energy of the exciting photons, such that, for a given device length and photon energy there is an optimal electric field for which the electron transit time is minimized. The hole transit time was observed to decrease monotonically with increasing electric field, thus making it difficult to optimize the electron and hole responses simultaneously. Accounting for the hole response was found to increase the magnitude of the optimal field. The detector response was also observed to degrade significantly as the energy of the exciting photons was increased.