Transit Time and RC Time Constant Trade-offs in MSM Photodetectors

Abstract

Abstract: The speed of response of Metal-Semiconductor-Metal (MSM) devices is determined by both the RC time constant and transit time of the optically generated carriers. A trade-off exists between these two parameters; reduction of transit time will increase the RC time constant, hence miniaturization of dimensions will not always increase speed of response. We have derived expressions which show that given the total available area, and minimum geometry allowed by the technology, what is the optimal design, both in terms of rise time and gain-bandwidth product, of the detector. This allows substantial improvement in device response with no processing penalty.