Photocurrents in a metal-semiconductor-metal photodetector

Photocurrents in a metal-semiconductor-metal (MSM) photodetector have been analyzed in a one-dimensional structure using both time-dependent and steady-state continuity equations. Analytical solutions are presented for the carrier concentrations as well as for the currents, which form a valuable tool for the investigation of the detector behavior under various bias conditions. Applying these expressions to a GaAs device, we have studied the influence of carrier diffusion, recombination, and drift on the photocurrents as a function of the applied bias voltage. We also show that the switching time at low bias voltage is dominated by a voltage-independent diffusion time constant which is of particular interest when using the device as an optoelectronic sampling gate. On the other hand, carrier recombination is found to have minimal influence on DC characteristics and pulse response.