Numerical modeling of the effect of optical pulse position on the impulse response of a Metal-Semiconductor-Metal (MSM) photodetector (low field condition)

We present a numerical modeling of the effect of optical pulse position on the impulse response of a GaAs back-gated Metal-Semiconductor-Metal (MSM) photodetector at low bias voltages. The backside contact of the photodetector is set to the floating condition (disconnected from the external circuit). Experimentally the device response to the optical pulse is strong only when the position of the optical pulse is around the anode contact. We have used a one-dimensional time-dependent nonlinear ambipolar transport equation to model this behavior. Our numerical modeling results agree well with the reported experimental findings.