Analysis of optical pulse’s position effect on temporal response characteristics of GaAs metal-semiconductor-metal photodetector

Photocurrents in a GaAs metal-semiconductor-metal (MSM) photodetector have been numerically modelled as a function of optical pulse’s position in a one-dimensional structure using Ambipolar transport theory and discrete Fourier transform method. The modelled results represent the carriers’ concentrations as well as the maximum value of the photocurrents that pass through the device when the optical pulse position changes on the device active region (i.e., the region between two top contacts). The simulation has been performed at low level injection of the excess carriers (i.e., photo-carriers) and with no bias voltage applied to the photodetector in equilibrium condition. The numerical simulation results show that for optical pulse position in the cathode region, the magnitude of the photocurrent is exactly the same but opposite direction of the anode region. The response of the photodetector is ‘zero’ when a pulse is positioned at the center of the active region. This important feature of the device could make it attractive for micro-scale positioning of high sensitive devices. The modelled results are qualitatively agreed with the experimentally observed behavior of the device.