Modeling a backgated GaAs metal-semiconductor-metal photodetector

We use a two-dimensional, drift-diffusion calculation to illustrate the physics behind the recently described GaAs metal-semiconductor-metal photodetector with an ohmic backgate provided by a p-doped layer. We calculate the transient response of this structure to a pulse of illumination. According to these simulations, the speed of the falling side of the response is improved by the backgate, which removes photogenerated holes from the active layer, but the degree of improvement depends on the chosen contact. The fastest fall time is found in the current at the cathode when both the cathode and backgate are grounded. We show why this is faster than the response of the current at either the anode or the backgate, and why this advantage is practically lost when the backgate is biased.