MODELING A BACKGATED GAAS METAL-SEMICONDUCTOR-METAL PHOTODETECTOR

We use a two-dimensional, drift-diffusion calculation to illustrate th e 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 illum ination. According to these simulations, the speed of the falling side of the response is improved by the backgate, which removes photogener ated holes from the active layer, but the degree of improvement depend s 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 sh ow why this is faster than the response of the current at either the a node or the backgate, and why this advantage is practically lost when the backgate is biased.