Modeling the effect of a buried layer in GaAs metal-semiconductor-metal photodetectors

When an undoped heterostructure layer is buried in a conventional GaAs metal-semiconductor-metal photodetector, it is intended to improve the transient response to a pulse of light by preventing carriers that are photogenerated deep in the device from reaching the electrodes. The physics behind this strategy are investigated by means of a two-dimensional, finite-difference simulation of a practical structure. It is argued that previous experimental tests are equivocal because they do not investigate fully all the circumstances that determine the benefit of a buried layer over simpler structures. The simulation suggests that, judged from the fall time of the transient response, there are additional factors to be considered. These include the nature of the active layer and whether the illumination has a dc component.