Surface Passivation and the Ultrafast Optical Response of Low-Temperature-Grown GaAs

Metal-semiconductor-metal photodetectors fabricated using low-temperature-grown GaAs have been passivated using AlGaAs cap layers in order to understand the influence of surface states and fields on the properties of these detectors. It has been found that passivation has little effect on the time response or persistent photoconductive tails associated with the detectors, but that responsivity and dark current can be enhanced in certain circumstances. The dependence of the temporal response on optical fluence and dc-voltage bias were observed for both passivated and unpassivated detectors.