PHOTOREFLECTANCE AND TIME-RESOLVED PHOTOREFLECTANCE IN DELTA-DOPED SUPERLATTICES

this paper we report a detailed study of photoreflectance (PR) in delt a-Si:GaAs superlattices. PR spectra yield three contributions: (1) fro m intrinsic GaAs; (2) Franz-Keldysh oscillations (FKO) due to the surf ace electric field, whose value is explained by a simple capacitor mod el; and (3) FKO attributed to the buffer/superlattice interface. We ob served the photovoltaic effect due to the probe beam in the PR arrange ment and achieved surface voltage reductions up to 30%. We also presen t a time-resolved PR technique, which allows us to discriminate these contributions in the time domain and gives us the PR characteristic de cay times. (C) 1998 American Institute of Physics.