INVESTIGATION OF OPTICAL-TRANSITIONS IN SUPERLATTICES USING PHOTOVOLTAGE SPECTRA

This paper presents the experimental set-up and the measurement proced ures of the photovoltage technique and reports a photovoltage spectros copy study of the subband structures and the optical transitions in Al As/GaAs superlattices at different temperatures ranging from 18 to 300 K. Below 100 K, the photovoltage spectra reflect the step-like distri bution of the two-dimensional state density, and a sequence of distinc t exciton transition peaks have been observed. The peaks are identifie d according to the selection rule of optical transitions and the calcu lated results. The experiments show that the photovoltage changes cons iderably with temperature. The mechanisms for the photovoltaic effect of superlattice and quantum well structures are given and the changes in photovoltage with temperature are discussed.