Study of the direct-indirect band-gap transition in GaAs/AlAs short-period superlattices using photocurrent spectroscopy

Abstract
We have unambiguously shown that low-energy optical transitions generate electrons that belong either to the Γ minimum of GaAs or to the X minimum of AlAs, depending on the mean aluminum concentration, for a series of 5-nm period GaAs/AlAs superlattices. We estimate the intensity of the potential responsible for the Γ-X mixing to be on the order of 1–2 meV. For this kind of study, the photocurrent technique, which gives well-structured spectra recorded on large spectral (≂0.7 eV) and temperature (4–300 K) ranges, appears more favorable than the photoluminescence excitation spectroscopy technique.