Above-barrier states in GaAs-AlGaAs superlattices studied by photoconductivity and photoreflectance

Abstract

The quasibound states at the above barrier region in AlGaAs-GaAs superlattices can be clearly observed at room temperature by photoconductivity as well as photoreflectance measurements. Concrete evidence are provided to confirm that free carrier confinement at barrier layer does exist. The barrier width dependence of the above barrier transition energies can be described quite well by the modified Messiah's calculation. The simple calculation using the constructive interference condition can only explain the transitions at lower energies, and fails with increasing transition energy.