Observation of the phase inversion in photoreflectance spectra from ZnSe/GaAs(001) heterostructures

Abstract

The pump photon energy dependence of photoreflectance (PR) of a ZnSe/GaAs heterostructure has been measured at 77 K. The phase inversion in the PR signal is observed for the pump photon energy when it decreases from above to below the excitonic absorption edge of ZnSe. The observation of the phase inversion in PR is explained in terms of the modulation of the built-in electric field at the interface of the ZnSe/GaAs heterojunction, not at the ZnSe surface. It provides evidence of a built-in triangular-well potential and of hole traps at the ZnSe/GaAs interface. This argument is confirmed by photoreflectance excitation spectroscopy.