Observation of interfacial states by using photocurrent difference spectroscopy for ZnSe/GaAs heterostructures

Photocurrent-difference spectroscopy (PDS), performed by measuring the difference between photocurrent spectra with and without additional laser illuminations, was demonstrated. The change in the photocurrent spectra, ΔPC, caused by the illuminations had a probe-energy dependency in the heterostructures. The ΔPC spectra varied with the energy of the additional illuminating lights. Compared to the conventional photocurrent spectra, the measured spectra were proven to be very sensitive to the interfacial electronic states in ZnSe/GaAs (001). Unusual features related to the interface states were observed and the possible origins of those peaks are discussed. The mechanism for the change in PC spectra is explained in terms of existence of trap states where the Fermi level is pinned at the interface. The influence of trap states on the photocurrent spectra was examined with above and below ZnSe-bandgap excitations.