Electronic Properties of the III-VI Layer Compounds GaS, GaSe and InSe,II: Photoemission

The valuence density of states of the III–VI layer compounds GaS, GaSe and InSe is discussed on the basis of the available ultraviolet photoelectron spectra. A new set of X-ray photoelectron spectra, measured homogeneously on the three compounds, are presented and the experimental features are interpreted on the basis of the valence band density of states, calculated by using the band structures obtained in the first paper of this series with the overlap-reduced tight-binding method. The overall similarity of the experimental spectra agrees with the theoretical findings. The dependence of less bound states on the polarization of the exciting radiation is understood on the basis of the computed energy levels. The fine structure shown by some UPS peaks is interpreted, and some experimental features are shown to depend essentially on the interaction between adjacent layers.