X-ray photoelectron spectroscopy of ferroelectric semiconductor SbSI crystals

Abstract

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels from the (110) and (001) planes for the ferroelectric semiconductor SbSI single crystal in the temperature range 215-390 K. The excitation source was Al Kmonochromatic radiation (1486.6 eV). XPS were analysed in the energy range 0-1400 eV. Experimentally obtained energies were compared with the results of theoretical ab initio calculations of surface and bulk atoms in the paraelectric and ferroelectric phases. The structure of VB is calculated and confirmed experimentally. Large shifts (3-5 eV) in the core-level binding energies of surface atoms relative to bulk atoms have been observed. They show a dramatic dependence on the surface crystallographic plane. This is the first observation of XPS shifts of that magnitude in solids. Influence of the phase transition on VB and core levels is studied and the mechanism of the XPS shifts in SbSI crystals is discussed.