XPS and XES emission investigations of d–p resonance in some copper chalcogenides

Abstract

Abstract Investigations of binary and ternary copper tellurides and selenides electron energy spectra are of interest because of the considerable sensitivity of their electrophysical and optical properties to the stoichiometry of these compounds. Ab initio theoretical calculations for these non-stoichiometric AI2−xBVI compounds are difficult due to the existence of 3d-electrons in copper. Thus investigations of their band structure and electron density by means of X-ray photoelectron (XPS) and X-ray emission (XES) spectroscopy are important. In this work XPS of binary Cu2Se, Cu1.84Se, Cu1.82Se, Cu2Te, Cu1.95Te, Cu1.9Te, Cu1.7Te, and ternary CuInSe2 are obtained and matched on a common binding energy scale with the corresponding XES. The results of this matching show that copper 3d-states appear to be in the center of the tellurium or selenium p-band, splitting it into two components nearly symmetrically relatively to the d-bands. The splitting value is proportional to the content of copper in all compounds and inversely proportional to the gaps in binary chalcogenides, which corresponds with the d–s, p-resonance model. Comparative analysis of the electronic structure of binary and ternary compounds raises questions about the role of indium in determining the optical properties of CuInSe2.