XPS studies of the Zn1-xCoxS electronic structure

Abstract

We have investigated electronic states of diluted magnetic semiconducting Zn1-xCoxS compounds, using X-ray photoelectron spectroscopy (XPS). The amount of Cox substituting Zn in the ZnS lattice was in the range 0<x<0.25. In order to evaluate the influence of Co on the electronic structure of these compounds, XPS spectra of both the core states and the valence band were analysed. We found that the addition of Co into the ZnS lattice did not affect the Zn 2p core levels but that in these alloys the S 2p doublets were split into two components, with a binding energy difference of 0.3 eV. The intensity ratio of the two S 2p components followed the changes in the Zn-Co ratio of the alloys. The binding energy of Co 2p core levels in the alloys was similar to that in CoO, indicating the similarity between the ionic strength (+2) of the Co-S and Co-O bonds. The valence band spectra revealed a significant contribution of Co 3d electrons to the density of states (DOS). The valence band DOS distribution was also calculated from theory, using a tight-binding version of the coherent potential approximation. According to the calculations, an increase in the Co content of the alloy should cause changes in the valence band DOS similar to those observed from the X-ray photoelectron spectra.