XPS STUDIES OF THE ZN1-XCOXS ELECTRONIC-STRUCTURE

We have investigated electronic states of diluted magnetic semiconduct ing Zn1-xCoxS compounds, using x-ray photoelectron spectroscopy (XPS). The amount of Co substituting Zn in the ZnS lattice was in the range 0 < x < 0.25. In order to evaluate the influence of Co on the electron ic structure of these compounds, xps spectra of both the core states a nd the valence band were analysed. We found that the addition of Co in to the ZnS lattice did not affect the Zn 2p core levels but that in th ese alloys the S 2p doublets were split into two components, with a bi nding 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 significa nt 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. Accor ding to the calculations, an increase in the Co content of the alloy s hould cause changes in the valence band Dos similar to those observed from the x-ray photoelectron spectra.