X-ray-induced photoemission studies were used to determine the energy levels of core electrons in ZnO, ZnS, ZnSe, and ZnTe. The investigated energy range extends from the Fermi level to about 1200 eV below the valence band. The observed Auger transitions in these compounds are in good agreement with the measured energy levels. Some of the uncertainties in using this technique for the study of electron energy levels in semiconducting or insulating crystals were investigated and are discussed. The measured energy levels are compared with published experimental data for the respective pure elements. Comparison is also made with energy values predicted by several different types of theoretical calculations. Significant conclusions are: (i) The location of the Zn $3d$ level in the zinc chalcogenides has been unambiguously determined and (ii) the discrepancy between our measured values and the theoretically determined energy values is angular momentum dependent.

• Received 11 May 1970

DOI:https://doi.org/10.1103/PhysRevB.2.4885