Location of theZn 3dStates in ZnO

Abstract
We have carried out uv photoemission measurements on hexagonal ZnO cleaved in vacuum. The results of this study have placed the Zn 3d core level at 7.5 ± 0.2 eV below the valence-band maximum, some 3 eV lower than predicted by Rössler's Green's-function (Korringa-Kohn-Rostoker) band calculation. This assignment is in excellent agreement with recent x-ray photoemission measurements and is shown to be consistent with the low value of the effective number of free electrons calculated from the reflectivity.