Surface reconstructions of ZnO cleavage faces

Abstract

A new sp 3 model of the electronic structure of ZnO is constructed and validated by comparison with bulk photoemission data. Using this model the atomic geometries ZnO cleavage faces, (1010) and (1120), are calculated. The model predicts the perpendicular displacement of O atom relative to Zn atom in the top layer to be 0.57 and 0.54 A, respectively, for the (1010) and (1120) surfaces, in reasonable agreement with the results of a low-energy electron diffraction intensity analysis for ZnO(1010). The model further predicts a surface state with energy near the top of the valence band for ZnO(1010), in correspondence with previous analyses for the (1010) surfaces of ZnS and ZnSe. An analogous calculation was performed using a next-nearest-neighbor tight-binding model of ZnO proposed by Ivanov and Pollmann. This latter model predicts no surface reconstruction and a rather different surface-state eigenvalue spectrum, in contradiction with the LEED results for ZnO(1010) and with the earlier analysis of ZnS and ZnSe. The origin of the differences between the two calculations is shown to be the inclusion of Zn 4p orbital in the sp 3 model but not in the Ivanov-Pollmann model.