Work function, electron affinity and band bending of zinc oxide surfaces

Abstract (0001)O, (1010) and (0001)Zn faces of ZnO have been prepared by Ar-ion bombardment and annealing at 700 K ((0001) and (0001)) and 825 K (1010). Work function, electron affinity and band bending have been evaluated by means of angle-resolved UPS. All quantities show time-dependent changes specific for each face. These changes are interpreted by assuming oxygen diffusion from the surface layer into near-surface bulk vacancies. This process initiates a redistribution of oxygen-derived states at the valence band maximum.