Hydrogen in ZnO revisited: Bond center versus antibonding site

Current controversy on the binding sites of H+ in ZnO can be explained by first- principles calculations. Previous infrared measurements from different groups indicate different H sites, either at the bond center (BC) site with a stretch frequency omega=3611 cm(-1) or antibonding (AB) site with omega=3326 cm(-1). This was puzzling because the BC site has lower energy by 0.2 eV. Here, we show that calcium, isovalent to Zn and found only in samples with the 3326 cm(-1) mode, binds H at the AB site. Large spatial undulation of charge explains the unexpected large binding between isovalent Ca and charged H+ of 0.7 eV.