Energetics and electronic structure of point defects associated with oxygen excess at a tilt boundary of ZnO

The formation energies and electronic structure of zinc vacancies and oxyge n interstitials at a tilt boundary of ZnO were investigated by a combinatio n of static lattice and first-principles molecular orbital methods. For bot h of the defect species, the formation energies were lower than those of th e bulk defects at certain sites in the grain boundary. The defects with low formation energies formed electronic states close to the top of the valenc e band. The interfacial electronic states observed experimentally in ZnO va ristors cannot be explained solely by the point defects associated with the oxygen excess: the effects of impurities should be significant for the sta tes.