New insights into the role of native point defects in ZnO

Using first-principles methods based on density functional theory and pseudopotentials, we have performed a detailed study of native point defects in ZnO. Contrary to the conventional wisdom, we find that native point defects are unlikely to be the cause of the frequently observed unintentional n-type conductivity. Oxygen vacancies, which have most often been invoked as shallow donors, have high formation energies in n-type ZnO, and are actually deep donors with a very high ionization energy. Zinc interstitials are shallow donors, but have high formation energies in n-type ZnO; in addition, they are fast diffusers, and thus unlikely to be stable in n-type ZnO. Zn antisites are also shallow donors, and have even higher formation energies than zinc interstitials. They may play a role under non-equilibrium conditions such as in irradiation experiments. Zinc vacancies are deep acceptors and may act as compensating centers in n-type ZnO. Oxygen interstitials are stable in the form of electrically inactive split interstitials as well as deep acceptors at the octahedral interstitial site under n-type conditions. Our results may provide a guide to more in-depth experimental studies of point defects in ZnO and their influence on the control of doping.