Abstract
We have investigated the electronic structures of n- or p-type doped ZnO based on ab initio electronic band structure calculations. We find unipolarity in ZnO; n-type doping using Al, Ga or In species decreases the Madelung energy while p-type doping using N species increases the Madelung energy, in addition to causing substantial localization of the N states. Codoping using reactive codopants, Al, Ga or In, enhances the incorporation of N acceptors in p-type codoped ZnO. We find the delocalized states of N for p-type ZnO codoped with N and Al (Ga).