Unipolarity of ZnO with a wide-band gap and its solution using codoping method

Abstract

We have investigated the electronic structures of p- or n-type-doped ZnO based on ab initio electronic band structure calculations. We find unipolarity in ZnO; p-type doping using Li or N increases the Madelung energy while n-type doping using Al, Ga, In or F species decreases the Madelung energy. We find a very weak repulsive interaction between Li acceptors in Li-doped ZnO (ZnO : Li) with a remarkable increase in the Madelung energy, in contrast with the case of ZnO : N. For ZnO : (2Li, F), total energy calculations show that the formation of the complex with Li Zn–F O–Li Zn which occupy the nearest-neighbor sites is energetically favorable with a decrease in the Madelung energy, which produces low-resistivity p-type ZnO crystals.