An interfacial complex in ZnO and its influence on charge transport

The segregation of native defects and Bi impurities to a high-angle grain boundary in ZnO is studied by first-principles calculations. It is found that the presence of Bi-Zn increases the concentration of native defects of acceptor type in the grain boundary. This leads to the formation of a Bi-Zn+V-Zn+O-i interfacial complex under O-rich conditions and exhibits a localized acceptor state. This state, which is different from that of the isolated impurity, gives the grain boundary p-type character and when embedded between n-type ZnO grains is consistent with the double Schottky barrier model for Bi-doped ZnO varistors.