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

We have investigated the electronic structures of p- or n-type-doped ZnO ba sed on ab initio electronic band structure calculations. We find unipolarit y 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. W e find a very weak repulsive interaction between Li accepters in Li-doped Z nO (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 th at the formation of the complex with Li-Zn-F-O-Li-Zn which occupy the neare st-neighbor sites is energetically favorable with a decrease in the Madelun g energy, which produces low-resistivity p-type ZnO crystals. (C) 2000 Else vier Science B.V. All rights reserved.