We investigate unipolarity in ZnO based on ab initio electronic band struct
ure calculations. We find that p-type doping using Li, N or As species caus
es an increase in Madelung energy, n-type doping using B, Al, Ga, In or F s
pecies gives rise to a decrease in Madelung energy. In order to solve the u
nipolarity, to fabricate p-type ZnO, we propose a codoping method using acc
eptors and reactive donors simultaneously. A codopant pair including Ga-rea
ctive donors and N-acceptors is eminently suitable for use in the codoping.
For Li-acceptors. F species is a good candidate for reactive donors. For A
s-accepters, Ga species is a preferable codopant. (C) 2001 Elsevier Science
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