Comparative Studies of Cation Doping of ZnO with Mn, Fe, and Co

MSINDO calculations were performed to elucidate the effect of doping and defects on the electronic properties of zinc oxide. The cyclic cluster Zn(48)O(48) served as a model for the bulk. Band gaps and stabilities of spin states were determined for doping with Mn, Fe, and Co. It was found that a substantial lowering of the band gap occurs for Mn and Co doping. In contrast, the Fe doping has a rather insignificant effect on the band gap. Additional defects such as oxygen vacancy, zinc interstitial, or zinc vacancy were also studied. In the case of substitution of zinc by two transition metal atoms, various spin states arise which can be classified as antiferromagnetic, ferrimagnetic, or ferromagnetic. We find that the spin state with the lowest multiplicity, antiferromagentic or ferrimagnetic, is more stable than the high-multiplicity ferromagnetic state in most considered cases, but additional zinc vacancies or mixed doping may reverse this trend.