Mg doping in wurtzite ZnO coupled with native point defects: A mechanism for enhanced n-type conductivity and photoluminescence

From first-principles calculations, we show that Mg energetically prefers to substitute Zn atoms rather than occupying interstitial octahedral or tetrahedral sites in ZnO structure. The Mg substitutions significantly reduce the formation energies of Zn/O vacancy and Zn interstitial defects, which consequently promotes the n-type conductivity and photoluminescence in ZnO. The defects form complexes with moderate binding energies, as supported by the shorter Mg-O bonds relative to Zn-O bonds. In agreement with available experimental data, Mg substitutions result in contraction along c-axis and extension along a-axis in wurtzite ZnO.