Effects of magnesium on phosphorus chemical states and p-type conduction behavior of phosphorus-doped ZnO films.

Effects of magnesium on phosphorus chemical states and p-type conduction behavior of phosphorus-doped ZnO (ZnO:P) films were investigated by combining experiment with first-principles calculation. Photoluminescence (PL) spectra show that Mg incorporation increases the amount of V(Zn), which makes more P(Zn)-2V(Zn) complex acceptor formed and background electron density decreased, leading to that MgZnO:P exhibits better p-type conductivity than ZnO:P. The p-type conductivity mainly arises from P(Zn)-2V(Zn) complex acceptor with a shallow acceptor energy of 108 meV. X-ray photoelectron spectroscopy (XPS) spectra reveal that phosphorus has two chemical states of P(Zn)-2V(Zn) complex and isolated P(Zn), with binding energy of P(2p3∕2) of 132.81 and 133.87 eV, respectively. The conversion of isolated P(Zn) to P(Zn)-2V(Zn) complex induced by Mg incorporation is observed in XPS, in agreement with the PL results. First-principles calculations suggest that the formation energy of nMg(Zn)-V(Zn) complex decreases with the increasing Mg content, well supporting the experiments from the PL spectra and XPS measurements.