First-principles Calculations for Geometrical Structures and Electronic Properties of nN-Mg codoped ZnO

We have investigated the geometrical structures, the electronic properties, and the formation energies of nN-Mg codoped ZnO in neutral state by adopting the first-principles calculations based on the density function theory (DFT). The calculated results indicate that N atoms prefer to occupy the substitution O site and Mg substitutes the Zn site of the nearest site of N, which act as an acceptor. Compared with the formation energies of various configurations in neutral state, it is found that 4N-Mg complex has the lowest formation energy using NO as dopant resource under Zn-rich condition, indicating that 4N-Mg codoping can enhance the N dopant solubility under this condition. Meanwhile, the Zn-rich condition is better for p-type doping than the O-rich condition. It demonstrates that 4N-Mg complex is in favor of achieving p-type conduction in ZnO. Simultaneously, analysis of density of states (DOS) of nN-Mg complex find that the valence band maximum (VBM) has a little raise near the Fermi energy level, indicating that the complexes are the typical p-type characteristic. However, for 4N-Mg complex, the Fermi level is located near the top of valence band. Furthermore, from the band structure and PDOS of 4N-Mg complex, it is observed that the complex produces an additional impurity band at the top of the valence band. Meanwhile, the PDOS value of 4N-Mg complex at the Fermi level is relatively large. In addition, 4N-Mg complex has much lower ionization energy of 0.167eV than that of other complexes. Therefore, better quality p-type conductivity is achieved by codoping 4N-Mg in ZnO.