First-principle calculation of electronic structure and stability in N-doped ZnO nanowires

The formation energies, band structure and density of states of the N-doped ZnO nanowires (NWs) were calculated by the first-principles method based on density functional theory. The effects of N doping content and N substitution doping position on the stability and band structure of ZnO NWs were investigated. The calculated results show that the undoped ZnO NWs are a direct band gap semiconductor with the band gap of 1.74 eV. The calculated formation energy is the lowest (i.e., 4.398 eV) at N doping content of 2.08% (in mole fraction) (i.e., one N atom dopant substituting an oxygen atom of the outmost position in the ZnO NWs). Also, the calculated formation energy is the lowest (i.e., 8.508 eV) at N doping content of 4.16% (in mole fraction) (i.e., two N atoms substituting the oxygen atoms at the outmost and core positions of the first layer in the ZnO NWs). The calculated impurity levels are 0.49 eV and 0.63 eV above the valence band maximum at different N-doping contents in the ZnO NWs, respectively. It was indicated that the ZnO NWs with a lower doping content might be easier to realize p-type doping, compared to the ZnO NWs with a higher N doping content. The calculated results can provide a theoretical reference data for the experimental studies on the growth of p-type N-doped ZnO NWs.