Investigations On V-doped Zno By First-principles Calculations

Diluted magnetic semiconductors(DMS), which can utilize both spin and charge attributes of the electron to process and store data, are expected to have wide applications in the field of magnetics, optics, electronics, etc. As a kind of material with high doping concentration and ferromagnetism above room temperature, ZnO-based DMSs have also attracted much attention. In this paper, the geometrical structure, electronic structure, magnetic and optical properties of V-doped ZnO are investigated by the first-principles calculations based on the density functional theory.The formation energy, geometry and electronic structure for V occupying Zn site, O site and the interstitial site were calculated respectively. Results show that V dopant prefers to occupy Zn site and the Zn-rich condition is better for this doping than the O-rich condition. Pure ZnO is a kind of semiconductor with direct bandgap. With V-doping, the bandstructure is largely spin splitted near the Fermi level, leading to a high rate of spin-polarization.Calculations have been carried out in there configurations with different V concentration. The obtained results indicate that the total magnetic moment per supercell is mainly from the doped V atom and almost independent of V concentration. V dopants tend to cluster together rather than distribute themselves evenly over the lattice, and couple ferromagnetically with each other through RKKY interaction. The investigation on the intrinsic defects reveals that the O vacancy can enhance the ferromagnetism, while Zn vacancy can weaken the ferromagnetism of the systemThe optical properties of ZnO calculated in this study are in good agreement with the experimental results. Insertion of V atom leads to the change of electronic structure and optical properties. During the transition, electrons in valence band firstly transfer to the impurity level in the low energy range and then to the conduction band, inducing longer wavelength of absorbed photon, redshift of the optical absorption edge, and smaller energy band gap.