Effects of stress and point defect on the physical properties of ZnO:Nd

The magnetism sources and mechanism of Nd doping and point defect are frequently controversial. To solve these controversies, ZnO supercell models with different doping modes of Nd were constructed, and the geometric structure optimization and energy calculation of the established models were calculated based on the generalized gradient approximation method of density functional theory. Calculation results indicated that the formation energy of Nd doped ZnO systems completely followed the sequence Zn15NdO16 > Zn15NdO15 > Zn14NdO16. For systems in which Nd doping and Zn vacancy coexist, a strong hybrid coupling electron exchange effect was present among the unpaired O-2p that was nearest to the Zn vacancy, the Zn-4 s orbit that was second nearest to the Zn vacancy, and the Nd-3d orbit. Therefore, the magnetism originated from the RKKY double-exchange interaction, which was based on the hole carriers in the complexus as the medium. In contrast with the Nd doping system, systems with coexisting Nd doping and O vacancy did not exhibit increased magnetism. Thus, the systems are worthless in designing and preparing dilute magnetic semiconductors. The magnetic moment of the systems with coexisting Nd doping and Zn vacancy was the largest. Thus, the systems are valuable in such design and preparation. The absorption spectra of Zn16NdiO16 and Zn15NdO16 were red shifted under the condition without stress, whereas the absorption spectrum of Zn15NdO16 with stress was blue shifted and the magnetic moment increased. The Curie temperature of Nd double-doped ZnO system was higher than room temperature when the Nd-Nd distance was the shortest.