Theoretical Study Of GaN Surface Point Defects And Diffusion

In this thesis, theoretical study of the native point defects in GaN bulk and spin surfaces have been investigated by using the first-principles based on the Density Functional Theory. All calculations are used the Castep package of Materials Studio 4.0.Firstly, the electronic structures of pure and native vacancy defects in GaN (Ga0.875N, Ga0.750N, GaN0.875 and GaN0.750) are calculated in details. The results indicate that the band of GaN broadens with decreasing Ga or N vacancy. VGa is acceptor defect and VN is donor defect. The conductivity of GaN decreases with the increasing of vacancy of N.Secondly, in periodicity boundary condition, we studied the native point defects in GaN (0001) crystal surface. The electron location function (ELF) shows that the electronic density changes at both atomic vacancies and antisites. There is an obvious absence of electronic areas where the vacancy of Ga has dangling bonds of N, which is favourable for the sdsorption of metal atoms. In contrast, at the vacancy of N, there is more electron distribution (ELF: 0.16-0.45), which is profitably available to combine electronegative atoms. The densities of states are computed to investigate the effect of Ga and N vacancy on the electronic structure, respectively. In the case of N vacancy defect, the Fermi energy shifted to the conduction band making it an n-type GaN (donor). While in the case of Ga vacancy, the Fermi energy shifted to the valence band making it an acceptor.Thirdly, by analysis the change of atom configuration in hexagonal GaN (0001) surface, caused by point defects, we concluded that vacancy defects affected little host lattice, the GaN strongly bonded with nearest-neighbor Ga on the surface to form metal binding. The results also showed that NGa defect maked surrounding N atoms spontaneously toward NGa atom, interstitial Ga instead of Ga1 atom maked the Ga1 atom relaxed to vacuum space. Finally by investigating the calculated defect formation energies, we found that interstitial Ga more easily appeared than interstitial N, under the Ga-rich condition, the GaO, GaN and VN formation are favorable, however, under the N-rich condition although the point defects of VGa and VN easily appear, the formation energies NO and GaO are lower than of VN.Meanwhile, we also calculated the vacancy defects formation energies, which lying in GaN(0001) crystal surface. The results show that no matter rich Ga or rich N, N vacancy defect formation is favorable. VN maked Ef move to conduction band, formed donor defect.Finally, the ab initio molecular dynamic simulated of the N vacancy diffusion in GaN spin surface.