First-principles calculations of ZnO polar surfaces and N adsorption mechanism
ZnO 极性表面及其N原子吸附机理的第一性原理研究

Structural and electronic properties of clean polar ZnO surfaces are studied by using the first-principles ultra-soft pseudo-potential approach to the plane wave, based on the density functional theory. Furthermore, the relaxations, bandstructures, and densities of states for ZnO(0001) and ZnO(000 1 ) surfaces and the N adsorption for ZnO(0001) surface are studied. The calculation results reveal that the relaxation of ZnO(000 1 ) surface is stronger than that of ZnO(0001) surface, so ZnO(0001) surface has a better integrity. Compared with the ZnO bulk, the ZnO(0001) surface has a narrow bandgap, and big conductivity due to the delocalizing characters. However, the bandgap of the ZnO(000 1 ) surface widens, the empty energy levels appear near the top of bandgap due to the existence of O -2p states, and the body electrons transite easily to the surface, under the thermal excitation, and resulting in negative charges.We find that the face-centered site is the stablest adsorption position of ZnO (0001) surface, and the formation energy is lowest in the first layer when N atoms are embeded in the ZnO (0001) surface. Therefore, N atoms easily accumulate on the surface layer rather than occupy the positions in the body.