Role of cross section on the stability and electronic structure of Ag-doped ZnO nanowires

Semiconductor nanowires (NWs) exhibit tunable physical properties intrinsically related to their reduced dimensionality, quantum size effect, morphology, and surface effects. By using density functional theory, we investigated the cross-sectional effect on the electronic structure of Ag-doped ZnO NWs. Three types of NWs have been considered: hexagonal cross-sectional ZnO NWs with zigzag and armchair surfaces, respectively, and triangular cross-sectional ZnO NW with zigzag surface. The results show that Ag prefers to substitute surface Zn atoms and induces typical p-type characteristic for all kinds of NWs. Moreover, single Ag doping could create a much shallower acceptor with a smaller hole effective mass in triangular ZnO NW than in the two hexagonal ZnO NWs. With the increase of Ag concentration, the p-type doping becomes much less effective overall. However, double Ag substituting in the zigzag surface of triangular ZnO NW improves the p-type properties, while substituting in the angle site seriously damage the p-type conduction. As the triangular ZnO NWs and prismatic ZnO nanoparticles have been synthesized recently, on the basis of our results, we expect that effective p-type could be achieved via incorporating Ag in triangular ZnO NWs experimentally.