Revealing the surface origin of green band emission from ZnO nanostructures by plasma immersion ion implantation induced quenching

Surface defect passivation for ZnO nanocombs (NCBs), random nanowires (RNWs), and aligned nanowires (ANWs) was performed through a metal plasma immersion ion implantation with low bias voltages ranging from $0\text{to}10\mathrm{kV}$ , where Ni was used as the modification ion. The depth of surface-originated green band (GB) emission is thus probed, revealing the surface origin of the GB. It is also found that the GB is closely related to oxygen gas content during growth of the nanostructures. The GB origin of NCBs and RNWs grown with higher oxygen content is shallower $(\sim 0.5\mathrm{nm})$ , which can be completely quenched with no bias applied. However, the GB origin of ANWs grown at lower oxygen content is much deeper $(\sim 7\mathrm{nm})$ with a complete quenching bias of $10\mathrm{kV}$ . Quenching of the GB can be attributed to passivation of the surface hole or electron trapping sites (oxygen vacancies) by Ni ions.