The schematic of the surface band bending of ZnO NWs. The energy bands bend upwards as they approach the surface due to the formation of the built-in electric field near the surface, finally results in a surface depletion region and electron–hole separation. Doping of In increases the electron concentration and reduces the width of surface depletion region W, which facilitates the electrons to transport to the surface.
Duan et al. Nanoscale Research Letters 2013 8:493 doi:10.1186/1556-276X-8-493