Nanostructure growth-induced defect formation and band bending at ZnO surfaces

Morphological, electrostatic, and optical techniques reveal spontaneous growth of nano-“mounds” on ZnO polar surfaces in air creating native point defects at and under the surface that increase work function locally by hundreds of meV. Nanoscale surface photovoltage spectroscopy reveals Zn vacancies with gap states whose density grows with nano-mound proximity over hundreds of nanometers. The low activation energy for ZnO nano-mound growth with oxygen indicates interstitial Zn diffusion that feeds nanostructure growth, generating deep level acceptors that increase n-type band bending and impact Schottky barrier formation.