Scanning tunneling spectroscopy of a two-dimensional electron gas on the surface of ZnO

Scanning tunneling microscopy and spectroscopy are employed in studies of ZnO single crystals. In particular we focus on spatially resolved tunneling spectroscopy of electron accumulation layers, produced by low-energy implantation of hydrogen ions on the oxygen (0001¯) face. These layers constitute a quantized two-dimensional electron gas system on the free surface. The tunneling current-voltage $\mathrm{}(I-V)\mathrm{}$ and $dI/dV$ vs $V$ curves acquired after implantation show structures which reflect the energy minima of the two-dimensional electronic subbands and localized surface states.