Comparative study of the (0001) and 000(1)over-bar surfaces of ZnO

The authors compare the surface and optical properties of the Zn-polar (0001) and O-polar (0001) surfaces of bulk ZnO samples. For optical characterization, steady-state photoluminescence using a He-Cd laser was measured at 15 and 300 K. At room temperature, the (0001) surface demonstrates nearly double the near-band-edge emission intensity seen for the (0001) surface. Using scanning Kelvin probe microscopy, the authors have measured surface contact potentials of 0.39 +/- 0.05 and 0.50 +/- 0.05 V for the (0001) and (0001) surfaces, respectively. The resulting small difference in band bending for these two surfaces indicates that charge transfer between the surfaces is not a dominant stabilizing mechanism. Conductive atomic force microscopy studies show enhanced reverse-bias conduction in localized regions on the (0001) vs (0001) surface. The differences in surface conduction and band bending between the two polar surfaces can be attributed to their chemical interactions with hydrogen and water in the ambient. (c) 2006 American Institute of Physics.