Evidence for an electrically conducting layer at the native zinc oxide surface
Measurement of the electrical properties of high-resistivity zinc oxide (ZnO) is strongly influenced by the sample ambient. Temperature-dependent Hall-effect measurements were performed on Li- and Cu-doped bulk crystals in both air and vacuum. Repeating the measurements under a given test ambient produced stable results. Changing the ambient systematically changed the measured results. We explain this behavior in terms of a surface conducting channel that exists in vacuum but is destroyed upon exposure to air. We proposed that the surface conducting layer is eliminated in air due to changes of the surface condition (i.e., molecular adsorption from the gas phase and/or surface reconstruction mechanisms).
Kiesel, P. ; Schmidt, O. ; Geis, A. W. ; Johnson, N. M. ; Van de Walle, C. G. . Evidence for an electrically conducting layer at the native zinc oxide surface. Nitride Seminar, Materials Dept., UCSB; 2005 February 4; Santa Barbara; CA.