Analysis of a conducting channel at the native zinc oxide surface
The measured electrical properties of high-resistivity zinc oxide (ZnO) bulk and epi-samples are 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 propose that the surface conducting layer is eliminated in air due to changes of the surface condition (e.g., molecular adsorption from the gas phase and/or surface reconstruction mechanisms).
Schmidt, O. ; Geis, A. W. ; Kiesel, P. ; Johnson, N. M. ; Waag, A.; Doehler, G. Analysis of a conducting channel at the native zinc oxide surface. E-MRS Spring Meeting 2005, Strasbourg; 2005 May/June 31-03; Strasbourg; France.