Local conductance of a ZnO epifilm with a columnar-grain structure was studied by conductive-mode atomic force microscopy. The probe-ZnO junction at the grain boundary with high density edge threading dislocations behaved as a Schottky contact while the junction at the epitaxial core behaves as an ohmic contact, resulting in the non-uniformity of conductance throughout the film. The calculated Schottky barrier was 0.4eV. The point defects of doubly charged Zn vacancies accumulated at the edge threading dislocations induce local band bending of ZnO, thus contributing to the Schottky nature at the grain boundary.

Effect of Threading Dislocations on Local Contacts in Epitaxial ZnO Films. Lin, C.Y., Liu, W.R., Chang, C.S., Hsu, C.H., Hsieh, W.F., Chien, F.S.S.: Journal of the Electrochemical Society, 2010, 157[3], H268-71