Low-temperature conductivity of ZnO films prepared by chemical vapor deposition

Abstract

c-axis-oriented ZnO films were prepared in O2 atmosphere by chemical vapor deposition using zinc acetylacetonate for source material. A minimum value of resistivity, 2.44 Ω cm, was obtained at a film formation temperature of 550 °C. The resistivity of the films was measured at low temperatures (87–297 K). For temperatures between 200 and 297 K band conduction included boundary scattering due to both thermionic emission and thermal-field emission at the grain-boundary barriers in the films, and the activation energy obtained ranged from 1.45 to 6.32×10−2 eV. For temperatures lower than about 200 K, the conductivity deviated from linear Arrhenius plots suggesting variable range-hopping conduction. Discussions based on assumed electron mobility and concentration lead to variable range-hopping conduction by localization of electrons in impurity levels in the intermediate concentration region. Mott’s parameters in the variable range-hopping conduction were estimated for the films.