Low resistivity polycrystalline ZnO:Al thin films prepared by pulsed laser deposition

Abstract

The preparation of low resistivity polycrystalline Al-doped ZnO (AZO) thin films on glass substrates by a pulsed laser deposition method is described, including a description of conditions necessary to obtain low resistivity on the order of 1×10−4 Ω cm. The resistivity of transparent conducting AZO films obtained was affected by both the target sintering conditions and the deposition conditions. A decrease in carrier concentration associated with a increase in deposition temperature is ascribed to an increase of oxygen content in the films, resulting from enhancement of oxidation on the substrate surface. An increase in Hall mobility associated with increases of either the deposition temperature or film thickness is attributed to imperfections of the ZnO lattice, as evidenced by improvement of the crystallinity such as an increase of crystallite size. It was found that the mobility is also greatly influenced by a combination of ionized impurity scattering and grain boundary scattering or dislocation scattering. In particular, carrier transport, even in AZO films with high mobility above approximately 30 cm2/V s as well as a carrier concentration on the order of 1020–1021 cm−3, was found to be affected by imperfections of the ZnO lattice.