Spatial variation in structural, morphological and optical properties of aluminum-doped ZnO thin films grown by 30°-incident radio frequency magnetron sputtering

The effect of discharge power and spatial variation, across a distance of 60 mm, in structural, morphological, optical, and electrical properties of aluminum-doped ZnO thin films grown by 30°-incident radio frequency (rf)-magnetron sputtering were investigated. A significant change in orientation of crystallites of films corresponding to central and near-edge regions of the samples was observed. With increase in rf power, films of both central and near-edge regions of the sample exhibited decrease of c-axis orientation perpendicular to substrate surface and the deterioration was relatively severe for the central regions. For all films, visible transmittance was more than 80%, and remained uniform spatially. The optical bandgap of the central portions was found to be higher than that of the near-edge regions of films except the 75 W film for which both portions had the same bandgap. Dark resistivity at the center of the sample was always lower than that at the edge, away from the center. The observed variation in the film properties are discussed in terms of tilt of the substrates and bombardment of the growing films by energetic particles.