Preferential zinc sputtering during the growth of aluminum doped zinc oxide thin films by radio frequency magnetron sputtering

Aluminum doped ZnO is one of the main candidates to replace indium tin oxide used as a transparent conducting oxide. Despite the intensive research, the mechanism behind the poor thin-film-resistivity uniformity over the sample deposited by magnetron sputtering is not completely understood. Several independent reports correlate the mirroring of an erosion track on the substrate with energetic negative oxygen ions. However, their role on assisting the thin film growth is not known. In this work, the physical and chemical properties of aluminum doped ZnO are measured with a high spatial resolution at different thin film deposition pressures. The results show that Zn depletion by energetic negative oxygen ion re-sputtering is the main factor correlating with the resistivity and the band gap energy profiles of the deposited films.