Preparation of aluminum doped zinc oxide targets and RF magnetron sputter thin films with various aluminum doping concentrations

Abstract

© 2018, Prince of Songkla University. All rights reserved. In this work, aluminum doped zinc oxide (AZO) ceramic targets were prepared from ZnO powder and Al2O3 powder with varying amounts of Al2O3 doped in a range of 1-5 wt%. The mixed ZnO and Al2O3 powders were pressed at a pressure of 80 MPa into disks and sintered at 1,300 ∘C for 5 h in air. The crystal structures of the sintered targets were characterized by X-ray diffraction (XRD) technique. It was found that the XRD spectra showed a hexagonal (wurtzite) structure of ZnO for all Al2O3 doped films. However, as the amount of Al2O3 increased over 2 wt%, the gahnite (ZnAl2O4) phase could be observed in the XRD spectra. The AZO films were deposited on glass slides at room temperature and post-annealed at 500 ∘C in a vacuum for 1 h. The film structures, Al/Zn ratio between the Al and Zn atoms, and the electrical properties were characterized. It was found that an increase of Al2O3 content in the target gave a higher Al doping concentration in the film which resulted in more Al substitutions in the Zn sites which in turn resulted in an increase of carrier concentration. The crystal structure of the AZO films deposited from undoped and 1 wt% Al2O3-doped targets showed the (002) preferred orientation and drastically decreased at higher Al doping concentrations. The mobility of the charge carrier was affected by lower crystallinity due to grain boundary scattering. In addition, the excess Al in the film may play a role as impurity scattering centers. A decrease of Hall mobility resulted in increased resistivity. The minimum resistivity of 2.01x10-3 Ώ.cm could be achieved for the AZO films deposited from 1 wt% Al2O3-doped ZnO targets.