Narongchai Boonyopakorn, Ratthapol Rangkupan, and Tanakorn Osotchan

DOI: 10.14456/sjst-psu.2018.111

pp. 824 - 830

Abstract

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 Ω.cm could be achieved for the AZO films deposited from 1 wt%
Al₂O₃
-doped ZnO targets