A study on the epitaxy nature and properties of 3 wt% Ga-doped epitaxial ZnO thin film on Al2O3 (0001) substrates

Abstract

3 wt% Ga-doped ZnO (GZO) thin films were deposited on Al2O3 (0 0 0 1) substrates by RF magnetron sputtering at different growth temperatures ranging from 350 to 750 degrees C. The crystallinity, microstructure, epitaxial nature, and optical and electrical properties of the GZO thin films were examined by X-ray diffraction (XRD), transmission-electron microscopy (TEM), UV-visible spectroscopy and Hall measurements. XRD and TEM showed that the GZO thin films deposited below a growth temperature of 450 degrees C grew epitaxially with an orientation relationship of (0 0 0 1)[1 1 (2) over bar 0](GZO)parallel to(0 0 0 1)[1 1 (2) over bar 0](Al2O3). However, the GZO thin films deposited above 550 degrees C were in polycrystalline hexagonal wurtzite phase with c-axis preferred. The crystallinity of the GZO thin films deteriorated with increasing growth temperature. The GZO thin film deposited at 350 degrees C showed the lowest electrical resistivity of 1.13 x 10(-4) Omega cm. The electrical properties of the GZO thin films also deteriorated with increasing growth temperature. UV-visible spectroscopy showed that the GZO thin films are highly transparent (from 75% to 90%) in the visible region. In addition, the band gap of the deposited thin films decreased from 3.5 to 3.2 eV with increasing growth temperature. (C) 2011 Elsevier B.V. All rights reserved.