A study on the epitaxy nature and properties of 3 wt% ga-doped epitaxial ZnO thin film on Al₂O₃ (0 0 0 1) substrates

3 wt% ga-doped ZnO (gZO) thin films were deposited on Al₂O ₃ (0 0 0 1) substrates by RF magnetron sputtering at different growth temperatures ranging from 350 to 750 °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), UVvisible spectroscopy and Hall measurements. XRD and TEM showed that the gZO thin films deposited below a growth temperature of 450 °C grew epitaxially with an orientation relationship of (0001)[ _112̄0]gZO||(0001)[112̄0]A^l2O3. However, the gZO thin films deposited above 550 °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 °C showed the lowest electrical resistivity of 1.13×10^-4Ω cm. The electrical properties of the gZO thin films also deteriorated with increasing growth temperature. UVvisible 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.