A study on the epitaxy nature and properties of 3 wt% Ga-doped epitaxial ZnO thin film on Al 2O 3 (0 0 0 1) substrates

Abstract

3 wt% Ga-doped ZnO (GZO) thin films were deposited on Al 2O 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), UV–visible 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 ( 0 0 0 1 ) [ 1 1 2 ¯ 0 ] G Z O ‖ ( 0 0 0 1 ) [ 1 1 2 ¯ 0 ] A l 2 O 3 . 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 −4 Ω 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.