Effect of film thickness on the structural and electrical properties of Ga-doped ZnO thin films prepared on glass and Al2O3 (0001) substrates by RF magnetron sputtering method

Thin films of Ga-doped ZnO (GZO) were prepared on glass and Al2O3 (0001) substrates by using RF magnetron sputtering at a substrate temperature of 350 °C, RF power of 175 W, and working pressure of 6 mTorr. The effect of film thickness and substrate type on the structural and electrical properties of the thin films was investigated. X-ray diffraction study showed that GZO thin films on glass substrates were grown as a polycrystalline hexagonal wurtzite phase with a c-axis preferred, out-of-plane orientation and random in-plane orientation. However, GZO thin films on Al2O3 (0001) substrates were epitaxially grown with an orientation relationship of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(0001)\left[11\overline{2} 0 \right]_{GZO}||(0001)\left[ 11\overline{2} 0 \right]_{{{Al}_2}{O_3}}$$\end{document}. The structural images from scanning electron microscopy and atomic force microscopy showed that the GZO thin films on glass substrates had a rougher surface morphology than those on Al2O3 (0001) substrates. The electrical resistivity of 1000 nm-thick GZO thin films grown on glass and Al2O3 (0001) substrates was 3.04 × 10−4 Ωcm and 1.50 × 10−4 Ωcm, respectively. It was also found that the electrical resistivity difference between the films on the two substrates decreased from 9.48 × 10−4 Ωcm to 1.45 × 10−4 Ωcm with increasing the film thickness from 100 nm to 1000 nm.