Synthesis and characterization of doped-ZnO thin films over wide temperature range for applications as a transparent conducting material

In this study pure and Mg, Ga, Al-doped ZnO thin films were prepared using sol-gel and spin-coating methods. The effect of dopant ion substitution on structural, morphological, optical and low temperature electrical properties of thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-Visible spectroscopy, spectro fluorophotometer and two probe resistivity measurement method, respectively. The XRD result confirmed the wurtzite structure of prepared thin films without the presence of any characteristic impurity peak of Mg, Ga and Al. The average crystallite size of ZnO thin film was found to be 22.17 nm which was found to decrease to 21.13 nm, 16.06 nm and 16.03 nm when Mg2+, Ga3+ and Al3+ ions substitutes Zn2+ ions, respectively. The photoluminescence study had confirmed the presence of defect states in the prepared thin films. Furthermore, the low temperature dependent electrical study had shown that Ga-doping decreased the electrical resistivity and confirmed the presence of thermally activated and hopping type conduction mechanism up to 100 K. Thus, the ability of Ga-doping to facilitate the conduction process down up to 100 K, low activation energy of 0.23 eV and high optical transmittance in Ga and Ga-Mg doped-ZnO thin films makes it a suitable transparent and conductive material for optoelectronic devices.