Effect of gallium doping on the structural, optical and electrical properties of zinc oxide thin films prepared by spray pyrolysis

Gallium-doped zinc oxide (GZO) thin films were deposited onto glass substrates by the spray pyrolysis technique and the effect of gallium (Ga) doping on their structural, optical and electrical properties was investigated by X-ray Diffraction (XRD), Spectrophotometry and Current–Voltage (I–V) measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c-axis orientation. Ga doping resulted in deterioration of the film's crystallinity, increase in full width at half maximum (FWHM) and reduction in the mean crystallite sizes. All GZO thin films had relatively higher average transmittances, approximately 70–85% in the visible region as compared to the undoped ZnO thin films. Introduction of Ga led to a blue shift in the optical band gap from 3.26 eV to 3.30 eV and an increase in the Urbach energy from around 67 meV to 100 meV. Ga doping induced a decrease in sheet resistance leading to a minimum electrical resistivity of 1.2 Ω cm and a maximum figure of merit of 1.02×10−4Ω−1 for the 1 at% GZO thin film, indicating its suitability for optoelectronic applications, especially transparent electrode fabrication.