Elucidation of structural, morphological, optical and photoluminescence properties of single and (In, Ga) co-doped ZnO nanocrystalline thin films

Single and co-doped ZnO thin films are currently under intense investigation and development for optoelectronic applications. Here in this study, pristine, indium-doped (IZO), gallium-doped (GZO) and co-doped (IGZO) ZnO thin films were deposited on a glass substrate using radio frequency magnetron sputtering. A comparative study of all the films was carried out on the basis of their various properties. The effect of single and co-doping on the structural (X-ray diffraction (XRD) studies and Raman studies), morphological (field emission scanning electron microscopy and energy dispersive X-ray spectroscopy studies) and optical properties (ultraviolet–visible (UV–Vis) and photoluminescence (PL)) of the deposited films was investigated. X-ray photoelectron spectroscopy (XPS) characterization was employed to analyse the surface chemical composition and bonding of the deposited film. From the XRD patterns, it was found that the films were highly crystalline in nature and preferentially oriented along the (002) direction with a hexagonal wurtzite structure, consistent with Raman analysis. IGZO films displayed a dramatic improvement in the surface morphology as compared with the single dopant films due to the compensation effect of gallium and indium doping which reduced the lattice strain. The XPS analysis confirmed the presence of the oxidized dopants in each film. All thin films have shown excellent optical properties with more than 90% transmission in the visible range of light. The blue-shift of the absorption edge accompanied by the increase of the optical band gap confirmed the Burstein–Moss effect. The UV PL peak originated from the near band edge emission of crystalline ZnO, while the visible PL was associated with the radiative transition related to oxygen interstitial (Oi) defects in the ZnO structure.