Synthesis and characterization of Ca doped ZnO thin films by sol–gel method

Abstract

ZnO thin films were synthesized using sol–gel method at 0.25 and 0.5 M molarity concentration. Moreover, the obtained thin films were Calcium-doped with 1 and 5 at% concentration. In order to investigate the structural changes in the molecular binding between ZnO and Ca, Fourier Transform Infrared spectroscopy (FTIR), Micro-Raman Spectroscopy and X-ray diffraction (XRD) were performed. The surface morphology and the chemical constituents distribution of the films were studied through Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Atomic Force Microscopy (AFM), respectively. The optical and electrical properties were studied by UV–Vis spectroscopy, Spectral ellipsometry and electrical I–V measurements. The results show that the properties of prepared ZnO thin films were strongly influenced by the molarity concentration and Ca-dopant. The band shape obtained at FTIR is a band attributable to metal oxide bonds and can be attributed to the vibrational assignment of Zn–O bond. SEM-EDX and AFM investigations reveal an enlarged surface area due to the porous nature of the thin films and confirm the presence of Ca in the ZnO matrix. The XRD and Raman analyses indicate the achievement of the high crystalline quality and confirm the wurtzite phase of the synthesized thin films. The films transmittance spectra indicate values between 81 and 93% in the 350–800 nm wavelength region. We further performed I–V characteristics, resulting that Ca has a different impact of the electrical performances.