Synthesis and Characterization of Calcium-Doped Zinc Oxide Thin Films: Structural and Optical Properties

Calcium-doped zinc oxide (ZnO: Ca) thin films were synthesised by the chemical bath deposition (CBD) technique and investigated to determine the influence of calcium incorporation on their structural and optical properties. Zinc nitrate hexahydrate was used as the zinc precursor, diethanolamine as a complexing agent, and ammonia to adjust the alkaline bath conditions. Calcium nitrate was introduced to obtain nominal Ca concentrations of 1%, 2%, and 3%. The deposited films were characterised by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, and photoluminescence (PL). XRD analysis showed that the films retained the hexagonal wurtzite structure of ZnO. The crystallite/grain size estimated from the dominant (101) reflection decreased from 20.38 nm for undoped ZnO to 19.56, 17.76, and 18.01 nm for 1%, 2%, and 3% Ca-doped films, respectively. The optical band gap values were 3.65, 3.72, 3.79, and 3.70 eV for 0%, 1%, 2%, and 3% Ca, respectively. Photoluminescence measurements under different excitation wavelengths showed violet to near-ultraviolet emission, with a general shift toward shorter wavelengths as Ca concentration increased. The findings indicate that controlled Ca incorporation can modify crystallite size, optical band gap, and luminescence behaviour, making ZnO: Ca thin films promising for ultraviolet and blue-light optoelectronic applications.