Impact of calcium doping on the properties of ZnO thin films: A structural and optical analysis

This study examines the structural, morphological, optical, and photoluminescence (PL) properties of undoped zinc oxide (ZnO) and calcium-doped zinc oxide (ZnO:Ca) thin films. We studied calcium doped zinc oxide (ZnO: Ca) thin films deposited by RF-magnetron sputtering at room temperature using Ca doped nanocrystalline powder synthesized by sol-gel method under supercritical ethanol conditions. All samples crystallized in a hexagonal wurtzite structure with an average grain size of approximately 35 nm, as determined by X-ray diffraction (XRD). The films exhibit a polycrystalline nature with a strong preferential orientation along the (002) plane. Transmission electron microscopy (TEM) analysis of the aerogel powders reveals the presence of small ZnO:Ca nanoparticles. Scanning electron microscopy (SEM) images confirm that the films are compact, adherent, and composed of densely packed hexagonal flakes and spherical grains. Atomic force microscopy (AFM) shows that the doping process induces significant modifications in the surface microstructure of the thin films. Optical characterization reveals that the incorporation of calcium enhances the transparency of the films in the visible spectral range and causes a blue shift in the optical bandgap, increasing from 3.23 eV for undoped ZnO to 3.42 eV for films with higher Ca doping concentrations. This bandgap variation is attributed to the Burstein-Moss effect. Room-temperature photoluminescence spectra display a dominant green emission, which is primarily associated with oxygen vacancy defects in the ZnO matrix. These findings demonstrate the potential of Ca-doped ZnO thin films for use in light-emitting devices, such as light-emitting diodes and displays.These findings demonstrate the potential of Ca-doped ZnO thin films for use in light-emitting devices, such as light-emitting diodes and displays.