Effect of thickness, annealing temperature, and molarity on the structural and optical properties of ZnO thin films grown by the SILAR method

Zinc oxide (ZnO) thin films were synthesized using the Successive Ionic Layer Adsorption and Reaction (SILAR) method to investigate the effects of film thickness, annealing temperature, and precursor molarity on their structural, morphological, and optical properties. A series of ZnO films were prepared by varying the number of SILAR cycles (25–40), annealing temperatures (200–350 °C), and molarities (0.05–0.15 M). Structural characterization via X-ray diffraction (XRD) revealed that all films exhibit a polycrystalline hexagonal wurtzite structure with (002) as the preferred orientation, and crystallinity improved with increasing thickness, temperature, and molarity. Scanning Electron Microscopy (SEM) images confirmed homogeneous surface coverage with a flower-like morphology, while Energy Dispersive X-ray Spectroscopy (EDAX) analysis showed that the Zn/O ratio increased with all three parameters. Optical properties assessed by UV–Vis spectroscopy indicated a reduction in optical band gap values from 3.65 eV to 2.83 eV, correlating with enhanced crystallinity and reduced defect densities. The results demonstrate that increasing precursor molarity has a more pronounced effect on film quality compared to thickness and annealing temperature. This study provides a comprehensive analysis of parameter-dependent growth behavior, enabling the optimization of ZnO thin films for applications in optoelectronic devices. © 2025 Elsevier B.V.