Impact of Precursor Molar Concentration on the Structural and Optical Properties of ZnO Thin Films Synthesized by Ultrasonic Spray Pyrolysis

Abstract

This study investigates the synthesis and characterization of zinc oxide (ZnO) thin films deposited on silicon substrates using the ultrasonic spray pyrolysis (USP) method at varying precursor molar concentrations (0.3 M, 0.4 M, and 0.5 M) of zinc acetate dihydrate (Zn(C₂H₃O₂)₂·2H₂O). The structural, morphological, and optical properties of the films were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) measurements. XRD results showed an improvement in crystallinity with increased precursor concentration, with the highest intensity and sharpest peaks observed in the 0.5 M sample, indicating enhanced film quality. UV-Vis measurements showed a distinct absorption edge in the UV region, characteristic of ZnO’s wide band gap. PL spectra exhibited strong near-band-edge emissions, along with defect-related emissions linked to oxygen vacancies and zinc interstitials. Higher molar concentrations correlated with reduced defect luminescence, suggesting fewer vacancies and other defects, thus improving the overall optical performance of the ZnO films. These results demonstrate that precursor molar concentration plays a critical role in determining the structural and optical quality of ZnO thin films, supporting their potential for optoelectronic applications.