Morphological and Optical Studies of ZnO-Silica Nanocomposite Thin Films Synthesized by Time Dependent CBD

ZnO-SiO₂ nanocomposite thin films were synthesized using a facile and cost-effective chemical bath deposition for different growth durations, under alkaline conditions on microscopic glass slides. Effect of deposition time on the morphological and optical properties were thoroughly investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), transmittance and time-resolved photoluminescence studies, etc. XRD patterns confirmed the formation of ZnO and diffused ZnO-Silica phases of hetero-structures at a particular growth time starting from the amorphous silica phase. SEM micrographs revealed an appreciable change in morphology of the particles with increasing growth time. Uniform porous films with improved surface coverage resulted on the substrate after an incubation period of 2 h. The EDX spectra confirmed that the thin films composed of ZnO and silica co-exist without any other impurities. It was observed that transmittance of the films decreased with increase in growth duration, whereas a slight variation in band gap was observed. The observed diminutive red shift in the band gap is due to a slight change in the transmission cut off edge. Laser-induced, time-resolved photoluminescence studies were conducted using pulse excitation in the nano-sec time domain. It showed an appreciable decrease in deep defect level emission at higher deposition duration, which arose due to unintentional doping in ZnO, creating a large number of native defects.