Influence of annealing temperature on structural and optical properties of sol-gel derived Ba0.9Gd0.1TiO3 thin films for optoelectronics

In this study, Ba0.9Gd0.1TiO3 (BGT) ferroelectric thin films have been fabricated on SiO2/Si and fused silica substrates using sol-gel technique. The effect of annealing temperature on the structural, surface morphology and optical properties of BGT thin films has been profoundly studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and ultraviolet-visible spectrophotometry (UV-Vis). XRD patterns verify the existence of the perovskite structure with a tetragonal phase in the films annealed at 700 °C and above. The microstrain and dislocation density are found to decrease as the annealing temperature increases indicating that the film's quality is improved. The inter-correlation between average grain size and surface roughness with the annealing temperature is extracted from the AFM results to conclude that the film morphologies are strongly dependent on annealing temperature. In addition, the transmittance spectra illustrate that all the BGT samples exhibit high transmittance in the wavelength region ranging from 400 nm to 800 nm. The optical band gap of the BGT thin films has been evaluated from the transmittance spectra and it shows a decreasing trend as the annealing temperature increases, which is mainly attributed to the quantum size effect.