Optical and structural properties of low thickness lead zirconate titanate films on sapphire substrates prepared via sol-gel method

Lead zirconate titanate (PZT) thin films in the range of 35-90 nm were deposited on a sapphire (1000) substrate using the sol-gel preparation method by diluting a PZT solution at different levels and using dichloromethane as the solvent. The microstructure, surface morphology, and stoichiometry of the films were studied by x-ray diffraction, atomic force microscopy, and Rutherford backscattering. Very smooth films characterized by single perovskite and mixed pyrochlore/perovskite polycrystalline phases were obtained and their optical properties were studied by spectroscopic ellipsometry in the ultraviolet-visible-near-infrared region. The refractive index was evaluated by analyzing the spectroscopic ellipsometry spectra. The ellipsometric data were also used to evaluate the bandgap energy of the films. The results show that the optical parameters of the films depend on the crystalline structure and demonstrate that higher bandgaps are obtained for perovskite films as compared to pyrochlore or mixed pyrochlore/perovskite structures. Data also confirm the higher bandgap of the amorphous structure compared to the polycrystalline PZT phases.