Effects of defects, grain size, and thickness on the optical properties of BaTiO<inf>3</inf> thin films

© 2017 Elsevier B.V. Barium titanate (BaTiO3) thin films were grown on Au/Si:B (111) substrates using an electron beam physical vapor deposition (EB-PVD) method. Investigation was made of the effects of grain size and strain on the temperature-dependent optical properties of these thin films, controlled using post-deposition annealing treatments at 400 °C and 550 °C. The structural, morphological, and optical properties of the deposited films were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and luminescence spectroscopy, respectively. The XRD and AFM analyses revealed the tetragonal crystal structure of the films. The luminescence spectra properties were attributed to recombination of the self-trapped excitons that formed localized states in the forbidden gaps (produced by impurities and oxygen vacancies), modulated by thermal treatment and the presence of oxygen. With increasing thickness, the blue and violet emission energies increased from 2.60 to 2.66 eV, and from 2.82 to 2.90 eV, respectively. This work shows that extrinsic and intrinsic defects can induce and enhance luminescence.