Structural and optical properties of annealed W-dopedBaTiO3 thin films prepared by pulsed laser deposition

Abstract

Tungsten-doped barium titanate thin films have been prepared on glass and silicon substratesby laser ablation. The films were compositionally, structurally and optically characterized.Rutherford backscattering spectroscopy simulation gave the composition to beBa0.85W0.05Ti0.94O3.2 with acationic ratio (Ba+W)/Ti of 0.95. All the films without annealing were amorphous. The calculated lattice constantsthrough the diffraction patterns on the silicon substrate indicated the high probability ofthe film having a cubic symmetry. Atomic force microscopy results showed the film surfaceto be smooth with a maximum roughness of 5 nm, varied grain size distributionand average grain size of 50 nm. Through the Swanepoel envelope method, therefractive index dispersion was obtained. Maximum and minimum refractive indices of2.6 and 2.32 at 475 and 812 nm, respectively, were calculated. Analysis of thedependence of the refractive index and the dielectric constant on wavelength led to thedetermination of the high-frequency dielectric constant and the carrier density effective mass ratio(Nc/m*). The single-oscillator model proved to be adequate for describing the dispersion behaviour.Through this model, the dispersion parameter, average oscillator parameter and strengthwere determined. The optical band gap obtained on annealed sample was 3.8 eV byassuming a direct transition.