Structure-related optical properties of laser-deposited BaxSr1-xTiO3 thin films grown on MgO(001) substrates

Thin films of BaxSr1-xTiO3 (BST), with 0 less than or equal to x less than or equal to 1, were grown on MgO (001) substrates by off-axis laser deposition at elevated substrate temperatures. The influence of the growth temperature and the film composition on the crystalline and morphological properties (film structure, grain size and shape, surface roughness), as well as on the refractive index n (lambda = 550 nm) and the optical band gap energy, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV-vis spectral reflectometry. The dispersion of the refractive index was analyzed in terms of the parameters E-o and E-d of the single oscillator dispersion model of Wemple and DiDomenico. The films with x < 1 show epitaxial growth of close-packed columnar grains with smooth surfaces and near-bulk optical properties, whereas the packing density of pure BaTiO3 films seems to be reduced and the surface roughness is increased. A relative decrease in the sticking coefficient of the ad-molecules in the temperature range 730-840 degrees C was found for Ba0.65Sr0.35TiO3.