Surface Morphology and Dielectric Properties of Stoichiometric and Off-Stoichiometric SrTiO₃ Thin Films Grown by Molecular Beam Epitaxy

Abstract

SrTiO 3 thin films are epitaxially grown on Nb-doped SrTiO 3 substrates by atomic-layer-controlled molecular beam epitaxy. It is found that the morphology and the dielectric properties of the films strongly depend on the cation composition. Atomic force microscopy images show that particle-free surfaces are obtained in stoichiometric SrTiO 3 and 15% Ti-rich films. For the stoichiometric film, in particular, atomically flat surfaces with steps and terraces are observed. The dielectric constant of the stoichiometric thin film at 25 K reaches a maximum of 1850 at the bias voltage of -1.2 V. The dielectric constant rapidly decreases to about 25% of the maximum value by the application of -1.2±5.3 V, indicating excellent tunability of the dielectric constant by the dc voltage. The saturated polarization is more than 10 µC/cm 2 .