Optical characterization of ferroelectric Strontium-Bismuth-Tantalate (SBT) thin films

Strontiumbismuthtantalate (SBT) is a new kind of dielectric layer material for use in semiconductor devices. The optical layer parameters of SBT were characterized by spectroscopic ellipsometry using the well-known Cauchy model as well as the Adachi model (Phys. Rev. B 35 (1987) 74547463). A comparison of both models was performed. Furthermore, these optical data were compared with the physical and chemical behavior examined by Rutherford backscattering (RBS) and X-ray diffraction (XRD). As a result, it was possible to fit the measured spectra with both optical models. But with the Adachi model, it was possible to evaluate the optical layer parameters in a wider range than in the measured spectral range cove ring the region of the band gap. The Adachi model provides electronic layer parameters like the transition energy E0. Our investigations also include the determination of the stoichiometry dependence of the optical layer parameters.