Spectroscopic ellipsometry study of SrBi2Ta2O9 ferroelectric thin films

Optical properties of SrBi2Ta2O9 (SBT) ferroelectric thin films were invest igated by spectroscopic ellipsometry at room temperature in the 1.5-5.5 eV spectral range. The films were grown on platinized silicon (Pt/Ti/SiO2/Si) with a Bi/Sr ratio (x) range from 1.2 to 2.8 by pulsed-laser deposition. Th e measured pseudodielectric functions of the samples indicate the band-gap energy of SBT shifts to lower energies as x increases. The optical constant s and band-gap energies of the SBT films were determined through multilayer analyses on their pseudodielectric functions. The band-gap energy of SBT i s found to shift to lower energies quite linearly with x. The band-gap ener gy at stoichiometric composition (x=2) is estimated to be 4.1 eV. (C) 2001 American Institute of Physics.