Abstract

Ferroelectric oxide thin films are being widely investigated for photonics applications. BaTiO₃ is particularly attractive because of its large linear electro-optic coefficient, second-harmonic-generation (SHG) coefficient, and photorefractive effect. For efficient devices the films must be epitaxial and of controlled crystallographic orientation. It has proven difficult to use x-ray diffraction (XRD) to determine the crystallographic orientation for several reasons. In bulk BaTiO₃ the tetragonality is only 1%, leading to only a small splitting between the 00l and h00 lines. In a-axis-oriented films only the 00l lines are observed, and in c-axis, oriented films only the 00l lines are observed, and these lines may be shifted with respect to the line positions of the bulk material because of stresses or smaller tetragonality in the films.¹ Thus, the unambiguous assignment of the XRD lines to the correct orientation requires a high degree of absolute accuracy in the diffraction angles and a knowledge of the strain and tetragonality of the film.

© 1995 Optical Society of America