Birefringence and electro-optic effect in epitaxial BST thin films

The birefringence and electro-optic (EO) effect of barium strontium titanate ((Ba, Sr)TiO3, BST) epitaxial films formed on strontium titanate single crystal substrates were evaluated using a new system employing transmission geometry. The BST films had a strained lattice with a large lattice parameter along the thickness direction. Small birefringence was induced in the as-deposited film by the alignment of the c-axis in the film plane. The birefringence was enhanced by application of electric field before the measurement of the EO-effect. The electric field dependence of the birefringence was a nearly parabolic without a hysteresis shape, indicating that the EO-effect of BST epitaxial film was dominantly determined by the Kerr effect to reduce the birefringence. The Kerr coefficient of the BST film was determined to be 3.44 × 10−17 m2/V2.