Strain engineering of electro-optic constants in ferroelectric materials

Electro-optic effects allow control of the ow of light using electric fields, and are of utmost importance for today’s information and communication technologies, such as TV displays and fiber optics. The search for large electro-optic constants in films is essential to the miniaturization and increased efficiency of electro-optic devices. In this work, we demonstrate that strain-engineering in PbTiO3 films allows to selectively choose which electro-optic constant to improve. Unclamped electro-optic constants larger than 100 pm V−1 are predicted, either by driving the softening of an optical phonon mode at a phase transition boundary under tensile strain, or by generating the equivalent of a negative pressure via compressive strain to obtain large piezoelectric constants. In particular, a r13 electro-optic coefficient twice as large as the one of the commonly used LiNbO3 electro-optic material is found here when growing PbTiO3 on the technologicallyimportant Si substrate.