Strain engineering of electro-optic constants in ferroelectric materials

Abstract

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 PbTiO 3 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 r 13 electro-optic coefficient twice as large as the one of the commonly used LiNbO 3 electro-optic material is found here when growing PbTiO 3 on the technologicallyimportant Si substrate.

Design rules for strong electro-optic materials

“…The Pockels effect is most commonly used for optical modulation in the telecommunications industry, where LiNbO 3 (LNO), with an unclamped Pockels coefficient of r 51 = 33 pm/V 11 , is the current "gold standard" material 1,12,13 . Due to the complexity of integrating LNO [14][15][16][17] on Si, however, perovskite titanates have recently become the primary subjects of both theoretical [18][19][20][21][22] and experimental 7,17,[23][24][25][26][27][28][29][30][31][32] studies on the use of the Pockels effect in Si photonics. The main focus of these efforts has been BaTiO 3 (BTO), due to its integrability with Si (001) 27,28,33 and its very large unclamped Pockels effect (r 42 = 1300 pm/V 34 ), which can retain bulk-like values even in thin films 7 .…”

“…Recent theoretical studies of the Pockels effect in perovskite titanates [18][19][20] offer a systematic way forward. Fredrickson et al 19 explored strain engineering in BTO.…”

Designing Multifunctionality via Assembling Dissimilar Materials: Epitaxial AlN/ScN Superlattices

“…One example to test this idea is to (i) combine AlN (or GaN or InN) with ScN to form superlattices, since AlN, GaN and InN ground states are wurtzite [2,3] while ScN has been predicted to exhibit a (meta)stable layered phase in its hexagonal form [4][5][6]; and (ii) choose the control knob to be the epitaxial strain, since it is known to be an effective tool to enhance properties and generate novel phenomena [7][8][9][10][11][12][13]. For instance, epitaxial strain can turn the nominally paraelectric SrTiO 3 into a ferroelectric [8,9], as well as induce phase transitions and large piezoelectric, dielectric, elasto-optic and electro-optic responses in many systems (see, e.g., Refs.…”

“…For instance, epitaxial strain can turn the nominally paraelectric SrTiO 3 into a ferroelectric [8,9], as well as induce phase transitions and large piezoelectric, dielectric, elasto-optic and electro-optic responses in many systems (see, e.g., Refs. [7,[11][12][13]).…”

“…where (ε −1 ) ij is the inverse of the optical dielectric tensor (approximated by the electronic dielectric tensor). Two different types of EO coefficients should be distinguished [13,25,26], namely the clamped (strain-free) versus the unclamped (stress-free for σ 33 but clamped in-plane) ones.…”