Transfer-Heterogeneous Epitaxy Enables Exceptional Electrooptic Response of BaTiO₃ Thin Films Integrated on Silicon.

Abstract

Electro-optic (EO) modulators are pivotal for silicon photonics; yet, the absence of inherent linear EO effects in silicon necessitates the heterogeneous integration of functional materials. While barium titanate (BaTiO₃, BTO) offers exceptional EO coefficients (∼1300 pm/V), direct epitaxial growth on silicon, though achievable under carefully controlled conditions, faces challenges including lattice mismatch and silicon oxidation that can limit substrate versatility and processing flexibility. Here, we introduce a "transfer-heterogeneous epitaxy" strategy that overcomes this barrier: a single-crystalline SrTiO₃ (STO) template layer is first transferred onto silicon-on-insulator (SOI) using a water-soluble, lattice-matched Sr₄Al₂O₇ sacrificial layer, followed by epitaxial growth of high-quality BTO. This approach yields BTO films with controllable domain orientations and achieves a competitive effective Pockels coefficient of 225 pm/V─7-fold higher than lithium niobate. The approach further enables direct integration on amorphous SiO₂ and other arbitrary substrates, overcoming epitaxial constraints. Our work provides a scalable route to high-performance photonic and ferroelectric devices and helps in the realization of ultra-broadband communication and post-Moore computing.