Enhanced Electro‐Optic Coefficients in Single‐Crystalline BaTiO₃ Thin Films Enabled by Domain Alignment

Abstract In silicon photonics, BaTiO₃ (BTO) emerges as a promising electro‐optic (EO) integrated material due to its excellent EO modulation capabilities. Nevertheless, the EO response of multi‐domain BTO thin films tends to be lower than that of bulk materials. BTO thin films are fabricated with strong EO responses utilizing the pulsed laser deposition technique. Considering the importance of the SrTiO₃ (STO) buffer layer, a series of epitaxial BTO thin films are deposited on STO substrates with engineered domain alignment. Given the contribution of domain variants in BTO thin films to their EO response, specific electrode patterns are designed to enhance their performance. An effective Pockels coefficient of 286 pm V⁻¹ is determined for the BTO thin film via the transmission geometry method, which surpasses recent reports. Through domain engineering in the BTO thin film, the remarkable enhancement in the EO response arising from in‐plane polarization (a‐axis) characteristics is confirmed. Simultaneously, utilizing the Second Harmonic Generation (SHG) optical probe, deep exploration into the domain dynamics within BTO thin films is conducted. These findings provide insights into the contribution of domain variants to the EO response and shed light on further developing silicon‐based heterogeneously integrated devices.