Crystal domain orientation control of epitaxial BaTiO3 films integrated on silicon for large electro-optic response

Abstract

BaTiO3 (BTO) is a ferroelectric material that has a large Pockels coefficient. Recently, there has been increasing interest in epitaxial BTO films integrated on silicon as a promising material platform for building electro-optic (EO) modulators. For BTO integration on Si, a SrTiO3 (STO) buffer layer was first deposited on a Si (001) substrate by molecular beam epitaxy. BTO films were then grown on this STO-buffered Si template via pulsed laser deposition at various oxygen pressures (10–50 mTorr) and substrate temperatures (600–760 °C). We found that the measured electro-optic response of the BTO films is highly dependent on their domain orientations and film thickness. By adjusting the oxygen deposition pressure and substrate temperature, we were able to grow a-oriented BTO films which are a preferred domain structure for EO modulators due to the large Pockels effect in this configuration. An effective Pockels coefficient of up to 432 pm/V was demonstrated in 500 nm thick BTO films in transmission measurements using 1550 nm light, showing the potential of BTO films for use in integrated silicon photonic devices.