Nat. Mater. https://doi.org/gfh3qg (2018)

Silicon is a popular material for constructing nanoscale optical devices, but has the drawback of not having an electro-optic Pockels effect due to its centrosymmetric crystalline structure. Now, Stefan Abel and co-workers from Switzerland, the USA and Spain have developed a fabrication process to allow materials with a large Pockels effect to be integrated with nanoscale silicon photonic devices. The team epitaxially grew single-crystalline BaTiO3 on a silicon substrate. Then, a 5- to 10-nm-thick Al2O3 layer was deposited on the BaTiO3 layer in order to bond the BaTiO3 layer and another silicon wafer covered with SiO2. Using these multilayers, optical waveguides and plasmonic phase modulators were fabricated supporting data modulation up to 50 Gbit s–1. The scientists experimentally measured that the Pockels coefficients in the structures were r42 = 923 ± 215 pm V–1 and r33 = 342 ± 93 pm V–1.