Epitaxial single-crystal rare-earth oxide in horizontal slot waveguide for silicon-based integrated active photonic devices

We have epitaxially grown high-quality single-crystal rare-earth oxide thin films, including Gd₂O₃ and erbium-incorporated (ErGd)₂O₃, on silicon-on-insulator substrate, and investigated their optical properties when embedded in horizontal slot waveguides. (ErGd)₂O₃ with an erbium concentration in the mid-10²¹ cm^-3 range shows well-resolved Stark-split photoluminescence emission peaks in the telecommunications band and a photoluminescence lifetime-concentration product as large as 2.67×10¹⁸ s·cm^-3 at room-temperature. Using these materials, horizontal slot waveguides with strong optical confinement in low-refractive-index rare-earth oxide layers, have been fabricated for silicon-based integrated active photonic devices. Thanks to the strong light-matter interaction, a large waveguide modal absorption of 88 dB/cm related to erbium ions is achieved, leading to a large potential optical gain. Intense emissions from the waveguides are also observed, with a radiation efficiency on the order of 10^-4. These results indicate that a combination of epitaxial rare-earth oxide thin films and horizontal slot waveguides provides a promising platform for light amplification and generation on silicon.