28Silicon-on-insulator for optically interfaced quantum emitters

The coherence of optical emitters in silicon waveguides is impaired by the coupling to the surrounding bath of 29Si nuclear spins. We eliminate this obstacle by fabricating isotopically enriched silicon-on-insulator (SOI) chips. To this end, we use molecular beam epitaxy to grow a 0.4μm thin 28Si layer with a 29Si concentration <0.006% on a 70nm thin SOI seed chip. the resulting layer reveals a high crystalline quality and has a low defect concentration, determined from secondary ion mass spectroscopy, dark field plane-view and cross-view transmission electron microscope images as well as X-ray diffraction. With its low surface roughness, measured by atomic force microscopy, the grown layer is a promising material for the integration of optically interfaced quantum emitters in low-loss nanophotonic waveguides that are free from nuclear spins.