High-Quality GaP Planar Coalescence over Embedded Dielectric Microstructures

We demonstrate for the first time the planar coalescence of high-quality GaP over SiO2 gratings via an entirely molecular beam epitaxy approach. This establishes a strong foundation for a GaP-on-insulator nanophotonics platform that can be coherently grown on Si and is compatible with visible and near-infrared quantum information processing. A two-stage approach combining periodic supply epitaxy for selective-area lateral epitaxial overgrowth with planar coalescence, originally developed in the GaAs system, was utilized to seamlessly encapsulate dielectric structures aligned to [010] in GaP and restore the planar (100) epitaxial surface. GaP was shown to have improved deposition selectivity and greater temperature compatibility as compared to its arsenide counterpart, as well as a superior growth morphology on par with vapor-phase epitaxy coalescence demonstrations. Further, by orienting the SiO2 gratings along the [011] direction, high-aspect-ratio voids can be embedded underneath a restored planar surface in a single regrowth step. The ability to seamlessly incorporate noncrystalline materials and laterally structure GaP without the need for damaging processes such as etching unlocks an all-epitaxial GaP-on-insulator platform for nanophotonic and quantum applications.