Optomechanical Cavities Based on Epitaxial GaP on Nominally (001)-Oriented Si

Gallium Phosphide (GaP) has recently received considerable attention as a suitable material for building photonic integrated circuits due to its remarkable optical and piezoelectric properties. Usually, GaP is grown epitaxially on III–V substrates to keep its crystallinity and later transferred to silicon wafers for further processing. Here, an alternative promising route for the fabrication of optomechanical (OM) cavities on GaP epitaxially grown on nominally (001)-oriented Si is introduced by using a two-step process consisting of a low-temperature etching of GaP followed by selective etching of the underneath silicon. The low-temperature (–30 °C) during the dry-etching of GaP hinders the lateral etching rate, preserving the pattern with a deviation between the design and the pattern in the GaP layer lower than 5%, avoiding the complex process of transferring and bonding a GaP wafer to a silicon-on-insulator wafer. To demonstrate the quality and feasibility of the proposed fabrication route, suspended OM cavities are fabricated and experimentally characterized. The cavities exhibit optical quality factors between 10³ and 10⁴ at telecom wavelengths, and localized mechanical resonances ≈3.1 GHz with quality factors ≈63 when measured at room temperature. These results suggest a simple and low-cost way to build GaP-based photonic devices directly integrated on industry-standard Si(001) photonic wafers.