Cavity Engineering of Photon-Phonon Interactions in Si Nanocavities

The ever-increasing demand for faster, smaller, and energy-efficient devices has pushed the frontiers of research toward silicon photonics to meet the challenges for fabricating the next generation of computing systems. In order to design new devices at the nanoscale, it is important to understand and be able to control material properties, which may differ significantly from their bulk counterparts. Here, we demonstrate very large tunability of phonon-photon interactions in Si nanowire cavities by engineering the cavity mode at the emission wavelength. Raman scattering measurements performed to quantify these interactions reveal that the anti-Stokes to Stokes scattering ratio can vary from 0.035 to 0.405 in Si nanowires compared to a value of 0.1 for bulk Si, demonstrating tunability by over an order of magnitude. Moreover, a ratio of 0.85 was attained at a temperature of 580 K, which is the highest value ever reported for Si. Cavity modes that can be easily changed by changing the nanowire diameter, cavity geometry, or excitation wavelength provide efficient ways of tuning these interactions. Nanocavity engineering offers a new approach for tuning phonon-photon interactions in silicon and opens up new avenues of research and applications in the fields of silicon photonics, Raman lasers, telecommunication, and optical cooling.