Localized and Traveling Surface Phonon Polariton Modes in Triangular 4H-Silicon Carbide One-Dimensional Gratings

Surface phonon polaritons (SPhPs) are a low-loss alternative to surface plasmon polaritons with the potential for mid-infrared to terahertz nanophotonic devices including biochemical sensing, imaging, and optical logic.

In this study, the exploration of SPhP modes on 4H-SiC substrates featuring one-dimensional triangular gratings is undertaken. FTIR reflection spectrum revealed the presence of two distinct SPhP modes, each with their unique characteristics. Through a careful analysis of their group velocities determined through modeling and experiment, it was discerned that one of these modes is localized, while the other exhibits traveling behavior. Finite element calculations using COMSOL were employed to better understand the origin of these SPhP resonances. These calculations yielded results that closely matched the experimental observations.

To further enhance comprehension of SPhP modes and their behaviors within the material, Raman scattering depth scans were conducted using a confocal Raman microscopy system. The results of these scans clarify the coupling between the SPhP modes and bulk Raman modes, mediated by the material's polarization properties. In particular, it’s found that the localized modes are concentrated at the top of triangular gratings while the traveling modes are localized on the substrate within the triangular gratings. This study provides a mechanism to control the group velocity of the traveling modes by engineering the geometric parameters of triangular gratins. Moreover, these investigations revealed the presence of electron-phonon coupling in the LO modes, adding a layer of complexity to the intricate interplay of phenomena at the nanoscale.