Resonant enhancement of Raman scattering by surface phonon polaritons in GaAs nanowires

Surface optical phonons are normally considered as subtle and poorly reproducible features in the Raman spectra of nanostructured semiconductors, from which little or no information about the sample can be extracted. The present study demonstrates the potential for changing this situation. For a common type of GaAs semiconductor nanowire (NW), we have shown that due to a combination of size-resonant light concentration, tapered shape and favourable scattering geometry, the surface phonon polariton (SPhP) Raman signal can be enhanced by orders of magnitude. The high signal gain enables routine detailed characterisation of the SPhP peak on an individual NW level, revealing its polarisation properties and spectral shift under variation of the dielectric environment. This detailed characterisation was conducted using very low excitation power density despite high absorption of the excitation light in the NW material. The findings provide an effective way to use SPhP Raman scattering in the characterisation of dielectric NWs and the prospect of developing novel surface sensors.