Size and shape effects in the Raman scattering by single GaN nanowires
Résumé
The work is focused on the dependence of the Raman scattering properties of single GaN nanowires on their size and aspect ratio. We found that, the Raman scattering by optical phonons of hexagonal GaN nanowires evolves with decreasing nanowire diameter. Below 100 nm diameter, strongly polarized Raman scattering is detected when in-coming and out-going light polarizations are parallel to the nanowire axis, which is interpreted in terms of optical antenna effects. Moreover, we observe additional vibrational modes between the longitudinal and transverse phonon frequencies of GaN which are not present in bulk GaN. Based on a numerical dielectric confinement model, these modes are tentatively assigned to confined and surface phonons. The results presented in this work contribute to the understanding of the optical and vibrational properties of semiconductor nanowires.