Breakdown of the Selection Rule of Raman Spectra in a Single GaN Nanocolumn

Abstract

We study micro-Raman spectroscopy in free-standing single GaN nanocolumns with 0.45-2.1 μm diameters, which are synthesized by rf-plasma-assisted molecular beam epitaxy. We clearly observe the breakdown of the polarization selection rule of Raman spectra from E₂^H phonon, when the diameter of nanocolumn is thinner than four times the wavelength of incident light inside the sample. The selection rule gets recovered with increasing diameter of nanocolumn. Moreover, we observe quasi-TO phonon modes, which strongly affects the Raman spectra from the A₁(TO) and E₁(TO) phonons. [DOI: 10.1380/ejssnt.2012.321]