Optical phonons in core-shell semiconductor prism nanowires affected by the cross-section shape

Abstract

As building blocks of modern optoelectronic devices, semiconductor core-shell nanowires are usually prisms. The Raman spectra of the nanowires can vary with the cross-section shape and size. In the framework of the dielectric continuum and Loudon's uniaxial crystal models, we investigate the influence of cross-section shape on the optical phonons in prism core-shell nanowires. It is found that while the layer components decide the modes contained in the optical phonon spectra, the shape of a cross-section mainly affects the linewidth of a spectrum. Our calculations show that the electrostatic potentials of phonons have symmetry with the cross-section, while the dispersion relationships extend to bands in prism nanowires due to the cross-section's anisotropy, in contrast with the single dispersion lines in cylindrical ones. The anisotropy of optical phonons becomes apparent in the nanowires with fewer cross-section sides. Increasing the core area can narrow the dispersion bands, approaching the single lines of cylindrical nanowires as the area gets infinitely large. Reducing the gap between the layers' components can make the anisotropy of optical phonons weaker but not disappear. The theoretical results help to interpret the variation of the Raman spectra with the cross-section shape in the nanowires and related optical and electrical properties.