Optical phonons and their transformation in cylindrical wurtzite core-multishell nanowires with ternary mixed crystal effect

Abstract

The whole optical phonon spectrum of quasiconfined (CO), propagating (PR), and interface (IF) modes in wurtzite III-nitride cylindrical core-multishell nanowires (CMSNWs) is obtained based on the dielectric continuum and Loudon's uniaxial crystal models considering the ternary mixed crystal effect. A transfer matrix method calculation shows that there are six types of CO modes and one type of PR mode in a three-layered CMSNW. For any fixed component, only permitted types of CO modes exist in allowable frequency regions, while the PR modes appear only when components are almost the same in all layers, originating from anisotropic optical phonons in bulk wurtzite nitride. The whole spectrum reveals two mode transformations: one is between PR and IF modes by adjusting components in different layers; the other is continuous among five possible modes at any fixed component with connected frequency regions. The dispersion relations and corresponding electrostatic potentials of the whole optical phonon spectrum are helpful to understand the frequency-dependent electron–phonon interaction in the future. The analysis process can be extended to arbitrary nitride cylindrical CMSNWs for the modulation of optical phonon related properties.