Quasi-confined optical phonon modes in a free-standing GaN nanowire with ring geometry

Within the framework of the dielectric continuum model and Loudons uniaxial crystal model, the quasi-confined (QC) phonon modes and corresponding Frohlich-like Hamiltonian in GaN nanowires with ring geometry are investigated. The dispersion relations and electron-QC phonon coupling strength are calculated numerically. Results reveal that the dispersions of the QC modes are obvious only when the wave number k(z) and the azimuthal quantum number m are small. Meanwhile, the behaviors of QC modes reducing to surface optical phonon modes are observed. Moreover, the lower-order QC modes in the higher frequency region make more contributions to the electron-QC phonon coupling strengths. Furthermore, the electron-QC coupling functions sometimes can get the maximum value at certain k(z) and m, which is attributed to the "modulating" effect of the dielectric functions ratio (is an element of(z)/is an element of(t)) due to the anisotropy of the wurtzite nitride crystals. (c) 2012 Elsevier Ltd. All rights reserved.