Polar oscillation and dispersion properties of quasi-confined optical phonon modes in a wurtzite GaN/AlxGa1 xN nanowire

Under the dielectric continuum model and Loudon’s uniaxial crystal model, the properties of the quasi-confined (QC) optical phonon dispersions and the electron–QC phonons coupling functions in a cylindrical wurtzite nanowire are deduced via the method of electrostatic potential expanding. Numerical computations on a GaN/Al0.15Ga0.85N wurtzite nanowire are performed. Results reveal that, for a definite axial wave number kz and a certain azimuthal quantum number m, there are infinite branches of QC modes. The frequencies of these QC modes fall into two regions, i.e. a high frequency region and a low frequency region. The dispersion of the QC modes are quite apparant only when kz and m are small. The lower-order QC modes in the higher frequency region play more important role in the electron–QC phonon interactions. Moreover, for the higher-order QC modes in the high frequency region, the electrostatic potentials ‘‘escaping’’ out of the well-layer material nearly could be ignored.