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/Al_0.15Ga_0.85N wurtzite nanowire are performed. Results reveal that, for a definite axial wave number k_z 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 k_z 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.