Interface optical phonon localization in graded GaN thin films

We use the macroscopic dielectric continuum model to calculate the dispersion relation of interface localized optical-phonon modes in GaN thin films grown on 6H-SiC or sapphire substrate, considering the presence of a multilayered AlxGa1−xN interfacial region between the film and the substrate. The main influence of the number of layers n at the interface, which depends on the molar concentration x of the alloy AlxGa1−xN, is to preclude localization of interface phonons. A small change on the phonon frequencies and branch slopes is also observed.