Angular dispersion of polar phonons in a hexagonal GaN–AlN superlattice

Raman spectra of a wurtzite GaN (6.3 nm)–AlN (5.1 nm) superlattice have been recorded under visible excitation. When the orientation of the phonon wavevector is varied, the angular dispersion of polar phonons from the superlattice is clearly evidenced. These experimental data are found to be in good agreement with the results of a previous calculation based on a dielectric continuum model, taking into account the strain of the two types of layers, which predicts dispersive interface and quasi-confined modes.