Anisotropy effects on polar optical phonons in wurtzite GaN/AlN superlattices

The dispersion of polar optical phonons in wurtzite AlN/GaN heterostructure s grown along the [0001] direction, with particular emphasis on AlN/GaN sup erlattices, has been calculated within the dielectric continuum model frame work. A detailed analysis is given for the interface and confined modes. Fe atures in the dispersion curves are evidenced which are due to the anisotro py of wurtzite crystals. The frequency range for the extraordinary phonons (interface and confined modes) strongly depends on the zone center optical phonon frequencies of bulk GaN and AlN. Moreover, the latter modes are not entirely confined inside one type of layer, but can penetrate inside the su rrounding material. Proper confinement of extraordinary phonons can, howeve r, be achieved for zero in-plane wave vector. [S0163-1829(99)10747-1].