Phonon spectrum and group velocities in wurtzite hetero-structures

We calculated acoustic phonon spectrum and group velocities in three-layered wurtzite heterostructures. The heterostructure layer thickness has been chosen on the order of the room-temperature dominant phonon wavelength so that phonon spectrum is strongly modified compared to bulk. We derived equations of motion for different phonon polarizations in the anisotropic medium approximation, which allowed us to include the specifics of the wurtzite lattice. It has also been demonstrated that the phonon group velocity in the core layer can be made higher or lower than that in the corresponding bulk material by a proper selection of the cladding material and its thickness. Obtained results add to the concept of phonon engineering by demonstrating a possibility of enhancement of phonon transport, i.e., thermal conduction, along certain direction in heterostructures with properly tuned parameters.