Phonon coherence in GaN/InN Superlattices

The diffusive picture of phonon transport is replaced by the so-called ballistic one at nanoscale lengths, where interfaces and boundaries play an important role. A phonon approaching an interface can be specularly (coherent) reflected or diffusively (incoherent) scattered in all directions. The wave interference effects of phonons yield phonon band gaps and modified phonon dispersion relations. These materials are known as phononic crystals and could be used as phonon sources, filters, and detectors.¹ Superlattices (SL) have been proven ideal for realizing phononic crystals. These SLs would serve as a source of coherent phonons, as long as the phonons can propagate coherently within these structures. We use molecular dynamics simulations to estimate the phonon coherence length in GaN/InN SLs of different layer thicknesses to investigate this effect. We also study the impact of such coherence on the thermal transport properties of the studied systems.
[1] Nature 503, 2013, p 209