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To effectively regulate thermal transport for the near-junction thermalmanagement of GaN electronics, it is imperative to gain an understanding of thephonon characteristics of GaN nanostructures, particularly the topologicalphonon properties connected to low-dissipation surface phonon states. In thiswork, a comprehensive study on phonon modes and topological phonon propertiesis performed from first principles in (GaN)x/(AlN)x and (AlGaN)x/(GaN)x(x=1,2,3) superlattices. Phonon modes, including the dispersion relation,density of states, and participation ratio, were calculated for six GaNsuperlattices. The participation ratio results did not reveal the localizedphonon mode. In topological phonon analyses, it is found that Weyl phonons witha Chern number of 1(-1) are present in all six GaN superlattices, consisting oftrivial (GaN) and nontrivial (AlN and AlGaN) combinations. These phonons arelocated on either side of the kz = 0 plane symmetrically in the Brillouin zone.With the increase in the number of phonon branches in superlattices, the numberof Weyl phonon points also increases from dozens to hundreds. One Weyl phononwith significant and clean surface states is selected and analyzed for each GaNsuperlattice. Among them, the Weyl phonon in (GaN)2/(AlN)2 superlattice mainlyresults from the lattice vibrations of Al and Ga atoms, while the Weyl phononsin other superlattices mainly result from the lattice vibrations of N atoms.The Weyl phonons at opposite kz planes form pairs in (GaN)2/(AlN)2, AlGaN/GaN,and (AlGaN)2/(GaN)2. Effects of strain including biaxial and uniaxial strain onWeyl phonons in GaN/AlN and AlGaN/GaN superlattices are investigated. Resultsindicate that Weyl phonons persist in large strain states, however, nomonoclinic trend is observed due to the accidental degeneracy of thesesuperlattices.

Phonon modes and topological phonon properties in (GaN)x/(AlN)x and (AlGaN)x/(GaN)x superlattices