Screw dislocation induced phonon transport suppression in SiGe superlattices

S Hu and HP Zhang and SY Xiong and HG Zhang and HY Wang and YZ Chen and S Volz and YX Ni, PHYSICAL REVIEW B, 100, 075432 (2019).

DOI: 10.1103/PhysRevB.100.075432

Screw dislocations are known to impede the thermal transport of homogeneous nanowires by reducing the phonon relaxation time without affecting the phonon group velocity. By using molecular dynamics simulations in this study, we show that the impact of screw dislocation on the thermal conductivity of the SiGe superlattice nanowires depends on the period length. The analysis of phonon transmission spectra and phonon mean free paths indicate that strong phonon-screw dislocation scatterings occur for phonons in the frequency range of 3-8 THz. The screw dislocations change the phonon scattering mechanisms, which is the main cause of the thermal conductivity reduction. Contrary to the case of homogeneous nanowires, a sizable decrease in the phonon group velocity is found in superlattices with screw dislocations. This phenomenon is attributed to the larger number of Si-Ge bonds in the vicinity of the interface due to the slipping of the atomic planes. In contrast to the decreased thermal conductivity, the phonon propagation in the interface region of the nanowires is enhanced by screw dislocations. Our findings provide critical insights into the understanding of dislocation-heat transfer relationship in materials, especially in heterostructures where interfaces are vital for thermal transport.

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