2, LITEN, CEA-Grenoble, Grenoble, , France
Dopants play a very important role in engineering semiconductor materials. They can strongly influence the phonon scattering processes and thereby the thermal conductivity. We have recently shown how Boron, when substituted in place of Carbon in 3C-SiC, acts as a “super-scatterer” and exhibits resonant phonon scattering which is one to two orders of magnitude higher than Nitrogen and other defects . This opens a new path to tailor thermal conductivities where required values range from very low in thermoelectric materials to very high in power electronics applications.
While the mass difference caused by Boron and Nitrogen is the same when substituting Carbon, it is the large perturbation in the 2nd order inter-atomic force constants (IFCs) which leads to a resonance. This large IFC perturbation is the result of a small lattice distortion accompanied by a change from tetrahedral to threefold symmetry around the Boron atom. In order to understand the physics behind and the factors causing resonance in semiconductors, we explored such symmetry breaking lattice distortions with the help of a simple 1D mono-atomic linear chain. We found that small lattice distortions emanating from two or more close energy minima in potential energy surface lead to a very large IFC perturbation resulting in resonant phonon scattering. Such a behavior is characterized by a peak in the trace of imaginary part of the T matrix (which is closely related to the scattering rates) and reflection coefficient approaching unity.
Finally, we also show how a similar distortion by Boron in diamond causes an equally large IFC perturbation but does not result in resonant scattering. We demonstrate how a large value of the casual Green's function is required in addition to a large IFC perturbation.
We acknowledge support from EU Horizon 2020 grant 645776 (ALMA) –www.almabte.eu
 A. Katre, J. Carrete, B. Dongre, G. K. H. Madsen, and N. Mingo, Physical Review Letters 119, 075902 (2017).