Abstract
Silicon carbide (SiC) is a wide band gap semiconductor with many industrial applications.
Among many of its useful properties is its high thermal conductivity which makes it advanta-
geous for thermal management applications. In this paper we present ab initio calculations of
the in-plane and cross-plane thermal conductivities, in and out, of the hexagonal polytypes
of SiC: 2H, 4H and 6H. The phonon Boltzmann transport equation is solved iteratively using
as input interatomic force constants determined from density functional theory. Both in
and out decrease with increasing n in nH SiC because of additional low-lying optic phonon
branches. These optic branches are characterized by low phonon group velocites, and they
increase the phase space for phonon-phonon scattering. Also, for a given n, in is found to be
larger than out. At electron concentrations present in the experimental samples, scattering
of phonons by electrons is shown to be negligible except well below room temperature where
it can give a signi cant reduction to the lattice thermal conductivity. This work highlights
the power of ab initio approaches in giving quantitative, predictive descriptions of thermal
transport in materials. It helps explain the qualitative disagreement that exists among dif-
ferent sets of measured thermal conductivity data and inform the relative quality of samples
from which measured data is obtained.
