Phonon thermal transport in 2H, 4H and 6H silicon carbide from first principles

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 signicant 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.