Thermal Conductivity of Pure and Impure Silicon, Silicon Carbide, and Diamond

Thermal conductivity measurements on high-purity SiC and impure Si and SiC have been made over the temperature range from 3° to 300°K. These results show that the thermal conductivity K, of the highest purity SiC is intermediate between those of pure Si and pure diamond, and at 300°K is greater than that of copper. The heat transport in SiC is produced by phonons and these are scattered by other phonons, isotopes, and the crystal boundaries in the pure material. In impure SiC the phonons are also scattered by the electrically active impurities Al and N. These impurities reduce the K of SiC in much the same way that B and P impurities do in Si. The N impurities in natural diamonds also reduce their K below that of ideally pure diamond, but the effect is rather different since N is not electrically active.