Thermal conductivity of isotopically pure and Ge-doped Si epitaxial layers from300to550K

The thermal conductivity of epitaxial layers of Si is measured in the temperature range $300<T<550\mathrm{K}$ using time-domain thermoreflectance. The analysis of the thermoreflectance data uses the ratio of the in-phase and out-of-phase signals of the lock-in amplifier to achieve a precision of $\pm 5\%$. Comparisons are made between epitaxial layers of isotopically pure ${}^{28}\mathrm{Si}$, Si with a natural isotope abundance, and Ge-doped Si. At $297\mathrm{K}$, the thermal conductivity of ${}^{28}\mathrm{Si}$ epitaxial films is $16\pm 5\%$ larger than the thermal conductivity of natural Si. The thermal resistance created by mass-disorder scattering of phonons is in good agreement with theory for natural Si and for Ge-doped Si with a Ge concentration of $1.4\times {10}^{19}{\mathrm{cm}}^{-3}$.