Thermal conductivity of isotopically pure and Ge-doped Si epitaxial layers from 300 to 550 K

The thermal conductivity of epitaxial layers of Si is measured in the temperature range $300lTl550\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ 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 $\ifmmode\pm\else\textpm\fi{}5%$. Comparisons are made between epitaxial layers of isotopically pure $^{28}\mathrm{Si}$, Si with a natural isotope abundance, and Ge-doped Si. At $297\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the thermal conductivity of $^{28}\mathrm{Si}$ epitaxial films is $16\ifmmode\pm\else\textpm\fi{}5\phantom{\rule{0.2em}{0ex}}%$ 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 $1.4\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$.