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 300<T<550 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 ±5%. Comparisons are made between epitaxial layers of isotopically pure ²⁸Si, Si with a natural isotope abundance, and Ge-doped Si. At 297 K, the thermal conductivity of ²⁸Si epitaxial films is 16±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 × 10¹⁹ cm^-3.