The distribution of phonons that carry heat in crystals has typically been studied through measurements of the thermal conductivity as a function of temperature or sample size. We find that of semiconductor alloys also depends on the frequency of the oscillating temperature field used in the measurement and hence demonstrate a novel and experimentally convenient probe of the phonon distribution. We report the frequency dependent of In₀. ₄₉Ga₀. ₅₁P, In₀. ₅₃Ga₀. ₄₇As, and Si₀. ₄Ge₀. ₆ as measured by time-domain thermoreflectance over a wide range of modulation frequencies 0. 1<f<100. 3em{0ex}MHz and temperatures 88<T<3000. 3em{0ex}K. The reduction in at high frequencies is consistent with a model calculation that assumes that phonons with mean free paths larger than the thermal penetration depth do not contribute to the thermal conductivity measured in the experiments.
Koh et al. (Thu,) studied this question.