Thermal conductivity of bulk and nanoscaled Si/Ge alloys from the Kinetic Collective Model

Several hitherto unexplained features of thermal conductivity in group IV materials, such as the change in the slope as a function of sample size for pure vs. alloyed samples and the fast decay in thermal conductivity for low impurity concentration, are described in terms of a transition from a collective to kinetic regime in phonon transport. We show that thermal transport in pure bulk silicon samples is mainly collective, and that impurity/alloy and boundary scattering are responsible for the destruction of this regime with an associated strong reduction in thermal conductivity, leaving kinetic transport as the only one allowed when those resistive scattering mechanisms are dominant.