  A Full Band Monte Carlo simulator has been developed to consider phonon
transmission across interfaces that are perpendicular to the heat flux. This
solver of the Boltzmann transport equation which does not require any
assumption on the shape the phonon distribution can naturally consider all
phonon transport regimes from the diffusive to the fully ballistic regime.
Hence, this simulator is used to study single and double Si/Ge heterostructures
from the micrometer scale down to the nanometer scale i.e. in all phonon
transport regime from ballistic to fully diffusive. A methodology to estimate
the thermal conductivities and the thermal interfaces is presented.
