Heat transport in amorphous silicon: Interplay between morphology and disorder

We present a theoretical study of the thermal conductivity (κ) of amorphous silicon (a-Si) based on molecular and lattice dynamics. We find that the majority of heat carriers are quasi-stationary modes; however the small proportion (≃3%) of propagating vibrations contributes to about half of the value of κ. We show that in bulk samples the mean free path of several long-wavelength modes is on the order of microns; this value may be substantially decreased either in thin films or in systems with etched holes, resulting in a smaller thermal conductivity. Our results provide a unified explanation of several experiments and show that kinetic theory cannot be applied to describe thermal transport in a-Si at room temperature.