Phonon transport in periodic silicon nanoporous films with feature sizes greater than 100 nm

The thermal conductivities of solid silicon thin films and silicon thin films with periodic pore arrays are predicted using a Monte Carlo technique to include phonon-boundary scattering and the Boltzmann transport equation. The bulk phonon properties required as input are obtained from harmonic and anharmonic lattice dynamics calculations. The force constants required for the lattice dynamics calculations are obtained from forces calculated using density functional theory. For both solid and porous films, the in-plane thermal conductivity predictions capture the magnitudes and trends of previous experimental measurements. Because the prediction methodology treats the phonons as particles with bulk properties, the results indicate that coherent phonon modes associated with the secondary periodicity of the pores do not contribute to thermal transport in porous films with feature sizes greater than 100 nm.