Cross-plane heat conduction in thin films with ab-initio phonon dispersions and scattering rates

We present a first-principles study of the cross-plane thermal conductivity kappa(perpendicular to) in a wide variety of semiconductor thin films. We introduce a simple suppression model that matches variance-reduced Monte Carlo simulations with ab-initio phonon dispersions and scattering rates within <= 5% even for anisotropic compounds. This, in turn, enables accurate kappa(perpendicular to) reconstruction from tabulated cumulative conductivity curves kappa(Sigma)(Lambda(perpendicular to)). We furthermore reveal, and explain, a distinct quasiballistic regime characterised by a fractional thickness dependence kappa(perpendicular to) similar to L2-alpha in alloys (where alpha is the Levy exponent) and logarithmic dependence kappa(perpendicular to) similar to ln(L) in single crystals. These observations culminate in the formulation of two compact parametric forms for kappa(perpendicular to) (L) that can fit the firstprinciples curves across the entire ballistic-diffusive range within a few percent for all investigated compounds. Published by AIP Publishing.