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

摘要

We present a first-principles study of the cross-plane thermal conductivity k_⊥ 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 k_⊥ reconstruction from tabulated cumulative conductivity curves k_Σ;(Λ_⊥). We furthermore reveal, and explain, a distinct quasiballistic regime characterised by a fractional thickness dependence k_⊥ ～ L~(2-α) in alloys (where α is the Levy exponent) and logarithmic dependence k_⊥ ～ ln(L) in single crystals. These observations culminate in the formulation of two compact parametric forms for k_⊥(L) that can fit the first-principles curves across the entire ballistic-diffusive range within a few percent for all investigated compounds.