Non-Equilibrium Thermal Resistance from Phonons and Electrons Across Solid Interfaces

Understanding interfacial thermal resistance has focused on atomistic-scale phenomena such as carrier transmission functions across the interface. In this presentation, we discuss a phenomenon at micrometer scale for interfacial resistance: relaxation of non-equilibrium carriers through scattering. The widely used Landauer formalism assumes incident carriers have an equilibrium distribution, but the actual distribution can be highly non-equilibrium due to the interfacial scattering. The carriers with non-equilibrium distribution are relaxed by carrier scattering at micrometer scale and the Boltzmann’s H-theorem dictates entropy generation and thermal resistance during this relaxation process. To capture such process, we solve the Boltzmann transport equation with ab initio inputs. Our work shows two important facets of carrier non-equilibrium near interface and interfacial thermal resistance. First, we highlight significance of spectral heat flux mismatch for the interfacial thermal resistance. An example is a Si-SiGe alloy interface where the phonon dispersion is matched exactly but exhibits a substantial interfacial resistance. Second, we discuss the energy exchange between electrons and phonons in metal-insulator interfaces. We focus on how electron-phonon scattering influences the relaxation of thermal carriers near the interface as well as its impact on the entropy generation and non-equilibrium thermal resistance.