Thermal conductivity in semiconductor thin films and nanowires

Abstract

Summary form only given. In this talk we present a self-consistent model for calculating the lattice thermal conductivity in semiconductor thin films and nanowires. The model is based on the solution of the phonon Boltzmann equation. It rigorously takes into account modification of the acoustic phonon dispersion in low-dimensional structures with the lateral feature size of 10 nm - 30 nm, and change in the non-equilibrium phonon distribution due to partially diffuse scattering from rough boundaries and interfaces. It is shown that the presence, of distinctive boundaries in such structures leads to a transformation of the acoustic branches of phonon dispersion to quasi-optical branches characterized by a low group velocity and different cut-off frequencies. This transformation affects both in-plane and cross-plane thermal conduction in low-dimensional structures. In this talk we also analyze three-phonon Umklapp scattering processes in thin films and nanowires and compare them with those in bulk semiconductors. The predictions. of the thermal conductivity. values based on our model are in good agreement with available experimental data for silicon thin films and nanowires. The described changes in phonon transport in semiconductor thin films and nanowires bear important consequences for nanostructure and device simulation since neither Fourier beat theory nor Debye approximation are accurate at nanometer length scale. The observed modification of the thermal resistance of the low-dimensional structures has to be taken into account in simulation of thermal transport in deep-submicron devices since, it strongly affects the electrostatic, discharge voltage (EDS) and other reliability characteristics. The change in the acoustic phonon dispersion and group velocity may be partially responsible for the experimentally observed drop of EDS in devices based on thin-film silicon-on-insulator (SOI) wafers.