Lattice Thermal Conductivity Reduction Due to Diffusive Boundary Scattering in Nanowires

摘要

Diffusive Boundary scattering of phonons due to rough surfaces was investigated for silicon nanowire structures. The roughness of the surface was modeled as a Gaussian distribution. The effects of surface roughness, incident phonon wavelength and angle were taken into account by employing the Bechmann-Kirchhoff (BK) surface scattering model for Electromagnetic waves. The BK model is more accurate than conventional approaches, where surface roughness (SR) are usually modeled based on experimental fitting parameters or only phonon wavelength. The SR model is implemented within a particle based Monte Carlo phonon transport simulator to calculate the thermal conductivity of different nanowire structures. The simulation results are benchmarked against experimental data. The reduction of thermal conductivity as a function of the degree of roughness and its dependence on temperature and phonon wavelength has been discussed. It is found that for a 70-nm width, 6-μm long silicon structure, using 2.3-nm SR height and 8.9-nm SR correlation length, an 89% reduction in thermal conductivity occurs at 300K. These observations can be useful in designing materials with low thermal conductivity for thermoelectric cooling purpose.