Molecular Dynamics Simulation of Thermal Conductivity in Bulk Silicon and Nanowires

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Abstract With the advancement of nanofabrication technologies, nanowires may be produced for both fundamental studies and practical applications. Understanding the heat conduction mechanisms in these nanodevices is important for a number of technological areas such as electronics and thermoelectrics. In this work, we investigate the thermal conductivity of silicon single crystals and silicon nanowires based on molecular dynamics (MD) simulations and the Stillinger-Weber potential. Although the simulated crystal size is much smaller than the phonon mean free path and shorter than a range of the bulk phonon wavelengths, we show that the periodic boundary conditions together with a spectral analysis lead to reasonable values of the thermal conductivity in bulk silicon. The simulated thermal conductivity of a 2.14nm × 2.14nm square cross-sectional nanowire with rigid boundaries is found to be 40 times smaller than bulk Si at 500 Kelvin. In addition to the MD simulations, the BTE is solved under the relaxation time approximation by considering various specular/diffusive scattering rates of phonons at the surfaces. Through a comparison of the nanowire thermal conductivity obtained by both methods, we quantify the surface scattering properties and give explanations to the observed discrepancies.