Analysis of phonon transport in silicon nanowires including optical phonons

Abstract

The present study identifies and investigates the dominant phonon contribution to the thermal conductivity of silicon nanowires at room temperature. We have employed the full phonon dispersion model including the heat transfer by optical phonons and have conducted a phonon band-to-band analysis in order to elucidate the energy transport mechanisms of each phonon band with a different polarization and frequency. The longitudinal acoustic phonon bands of 4 similar to 8 THz is found to mainly contribute to the thermal conductivity of silicon nanowires (approximately 60%), whose diameters range from 37 to 115 nm. Although the contribution of optical phonons to the thermal conductivity is less than 10% even at nanometer-scale diameters, optical phonons can interact with acoustic phonons and modify their contribution to the thermal conductivity, especially at high frequencies. The results obtained from this study provide detailed information on which phonons of a certain polarization and frequency are dominant heat carriers in silicon nanowires.