Phonon mean free path spectrum and thermal conductivity for Si_(1-x)Ge_x nanowires

摘要

We reformulate the linearized phonon Boltzmann transport equation by incorporating the direction-dependent phonon-boundary scattering, and based on this equation, we study the thermal conductivity of Si_(1-x)Ge_x nanowires and derive their phonon mean free path spectrum. Due to the severe suppression of high-frequency phonons by alloy scattering, the low frequency phonons in Si_(1-x)Ge_x nanowires have a much higher contribution to the thermal conductivity than pure silicon nanowires. We also find that Si_(1-x)Ge_x nanowires possess a stronger length-dependent, weaker diameter-dependent, and weaker surface roughness-dependent thermal conductivity than silicon nanowires. These findings are potentially useful for engineering Si_(1-x)Ge_x nanowires for thermoelectric applications.