Significant reduction of thermal conductivity in silicon nanowires by shell doping

Reducing the thermal conductivity of silicon nanowires (SiNWs) can enhance the thermoelectric figure of merit. Applying non-equilibrium molecular dynamics simulation, we demonstrate that the thermal conductivity of SiNWs can be reduced remarkably by shell doping due to both impurity scattering and interface scattering associated with the peculiar structure of shell-doped SiNWs. In order to reveal the origin of the reduction of thermal conductivity, we perform the vibrational eigenmodes analysis and find the strong localization of phonon modes from 9.0 THz to 16.0 THz in shell-doped SiNWs. Furthermore, we evaluate the spatial distribution of localized modes and demonstrate that the strong localization of phonons in the shell-doped region suppresses thermal transport in shell-doped SiNWs greatly and is responsible for the significant reduction of thermal conductivity.