Effect of morphology on the phonon thermal conductivity of Si, Ge, and Si/Ge core/shell nanowires

An additional factor in reducing thermal conductivity for thermoelectric applications of semiconductor nanowires is a change in morphology. In this paper, for Si, Ge and core/shell Si/Ge nanowires the effect of the volume fraction and the type of core material on thermal conductivity at 300 K is investigated by means of nonequilibrium molecular dynamics. Nanowires with experimentally observed $\langle$100$\rangle$, $\langle$110$\rangle$, $\langle$111$\rangle$ and $\langle$112$\rangle$ orientations and different cross sections were taken into account. It was found that for $\langle$112$\rangle$-oriented Si-core/Ge-shell nanowires with a core volume fraction of $\sim$30% the thermal conductivity is the lowest (5.76 W/(m $\cdot$ K)), while the thermal conductivity values for pure Si and Ge nanowires are 13.8 and 8.21 W/(m $\cdot$ K), respectively.