Effects of Silicide Inclusion Shape on Thermal Transport of Silicon-based Nanowires and Nanocomposites for Thermoelectric Applications

Efficient silicon-based thermoelectric materials compatible with the existent electronic technology would provide excellent on-chip cooling opportunities. However, the high thermal conductivity of silicon has historically limited its thermoelectric performance. Here, we demonstrate the high potential of silicon-based nanocomposites by fabricating silicon nanowires with nickel silicide nanoinclusions with a scalable and economic sintering process. Preliminary measurements of the thermal conductivity of single nanowires from 40 to 325 K show a reduction of the thermal conductivity of a factor of 4 compared to silicon nanowires of the same length. We demonstrate that this reduction is probably a due to an increased phonon scattering with the inclusions, which grow epitaxially and form rhombohedral shapes. In order to better predict the thermal conductivity with non-spherical shapes, we combine ray tracing simulations and classical transport theories to demonstrate that the thermal conductivity reduction can be maximized by using elongated inclusion shapes (i.e. triangles or T-shapes) with small neck sizes. The findings of this work expand the understanding of transport phenomena in complex nanoengineered materials and open promising optimization paths for silicon based thermoelectric materials.