Thermoelectric Power Factor of Ultra-Narrow Silicon Nanowires

The thermoelectric performance of materials is determined by the figure of merit ZT=σS2/(κe+κl), where σ is the electrical conductivity, S is the Seebeck coefficient and κe and κl are the electronic and lattice contributions to the thermal conductivity, respectively. The interrelation between these quantities has traditionally kept ZT low, around unity. Nanomaterials have recently attracted significant attention because at the nanoscale the length scale degree of freedom offers possibilities of independent design of σ, S and κl such that high ZT values can be achieved. This was demonstrated to be the case not only for the rare-earth and/or toxic usual TE materials, but also for traditionally poor TE materials such as Si. Bulk Si has a very high κl=140W/mK which results to ZT~0.01 at 300K. Silicon nanowires (NWs), on the other hand, have demonstrated ZT~1 (Fig. 1) [1, 2], which makes Si a promising and abundant TE material candidate with well established industrial scaling processes.