Planar and vertical nanostructures for thermoelectric generation

The reduction of phonon propagation at the nanoscale offers the opportunity to exploit, for thermoelectric applications, materials which are abundant on Earth and technologically feasible, such as silicon, but which have a high bulk thermal conductivity. We propose two strategies for the fabrication of thermoelectric devices based on large collections of silicon nanostructures, and we report the results of thermal conductivity measurements in both cases. At first, we describe the fabrication process of a silicon nanowire thermoelectric generator based on nanowire forests. We describe also a possible solution to reduce the parasitic electrical resistance of the substrate. Then, we illustrate a strategy based on planar silicon nanofabrication techniques. Devices based on suspended nanostructures are shown, and the effect of localized phonon scattering centers on the reduction of the thermal conductivity is reported.