Effect of nanostructuring on thermoelectric performance of SiGe thin films

We experimentally investigated the effect of nanostructuring on the thermoelectric performance of SiGe thin films. Nanoscale porous structures were fabricated using lithography in a top-down approach to reduce the thermal conductivity of the thin films and the thermoelectric figure of merit (ZT) was evaluated. The thermal conductivity of nanostructured SiGe thin films is up to 24% lower than that of thin film without nanostructure while the electrical conductivity is up to about 19% lower, resulting in a 4% increase in ZT value to 0.041 at RT. Since the mean free path (MFP) of phonons in SiGe is short compared to the characteristic length of the nanostructures, the effect of nanostructuring on thermoelectric performance is limited. Nanostructuring is known as a promising method to increase ZT values. However, it is only effective when the thermal phonon MFPs are comparable to the characteristic length of the nanostructure.