Enhanced thermoelectric figure of merit in SiGe alloy nanowires by boundary and hole-phonon scattering

We report the thermoelectric characteristics of individual p-type SiGe alloy nanowires for diameters of 100 to 300 nm and temperatures between 40 to 300 K. A technique that allows for electrical and thermal characterization on the same nanowire was developed in this work. Experimental data provide evidence of the scattering of low-frequency phonons by the boundary of the nanowires. The thermal conductivities for SiGe alloy nanowires with different free carrier concentrations reveal that the long free path phonons are also scattered by hole-phonon interactions. Combined boundary and hole-phonon scattering mechanisms with alloy scattering resulted in thermal conductivities as low as 1.1 W/m-K at 300 K, which is one of the lowest measured for SiGe alloys and is comparable to that of bulk silica. The enhanced thermal properties observed in this work yielded ZT close to 0.18 at 300 K-more than a factor of 2 higher than the bulk SiGe alloy. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3647575]