Improved Thermoelectric Properties of Si_xGe_1−x by the “Nanoparticle-in-Alloy” Approach

We theoretically find that embedding silicide nanoparticles in Si_xGe_1-x alloys is able to considerably improve the figure of merit (ZT). We have computed the thermal conductivity as a function of the sizes of NiSi₂ and CoSi₂ nanoparticles. We find that the optimal nanoparticle diameters minimizing the composite’s thermal conductivity are 6.9 nm for NiSi₂ and 12.6 nm for CoSi₂ at room temperature. We provide validity ranges of nanoparticle volume fractions that will not reduce the thermoelectric power factor, but will considerably decrease the thermal conductivity. Embedding NiSi₂ or CoSi₂ nanoparticles in Si_xGe_1-x may lead to a 5-fold increase of figure of merit (ZT ∼ 0.5) at room temperature and 2.8 times increase (ZT ∼ 2.0) at 900 K. The proposed materials with high figures of merit are promising candidates to be used in integrated micro refrigerators in chips and thermoelectric power generation and waste heat recovery.