Thermoelectric Figure-of-Merit of Nanostructured Silicon with a Low Concentration of Germanium

The thermoelectric properties of nanostructured silicon (Si) with a low concentration of germanium (Ge) are investigated. A low concentration of Ge leads to a significant cost reduction of the final product since Ge is at least 100 times more expensive than Si. By using only 5 atomic {\%} Ge (Si$_{95}$Ge$_{5})$, we have achieved a thermoelectric figure-of-merit (\textit{ZT}) of 0.95, similar to the \textit{ZT} in the large grained Si$_{80}$Ge$_{20}$ alloy that is three times more expensive, and is almost four times that of the large grained bulk Si. The enhancement in the thermoelectric \textit{ZT} for the nanostructured Si$_{95}$Ge$_{5}$ is mostly due to the reduced thermal conductivity caused by phonon scattering at the increased grain boundaries and the Ge alloying effect.