Recently, we have demonstrated thermoelectric power factor enhancement of bulk SiGeAu composites at room temperature by thermal management with resonant level effect. In terms of the application to the thermoelectric generation from low temperature wasted heat, the thermoelectric properties in the low temperature range should be investigated. In this study, we evaluate the temperature dependences of thermoelectric properties of P- and B-doped SiGeAu samples. Accompanying the thermoelectric power factor enhancement of P-doped SiGeAu sample by thermal management with resonant level effect, ZT was higher than practically-used SiGe in the range from room temperature to 200 ºC. This study indicates that SiGeAu composites can be used for reusing low temperature wasted heat.

A 2-inch diameter Mg₂Si crystal was synthesized via the vertical gradient freeze (VGF) method in an open-tube system using pyrolytic boron nitride crucibles coated with boron nitride. Using this open-tube system, Mg evaporation was significantly prevented under Ar gas flow. Many grain boundaries were observed at the crystal cross section. A 5-mm square wafer without grain boundaries was cut out from the crystal and characterized by X-ray rocking curve (XRC) analysis, exhibiting a sharp single peak with a full width at half maximum (FWHM) of 50.4 arcsec. This indicates good crystallinity of the single crystalline area of the synthesized crystal.

We report the preliminary results of the deposition of Mg₂Si thin films using high-power impulse magnetron sputtering (HiPIMS). HiPIMS operates using deposition equipment similar to DC magnetron sputtering but with repetitive electric current pulses to achieve higher current densities, generating ionized sputtered particles. The HiPIMS method was used to deposit Mg₂Si thin films on unheated silicon and sapphire substrates using a Mg₂Si sintered target, which were subjected to SEM-EDS characterization. The peak power density was evaluated to be 0.5 kW/cm² or less, which was considered to exceed the DC sputtering regime. The film thickness was evaluated to be approximately 200 nm after 30 min of deposition. The composition ratio of Mg to Si on the film was approximately 2:1, which was close to that of the target. A crack-free surface morphology was achieved by applying a substrate bias voltage of 200 V.

We investigated the thermoelectric properties of melt-grown Mg₂Sn crystals doped with various impurities such as Al, Bi, Sb, P, In, Ag, Au, W, and Mo; a large difference in the carrier concentration was observed for each impurity. The Bi- and Sb-doped Mg₂Sn crystals showed n-type conductivity and had enough electron concentrations in the order of 10¹⁹ cm^-3 by doping, and the maximum figure of merit (ZT) of 0.35 was observed in the crystal doped with 1.5 at% of Bi at 550 K. The Ag-, P-, In-, Au-, W-, and Mo-doped materials exhibited p-type conductivity. The Ag-doped samples had sufficient hole concentrations of more than 10¹⁹ cm^-3, and the ZT reached 0.25 in the sample doped with 1.0 at% of Ag at 450 K. The P- and Sb-doped Mg₂Sn crystals became dark gray powder within 1–2 weeks, but the crystals doped with the other impurities did not. This result suggested that the oxidation resistance of Mg₂Sn crystals varied greatly depending on the type of dopant impurity.

Close-spaced evaporation (CSE) is a film deposition process that enables epitaxial growth and is scalable to large areas. Mechanical activation of the source by ball milling can extend the growth window in CSE of BaSi₂ down to 700 °C. However, the close arrangement of the powder source (BaAl₄–Ni) and the substrate might contaminate the films. This study investigated the structural and electrical properties of the BaSi₂ films grown by CSE. It is found that the CSE BaSi₂ films are not significantly contaminated by powder particles and Ni. In addition, semiconducting properties with low carrier density and high mobility are revealed by Hall effect measurement.