High Thermoelectric Performance in Polycrystalline GeSiSn Ternary Alloy Thin Films.

Group IV materials are promising candidates for highly reliable and human-friendly thin-film thermoelectric generators, used for micro-energy harvesting. In this study, we investigated the synthesis and thermoelectric applications of a Ge-based ternary alloy thin film, GeSiSn. The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline GeSiSn layers on an insulating substrate. The small compositions of Si and Sn in GeSiSn ( < 0.15 and < 0.05) lowered the thermal conductivity (3.1 W m K) owing to the alloy scattering of phonons, while maintaining a high carrier mobility (approximately 200 cm V s). The solid-phase diffusion of Ga and P allowed us to control the carrier concentration to the order of 10 cm for holes and 10 cm for electrons. For both p- and n-type GeSiSn, the power factor peaked at = 0.06 and = 0.02, reaching 1160 μW m K for p-type and 2040 μW m K for n-type. The resulting dimensionless figure of merits (0.12 for p-type and 0.20 for n-type) are higher than those of most environmentally friendly thermoelectric thin films. These results indicate that group IV alloys are promising candidates for high-performance, reliable thin-film thermoelectric generators.