High Thermoelectric Performance in Polycrystalline GeSiSn Ternary Alloy Thin Films
Shintaro Maeda, Takamitsu Ishiyama, Takeshi Nishida, Tomoki Ozawa, Noriyuki Saitoh, Noriko Yoshizawa, Takashi Suemasu, Kaoru Toko
Abstract
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, Ge1–x–ySixSny. The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline Ge1–x–ySixSny layers on an insulating substrate. The small compositions of Si and Sn in Ge1–x–ySixSny (x < 0.15 and y < 0.05) lowered the thermal conductivity (3.1 W m–1 K–1) owing to the alloy scattering of phonons, while maintaining a high carrier mobility (approximately 200 cm2 V–1 s–1). The solid-phase diffusion of Ga and P allowed us to control the carrier concentration to the order of 1019 cm–3 for holes and 1018 cm–3 for electrons. For both p- and n-type Ge1–x–ySixSny, the power factor peaked at x = 0.06 and y = 0.02, reaching 1160 μW m–1 K–2 for p-type and 2040 μW m–1 K–2 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.