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–y Si x Sn y . The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline Ge1–x–y Si x Sn y layers on an insulating substrate. The small compositions of Si and Sn in Ge1–x–y Si x Sn y (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–y Si x Sn y , 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.

Remarkable progress has been made in germanium-based thin-film transistors in recent years. However, achieving both high field-effect mobility and a high on–off ratio is difficult because the crystallinity of polycrystalline Ge degrades as it becomes thinner. In this study, we investigated the interfacial nucleation control and grain size enlargement in the solid-phase crystallization of amorphous Ge thin films (≤50 nm). A bilayer structure consisting of top nucleation and bottom nucleation suppression layers promoted nucleation at the surface rather than at the substrate interface, resulting in a significant enlargement of the grain size. In addition, Sn doping in Ge increased the grain size to 12 μm, which was larger than that of most polycrystalline Ge thin films and contributed to the reduction in acceptor defects and improvement in hole mobility. The resulting hole mobility (260 cm2 V–1 s–1) and hole concentration (3 × 1017 cm–3) in the GeSn layer were among the highest for polycrystalline Ge-based thin films. These results will contribute to the realization of low-temperature Ge-based thin-film transistors that could be superior to single-crystal Si transistors, leading to innovations in display devices.