Nanostructural effect on thermoelectric properties in Si films containing iron silicide nanodots

Abstract

Thin film thermoelectric materials have drawn much attention for realizing one-chip stand-alone power sources of Internet of Things devices. Here, we fabricate two types of the nanostructured Si films with high crystallinity: Si films containing β-FeSi 2 nanodots with a wider nanodot size distribution of ∼5-120 nm and Si films containing α-FeSi 2 nanodots with a narrow size distribution of ∼5-20 nm. The thermal conductivity of these films is lower than those of Si-silicide nanocomposite bulks. Interestingly, Si films containing β-FeSi 2 nanodots show about two times lower thermal conductivity than Si films containing α-FeSi 2 nanodots. This is because the widely-size-distributed β-FeSi 2 nanodots can effectively work as phonon scattering centers due to hierarchical architectures. These films also exhibited a high power factor due to the small amount of point defects and single crystalline epitaxial interfaces, regardless of the iron silicide phase of nanodots. These detailed investigations will open a road for realizing high-performance thin film thermoelectric materials.

Silicon-based low-dimensional materials for thermal conductivity suppression: recent advances and new strategies to high thermoelectric efficiency

“…Sakane et al 65) revealed hierarchical phonon scattering of FeSi 2 QDs in suppressing k. Two phases of iron silicide QDs were formed in a Si matrix by solid phase epitaxy (SPE) under different temperature and exhibited almost the same PF (∼2650 μW mK −2 at RT), QDs of α-FeSi 2 with a uniform size of ∼5-20 nm was weaker in restricting phonons than that of β-FeSi 2 [Fig. 6(c)], which distributed in a widely hierarchical size of ∼5-120 nm.…”