Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

We have investigated the intrinsic thermoelectric properties of epitaxial β -FeSi 2 thin films and the impact of phosphorus (P) doping. Epitaxial β -FeSi 2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β -FeSi 2 thin films on Si(111) substrates, and MBE of β -FeSi 2 thin films on epitaxial β -FeSi 2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β -FeSi 2 /Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β -FeSi 2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β -FeSi 2 . We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β -FeSi 2 . A route to enhance the thermoelectric performance of β -FeSi 2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.