Thickness-dependent properties of ultrathin bismuth and antimony chalcogenide films formed by physical vapor deposition and their application in thermoelectric generators

In this work, a simple cost-effective physical vapor deposition method for obtaining high-quality Bi₂Se₃ and Sb₂Te₃ ultrathin films with thicknesses down to 5 nm on mica, fused quartz, and monolayer graphene substrates is reported. Physical vapor deposition of continuous Sb₂Te₃ ultrathin films with thicknesses 10 nm and below is demonstrated for the first time. Studies of thermoelectrical properties of synthesized Bi₂Se₃ ultrathin films deposited on mica indicated opening of a hybridization gap in Bi₂Se₃ ultrathin films with thicknesses below 6 nm. Both Bi₂Se₃ and Sb₂Te₃ ultrathin films showed the Seebeck coefficient and thermoelectrical power factors comparable with the parameters obtained for the high-quality thin films grown by the molecular beam epitaxy method. Performance of the best Bi₂Se₃ and Sb₂Te₃ ultrathin films is tested in the two-leg prototype of a thermoelectric generator.