Thermoelectric Properties of Substoichiometric Electron Beam Patterned Bismuth Sulfide

Abstract

Direct patterning of thermoelectric metal chalcogenides can be challenging and is normally constrained to certain geometries and sizes. Here we report the synthesis, characterization, and direct writing of sub-10 nm wide bismuth sulfide (Bi₂S₃) using a single-source, spin-coatable, and electron-beam-sensitive bismuth(III) ethylxanthate precursor. In order to increase the intrinsically low carrier concentration of pristine Bi₂S₃, we developed a self-doping methodology in which sulfur vacancies are manipulated by tuning the temperature during vacuum annealing, to produce an electron-rich thermoelectric material. We report a room-temperature electrical conductivity of 6 S m^-1 and a Seebeck coefficient of -21.41 μV K^-1 for a directly patterned, substoichiometric Bi₂S₃ thin film. We expect that our demonstration of directly writable thermoelectric films, with further optimization of structure and morphology, can be useful for on-chip applications.

Keywords: bismuth sulfide; electron beam lithography; sulfur vacancy; tellurium-free; thermoelectric; thin film; xanthate.