Contrasting roles of Bi-doping and Bi2Te3 alloying on the thermoelectric performance of SnTe

Abstract

Previous studies have revealed that both Bi doping and Bi₂Te₃ alloying are successful strategies to optimize the thermoelectric performance of SnTe; however, detailed and thorough investigations on exactly how they differ in modulating the band structure and microstructure were seldom given. Through a systematic comparison between Bi-doped and Bi₂Te₃-alloyed SnTe, we find in this work that despite the fact that they both contribute to the valence band convergence of SnTe, Bi₂Te₃ alloying induces little effect on the hole concentration unlike the typical n-type feature of Bi-doping; moreover, Bi₂Te₃ alloying tends to produce dense dislocation arrays at micron-scale grain boundaries which differs significantly from the substitutional point defect character upon Bi-doping. It was then found that Bi₂Te₃ alloying exhibits a relatively higher quality factor (B ∼ μ_w/κ_lat) at higher temperatures than Bi-doping. Subsequent Ge-doping in Bi₂Te₃-alloyed samples results in further valence band convergence and hole concentration optimization and eventually results in a maximum figure of merit ZT of 1.4 at 873 K in the composition of (Sn_0.88Ge_0.12Te)_0.97-(BiTe_1.5)_0.03.