摘要
Thermoelectric superlattices are expected to decouple the strong correlation between various thermo-electric parameters,and are an important strategy for excellent thermoelectric performances.The superlattices of(Bi_(2))m(Bi_(2)Te_(3))n homologous series are well-known for low lattice thermal conductivity and intriguing topological surface states.However,the impacts of electronic structure on the thermo-electric performance were still not well-understood in(Bi_(2))m(Bi_(2)Te_(3))n.To cope with this issue,Bi_(2)eBi_(2)Te_(3)superlattice-like films with adjustable Bi_(2)/(Bi_(2)+Bi_(2)Te_(3))molar ratio(R)were successfully fabricated by the molecular beam epitaxy technique.Angle-resolved photoemission spectroscopy measurements com-bined with theoretical calculations revealed the conduction band evolution from single-valley to multi-valley as R≥0.30,leading to intrinsically high carrier effective mass and improved thermoelectric power factor.Also,the superlattice film(R=0.46)with the structure close to Bi_(4)Te_(3)possesses the topological surface state feature around the high symmetry point.As a result of the high effective mass of 3.9 m0 and very high electron density of_(2).31×10^(21)cm^(-3),the film with R=0.46 acquired the highest power factor of 1.49 mW·m^(-1)·K^(-2)at 420 K,outperforming that of other(Bi_(2))m(Bi_(2)Te_(3))n superlattices.This work lays an essential foundation on understanding the electronic structure and further improving thermoelectric performances of(Bi_(2))m(Bi_(2)Te_(3))n homologous series.
基金
Y.J.Ouyang and M.Zhang contributed equally to this work.The work was supported by National Key Research and Development Program of China(Grant No.2021YFA0718700,2019YFA0704900)
the National Natural Science Foundation of China(Grant No.92163211)
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing of Wsluhan University of Technology(2023-KF-1).
