Power Factor Anisotropy of p-Type and n-Type Conductive Thermoelectric Bi-Sb-Te Thin Films |
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Authors: | K. Rothe M. Stordeur H. S. Leipner |
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Affiliation: | (1) State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing, 100084, P.R. China;(2) Department of Chemistry, Harbin Institute of Technology, Harbin, 150001, P.R. China; |
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Abstract: | The best films for thermoelectric applications near room temperature are based on the compounds Bi2Te3, Sb2Te3, and Bi2Se3, which as single crystals have distinct anisotropy in their electrical conductivity σ regarding the trigonal c-axis, whereas the Seebeck coefficient S is nearly isotropic. For p- and n-type alloys, P ⊥c > P ||c, and the power factors P ⊥c of single crystals are always higher compared with polycrystalline films, where the power factor is defined as P = S 2 σ, ⊥c and ||c are the direction perpendicular and parallel to the c-axis, respectively. For the first time in sputter-deposited p-type (Bi0.15Sb0.85)2Te3 and n-type Bi2(Te0.9Se0.1)3 thin films, the anisotropy of the electrical conductivity has been measured directly as it depends on the angle φ between the electrical current and the preferential orientation of the polycrystals (texture) using a standard four-probe method. The graphs of σ(φ) show the expected behavior, which can be described by a weighted mixture of σ ⊥c and σ ||c contributions. Because (σ ⊥c/σ ||c) p < (σ ⊥c/σ ||c) n , the n-type films have stronger anisotropy than the p-type films. For this reason, the angular weighted contributions of P ||c lead to a larger drop in the power factor of polycrystalline n-type films compared with p-type films. |
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