Power Factor Anisotropy of p-Type and n-Type Conductive Thermoelectric Bi-Sb-Te Thin Films

The best films for thermoelectric applications near room temperature are based on the compounds Bi 2 Te 3 , Sb 2 Te 3 , and Bi 2 Se 3 , 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 (Bi 0.15 Sb 0.85 ) 2 Te 3 and n -type Bi 2 (Te 0.9 Se 0.1 ) 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