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

• Published in: Journal of electronic materials Vol. 39; no. 9; pp. 1395 - 1398
• Main Authors: Rothe, K., Stordeur, M., Leipner, H. S.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Boston Springer US 01.09.2010; Springer; Springer Nature B.V
• Subjects: Anisotropy; Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Electronics and Microelectronics; Exact sciences and technology; Instrumentation; Materials Science; Methods of deposition of films and coatings; film growth and epitaxy; Optical and Electronic Materials; Physics; Single crystals; Solid State Physics; Temperature; Thermoelectric effects; Thin films; anisotropy; bismuth telluride; magnetron sputtering; antimony telluride; bismuth selenide; Thermoelectric properties; thin films; Bismuth Selenides tellurides; Electrical conductivity; Polycrystals; Phosphorus alloys; Texture; Thin films; Bismuth selenides; Thermoelectric materials; Cathode sputtering; Bismuth tellurides; Calcium nitride; Thermoelectric power; Physical vapor deposition; Antimony tellurides; Temperature dependence; Antimony; Seebeck effect; Preferred orientation; Monocrystals; Anisotropy; Sputter deposition
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-010-1329-7

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  < ( 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.