K. Rothe, M. Stordeur, H. S. Leipner Power factor anisotropy of ptype and ntype conductive thermoelectric BiSbTe thin films. J. Electron. Mater. 39, 9 (2010), 13951398
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 sigma regarding the trigonal caxis, whereas the Seebeck coefficient S is nearly isotropic. For p and ntype alloys, P_perpendicular c > P_c, and the power factors P_perpendicular c of single crystals are always higher compared with polycrystalline films, where the power factor is defined as P = S ^2 sigma, perpendicular c and c are the direction perpendicular and parallel to the caxis, respectively. For the first time in sputterdeposited ptype (Bi0.15Sb0.85)2Te3 and ntype Bi2(Te0.9Se0.1)3 thin films, the anisotropy of the electrical conductivity has been measured directly as it depends on the angle phi between the electrical current and the preferential orientation of the polycrystals (texture) using a standard fourprobe method. The graphs of sigma(phi) show the expected behavior, which can be described by a weighted mixture of sigma_perpendicular c and sigma_c contributions. Because (sigma_perpendicular/sigma_c) p < (sigma_perpendicular/sigma_c) n , the ntype films have stronger anisotropy than the ptype films. For this reason, the angular weighted contributions of P c lead to a larger drop in the power factor of polycrystalline ntype films compared with ptype films. Keywords: anisotropy, doping, conduction, thermoelectrics, sputter © Springer
