Low-temperature characterization and micropatterning of coevaporated Bi 2 Te 3 and Sb 2 Te 3 films

Thermoelectric (TE) properties of the coevaporated Bi 2 Te 3 and Sb 2 Te 3 films are measured from 100 to 300 K for Seebeck coefficient α S and from 5 to 300 K for electrical resistivity ρ e , mobility μ e , and Hall coefficient R H . For the low-temperature characterization of TE films, the conditions for coevaporation deposition of Bi, Te, and Sb to form Bi 2 Te 3 and Sb 2 Te 3 films are also investigated, including substrate material, substrate temperature T sub , and elemental flux ratio (FR). The resublimation of Te occurring above 473 K significantly affects the film composition and quality. Our optimal deposition conditions for Bi 2 Te 3 films are T sub = 533 K and FR = 2.4 , and those for Sb 2 Te 3 films are T sub = 503 K and FR = 3.0 . The TE properties of both films are strongly temperature dependent, while Bi 2 Te 3 films show a stronger temperature dependence than Sb 2 Te 3 films due to different major scattering mechanisms. α S of both the coevaporated films are close to or higher than those of bulk materials, but ρ e is much higher (due to lower carrier concentrations for Sb 2 Te 3 films and lower μ e for Bi 2 Te 3 films). Also, no freeze-out regime is found for both Bi 2 Te 3 and Sb 2 Te 3 films at low temperatures. The room-temperature power factors of α S 2 / ρ e for Bi 2 Te 3 and Sb 2 Te 3 films are 2.3 and 2.0 mW / K 2 m , and the maxima are 2.7 mW / K 2 m for Bi 2 Te 3 at T = 220 K and 2.1 mW / K 2 m for Sb 2 Te 3 at T = 280 K . Shadow mask technique is successfully used for the micropatterning ( 20 μ m ) of TE films with no significant change in properties.