Optimizing the Structural, Electrical and Thermoelectric Properties of Antimony Telluride Thin Films Deposited on Aluminum Nitride-coated Stainless Steel Foil

In this study, we examined the thermoelectric (TE) properties of co-evaporated p-type antimony telluride (Sb(2)Te(3)) thin films on aluminum nitride (AlN)-coated stainless steel foil substrates. We investigated the influence of composition and substrate temperature on the thin-film microstructure and transport properties, by varying the tellurium (Te) concentration in the thin films as well as the substrate temperature during deposition (room temperature (RT) and 300 °C). Thin films prepared with an RT substrate were further annealed at 264 °C to obtain crystallized thin films with high phase purity. Columnar thin films with large grains and a standard multi-oriented crystal structure were obtained when thin films were deposited on substrates heated to 300 °C. Thin films deposited at RT and subsequently annealed at 264 °C had a dense, layered microstructure, with a preferential c-axis or (00 l) texture as the compositions approached phase stoichiometry. The temperature dependence of the thermoelectric properties was measured, and variations were interpreted in terms of the deviation from stoichiometry and the obtained microstructure. A maximum power factor (PF) of 0.87 mW/m ∙ K(2) was obtained for off-stoichiometric 65.0 at% Te thin film, which was the highest among the samples deposited at high substrate temperatures. A higher PF of 1.0 mW/m ∙ K(2) was found for off-stoichiometric thin films with 64.5 at% Te, which was deposited at RT and subsequently annealed. The improvement of thermoelectric power in films containing excess Te could be related to energy dependent carrier scattering at the Sb(2)Te(3)/Te interface.