Thermoelectric characteristics of electrochemically deposited Bi ₂Te ₃ and Sb ₂Te ₃ thin films of relevance to multilayer preparation

Thermoelectric thin films of Bi ₂Te ₃ and Sb ₂Te ₃ were synthesized on a gold-coated silicon substrate from an aqueous acid bath at room temperature by electrochemical deposition. Both constant potential deposition and pulsed potential deposition were employed and the influence of the deposition conditions on the elemental composition, crystal structure and surface morphology of the films was investigated. After transfer of the films to an insulating substrate, the thermoelectric and transport properties of the as-deposited and annealed films were measured. The results show that the as-deposited Bi ₂Te ₃ thin films are polycrystalline with n-type semiconducting properties, while the as-deposited Sb ₂Te ₃ films displayed an amorphous structure. Annealing the as-deposited Sb ₂Te ₃ films caused them to crystallize as Sb ₂Te ₃ and in addition, resulted in a separate Te phase. The annealed films showed p-type semiconducting properties. For both systems, the thermoelectric properties of the films are consistently lower than their bulk counterparts. The reasons for the inferior thermoelectric properties are different for the two material types. Based on the studies of electrodeposition of the two compounds, an electrochemical method for preparation of multilayers composed of alternating Bi ₂Te ₃ and Sb ₂Te ₃ layers was explored.