Thin film thermocouples of textured polycrystalline topological insulators

Surface-mounted thin film thermoelectric (TE) devices hold significant contemporary interest for applications in localized cooling, power generation, and sensing. In this work, we report on the performance of thin film thermocouples of Bi₂Te₃ - Sb₂Te₃ and BiSb - Sb₂Te₃ deposited using a combination of pulsed laser ablation and magnetron sputtering in a combinatorial growth system of base pressure 5 x 10^-8 torr. Firstly, the plain films of Bi₂Te₃, Sb₂Te₃, and BiSb were investigated for their electrical conductivity, charge carrier concentration, and carrier mobility in the temperature range of 2 to 300 K. The ambient temperature Seebeck coefficients of BiSb, Sb₂Te_3, and Bi₂Te₃ were measured against copper with a laser heating technique. Next, single TE junctions of n-BiSb and p- Sb₂Te₃ and n- Bi₂Te₃ - p- Sb₂Te₃ were characterized and yielded a response of 270 µV/K and 250 (±10) µV/K respectively. This first-time comparative study shows that BiSb is a superior n-type counter electrode for Sb₂Te₃ compared to the n-type Bi₂Te₃. Moreover, Bi₂Te₃ is prone to Te antisite disorder which affects its TE properties significantly. In contrast, BiSb, being a solid solution, has less stringent demand on stoichiometry control, and it is also less prone to oxidation compared to Bi₂Te₃. Our results establish that BiSb is a viable counter electrode for surface-mounted TE devices in conjunction with the p-type Sb₂Te₃.