Pulsed laser deposition and annealing of Bi2−xSbxTe3 thin films for p-type thermoelectric elements

• Bi2−xSbxTe3p-type films were fabricated by pulsed laser deposition (PLD).
• A combined PLD-thermal evaporation system allows for annealing the films in Te vapor.
• Thermoelectric power factor values equal or higher than bulk were recorded.
• Low-pressure PLD results in disordered or nanocrystalline metal-rich films.
• Annealing of the films leads to (0 0 l) crystallographic alignment and improved stoichiometry.

Pulsed laser deposition is suggested as a convenient method for fabrication of Bi2−xSbxTe3 thin films for p-type thermoelectric elements. However, challenges with controlling the stoichiometry and the microstructure of the films need to be addressed. Annealing of the films in an environment of nitrogen and tellurium vapor provided a means to producing Bi2−xSbxTe3 thin films with power factor values similar or greater than bulk materials. Films deposited at 2 mTorr, 375 °C with a laser power of 1.6 W were metal-rich and disordered, with small negative Seebeck coefficients. Upon annealing these films become single phase with a stoichiometry close to 2:3, textured with the basal plane parallel to the substrate, and exhibit excellent p-type thermoelectric characteristics. Interestingly, using this particular deposition and annealing sequence no secondary phases (e.g. crystalline tellurium) are formed.