Different point defects originated from dissimilar deposition conditions in n-type Cu-doped Bi2Te3 films; crystal structure and thermoelectric property depending on Te-vacancy concentration

We found that two types of Cu-doped Bi2Te3 thin films fabricated by dissimilar sputter process had different microstructures and non-stoichiometries (Bi:Te ratios). We investigated the different levels of Te-vacancy (VTe2+) concentration in the films affected the point defects and the thermoelectric property of the films. The Cu additives were substituted for the Bi-sites (form CuBi2− defects) in case of a low Te-vacancy concentration (VTe2+) in the Bi2Te3 thin film. In the high VTe2+-defect concentration case, the CuBi2−-formation reaction was thought to be inhibited and evidences for the Cu-additive intercalating into a van der Waals layer (a CuvdW defect) were detected. We examined the lattice parameter, the thermoelectric properties, and the carrier transport properties of the two types of thin films with the different Te-vacancy concentrations as evidences for the different point defect formation characteristics between them. The Te-vacancy (VTe2+) dependency of the point defects formation (CuBi2− or CuvdW) in this system can suggest the clue to control an atomic scale Cu-site in n-type Cu doped Bi2Te3 thin films.