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

Abstract

We found that two types of Cu-doped Bi 2 Te 3 thin films fabricated by dissimilar sputter process had different microstructures and non-stoichiometries (Bi:Te ratios). We investigated the different levels of Te-vacancy ( V T e 2 + ) 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 C u B i 2 − defects) in case of a low Te-vacancy concentration ( V T e 2 + ) in the Bi 2 Te 3 thin film. In the high V T e 2 + -defect concentration case, the C u B i 2 − -formation reaction was thought to be inhibited and evidences for the Cu-additive intercalating into a van der Waals layer (a C u v d W 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 ( V T e 2 + ) dependency of the point defects formation ( C u B i 2 − or C u v d W ) in this system can suggest the clue to control an atomic scale Cu-site in n-type Cu doped Bi 2 Te 3 thin films.