Doping amount dependence of phase formation and microstructure evolution in heavily Cu-doped Bi2Te3 films for thermoelectric applications

Abstract

Heavily Cu-doped Bi₂Te₃ films with different Cu contents (∼47.9 at%) were prepared by co-sputtering with Cu and Bi₂Te₃ targets at room temperature and post-annealing at ∼500 °C. When the Cu content increased, the lattice parameters of the c-axis gradually increased with the increase of Cu intercalation into van der Waals gaps between the quintets of the Bi₂Te₃ layers. When a Cu content of above 43.7 at% was added, formation of a Cu₂Te phase was detected along with the phase transition from Bi₂Te₃ to Te-deficient Bi_xTe_y in the films annealed at 300 °C. The porous column structure of the pure Bi₂Te₃ film became gradually dense with the increase of Cu content. When the Cu content was increased, the thermoelectric power factors of heavily Cu-doped Bi₂Te₃ films were enhanced by the increase of carrier concentration.