Doping amount dependence of phase formation and microstructure evolution in heavily Cu-doped Bi2Te3 films for thermoelectric applications
Heavily Cu-doped Bi2Te3 films with different Cu content (~ 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 by the increase of Cu-intercalation into van der Waals gaps between the quintets of the Bi2Te3 layers. When Cu content above 43.9 at.% was added, formation of a Cu2Te phase was detected along with the phase transition from Bi2Te3 to Te-deficient BixTey in the films annealed at 300 °C. The porous column structure of pure Bi2Te3 film became gradually dense with the increase of Cu content. When Cu content was increased, the thermoelectric power factors of heavily Cu-doped Bi2Te3 films were enhanced by the increase of carrier concentration.