Tailoring band structure and Ge precipitates through Er and Sb/Bi co-doping to realize high thermoelectric performance in GeTe

The intrinsic carrier concentration in most thermoelectric materials deviates from the optimal range. Doping is the most effective way to optimize the carrier concentration, yet the accompanying increase of carrier-ionized impurity scattering usually results in undesirable loss in carrier mobility. For GeTe thermoelectric material with ultrahigh carrier concentration, selecting suitable dopants that could simultaneously reduce carrier concentration and improve carrier mobility for enhancing thermoelectric performance is crucial and difficult. Herein, we discover that dilute Er doping in GeTe can simultaneously reduce carrier concentration and increase carrier mobility. The reason of the increase of carrier mobility after Er doping is the reduction of Peierls distortion degree lowering the conductivity effective mass m* Drude and the decrease of Ge precipitates weakening the carrier scattering from Ge vacancies. Moreover, Er doping promotes the convergence of L and Σ valence bands and then increases density of states effective mass m*. Finally, by using Sb or Bi doping to reduce carrier concentration and lattice thermal conductivity, a high ZT_ave of 1.22 and 1.26 within 300–773 K in Ge_0.93Er_0.01Bi_0.06Te and Ge_0.89Er_0.01Sb_0.1Te samples are realized, respectively. This work demonstrates that the rare earth metals Er doping can improve the thermoelectric performance of GeTe that will facilitate the exploration of advancing thermoelectric performance of GeTe and other materials via rare earth metals doping.