Improved thermoelectric properties of Ge2Sb2Te5 films by Bi doping: Experiments and first-principles calculation

The high carrier concentration and low Seebeck coefficient limit the thermoelectric properties of Ge2Sb2Te5 materials. In this paper, Bi-doped Ge2Sb2Te5 thin films with different doping amounts were prepared by magnetron sputtering. The thermoelectric properties of Bi-doped Ge2Sb2Te5 were measured by experiments and predicted by density functional theory and Boltzmann transport theory. The results show that Bi atoms occupy Ge vacancies and bond with Te atoms. The replacement of Ge2+ vacancy with Bi3+ effectively modulates the carrier concentration and improves the Seebeck coefficient. Bi doping increases the degeneracy of the valence band and density of state near the valence band maximum (VBM), and thereby beneficial for the thermoelectric properties of p-type Ge2Sb2Te5, while not desirable for n-type. At 673 K, the power factor of the sample at 20 W doping power reaches 549.56 μWK-2m-1, which is nearly fifteen times that of the intrinsic Ge2Sb2Te5.