Temperature and carrier concentration dependence of thermoelectric properties of GeBi4Te7

Abstract

We investigate the temperature and carrier concentration dependence of thermoelectric properties including the Seebeck coefficient and thermoelectric power factor of GeBi4Te7 compound by the ab initio electronic structure calculations within density functional theory (DFT). The DFT Kohn-Sham equation is solved by employing the local density approximation (LDA) as well as the screened-exchange local density approximation (sX-LDA). We obtain a band gap of 0.13 eV in sX-LDA for GeBi4Te7 while the LDA calculation predicts a metallic electronic structure due to its well-known bandgap underestimation problem. The optimal concentration to maximize the thermoelectric power factor is found to be 1.8 × 1020 cm −3 for p-type doping and 3.0 × 1020 cm−3 for n-type doping at room temperature, yielding the power factors of 10.2 and 8.2 μWcm −1K −2, respectively. Anisotropy of transport coefficients also depends on the doping type indicating that the in-plane and the perpendicular direction is preferred in p-type and n-type doping, respectively.