Enhanced Thermoelectric Performance in GeTe by Synergy of Midgap state and Band Convergence
Zhe Guo, Gang Wu, Xiaojian Tan, Ruoyu Wang, Zongwei Zhang, Guangjie Wu, Qiang Zhang, Jiehua Wu, Guoqiang Liu, Jun Jiang
Abstract
Abstract The good co‐existence of midgap state and valence band degeneracy is realized in Bi‐alloyed GeTe through the In‐Cd codoping to play different but complementary roles in the valence band structure modification. In doping induces midgap state and results in a considerably improved Seebeck coefficient near room temperature, while Cd doping significantly increases the Seebeck coefficient in the mid‐high temperature region by promoting the valence band convergence. The synergistic effects obviously increase the density of state effective mass from 1.39 to 2.65 m 0 , and the corresponding carrier mobility still reaches 34.3 cm 2 V −1 s −1 at room temperature. Moreover, the Bi‐In‐Cd co‐alloying introduces various phonon scattering centers including nanoprecipitates and strain field fluctuations and suppresses the lattice thermal conductivity to a rather low value of 0.56 W m −1 K −1 at 600 K. As a result, the Ge 0.89 Bi 0.06 In 0.01 Cd 0.04 Te sample obtains excellent thermoelectric properties of zT max ≈2.12 at 650 K and zT avg ≈1.43 between 300 and 773 K. This study illustrates that the thermoelectric performance of GeTe can be optimized in a wide temperature range through the synergy of midgap state and valence band convergence.