Vacancy driven microstructural induced thermoelectric performance in GeTe based compounds

Khasim saheb Bayikadi^1*, Chien Ting Wu⁴, Li-Chyong Chen³, Kuei-Hsien Chen², Fang-Cheng Chou³, Sankar Raman¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
³Center for condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
⁴Taiwan Semiconductor Research Institute, TSMC, Hsinchu, Taiwan

* Presenter:Khasim saheb Bayikadi, email:khasimsaheb@gate.sinica.edu.tw

In addition to the Ge-vacancy control of GeTe, the antimony (Sb) substitution of GeTe for the improvement of thermoelectric performance is explored for Ge_0.9Sb_0.1Te. The concomitant carrier concentration (n) and the aliovalent Sb ion substitution led to an optimal doping level of x = 0.10 to show ZT ~ 2.35 near 800 K, which is significantly higher than those single- and multi-element substitution studies of the GeTe system reported in the literature. In addition, Ge_0.9Sb_0.1Te demonstrates an impressively high power factor of 36 mW cm^-1 K^-2 and a low thermal conductivity of 1.1 W m^-1 K^-1 at 800 K. The enhanced ZT level for Ge_0.9Sb_0.1Te is explained through a systematic investigation of micro-structural change and strain analysis from room temperature to 800 K. A significant reduction of lattice thermal conductivity (k_lat) is identified and explained by the Sb substitution-introduced strained and widened domain boundaries for the herringbone domain structure of Ge_0.9Sb_0.1Te. The Sb substitution created multiple forms of strain near the defect centre, the herringbone domain structure, and widened tensile/compressive domain boundaries to support phonon scattering that covers a wide frequency range of the phonon spectrum to reduce lattice thermal conductivity effectively.

Keywords: GeTe, Microdomains, herringbone structure, strain, thermoelectric performance