Resonant level-induced high thermoelectric response in indium-doped GeTe

By Lihua Wu, Xin Li, Shanyu Wang, Tiansong Zhang, Jiong Yang, Wenqing Zhang, Lidong Chen, Jihui Yang. 2017

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Resonant levels are promising for high-performance single-phase thermoelectric materials. Recently, phase-change materials have attracted much attention for energy conversion applications. As the energetic position of resonant levels could be temperature dependent, searching for dopants in phase-change materials, which can introduce resonant levels in both low and high temperature phases, remains challenging. In this study, possible distortions of the electronic density of states due to group IIIA elements (Ga, In, Tl) in GeTe are theoretically investigated. Resonant levels induced by indium dopants in both rhombohedral and cubic phase GeTe have been demonstrated. The experimental Seebeck coefficients of InxGe1−xTe exhibit a large enhancement compared with those observed for other prior dopants. Indium dopants reduce the defect concentrations in GeTe, and thus, they lower the carrier concentrations and suppress the electronic component of the total thermal conductivity. The enhanced Seebeck coefficient, together with the suppressed thermal conductivity, leads to a reasonably high ZT of 1.3 at a temperature near 355 °C in In0.02Ge0.98Te. The corresponding average ZT is enhanced by ~70% across the entire temperature range of the rhombohedral and cubic phases. These observations indicate that indium-doped GeTe is a promising base material for achieving an even higher thermoelectric performance. The promising heat-to-electricity conversion efficiency of phase-change materials can be enhanced with indium dopants. Germanium telluride (GeTe) has a high thermoelectric response because it stores latent heat through temperature-dependent changes to its crystal phase. Now, researchers in China and the USA have used quantum simulations to investigate electronic routes to further boost energy harvesting by GeTe. Their computations searched through numerous chemical elements and found that adding small quantities of indium atoms opens up new resonant energy levels that could lead to extra heat retention in both of GeTe's phases. Experimental synthesis of indium-doped GeTe demonstrated the validity of this approach, with optimized samples showing a 70% improvement in thermoelectric conversion across a wide temperature range. In both the rhombohedral and the cubic phase GeTe, resonant levels induced by indium dopants have been demonstrated. The experimental Seebeck coefficients of InxGe1−xTe show large enhancement as compared with other prior dopants. The enhanced Seebeck coefficient, combined with the reduced thermal conductivity, leads to a reasonably high ZT of 1.3 near 355 °C in In0.02Ge0.98Te. The average ZT is enhanced by ~70% across the whole temperature range. The present results suggest that indium-doped GeTe can be a promising base-material for even higher thermoelectric performance.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/2c994d62daca19e5dfcc06dfcd996134d61a8e5e