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Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3

Abstract

Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (σ) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (Z T=S2·σ·T·κ−1) exceeding 2, where T is the absolute temperature and κ is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 yields unusually large |S|, approximately five times larger than that of SrTiO3 bulks, while maintaining a high σ2DEG. In the best case, we observe |S|=850 μV K−1 and σ2DEG=1.4×103 S cm−1. In addition, by using the κ of bulk single-crystal SrTiO3 at room temperature, we estimate ZT2.4 for the 2DEG, corresponding to ZT0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements.

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Figure 1: Structure and TE response of the 2DEG confined in an MQW composed of SrTiO3 (barrier)/SrTi0.8Nb0.2O3 (well)/SrTiO3 (barrier).
Figure 2: 2DEG localized at the TiO2/SrTiO3 heterointerface.
Figure 3: Giant Seebeck coefficient |S| originating from the 2DEG localized in a unit cell layer of SrTiO3.
Figure 4: TE figures of merit, Z T, of the 2DEGs and the SrTiO3-bulk samples as a function of carrier concentration at room temperature.

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Acknowledgements

This work was financially supported by the Industrial Technology Research Grant Program in 2005 from the New Energy and Industrial Technology Development Organization (NEDO) and a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (No. 18686054).

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Correspondence to Hiromichi Ohta.

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Ohta, H., Kim, S., Mune, Y. et al. Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3. Nature Mater 6, 129–134 (2007). https://doi.org/10.1038/nmat1821

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