Paper EM+NS+TF-FrM3
Tuning Thermoelectric Power Factor in Pnictogen Chalcogenides through S and Cl Doping
Friday, November 1, 2013, 9:00 am, Room 102 A
| Session: |
Nanoelectronic Interfaces, Materials, and Devices/Crystalline Oxides on Semiconductors |
| Presenter: |
G. Ramanath, Rensselaer Polytechnic Institute |
| Authors: |
R.J. Mehta, Rensselaer Polytechnic Institute
F. Devender, Rensselaer Polytechnic Institute
R.P. Ramprasad, University of Connecticut
D. Parker, Oak Ridge National Laboratory
D.J. Singh, Oak Ridge National Laboratory
T. Borca-Tasciuc, Rensselaer Polytechnic Institute
G. Ramanath, Rensselaer Polytechnic Institute
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| Correspondent: |
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High figure of merit (ZT) thermoelectric materials are attractive for solid state refrigeration of nanoelectronic devices. ZT enhancement is an exacting challenge because it entails achieving high Seebeck coefficient α, high electrical conductivity σ and low thermal conductivity k, while these properties are usually unfavorably coupled. We recently demonstrated 25-250% ZT increases in pnictogen chalcogenides [1] by combining sub-atomic percent S doping-induced power factor α2σ increases [2], and nanostructuring-induced decrease in k. Here, we show that S and Cl doping alter the electronic band structure near the Fermi level, impacting carrier concentration and mobility pnictogen chalcogenides. In Sb2Te3, we find that S doping increases a by suppressing Sb-antisite defect formation. In our quest for optimizing S concentration, we discovered that adventitious Cl confounds the trend between S doping and α2σ. Synthesis with Cl-free precursors eliminates this effect and we obtain the remarkable result of both α and σ increasing with S content, contrary to the usually observed inverse correlation between σ and α. Additionally, we find that Cl doping at a fixed S content result in maxima of these properties at slightly different concentrations. Extended X-ray absorption fine structure analyses reveal that Cl occupies interstitial sites while S occupies Bi sites. We show that these results, together with first principles calculations, provide a framework for obtaining ZT>1.5 by optimizing doping and stoichiometry in pnictogen chalcogenides through the manipulation of the electronic structure near the Fermi level.
1. R.J. Mehta, Y. Zhang, C. Karthik, B. Singh, R.W. Siegel, T. Borca-Tasciuc, G. Ramanath, Nat. Mater. 11, 233-240 (2012).
2. R.J. Mehta, Y. Zhang, H. Zhu, D.S. Parker, M. Belley, D. J. Singh, R. Ramprasad, T. Borca-Tasciuc, G. Ramanath, Nano Lett. 12, 4523−4529 (2012).