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Fust, Sergej; Faustmann, Anton; Carrad, Damon J.; Bissinger, Jochen; Loitsch, Bernhard; Doeblinger, Markus; Becker, Jonathan; Abstreiter, Gerhard; Finley, Jonathan J. and Koblmüller, Gregor (2019): Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs-AlGaAs Core-Shell Nanowires. In: Advanced Materials, Vol. 32, No. 4, 1905458

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Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core-shell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core-shell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as approximate to 65-85 mu V K-1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S-2 sigma approximate to 60 mu W m(-1) K-2 and S(2)G approximate to 0.06 pW K-2 within a single sub-band. Remarkably, these core-shell NW heterostructures also exhibit thermal conductivities as low as approximate to 3 W m(-1) K-1, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.

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