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Cross-plane Thermoelectric Transport in p-type La0.67Sr0.33MnO3/LaMnO3 Oxide Metal/Semiconductor Superlattices

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The cross-plane thermoelectric transport properties of La0.67Sr0.33MnO3LSMOLaMnOLMO oxide metalsemiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMOLMO superlattice heterostructures on 100-strontium titanate substrates. X-ray diffraction and high-resolution reciprocal space mapping indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively, this coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMOLMO superlattices reveal a lowering of the effective barrier height to 223 meV as well as an increase in cross-plane conductivity by an order of magnitude compared to high resistivity superlattices. These results suggest that controlling the oxygen deficiency in the constituent materials enables modification of the effective barrier height and increases the cross-plane conductivity in oxide superlattices. The cross-plane LSMOLMO superlattices showed a giant Seebeck coefficient of 2560 uVK at 300 K that increases to 16,640 microVK at 360 K. The giant increase in the Seebeck coefficient with temperature may include a collective contribution from the interplay of charge, spin current, and phonon drag. The low resistance oxide superlattices exhibited a room temperature cross-plane thermal conductivity of 0.92 Wm K, this indicating that the suppression of thermal conductivities due to the interfaces is preserved in both low and high resistivity superlattices. The high Seebeck coefficient, the order of magnitude improvement in cross-plane conductivity, and the low thermal conductivity in LSMOLMO superlattices resulted in a two order of magnitude increase in cross-plane power factor and thermoelectric figure of merit ZT.

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  • Solid State Physics

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