Cross-plane thermoelectric transport in p-type La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/LaMnO{sub 3} oxide metal/semiconductor superlattices

• Published in: Journal of applied physics 2013-05, Vol.113 (19)
• Main Authors: Jha, Pankaj, Shakouri, Ali, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, Sands, Timothy D., School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, Jackson, Philip, Favaloro, Tela, Bomberger, Cory, Zide, Joshua, Hodson, Stephen, Xu, Xianfan
• Format: Article
• Language: English
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ELECTRIC CONDUCTIVITY; EPITAXY; ETCHING; LANTHANUM COMPOUNDS; MANGANATES; PULSED IRRADIATION; RESOLUTION; SEEBECK EFFECT; SEMICONDUCTOR MATERIALS; SPUTTERING; STRONTIUM COMPOUNDS; SUBSTRATES; SUPERLATTICES; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; THERMAL CONDUCTIVITY; THIN FILMS; X-RAY DIFFRACTION
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4804937

The cross-plane thermoelectric transport properties of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO)/LaMnO{sub 3} (LMO) oxide metal/semiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMO/LMO 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 LSMO/LMO 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 LSMO/LMO superlattices showed a giant Seebeck coefficient of 2560 {mu}V/K at 300 K that increases to 16 640 {mu}V/K 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 W/m 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 LSMO/LMO superlattices resulted in a two order of magnitude increase in cross-plane power factor and thermoelectric figure of merit (ZT), compared to the properties of superlattices with higher resistivity that were reported previously. The temperature dependence of the cross-plane power factor in low resistance superlattices suggests a direction for further investigations of the potential LSMO/LMO oxide superlattices for thermoelectric devices.