Thermoelectric La-doped SrTiO₃ epitaxial layers with single-crystal quality: from nano to micrometers

Abstract

High-quality thermoelectric La_0.2Sr_0.8TiO₃ (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO₃(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10⁻⁴ Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO₃ single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

Keywords:

• Functional oxides
• Thermoelectricity
• Molecular beam epitaxy
• La-doped SrTiO₃
• Integrated films

Classification:

• 50 Energy materials
• 302 Crystallization / Heat treatment / Crystal growth
• 306 Thin film / Coatings
• 210 Thermoelectronics / Thermal transport / insulators
• 201 Electronics / Semiconductor / TCOs

Acknowledgements

The European Commission is acknowledged for the funding of the project TIPS (H2020-ICT-02-2014-1-644453). J.G. acknowledges the Ramon y Cajal program (RYC-2012-11709). Part of this research (STEM characterizations) was conducted at the Center for Nanophase Materials Sciences (Oak Ridge National Laboratory), which is a DOE Office of Science User Facility. The joint laboratory RIBER-INL and J.-B. Goure are finally acknowledged for the MBE technical support.