Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nanometer to micrometer and mosaicity effects

TL;DR

This study reports the growth of high-quality La-doped SrTiO3 epitaxial layers with excellent structural and electrical properties across a range of thicknesses, highlighting their potential for opto-microelectronic applications.

Contribution

It demonstrates the successful epitaxial growth of atomically flat, low-mosaicity LaxSr1-xTiO3 layers with consistent thermoelectric properties from nanometer to micrometer scales.

Findings

Low electrical resistivity (<5 x 10^-4 ohm.cm) at room temperature.

Seebeck coefficient around -60 microV/K across all films.

Mosaicity correlates with thermoelectric properties.

Abstract

High-quality thermoelectric LaxSr1-xTiO3 (LSTO) layers (here with x = 0.2), with thicknesses ranging from 20 nm to 700 nm, 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{\deg}), and present very low electrical resistivity (<5 x 10-4 ohm.cm at room temperature), one order of magnitude lower than 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 around -60 microV/K have been found for all films, accordingly. Finally, a correlation is given between the mosaicity and the (thermo)electric properties. These functional LSTO films can be integrated on Si in opto-microelectronic devices as transparent conductor, thermoelectric elements or in non-volatile memory structures.