Potential of La-Doped SrTiO₃ Thin Films Grown by Metal–Organic Vapor Phase Epitaxy for Thermoelectric Applications

Abstract

La-doped SrTiO 3 thin films with high structural quality were homoepitaxially grown by the metal−organic vapor phase epitaxy (MOVPE) technique. Thermogravimetric characterization of the metal−organic precursors determines suitable flash evaporator temperatures for transferring the liquid source materials in the gas phase of the reactor chamber. An adjustment of the charge carrier concentration in the films, which is necessary for optimizing the thermoelectric power factor, was performed by introducing a defined amount of the metal−organic compound La(tmhd) 3 and tetraglyme to the liquid precursor solution. X-ray diffraction and atomic force microscopy verified the occurrence of the pure perovskite phase exhibiting a high structural quality for all La concentrations. The electrical conductivity of the films obtained from Hall-effect measurements increases linearly with the La concentration in the gas phase, which is attributed to the incorporation of La 3+ ions on the Sr 2+ perovskite sites by substitution inferred from photoemission spectroscopy. The resulting structural defects were discussed concerning the formation of occasional Ruddlesden−Popper-like defects. The thermoelectric properties determined by Seebeck measurements demonstrate the high potential of SrTiO 3 thin films grown by MOVPE for thermoelectric applications.

Laser-induced transverse voltage effect in c-axis inclined La x Sr1−x TiO3 thin films prepared by MOCVD

“…This may be attributed to the rise in both carrier concentration and mobility. When La is doped into LSTO films within the range of 0.2 and 0.4, the resistivity increases as the doping amount increases, which may be due to the decrease in carrier mobility, and the effective scattering of electrons by the high-density point defects and their induced strain fields in the surrounding lattice [19,23,42,43], at x = 0.4, the sharp increase in resistivity can also be attributed to the deterioration of the biaxial texture. 2.…”

“…Epitaxial STO thin films are primarily prepared by pulsed laser deposition (PLD) technique [30][31][32][33][34] and MBE [35,36]. However, these methods often operate under low oxygen partial pressures, which will cause oxygen vacancies in the films [37]. These extinct defects can provide strong phonon scattering, resulting in large thermal conductivity suppression [38,39], compromising their performance for LITV applications.…”