Abstract
High-quality thermoelectric La0.2Sr0.8TiO3 (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.
Highlights
Functional oxides present high chemical and thermal stability with a large degree of compositional freedom, which offers great flexibility to tune their physical properties [1,2]
The reflection high-energy electron diffraction (RHEED) patterns of the as-grown LSTO films are shown in Figure 1
The structural properties of the LSTO films have been measured by X-ray diffraction (XRD) (Figure 2)
Summary
Functional oxides present high chemical and thermal stability with a large degree of compositional freedom, which offers great flexibility to tune their physical properties [1,2]. With 15% La doping, a resistivity down to few 10−4 Ω cm can be reached by MBE at room temperature even after consequent suppression of oxygen vacancies by air-annealing [13] This difference can be due to (i) the non-equilibrium energetic character of PLD process, (ii) the higher residual background pressures of the PLD deposition chambers and (iii) the nonobvious stoichiometric transfer from the target to the film due to the dependence on laser fluence and difference in volatility or sticking coefficients between elements [14]. Growth conditions with the correlated structural and functional properties of the layers are described in detail
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