In situ anion-doped epitaxial strontium titanate films

Pacherová

Kocourek

et al. 2021

Sci Rep

Self Cite

In scientifically intriguing and technologically important multifunctional ABO3 perovskite oxides, oxygen vacancies are most common defects. They cause lattice expansion and can alter the key functional properties. Here, it is demonstrated that contrary to weak isotropic expansion in bulk samples, oxygen vacancies produce strong anisotropic strain in epitaxial thin films. This anisotropic chemical strain is explained by preferential orientation of elastic dipoles of the vacancies. Elastic interaction of the dipoles with substrate-imposed misfit strain is suggested to define the dipolar orientation. Such elastic behavior of oxygen vacancies is anticipated to be general for perovskite films and have critical impacts on the film synthesis and response functions.

Section: Resultssupporting

confidence: 63%

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Pacherová

Kocourek

et al. 2021

Sci Rep

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“…Epitaxial and polycrystalline STO films were grown by pulsed laser deposition, during which anion dopants and/or oxygen vacancies were introduced in-situ by varying the ambient gas (“ Methods ”) 33 . The content δ of oxygen vacancies/substitutions was to ~ 0.3 in SrTiO 3-δ X δ (Supplementary section S1 ).…”

Section: Resultsmentioning

confidence: 99%

“…Thin STO films (thicknesses of 80–100 nm) were grown by pulsed laser deposition, during which anion dopants and/or oxygen vacancies were introduced in-situ by varying the ambient gas 33 . Epitaxially polished (001) (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )O 3 substrates (LSAT) and silicon substrates covered with native surface oxide (Si/SiO 2 ) were used to prepare epitaxial and polycrystalline films, respectively.…”

Section: Methodsmentioning

confidence: 99%

The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions

Rusevich

Kotomin

et al. 2021

Sci Rep

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The electronic properties, including bandgap and conductivity, are critical for nearly all applications of multifunctional perovskite oxide ferroelectrics. Here we analysed possibility to induce semiconductor behaviour in these materials, which are basically insulators, by replacement of several percent of oxygen atoms with nitrogen, hydrogen, or vacancies. We explored this approach for one of the best studied members of the large family of ABO3 perovskite ferroelectrics — strontium titanate (SrTiO3). The atomic and electronic structure of defects were theoretically investigated using the large-scale first-principles calculations for both bulk crystal and thin films. The results of calculations were experimentally verified by studies of the optical properties at photon energies from 25 meV to 8.8 eV for in-situ prepared thin films. It was demonstrated that substitutions and vacancies prefer locations at surfaces or phase boundaries over those inside crystallites. At the same time, local states in the bandgap can be produced by vacancies located both inside the crystals and at the surface, but by nitrogen substitution only inside crystals. Wide-bandgap insulator phases were evidenced for all defects. Compared to pure SrTiO3 films, bandgap widening due to defects was theoretically predicted and experimentally detected.

“…We investigated the conductivity in epitaxial and polycrystalline films, where oxygen vacancies, nitrogen substitutions, or hydrogen substitutions were introduced in-situ during film growth. [39][40] To diminish possible impact of surface 2DEG, we determined the conductivity in the films sandwiched between the bottom and top electrodes in the vertical structures. To avoid injection of excess carriers and inspect intrinsic conductivity, we applied small-signal AC impedance spectroscopy.…”

mentioning

confidence: 99%

“…We investigated the conductivity in thin (80-100 nm) epitaxial and polycrystalline STO films, which were grown in pairs within a single pulsed laser deposition process, thus ensuring similar chemical composition for both films in each pair. 39 Epitaxial films were prepared on (001) (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates using epitaxial LaNiO3 bottom electrodes, whereas polycrystalline films were formed on Pt-coated Si substrates. Oxygen substitution was implemented by varying the gas ambience during deposition.…”

mentioning

confidence: 99%

Electrical conductivity in oxygen-substituted SrTiO3-δ films

Applied Physics Letters

Savinov

Dejneka

2021

Self Cite

Enhancement of electrical conductivity in fundamentally insulating ABO3 perovskite oxide ferroelectrics is crucial for innovative applications in resistive switching, photovoltaics, and catalysis. One of the methods to raise conductivity in bulk crystals or ceramics relies on the possibility to remove and/or substitute oxygen atoms. Here, we explored this approach for thin films of the representative perovskite oxide SrTiO3. Small-signal AC conductivity was investigated in epitaxial and polycrystalline films, where oxygen vacancies (VO), nitrogen (N), or hydrogen (H) were introduced in-situ during film growth. Hopping mechanism of conductivity was evidenced by the observed strong growth of AC conductivity with temperature, frequency, and AC voltage in all films. Small polarons were identified as charge carriers. Oxygen vacancies/substitutions were suggested to facilitate hopping probability by generating sites for carrier localization. Important ferroelectric devices were proposed to benefit from the revealed hopping conductivity owing to its unique increase with electric field.