SrTiO<sub>3</sub> termination control: a method to tailor the oxygen exchange kinetics

Hensling, Felix V. E.; Baeumer, Christoph; Rose, Marc‐André; Gunkel, Felix; Dittmann, Regina

doi:10.1080/21663831.2019.1682705

Cited by 16 publications

(16 citation statements)

References 82 publications

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“…2D electron systems at such interfaces offer a fascinating opportunity to study novel physics, which one day may lead to a new generation of oxide electronics [13]. Several reports show 2D electron systems can be tuned through gating [1][2][14][15][16][17], growth conditions [18][19][20][21][22], annealing [14,19,22,23], exposure to water [24,25], and by tuning the interfacial defect structure thermodynamically [9,[26][27]. Mainly, two mechanisms are discussed that contribute to the formation of 2D electron systems at an oxide heterointerface: (a) A polar discontinuity can lead to an electron transfer between the oxides, e.g., at the epitaxial-LaAlO 3 /SrTiO 3 interface [20,[27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

“…While there are other studies [19,[21][22][23]31,33,41,50,[52][53][54] that report changes in the oxygen vacancy profile at SrTiO 3 -based heterointerfaces, the involved dynamics of ions in a complex energy landscape, with strong concentration gradients and intrinsic electric fields, has not been discussed in detail yet. Consequently, several questions remain unclear: What are the driving forces involved in the oxygen vacancy redistribution?…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Zurhelle

Christensen

Menzel

et al. 2020

Phys. Rev. Materials

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In the search for an oxide-based 2D electron system with a large concentration of highly mobile electrons, a promising strategy is to introduce electrons through donor doping while spatially separating electrons and donors to prevent scattering. In SrTiO 3 , this can be achieved by tailoring the oxygen vacancy profile through reduction, e.g., by creating an interface with an oxygen scavenging layer. Through reduction, oxygen atoms are removed close to the interface, leaving behind oxygen vacancies in the SrTiO 3 lattice and mobile electrons in the SrTiO 3 conduction band. The commonly assumed picture is that the oxygen vacancies then remain confined close to the interface while the electrons leak a few nanometers into the bulk, resulting in an electron-defect separation and a highly mobile, oxide-based 2D electron system. So far it has remained unclear how the confinement and electron-defect separation develop over time. Here, we present transient finite element simulations that consider three driving forces acting on the oxygen vacancy distribution: diffusion due to the concentration gradient, drift due to the intrinsic electric field, and an oxygen vacancy trapping energy that holds oxygen vacancies at the interface. Our simulations show that at room temperature, three distinct regions are formed in SrTiO 3 within days: (1) Oxygen vacancies are partially held at the interface due to the oxygen vacancy trapping energy. (2) The accompanying positive space charge causes an oxygen vacancy depletion layer with large electron concentration and high mobility just below the interface. This electron-defect separation, indeed, leads to a highly conductive region. (3) While we are able to describe measured conductivity data with an oxygen vacancy trapping energy of −0.2 eV, this value does not prevent oxygen vacancy diffusion into the bulk: A diffusion front progresses into the bulk and leads to significant conductivity arising over the first micrometer within a couple of months. An enhanced oxygen vacancy trapping energy of −0.5 eV or below would suppress this loss of confinement, leading to a static and pronounced electron-defect separation. Consequently, our results highlight the importance of oxygen vacancy redistribution and suggest the trapping energy of oxygen vacancies at the interface as an important design parameter for oxygen-vacancy-based 2D electron systems.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Zurhelle

Christensen

Menzel

et al. 2020

Phys. Rev. Materials

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“…This task poses a huge challenge due to the high demands on the quality of thin films for the formation of 2DEGs. [ 9,26,30 ] The first step toward transferring the functional LAO/STO interface into more complex device structures is to achieve a 2DEG with metallic, interfacial transport properties onto a homoepitaxial STO thin film. While this appears to be a trivial task using state‐of‐the‐art oxide epitaxy, it turns out to be a remarkable challenge in the field.…”

Section: Figurementioning

confidence: 99%

“…For one, a crucial prerequisite is the TiO 2 ‐termination of the STO at the interface, which is essential to obtain charge‐transfer from crystalline LAO into STO and determines the dynamics of the generation of oxygen vacancies with view on amorphous LAO. [ 9,30,33,34 ] A common route for atomically defined termination is the chemical treatment of single crystalline substrates. [ 35 ] During thin film synthesis, however, the chemical termination of the growing layer is not necessarily well‐conserved.…”

Section: Figurementioning

confidence: 99%

Stoichiometry and Termination Control of LaAlO₃/SrTiO₃ Bilayer Interfaces

Yan

Börgers

Rose

et al. 2020

Adv Materials Inter

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Driven by the interest in fundamental physics and potential applications in novel electronic devices, intense effort is devoted to integration of oxide‐based 2D electron gases (2DEGs) with other functional materials. As a classic model system, LaAlO3/SrTiO3 (LAO/STO) has gained significant attentions. However, due to limitations in synthesis and high demands on the involved thin films, the formation of conductive interfaces between artificially grown STO and LAO thin films is an extreme challenge; oftentimes these interfaces remain insulating or show poor transport properties, which inhibits the development of all‐thin‐film devices. Here, by adopting high temperature growth to achieve step‐flow growth mode and fine‐tuning the laser fluence during pulsed laser deposition, high quality homoepitaxial STO thin films with sufficiently low point‐defect concentration and controllable surface termination are obtained. Fully metallic 2DEGs are then realized at interfaces between STO thin films and both crystalline and amorphous LAO overlayers. The observed slightly reduced mobility in the bilayer LAO/STO/STO structures as compared with single‐layer LAO/STO structures is related to residual defect formation during STO synthesis, yielding a disordered metallic oxide system. The results give prospect of multilayer interfaces potentially accessible in superlattice structures and provide a reliable starting point for back‐gated all‐thin‐film field‐effect devices.

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“…Experimentally, the p-type LaAlO 3 /SrTiO 3 interface was found to be electronically insulating 39,40,46 and only a few studies report on significant hole formation at the interface. 47 The observed insulating behavior of p-type interfaces is typically explained by the formation of oxygen vacancies on the SrTiO 3 side of the interface, i.e.…”

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confidence: 99%

Charge-transfer engineering strategies for tailored ionic conductivity at oxide interfaces

2020

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SrTiO₃ termination control: a method to tailor the oxygen exchange kinetics

Cited by 16 publications

References 82 publications

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Stoichiometry and Termination Control of LaAlO₃/SrTiO₃ Bilayer Interfaces

Charge-transfer engineering strategies for tailored ionic conductivity at oxide interfaces

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SrTiO3 termination control: a method to tailor the oxygen exchange kinetics

Cited by 16 publications

References 82 publications

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

Stoichiometry and Termination Control of LaAlO3/SrTiO3 Bilayer Interfaces

Charge-transfer engineering strategies for tailored ionic conductivity at oxide interfaces

Contact Info

Product

Resources

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SrTiO₃ termination control: a method to tailor the oxygen exchange kinetics

Stoichiometry and Termination Control of LaAlO₃/SrTiO₃ Bilayer Interfaces