X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO<sub>3</sub> Interfaces

Chikina, Alla; Caputo, Marco; Naamneh, Muntaser; Christensen, Dennis Valbjørn; Schmitt, Thorsten; Radović, M.; Strocov, Vladimir N.

doi:10.1002/adfm.201900645

Cited by 7 publications

(6 citation statements)

References 45 publications

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“…4,6,13 The d xy <d xz/yz band order observed in LAO/STO is actually universal across a wide range of systems based on TiO 2 -terminated STO almost independently of the growth conditions and oxygen deficiency. It starts from the paradigm LAO/STO interface 21 and survives under amorphous overlayers of LAO, 24,25 Si 26 and a variety of metals [27][28][29] on STO as well as for bare STO surfaces prepared under various conditions 30,31 and even reconstructed by sputtering/annealing. 32 This band order can though be tuned by applying pressure 33 or changing crystallographic orientations, 34 enhancement at the bottom of the GAO/STO images is due to the V O -derived IG states (see the SI).…”

Section: Resultsmentioning

confidence: 99%

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

et al. 2021

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Rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about two orders of magnitude has been demonstrated at the spinel/perovskite γ-Al 2 O 3 /SrTiO 3 interface compared to the paradigm perovskite/perovskite LaAlO 3 /SrTiO 3 . We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in γ-Al 2 O 3 /SrTiO 3 which depopulates electron states in the top STO layer. This rearrangement of the mobile electron system pushes the electron density away from the interface that reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel γ-Al 2 O 3 and perovskite SrTiO 3 . The band-order engineering exploiting the fundamental symmetry properties emerges as another route to boost the performance of oxide devices.

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Section: Resultsmentioning

confidence: 99%

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

et al. 2021

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“…(b) Oxygen atoms are removed close to the surface or an interface, leaving behind oxygen vacancies, which act as donor-type dopants, and electrons, which then form the 2D electron system [31][32][33]. This reduction can be achieved by exposure to a reducing atmosphere [34], photon irradiation [35][36][37][38][39], ion bombardment [40], or by growing an oxygen scavenging layer on top [41,42]. In the latter case, oxygen atoms are transferred from the oxide to the scavenging layer due to a difference in chemical potential, e.g., at the amorphous-LaAlO 3 /SrTiO 3 or γ -Al 2 O 3 /SrTiO 3 interface [42,43].…”

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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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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“…In contrast to using the light illumination to probe the interface properties, additional effects such as formation of oxygen vacancies is often experienced when irradiating with synchrotron radiation . A comprehensive investigation on photo‐induced oxygen vacancies was carried out by Gabel et al Figure a shows how irradiating LAO/STO with UV‐light from a synchrotron under controlled molecular oxygen dosing causes the emergence and disappearance of delocalized electrons probed using photoelectron spectroscopy .…”

Section: Light/matter Interactionmentioning

confidence: 99%

“…Chikina et al wrote metallic conducting areas between STO and silicon using X‐ray irradiation . Here, light was used both to induce oxygen vacancies and conductivity in STO by transfer of oxygen from STO to Si in addition to real‐time monitoring this process using photoemission.…”

Section: Light/matter Interactionmentioning

confidence: 99%

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO₃‐Based Heterointerfaces with External Stimuli

Christensen

Trier

Niu

et al. 2019

Adv Materials Inter

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Oxides are an exciting class of electronic materials which share key properties with conventional semiconductors, but also bring new intrinsic functionalities that are not used in most current electronics: superconductivity, ferro-, pyro-, and piezoelectricity, ferromagnetism, and multiferrocity. Among the large number of oxides, strontium titanate (SrTiO 3 , STO) has been the center of attention in numerous studies for more than half a century. STO both serves as a popular template for epitaxial growth of oxide thin films as well as by itself exhibiting an attractive palettes of properties, including Numerous of the greatest inventions in modern society, such as solar cells, display panels, and transistors, rely on a simple concept: An external stimulus is applied to a material and the response is then utilized. Oxides often exhibit a colorful palette of responses to external stimuli due to the close coupling between lattice, spin, orbital, and charge degrees of freedom. In particular, oxide heterostructures where oxide thin films are deposited on SrTiO 3 have proven to be a fertile playground for material scientists, and a vast amount of interesting theoretical and experimental studies showcase the wide tunabilities of these heterostructures when subjected to external stimuli. Here, the authors review how the properties of SrTiO 3 -based heterostructures can be changed by external stimuli using electric fields, magnetic fields, light, stress, particle bombardment, liquids, gases, and temperature. The application of a single stimulus or several stimuli combined often leads to unexpected changes in properties which can open up for designing new devices as well as expanding the boundaries of our understanding within fundamental science. Hall of Fame Article is a research scientist at the Technical University of Denmark, Department of Energy Conversion and Storage. He received his B.Sc. (2009) and M.Sc. (2012) in nanoscience from the University of Copenhagen, followed by his Ph.D. (2017) and postdoc (2018) from the Technical University of Denmark. His work is currently focused on the physics of oxide materials and oxide devices for information technology and energy harvesting, including oxide electronics, memristors, internet of things, and thermoelectricity. Felix Trier is a postdoctoral researcher at CNRS/Thales, University Paris-Saclay. He obtained his B.Sc. (2009) and M.Sc. (2012) in nanoscience from the University of Copenhagen. Then he earned his Ph.D. degree (2016) from the Technical University of Denmark. His current research is focused on fabrication and characterization of metallic oxide heterointerface devices for the study of the spin-charge interconversion in 2D Rashba systems. His work concerns the LaAlO 3 /SrTiO 3 heterointerface 2D metal and its electrostatic tunability.Nini Pryds is a Professor and head of the research section "Functional Oxides" at the Department of Energy Conversion and Storage, Technical University of Denmark (DTU), where he is leading a group of researchers working in the field...

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X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO₃ Interfaces

Cited by 7 publications

References 45 publications

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

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

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO₃‐Based Heterointerfaces with External Stimuli

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X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO3 Interfaces

Cited by 7 publications

References 45 publications

Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost

Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost

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

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO3‐Based Heterointerfaces with External Stimuli

Contact Info

Product

Resources

About

X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO₃ Interfaces

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

Band-Order Anomaly at the γ-Al₂O₃/SrTiO₃ Interface Drives the Electron-Mobility Boost

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO₃‐Based Heterointerfaces with External Stimuli