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1. Electrically coupling complex oxides to semiconductors: a route to novel material functionalities

   https://doi.org/https://doi.org/10.1557/jmr.2016.496  

   Ngai, J. H. ; Ahmadi-Majlan, K. ; Moghadam, J. ; Chrysler, M. ; Kumah, D. P. ; Walker, F. J. ; Ahn, C.H. ; Droubay, T. ; Du, Y. ; Chambers, S.A. ; et al ( January 2017 , Journal of materials research)

   Complex oxides and semiconductors exhibit distinct yet complementary properties owing to their respective ionic and covalent natures. By electrically coupling complex oxides to traditional semiconductors within epitaxial heterostructures, enhanced or novel functionalities beyond those of the constituent materials can potentially be realized. Essential to electrically coupling complex oxides to semiconductors is control of the physical structure of the epitaxially grown oxide, as well as the electronic structure of the interface. Here we discuss how composition of the perovskite A- and B- site cations can be manipulated to control the physical and electronic structure of semiconductor – complex oxide heterostructures. Two prototypical heterostructures, Ba1-xSrxTiO3/Ge and SrZrxTi1-xO3/Ge, will be discussed. In the case of Ba1-xSrxTiO3/Ge, we discuss how strain can be engineered through A-site composition to enable the re-orientable ferroelectric polarization of the former to be coupled to carriers in the semiconductor. In the case of SrZrxTi1-xO3/Ge we discuss how B-site composition can be exploited to control the band offset at the interface. Analogous to heterojunctions between compound semiconducting materials, control of band offsets, i.e. band-gap engineering, provide a pathway to electrically couple complex oxides to semiconductors to realize a host of functionalities. 

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2. Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

   https://doi.org/10.1002/adfm.201901597  

   Kumah, Divine P. ; Ngai, Joseph H. ; Kornblum, Lior ( July 2019 , Advanced Functional Materials)

   Functional oxides are an untapped resource for futuristic devices and functionalities. These functionalities can range from high temperature superconductivity to multiferroicity and novel catalytic schemes. The most prominent route for transforming these ideas from a single device in the lab to practical technologies is by integration with semiconductors. Moreover, coupling oxides with semiconductors can herald new and unexpected functionalities that exist in neither of the individual materials. Therefore, oxide epitaxy on semiconductors provides a materials platform for novel device technologies. As oxides and semiconductors exhibit properties that are complementary to one another, epitaxial heterostructures comprised of the two are uniquely poised to deliver rich functionalities. This review discusses recent advancements in the growth of epitaxial oxides on semiconductors, and the electronic and physical structure of their interfaces. Leaning on these fundamentals and practicalities, the material behavior and functionality of semiconductor–oxide heterostructures is discussed, and their potential as device building blocks is highlighted. The culmination of this discussion is a review of recent advances in the development of prototype devices based on semiconductor–oxide heterostructures, in areas ranging from silicon photonics to photocatalysis. This overview is intended to stimulate ideas for new concepts of functional devices and lay the groundwork for their realization.

    

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3. Perspective on functional metal-oxide plasmonic metastructures

   https://doi.org/10.1063/5.0134141  

   Sadeghi, Seyed M. ; Wing, Waylin J. ; Gutha, Rithvik R. ( February 2023 , Journal of Applied Physics)

   Plasmonic nanostructures and metasurfaces are appealing hosts for investigation of novel optical devices and exploration of new frontiers in physical/optical processes and materials research. Recent studies have shown that these structures hold the promise of greater control over the optical and electronic properties of quantum emitters, offering a unique horizon for ultra-fast spin-controlled optical devices, quantum computation, laser systems, and sensitive photodetectors. In this Perspective, we discuss how heterostructures consisting of metal oxides, metallic nanoantennas, and dielectrics can offer a material platform wherein one can use the decay of plasmons and their near fields to passivate the defect sites of semiconductor quantum dots while enhancing their radiative decay rates. Such a platform, called functional metal-oxide plasmonic metasubstrates (FMOPs), relies on formation of two junctions at very close vicinity of each other. These include an Au/Si Schottky junction and an Si/Al oxide charge barrier. Such a double junction allows one to use hot electrons to generate a field-passivation effect, preventing migration of photo-excited electrons from quantum dots to the defect sites. Prospects of FMOP, including impact of enhancement exciton–plasmon coupling, collective transport of excitation energy, and suppression of quantum dot fluorescence blinking, are discussed.

    

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4. 2D materials-assisted heterogeneous integration of semiconductor membranes toward functional devices

   https://doi.org/10.1063/5.0122768  

   Park, Minseong ; Bae, Byungjoon ; Kim, Taegeon ; Kum, Hyun S. ; Lee, Kyusang ( November 2022 , Journal of Applied Physics)

   Heterogeneous integration techniques allow the coupling of highly lattice-mismatched solid-state membranes, including semiconductors, oxides, and two-dimensional materials, to synergistically fuse the functionalities. The formation of heterostructures generally requires two processes: the combination of crystalline growth and a non-destructive lift-off/transfer process enables the formation of high-quality heterostructures. Although direct atomic interaction between the substrate and the target membrane ensures high-quality growth, the strong atomic bonds at the substrate/epitaxial film interface hinder the non-destructive separation of the target membrane from the substrate. Alternatively, a 2D material-coated compound semiconductor substrate can transfer the weakened (but still effective) surface potential field of the surface through the 2D material, allowing both high-quality epitaxial growth and non-destructive lift-off of the grown film. This Perspective reviews 2D/3D heterogeneous integration techniques, along with applications of III–V compound semiconductors and oxides. The advanced heterogeneous integration methods offer an effective method to produce various freestanding membranes for stackable heterostructures with unique functionalities that can be applied to novel electrical, optoelectronic, neuromorphic, and bioelectronic systems. 

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5. Anisotropic spin-orbit torque generation in epitaxial SrIrO 3 by symmetry design

   https://doi.org/10.1073/pnas.1812822116  

   Nan, T. ; Anderson, T. J. ; Gibbons, J. ; Hwang, K. ; Campbell, N. ; Zhou, H. ; Dong, Y. Q. ; Kim, G. Y. ; Shao, D. F. ; Paudel, T. R. ; et al ( August 2019 , Proceedings of the National Academy of Sciences)

   Spin-orbit coupling (SOC), the interaction between the electron spin and the orbital angular momentum, can unlock rich phenomena at interfaces, in particular interconverting spin and charge currents. Conventional heavy metals have been extensively explored due to their strong SOC of conduction electrons. However, spin-orbit effects in classes of materials such as epitaxial 5 d -electron transition-metal complex oxides, which also host strong SOC, remain largely unreported. In addition to strong SOC, these complex oxides can also provide the additional tuning knob of epitaxy to control the electronic structure and the engineering of spin-to-charge conversion by crystalline symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque on a ferromagnet with extremely high efficiency via the spin-Hall effect in epitaxial metastable perovskite SrIrO 3 . We first predict a large intrinsic spin-Hall conductivity in orthorhombic bulk SrIrO 3 arising from the Berry curvature in the electronic band structure. By manipulating the intricate interplay between SOC and crystalline symmetry, we control the spin-Hall torque ratio by engineering the tilt of the corner-sharing oxygen octahedra in perovskite SrIrO 3 through epitaxial strain. This allows the presence of an anisotropic spin-Hall effect due to a characteristic structural anisotropy in SrIrO 3 with orthorhombic symmetry. Our experimental findings demonstrate the heteroepitaxial symmetry design approach to engineer spin-orbit effects. We therefore anticipate that these epitaxial 5 d transition-metal oxide thin films can be an ideal building block for low-power spintronics. 

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