Electrically Coupling Multifunctional Oxides to Semiconductors: A Route to Novel Material Functionalities
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Electrically Coupling Multifunctional Oxides to Semiconductors: A Route to Novel Material Functionalities J. H. Ngai1, K. Ahmadi-Majlan1, J. Moghadam1, M. Chrysler1, D. P. Kumah2, C. H. Ahn2, F. J. Walker2, T. Droubay3, M. Bowden4, S. A. Chambers3, X. Shen5, D. Su5 1
Department of Physics, University of Texas-Arlington, Arlington, TX 76019, U.S.A.
2
Department of Applied Physics and Center for Research on Interface Structures and Phenomena,Yale University, New Haven, CT 06511, U.S.A. 3
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A. 4
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352 , U.S.A. 5
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, U.S.A.
ABSTRACT Complex oxides and semiconductors exhibit distinct yet complementary properties owing to their respective ionic and covalent natures. By electrically coupling oxides to semiconductors within epitaxial heterostructures, enhanced or novel functionalities beyond those of the constituent materials can potentially be realized. Key to electrically coupling oxides to semiconductors is controlling the physical and electronic structure of semiconductor – crystalline oxide heterostructures. Here we discuss how composition of the oxide can be manipulated to control physical and electronic structure in Ba1-xSrxTiO3/ Ge and SrZrxTi1-xO3/Ge heterostructures. In the case of the former we discuss how strain can be engineered through composition to enable the re-orientable ferroelectric polarization to be coupled to carriers in the semiconductor. In the case of the latter we discuss how composition can be exploited to control the band offset at the semiconductor - oxide interface. The ability to control the band offset, i.e. band-gap engineering, provides a pathway to electrically couple crystalline oxides to semiconductors to realize a host of functionalities. INTRODUCTION Developing materials that exhibit enhanced or novel functionalities is essential to address present challenges in energy harvesting and information technology. Heterostructures comprised of materials that exhibit dissimilar yet complementary electrical properties present a new approach to realize novel material functionalities. Key to realizing novel and enhanced functionalities in such composite structures is coupling the electrical properties of the constituent materials.
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In this regard, heterostructures comprised of covalently bonded semiconductors and ionic crystalline complex oxides are of particular interest due to the complementary properties exhibited by these materials. Complex oxides exhibit properties such as ferromagnetism, ferroelectricity and strongly correlated phenomena such as metal-insulator transitions. In comparison, semiconductors exhibit high carrier mobilities at room temperature and direct bandgaps. Thus, monolithically integrating crystalline oxides with semiconductors enables their respective properties to be potentially coupled to real
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