Electrically coupling complex oxides to semiconductors: A route to novel material functionalities
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D. Kumah, F.J. Walker, and C.H. Ahn Department of Applied Physics, Yale University, New Haven, CT 06511, USA; and Center for Research on Interface Structures and Phenomena, Yale University, New Haven, CT 06511, USA
T. Droubay, Y. Du, and S.A. Chambers Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
M. Bowden Enviromental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA
X. Shen and D. Su Brookhaven National Laboratory, Center for Functional Nanomaterials, Upton, NY 11973, USA (Received 1 July 2016; accepted 5 December 2016)
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, Ba1xSrxTiO3/Ge and SrZrxTi1xO3/Ge, will be discussed. In the case of Ba1xSrxTiO3/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 SrZrxTi1xO3/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, provides a pathway to electrically couple complex oxides to semiconductors to realize a host of functionalities.
I. INTRODUCTION
Materials that exhibit enhanced or novel functionalities are essential to the development of a range of technologies, such as 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. In this regard, heterostructures comprised of covalently bonded semiconductors and ionic crystalline complex oxides are of particular interest due to the potentially
Contributing Editor: Don W. Shaw a) Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2016.496
transformative material functionalities that can be realized.1–3 Complex oxides exhibit material behaviors that are not found or are difficult to achieve in more traditional semiconductors, such
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