IQIM Postdoctoral and Graduate Student Seminar
Rafael Jaramillo is an assistant professor in the Department of Materials Science and Engineering at MIT. His research sits in the big, fun space between materials science, solid state physics, and opto-electronic technologies. His current interests can be characterized as defect and phase engineering of chalcogenide semiconductors, with emphasis on developing processing methods to control sulfide and selenide thin films. Previously he worked as a postdoc at Harvard and at MIT on topics in oxide electronic materials and chalcogenide thin-film solar cells. He earned his PhD from The University of Chicago for work on antiferromagnetism and quantum phase transitions in chromium. Dr. Jaramillo is the recipient of numerous awards including the Rosalind Franklin Young Investigator Award from the Advanced Photon Source at Argonne National Laboratory, the Department of Energy SunShot Potdoctoral Fellowship, and the National Science Foundation Faculty Early Career Development Award (CAREER). He lives in Cambridge, MA with his wife and two young kids.
Abstract: Many semiconductors exhibit large and persistent photoconductivity due to lattice relaxations that follow light absorption; examples are ZnO, CuInS2, and AlGaAs [1-3]. We recently demonstrated that a similar phenomenon is responsible large and persistent photoconductivity in CdS . Sulfur vacancies are deep donors in the dark, but under photoexcitation they convert to shallow donors. This donor-level switching mechanism suggests a new way to control conductivity in electronic devices.
In this talk we will first discuss the mechanism of large and persistent photoconductivity. We will then introduce the concept of defect-level switching, and demonstrate electrical devices that operate by this mechanism. The devices exhibit bipolar resistive switching due to triggering the same lattice relaxations that cause photoconductivity – akin to photoconductivity, but without the photons. We also present complementary studies that support the defect-level switching hypothesis, including Raman spectromicroscopy, capacitance profiling, numerical simulation, and systematic material substitutions. We summarize with an outlook for defect-level switching as a new and generalizable mechanism for designing electronic devices, including selectors and memristors for analog computing, and employing a selection of different switching materials.
If time allows we will briefly discuss ongoing work in other fields including layered chalcogenides for integrated photonics, and chalcogenide perovskite semiconductors.
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 H. Yin, A. Akey & R. Jaramillo, Phys. Rev. Mater. 2, 084602 (2018).