IQIM Postdoctoral and Graduate Student Seminar

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 [4]. 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.

[1] S. B. Zhang, S.-H. Wei & A. Zunger, Phys. Rev. B 63, 075205 (2001).

[2] S. Lany & A. Zuner, Phys. Rev. B 72, 035215 (2005).

[3] P. M. Mooney, Journal of Applied Physics 67, R1–R26 (1990).

[4] H. Yin, A. Akey & R. Jaramillo, Phys. Rev. Mater. 2, 084602 (2018).