title: Esaki Diodes in van der Waals Heterojunctions with Broken-Gap Energy Band Alignment.
abstract: van der Waals (vdW) heterojunctions composed of two-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibits novel physics phenomena that can power a range of electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse, and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions and broaden the potential applications of 2D layered materials.
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.|Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Rusen
authors.initials: R
authors.lastname: Yan
authors.affiliation: Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Sara
authors.initials: S
authors.lastname: Fathipour
authors.affiliation: School of Applied and Engineering Physics, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Yimo
authors.initials: Y
authors.lastname: Han
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.|Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Bo
authors.initials: B
authors.lastname: Song
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.
authors.forename: Shudong
authors.initials: S
authors.lastname: Xiao
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.
authors.forename: Mingda
authors.initials: M
authors.lastname: Li
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.
authors.forename: Nan
authors.initials: N
authors.lastname: Ma
authors.affiliation: Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Protasenko
authors.affiliation: School of Applied and Engineering Physics, Cornell University , Ithaca, New York 14853, United States.|Kavli Institute at Cornell for Nanoscale Science , Ithaca, New York 14853, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Muller
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.|Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.|Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14583, United States.
authors.forename: Debdeep
authors.initials: D
authors.lastname: Jena
authors.affiliation: School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14583, United States.|Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.|Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14583, United States.
authors.forename: Huili Grace
authors.initials: HG
authors.lastname: Xing
keywords: Esaki diode; black phosphorus (BP); negative differential resistance (NDR); tin diselenide (SnSe2); tunneling junction; van der Waals heterojunction