title: Uncovering edge states and electrical inhomogeneity in MoS2 field-effect transistors.
abstract: The understanding of various types of disorders in atomically thin transition metal dichalcogenides (TMDs), including dangling bonds at the edges, chalcogen deficiencies in the bulk, and charges in the substrate, is of fundamental importance for TMD applications in electronics and photonics. Because of the imperfections, electrons moving on these 2D crystals experience a spatially nonuniform Coulomb environment, whose effect on the charge transport has not been microscopically studied. Here, we report the mesoscopic conductance mapping in monolayer and few-layer MoS2 field-effect transistors by microwave impedance microscopy (MIM). The spatial evolution of the insulator-to-metal transition is clearly resolved. Interestingly, as the transistors are gradually turned on, electrical conduction emerges initially at the edges before appearing in the bulk of MoS2 flakes, which can be explained by our first-principles calculations. The results unambiguously confirm that the contribution of edge states to the channel conductance is significant under the threshold voltage but negligible once the bulk of the TMD device becomes conductive. Strong conductance inhomogeneity, which is associated with the fluctuations of disorder potential in the 2D sheets, is also observed in the MIM images, providing a guideline for future improvement of the device performance.
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Di
authors.identifier: 0000-0001-9924-4838
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Xiao
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Lan
authors.initials: L
authors.lastname: Luan
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Wu
authors.affiliation: Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.affiliation: Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758.
authors.forename: Maruthi N
authors.initials: MN
authors.lastname: Yogeesh
authors.affiliation: Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758.
authors.forename: Rudresh
authors.initials: R
authors.lastname: Ghosh
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Zhaodong
authors.initials: Z
authors.lastname: Chu
authors.affiliation: Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758.
authors.forename: Deji
authors.initials: D
authors.lastname: Akinwande
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Qian
authors.initials: Q
authors.lastname: Niu
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712; kejilai@physics.utexas.edu.
authors.forename: Keji
authors.initials: K
authors.lastname: Lai
keywords: MoS2; edge states; electrical inhomogeneity; metal-insulator transition; microwave impedance microscopy