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 their applications in electronics and photonics. Because of the imperfections, electrons moving on these two-dimensional (2D) crystals experience a spatially non-uniform 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 (FETs) 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.

arXiv comment25 pages,5 figures, just accepted by Proceedings of the National Academy of Sciences 2016

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Cited by in corpus (24)

• Imaging Quantum Spin Hall Edges in Monolayer WTe2
• Intrinsic valley Hall transport in atomically thin MoS2
• One-dimensional edge contacts to a monolayer semiconductor
• Nanoscale Conductivity Imaging of Correlated Electronic States in WSe2/WS2 Moiré Superlattices
• Visualization of Local Conductance in MoS2/WSe2 Heterostructure Transistors
• Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors
• Quantitative Measurements of Nanoscale Permittivity and Conductivity Using Tuning-fork-based Microwave Impedance Microscopy
• Energy-resolved Photoconductivity Mapping in a Monolayer-bilayer WSe2 Lateral Heterostructure
• Enhanced Conductivity Along Lateral Homojunction Interfaces of Atomically Thin Semiconductors
• Optically Coupled Methods for Microwave Impedance Microscopy
• Ultra-high-resolution imaging of moiré lattices and superstructures using scanning microwave impedance microscopy under ambient conditions
• Interferometric Imaging of Nonlocal Electromechanical Power Transduction in Ferroelectric Domains
• Quasi-One-Dimensional Higher-Order Topological Insulators
• Edge states and spin-valley edge photocurrent in transition metal dichalcogenide monolayers
• Accuracy of Y-function methods for parameters extraction of two-dimensional FETs across different technologies
• Scanning gate microscopy mapping of edge current and branched electron flow in a transition metal dichalcogenide nanoribbon and quantum point contact
• Collective excitations in two-component one-dimensional massless Dirac plasma
• SQUID pattern disruption in transition metal dichalcogenide Josephson junctions due to non-parabolic dispersion of the edge states
• Width-dependent Photoluminescence and Anisotropic Raman Spectroscopy from Monolayer MoS${}_2$ Nanoribbons
• Graphene-driven correlated electronic states in one dimensional defects within WS${}_2$
• Phase Transition and Field Effect Topological Quantum Transistor made of monolayer MoS2
• Staircase-like transfer characteristics in multilayer MoS2 field-effect transistors
• Anomalous Bloch oscillation and electrical switching of edge magnetization in bilayer graphene nanoribbon
• Bandgap closing at the screw dislocations of WS2 spirals