Hole Transport in Exfoliated Monolayer MoS${}_2$

Abstract

Ideal monolayers of common semiconducting transition metal dichalcogenides (TMDCs) such as MoS${}_2$, WS${}_2$, MoSe${}_2$, and WSe${}_2$ possess many similar electronic properties. As it is the case for all semiconductors, however, the physical response of these systems is strongly determined by defects in a way specific to each individual compound. Here we investigate the ability of exfoliated monolayers of these TMDCs to support high-quality, well-balanced ambipolar conduction, which has been demonstrated for WS${}_2$, MoSe${}_2$, and WSe${}_2$, but not for MoS${}_2$. Using ionic-liquid gated transistors we show that, contrary to WS${}_2$, MoSe${}_2$, and WSe${}_2$, hole transport in exfoliated MoS${}_2$ monolayers is systematically anomalous, exhibiting a maximum in conductivity at negative gate voltage (V${}_G$) followed by a suppression of up to 100 times upon further increasing V${}_G$. To understand the origin of this difference we have performed a series of experiments including the comparison of hole transport in MoS${}_2$ monolayers and thicker multilayers, in exfoliated and CVD-grown monolayers, as well as gate-dependent optical measurements (Raman and photoluminescence) and scanning tunneling imaging and spectroscopy. In agreement with existing {\it ab-initio} calculations, the results of all these experiments are consistently explained in terms of defects associated to chalcogen vacancies that only in MoS${}_2$ monolayers -- but not in thicker MoS${}_2$ multilayers nor in monolayers of the other common semiconducting TMDCs -- create in-gap states near the top of the valence band that act as strong hole traps. Our results demonstrate the importance of studying systematically how defects determine the properties of 2D semiconducting materials and of developing methods to control them.

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Cited by in corpus (12)

• Full energy spectra of interface state densities for n- and p-type MoS2 field-effect transistors
• Band filling and cross quantum capacitance in ion gated semiconducting transition metal dichalcogenide monolayers
• Ionic Gate Spectroscopy of 2D Semiconductors
• Lateral Interfaces of Transition Metal Dichalcogenides: A Stable Tunable One-Dimensional Physics Platform
• Semiconducting van der Waals Interfaces as Artificial Semiconductors
• Symmetry breaking and spin-orbit coupling for individual vacancy-induced in-gap states in MoS2 monolayers
• Understanding interface properties in 2D heterostructure FETs
• Twist angle dependent electronic properties of exfoliated single layer MoS${}_2$ on Au(111)
• Full control of solid-state electrolytes for electrostatic gating
• Synthetic Semimetals with van der Waals Interfaces
• Design and implementation of a device based on an off-axis parabolic mirror to perform luminescence experiments in a scanning tunneling microscope
• Light-driven C-H bond activation mediated by 2D transition metal dichalcogenides