Abstract
Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.
Highlights
The first successful demonstration of field-effect transistors (FETs) based on monolayer molybdenum disulfide (MoS2) with appealing performance[1,2] has stimulated intensive research on two-dimensional (2D) transition metal dichalcogenides (TMDs)
Identifying the optimum thickness range is of significance for material synthesis and practical device application of the 2D TMDs
The sample preparation and device fabrication are detailed in Methods
Summary
The first successful demonstration of field-effect transistors (FETs) based on monolayer molybdenum disulfide (MoS2) with appealing performance[1,2] has stimulated intensive research on two-dimensional (2D) transition metal dichalcogenides (TMDs). Transistors of both single- and multilayer-MoS2 films have an exhibited high ratio of on-state to off-state current (Ion/Ioff > 106) with reasonable electron mobility[1,9,10,11]. All this makes the layered TMDs promising in fields of low-power switches/circuits[11,12], nonvolatile memory devices[13,14], ultrasensitive photodetectors[15,16], etc. The optimum layer thickness is defined by Wmax, beyond which Ion/Ioff is reduced below 103
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