Multilayer MoS2 Field-effect Transistors Research Articles

Where Does the Current Flow in Two-Dimensional Layered Systems?

In this Letter, we map for the first time the current distribution among the individual layers of multilayer two-dimensional systems. Our findings suggest that in a multilayer MoS2 field-effect transistor the "HOT-SPOT" of the current flow migrates dynamically between the layers as a function of the applied back gate bias and manifests itself in a rather unusual "contact resistance" that cannot be explained using the conventional models for metal-to-semiconductor contacts. To interpret this unique contact resistance, extracted from a channel length scaling study, we employed a resistor network model based on Thomas-Fermi charge screening and interlayer coupling. By modeling our experimental data we have found that the charge screening length for MoS2 is rather large (λMoS2 = 7 nm) and translates into a current distribution in multilayer MoS2 systems, which is distinctly different from the current distribution in multilayer graphene (λgraphene = 0.6 nm). In particular, our experimental results allow us to retrieve for the first time fundamental information about the carrier transport in two-dimensional layered systems that will likely play an important role in the implementation of future electronics components but that have not been evaluated in the past.

Intrinsic carrier mobility of multi-layered MoS2 field-effect transistors on SiO2

By fabricating and characterizing multi-layered MoS2-based field-effect transistors in a four terminal configuration, we demonstrate that the two terminal-configurations tend to underestimate the carrier mobility μ due to the Schottky barriers at the contacts. For a back-gated two-terminal configuration, we observe mobilities as high as 91 cm2 V−1 s−1 which is considerably smaller than 306.5 cm2 V−1 s−1 as extracted from the same device when using a four-terminal configuration. This indicates that the intrinsic mobility of MoS2 on SiO2 is significantly larger than the values previously reported, and provides a quantitative method to evaluate the charge transport through the contacts.

Comparative study of chemically synthesized and exfoliated multilayer MoS2 field-effect transistors

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer 2D crystal semiconductor MoS2. Electrical properties such as the FET mobility, subthreshold swing, on/off ratio, and contact resistance of chemically synthesized (s-) MoS2 are indistinguishable from that of mechanically exfoliated (x-) MoS2, however, flat-band voltages are different, possibly due to polar chemical residues originating in the transfer process. Electron diffraction studies and Raman spectroscopy show the structural similarity of s-MoS2 to x-MoS2. This initial report on the behavior and properties of s-MoS2 illustrates the feasibility of electronic devices using synthetic layered 2D crystal semiconductors.