Monolayer molybdenum disulfide (MoS₂) possesses a desirable direct bandgap with moderate carrier mobility, whereas graphene (Gr) exhibits a zero bandgap and excellent carrier mobility. Numerous approaches have been suggested for concomitantly realizing high on/off current ratio and high carrier mobility in field-effect transistors, but little is known to date about the effect of two-dimensional layered materials. Herein, we propose a Gr/MoS₂ heterojunction platform, i.e., junction field-effect transistor (JFET), that enhances the carrier mobility by a factor of ~ 10 (~ 100 cm² V⁻¹ s⁻¹) compared to that of monolayer MoS₂, while retaining a high on/off current ratio of ~ 10⁸ at room temperature. The Fermi level of Gr can be tuned by the wide back-gate bias (V_BG) to modulate the effective Schottky barrier height (SBH) at the Gr/MoS₂ heterointerface from 528 meV (n-MoS₂/p-Gr) to 116 meV (n-MoS₂/n-Gr), consequently enhancing the carrier mobility. The double humps in the transconductance derivative profile clearly reveal the carrier transport mechanism of Gr/MoS₂, where the barrier height is controlled by electrostatic doping.

Two-dimensional (2D) heterostructures often provide extraordinary carrier transport as exemplified by superconductivity or excitonic superfluidity. Recently, a double-layer graphene (Gr) separated by few-layered boron nitride demonstrated the Coulomb drag phenomenon: carriers in the active layer drag carriers in the passive layer. Here, we propose high-performance Gr/MoS₂ heterostructure transistors operating via Coulomb drag, exhibiting a high carrier mobility (∼3700 cm² V⁻¹ s⁻¹) and on/off-current ratio (∼10⁸) at room temperature. The van der Waals gap at the Gr/MoS₂ interface induces strong interactions between the interlayer carriers, whose recombination is suppressed by the Schottky barrier between p-Gr and n-MoS₂, clearly distinct from the presence of insulating layers. The sign reversal of lateral voltage clearly demonstrates the Coulomb drag in carrier transport. Hole-like behavior of electrons in the n-MoS₂ is observed in magnetic field, indicating strong Coulomb drag at low temperature. Our Coulomb drag transistor thus provides a shortcut for the practical application of 2D heterostructures.

Thickness-dependent bandgap and carrier mobility of two-dimensional (2D) van der Waals (vdW) layered materials make them a promising material as a phototransistor that detects light signals and converts them to electrical signals. Thus far, to achieve a high photoresponsivity of 2D materials, enormous efforts have been made via material and dielectric engineering, as well as modifying device structure. Nevertheless, understanding the effect of interplay between the thickness and the carrier mobility to photoresponsivity is little known. Here, we demonstrate the tunable photoresponsivity (R) of 2D multilayer rhenium disulfide (ReS₂), which is an attractive candidate for photodetection among 2D vdW materials owing to its layer-independent direct bandgap and decoupled vdW interaction. The gate bias (V_G)-dependent photocurrent generation mechanism and R are presented for the channel thickness range of 1.7–27.5 nm. The high similarity between V_G-dependent photocurrent and transconductance features in the ReS₂ phototransistors clearly implies the importance of the channel thickness and the operating V_G bias condition. Finally, the maximum R was found to be 4.1 × 10⁵ A/W at 14.3 nm with the highest carrier mobility of ∼15.7 cm²⋅V⁻¹⋅s⁻¹ among the fabricated devices after excluding the contact resistance effect. This work sheds light on the strategy of how to obtain the highest R in 2D vdW-based phototransistors.