Highly Tunable Carrier Tunneling in Vertical Graphene–WS₂–Graphene van der Waals Heterostructures

Abstract

Owing to the fascinating properties, the emergence of two-dimensional (2D) materials brings various important applications of electronic and optoelectronic devices from field-effect transistors (FETs) to photodetectors. As a zero-band-gap material, graphene has excellent electric conductivity and ultrahigh carrier mobility, while the ON/OFF ratio of the graphene FET is severely low. Semiconducting 2D transition metal chalcogenides (TMDCs) exhibit an appropriate band gap, realizing FETs with high ON/OFF ratio and compensating for the disadvantages of graphene transistors. However, a Schottky barrier often forms at the interface between the TMDC and metallic contact, which limits the on-state current of the devices. Here, we lift the two limits of the 2D-FET by demonstrating highly tunable field-effect tunneling transistors based on vertical graphene–WS2–graphene van der Waals heterostructures. Our devices show a low off-state current below 1 pA and a high ON/OFF ratio exceeding 106 at room temperature. Moreover, the carrier transport polarity of the device can be effectively tuned from n-type under small bias voltage to bipolar under large bias by controlling the crossover from a direct tunneling region to the Fowler–Nordheim tunneling region. Further, we find that the effective barrier height can be controlled by an external gate voltage. The temperature dependence of carrier transport demonstrates that both tunneling and thermionic emission contribute to the operation current at elevated temperature, which significantly enhances the on-state current of the tunneling transistors.

γ-Ray-Induced Surface-Charge Redistribution and Change of the Surface Morphology in Monolayer WS2

“…5 Bai et al tuned the tunnel current and conduction charge polarity (from n-type to bipolar) in a graphene−WS 2 − graphene field-effect tunnelling transistor by the application of an electric field. 6 Bisht et al studied the electronic charge-transfer mechanism in a WS 2 film as a function of its growth orientation. 7 Obviously, modulation of the electronic properties will affect the performance of a device, and studies of the strategies adopted for achieving the required changes hold immense significance.…”

“…It varies from 1.97 eV (direct) in a single layer to 1.92 eV (indirect) in a few layers to 1.2 eV in bulk. , Khan et al controlled the optoelectronics of WS 2 by tuning its Schottky barrier height via localized strain engineering . Bai et al tuned the tunnel current and conduction charge polarity (from n-type to bipolar) in a graphene–WS 2 –graphene field-effect tunnelling transistor by the application of an electric field . Bisht et al studied the electronic charge-transfer mechanism in a WS 2 film as a function of its growth orientation .…”

Tuning electronic properties and contact type in van der Waals heterostructures of bilayer SnS and graphene

“…Nowadays, several vdW heterostructures have been predicted theoretically or fabricated experimentally, such as graphene/phosphorene, 34 43 . Recently, dif-ferent types of vertical graphene-based vdW field effect transistors (FETs) have been demonstrated by using distinct electronic properties of 2D materials, like gatetunable interface Schottky barrier which enables transition between tunneling and thermionic processes in such transistors 44,45 . In fact, using graphene instead of metal as the contact can effectively alter the performance of devices based on heterostructures.…”

Graphene Strain-Effect Transistor with Colossal ON/OFF Current Ratio Enabled by Reversible Nanocrack Formation in Metal Electrodes on Piezoelectric Substrates

“…For example, quantum confinement in graphene nanoribbons can lead to the opening of a finite bandgap, ,,, which can be translated into an ON/OFF current ratio of ∼10 3 in GFETs. , GFETs with high-k gate dielectrics such as ferroelectric barium titanate can also demonstrate ON/OFF current ratios of ∼10 4 . Electrochemical modification of the graphene channel through the use of electrolyte gating with honey, organic liquids, etc., can also lead to ON/OFF current ratios exceeding 10 8 in GFETs, albeit with limited yield and relatively poor endurance. , Finally, vertical heterostructure designs of graphene with other semiconducting materials (Si, Ge, WS 2 ) have reported ON/OFF current ratios as high as ∼10 6 . ,,, …”

“…20,21 Finally, vertical heterostructure designs of graphene with other semiconducting materials (Si, Ge, WS 2 ) have reported ON/ OFF current ratios as high as ∼10 6 . 18, 19,22,23 Here, we introduce a novel straintronic approach to achieve colossal ON/OFF current ratios (>10 7 ) in GFETs at room temperature without compromising the high transconductance offered by the graphene channel. We harness strain-induced reversible cracking in high tensile strength source/drain metal contacts to graphene as the switching mechanism in graphene strain-effect transistors (GSETs).…”