Schottky Contact in Monolayer WS₂ Field‐Effect Transistors

Abstract

Monolayer (ML) WS 2 is a promising material to be the channel of nanoscale field-effect transistors (FETs). In ML WS 2 FETs, the interfacial properties between ML WS 2 and electrodes significantly affect the device performance, due to the possible existence of Schottky barriers at the interface. In this paper, the electronic and transport properties of both the lateral and the vertical interfaces between ML WS 2 and six common metals is calculated (Sc, Ti, Ag, Cu, Au, and Pt) by the density functional theory and the quantum transport simulation. n-type Schottky contact exists with the lateral electron Schottky barrier height (SBH) of 0.28, 0.36, 0.25, 0.46, 1.00 eV for Sc, Ti, Ag, Cu, and Au electrode, respectively, while p-type Schottky contact exists with the lateral hole SBH of 0.98 eV for Pt electrode. The average pinning factor at the lateral interface obtained from linear fitting to the SBHs and the Schottky-Bardin model is 0.32 and 0.28, respectively, suggestive of a strong Fermi level pinning originating from the metal induced gap states. The work reveals the properties of the lateral interfaces between ML WS 2 channels and electrodes theoretically for the first time, providing an instruction to design ML WS 2 devices.

Doping-free complementary WSe2 circuit via van der Waals metal integration

“…All the calculations were performed based on the DFT in conjunction with projector-augmented wave potentials, which is implemented in the Vienna ab initio Simulation Package (VASP) 31,32 . The generalized gradient approximation in the Perdew, Burke, and Ernzerhof (GGA-PBE) was used to describe the exchange and correlation potential 33 as PBE bandgap is a good approximation for the transport gap in an FET, and accordingly the SBHs calculated by PBE are closer to the experimental value 34,35 . vdW interaction is taken into account by the DFT-D3 approach 36 , and the energy cutoff for plane waves was set at 450 eV.…”

Physics of electron emission and injection in two‐dimensional materials: Theory and simulation

“…Rich contact phenomena, such as the formation of n ‐type and p ‐type Schottky contacts, ohmic contacts, and the strong metalization of the 2D semiconductors by contacting metals are identified in these materials. For monolayer WS 2 contacted by six common metals (Ag, Au, Cu, Pt, Sc, Ti), it is found that p ‐type Schottky contact exists only in contact with Pt electrode, while n ‐type Schottky contact are predicted for Sc, Ti, Ag, Cu, and Au electrode 178 . The WSe 2 /metal interfaces 192 exhibits a dominantly ohmic behavior.…”

“…The vertical Schottky barrier can be extracted from the spatial profile of the effective electrostatic potential across the contact region 177 (see Figure 15(D)) via DFT simulation. In contrast, the lateral Schottky barrier requires nonequilibrium Green's function transport calculation coupled with DFT for a source‐channel‐drain FET device configuration 53,175,176,178‐181 . By profiling the local device density of states (LLDOS) across the entire device (see Figure 15(E)), the electron (hole) lateral SBH () can be extracted from the LLDOS as the energy difference between the Fermi level in the source region to the conduction (valance) band edge energy at the flat‐band region of the 2D channel.…”

“…For 2D/3D heterostructure composed of bulk metals (e.g., Sc, Ti, Ag, Cu, Au, Pd, Pt, Cr, Ni, etc.) in contact with TMDC monolayers of WS 2 , 178 WSe 2 , 192 WTe 2 , 193 MoS 2 , 175,194 MoSe 2 , 195 and with black phosphorene, 196 and black‐phosphorene‐analogues such as SnS 197 and SnSe 198 are studied using DFT and quantum transport simulations. Rich contact phenomena, such as the formation of n ‐type and p ‐type Schottky contacts, ohmic contacts, and the strong metalization of the 2D semiconductors by contacting metals are identified in these materials.…”

Tunable Electronic Properties and Potential Applications of 2D GeP/Graphene van der Waals Heterostructure

“…Because the different individual layers are combined by weak vdW force, various vdW heterostructures can be fabricated and their formations are not impeded by lattice mismatch, leading to a large variety of possibilities to tailor the properties of heterostructures 21,28. Regarding to the electronic application of vertical heterostructure devices, the metal‐semiconductor interface usually introduces large Schottky barrier and contact resistances 29. To achieve preferable performance for electronic application of the 2D GeP semiconductor, it is essential to choose an appropriate metallic contact 30.…”