Role of Chalcogen Defect Introducing Metal-Induced Gap States and Its Implications for Metal–TMDs’ Interface Chemistry

Abstract

The contact resistance of the transition metal dichalcogenide (TMD) devices is not comparable to that of their silicon counterparts, probably due to a lack of clarity in their interface chemistry. Looking beyond the conventional Schottky−Mott rule, the metal chalcogen orbital overlaps, tunnel barrier, and metal-induced gap states (MIGSs) are crucial factors determining different metals' contact properties with TMDs. Exploring their properties helps TMDs' contact resistance engineering, driven mainly by their orbital overlaps and perturbing parameters. This work presents the interface chemistry of TMDs (MoS 2 , MoSe 2 , WS 2 , and WSe 2 ) with different metals (Au, Cr, Ni, and Pd) in detail using density functional theory computations. Additionally, the work discusses the role of the chalcogen vacancy and interstitial defects in the metal−TMD interactions and corresponding MIGS features. The investigations reveal that Au does not show any significant MIGS due to its weak interactions with all the TMDs. However, other investigated metals have a strong affinity with TMDs, making significant MIGS contributions. All the metals offer n-type doping characteristics to TMDs due to valence charge transfer from the metals toward TMDs. The chalcogen vacancy boosts the orbital overlaps of the TMDs with all the metals. The vacancy reduces metal−TMD interfacial distance, which can be a promising technique to reduce the tunnel barrier and contact resistance. The MIGS and defect-induced gap states (DIGSs) reflect the possibility of Fermi-level pinning in the TMDs' contacts with Cr, Ni, and Pd. Besides, the work discloses that the chalcogen vacancy converts an n-type Pd−TMD interface into p-type due to reverse charge transfer after the vacancy. Chalcogen interstitial impurity also helps with contact resistance engineering for some metal−TMD systems by reducing the bond distance of the metal TMDs. Our study highlights the possibility of defect-assisted and MIGS-based contact engineering at the metal−TMD interfaces.

MoS2 Field-Effect Transistor Performance Enhancement by Contact Doping and Defect Passivation via Fluorine Ions and Its Cyclic Field-Assisted Activation

“…Sulfur vacancies are found in MoS 2 as the intrinsic form of defects . These vacancies lead to midgap states (trap states), low mobility, hysteresis, and unreliability in MoS 2 FETs. − These can be passivated using foreign atoms like F, which are smaller in size compared to naturally existing S. To understand the possible effects of F bonding at S vacancies, DFT calculations were performed on an in-plane periodic 5 × 5 supercell of single-layer MoS 2 (computational methods detailed in the Methods section). For DFT calculations, three cases were considered (Figure S2): MoS 2 (i) without any S vacancy, (ii) with a single S vacancy, and (iii) with a F atom bonded at the S vacancy.…”

A DFT study of superior adsorbate–surface bonding at Pt-WSe2 vertically aligned heterostructures upon NO2, SO2, CO2, and H2 interactions

“…1 a, focusing on its geometric structure. The available chalcogen vacancies play a significant role in the electronic configuration of TMDs 44 . Subsequently, we investigate the properties of Pt-coated WSe 2 .…”

Defects and Defect Engineering of Two-Dimensional Transition Metal Dichalcogenide (2D TMDC) Materials

“…Also, electron density at the overlapping orbital regions of metal–TMDC increases, reducing contact resistance barriers at the interface. This defect engineering technique is more suitable for Au, Cr, Pd, and Ni metal contact with MoS 2 , MoSe 2 , WS 2 , and WSe 2 [ 18 ]. Interestingly, the S vacancies are mobile upon plasma irradiation, and they migrate and agglomerate along vacancy lines represented in Figure 14 b [ 2 ].…”

“…Additionally, anti-site defect formation during growth in MoTe 2 changes the magnetic properties of such materials [ 17 ]. Moreover, point defects, especially chalcogen vacancies in TMDC materials, reduce the contact resistance at the metal–TMDC interface [ 18 ]. Also, overlapping or merging of grain boundaries of TMDC materials impact both the electrical and optical properties.…”