Approaching the quantum limit in two-dimensional semiconductor contacts

Improving Contacts and Electrical Performances of Nanofilms of MoS2 Transistors through Ultrastrong vdW Integration with Dirac Semimetal PtTe2

“…The electrical performances of 2D devices are usually limited by their poor contacts; meantime, MoS 2 is one of the most extensively studied 2D materials. ,, Therefore, we choose MoS 2 as channel material and PtTe 2 as electrodes of the prototype device to investigate the electrical performance. First, we synthesized monolayer MoS 2 nanofilms on SiO 2 /Si substrate directly, followed by systematic characterizations to demonstrate their structure and high crystallinity, as displayed in Figure S3.…”

“…Since the vdW gap largely determines the interlayer coupling, it in turn, contributes the most to electron injection efficiency. , In view of the electronic structures (Figures d and e) for purely MoS 2 /PtTe 2 crystals (Figure d) and their heterostructure (Figure e), the Fermi level of MoS 2 is shifted into the conduction band (i.e., degenerate MoS 2 ) before and after forming heterostructures, resulting in a degenerate MoS 2 . A degenerate MoS 2 can eliminate the Schottky barrier and thus improve the contact properties, which is similar to the previous effect of semimetal bismuth and antimony. , Moreover, the PDOS values of MoS 2 and PtTe 2 undergo an obvious change after the formation of the heterostructure, providing further proof of strong covalent bonding-like orbital overlaps. Furthermore, the atomic Mulliken population analysis has been further performed for MoS 2 /PtTe 2 and MoS 2 /graphene heterostructures to analyze the charge redistribution, as shown in Figure S5.…”

“…To improve the contacts of 2D transistors, researchers have developed a variety of approaches, such as vacuum control, , post-treatment, , defect engineering, − metallization, , and the most widely used metal selection. − An important breakthrough in 2D materials contact research is achieved by using semimetallic bismuth as electrodes to suppress the gap states . Very recently, Li et al reported that the electrical contact of monolayer MoS 2 can be pushed close to its quantum limit through strong vdW interactions between MoS 2 and semimetal antimony (011̅2) . Given that Fermi level pinning is partially dependent on gap states resulting from defects at the metal–2D channel interactions, it is inevitable that defects would be generated during the metal deposition process, as shown in Figure c. , The Fermi level depinning can be realized by separating the metal and 2D materials by inserting an atomically thin insulating hexagonal boron nitride (h-BN), which can reduce the density of gap states. , However, the interlayer meanwhile introduces an additional tunnel barrier for the carrier injection.…”

“…Graphene is mostly used as an interlayer between metal and 2D semiconductors to suppress Fermi level pinning and reduce contact resistance . However, a large vdW gap is inevitably formed and acts as a wider tunnel barrier for carrier injection at the graphene–semiconductor interface owing to the intrinsic weak interlayer coupling of graphite. , …”

“…7 Very recently, Li et al reported that the electrical contact of monolayer MoS 2 can be pushed close to its quantum limit through strong vdW interactions between MoS 2 and semimetal antimony (011̅ 2). 21 Given that Fermi level pinning is partially dependent on gap states resulting from defects at the metal−2D channel interactions, it is inevitable that defects would be generated during the metal deposition process, as shown in Figure 1c. 22,23 The Fermi level depinning can be realized by separating the metal and 2D materials by inserting an atomically thin insulating hexagonal boron nitride (h-BN), which can reduce the density of gap states.…”