Geometry-dependent Halogen Contact Doping in W–WSe 2 –W Field-Effect Transistors: A First-Principles Quantum-Transport Study

High Resolution Image Download MS PowerPoint Slide Contact engineering is essential for improving carrier injection in atomically thin transition-metal dichalcogenide transistors. Here, we use first-principles calculations combined with the nonequilibrium Green’s function formalism to clarify how contact geometry determines the effectiveness of halogen contact doping in monolayer WSe 2 field-effect transistors. Edge-contact and hybrid-contact W–WSe 2 –W devices are systematically compared for intrinsic, Cl-doped, and Br-doped channels. In edge-contact devices, charge transfer from the W electrodes induces pronounced interfacial metallization and a finite density of states near the Fermi level. However, the transmission still exhibits a transport gap because the metal-induced states are not fully extended across the channel; transport near the Fermi level is therefore governed by quantum tunneling. Substitutional Cl and Br dopants shift the conduction-band edge toward the Fermi level. However, only Br-doped device enhance the transmission within the transport window, producing nearly an order-of-magnitude increase in current density under finite gate bias. In hybrid-contact devices, by contrast, halogen doping has a much weaker effect because dopant states strongly hybridize with the metallic contact region and do not efficiently modulate the channel transmission. The current density changes only weakly between 250 and 450 K, consistent with ballistic transport in which temperature enters mainly through the Fermi–Dirac distributions of the electrodes. The subthreshold swing falls below the classical thermionic limit in the short-channel regime, suggesting that quantum tunneling through the channel barrier contributes to the subthreshold transport. These results identify contact geometry as a key design parameter governing the utility of contact-region doping and provide atomistic guidance for reducing contact limitations in two-dimensional semiconductor transistors.