Fabrication of vertical van der Waals heterostructures for efficient contacts to 2D devices

Performance improvements in Si-based transistors have been driven by aggressive channel scaling. However, as the Si channel thickness approaches the few-nanometer regime, device performance deteriorates due to fundamental material limitations. To overcome the scaling barriers, 2D semiconductors with excellent crystallinity at atomic-scale thicknesses and superior gate controllability have emerged as promising candidates. Nevertheless, 2D field-effect transistors (FETs) still suffer from high contact resistance, and device performance remains contact-limited. A major origin of high contact resistance is Fermi-level pinning effect, arising from defect-induced gap states (DIGS) and metal-induced gap states (MIGS). In this work, we employ 2D metals as contact electrodes and form a clean, uniform van der Waals (vdW) interface between the 2D contact and the 2D channel. Supplying chalcogen vapor during the 2D contact fabrication enables defect healing of the 2D channel underlying the contacts, thereby suppressing DIGS. Furthermore, the vdW gap formed at the 2D-2D interface physically separate the 2D contact from the 2D channel, effectively mitigating MIGS. Based on our results, we successfully demonstrate high-performance p-type WSe₂ FETs with significantly improved contact characteristics.