Graphene‐Enhanced Metal Transfer Printing for Strong van der Waals Contacts between 3D Metals and 2D Semiconductors

2D semiconductors have shown great potentials for ultra-short channel field-effect transistors (FETs) in next-generation electronics. However, because of intractable surface states and interface barriers, it is challenging to realize high-quality contacts with low contact resistances for both p- and n- 2D FETs. Here, a graphene-enhanced van der Waals (vdWs) integration approach is demonstrated, which is a multi-scale (nanometer to centimeter scale) and reliable (approximate to 100% yield) metal transfer strategy applicable to various metals and 2D semiconductors. Scanning transmission electron microscopy imaging shows that 2D/2D/3D semiconductor/graphene/metal interfaces are atomically flat, ultraclean, and defect-free. First principles calculations indicate that the sandwiched graphene monolayer can eliminate gap states induced by 3D metals in 2D semiconductors. Through this approach, Schottky barrier-free contacts are realized on both p- and n-type 2D FETs, achieving p-type MoTe2, p-type black phosphorus and n-type MoS2 FETs with on-state current densities of 404, 1520, and 761 mu A mu m(-1), respectively, which are among the highest values reported in literature.