van der Waals epitaxial growth of ultrathin metallic NiSe nanosheets on WSe2 as high performance contacts for WSe2 transistors

A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts, which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process. Here, we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2, creating an interface that is essentially free from chemical disorder. The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moire pattern. Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 1.6x10(6) S.m(-1). The WSe2 transistors with the NiSe contact show field-effect mobilities (mu(FE)) more than double that with Cr/Au electrodes. This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials, and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides.