Physical understanding of graphene/metal hetero-contacts to enhance MoS2 field-effect transistors performance

Semiconducting transition metal dichalcogenide (TMD) is a promising two-dimensional material with a potential for next-generation nanoelectronic applications [1-3]. One of the most studied TMD materials, MoS₂, has become an emerging candidate in the field of flexible electronics. In this report, a monolayer graphene is sandwiched between the metal contact and the few-layer n-type MoS₂ film to form hetero-contacts, which enhances the electronic coupling between metal and MoS₂ and boost the electron injection into MoS₂, leading to a significant contact resistance reduction [4,5]. Over 70 devices are studied to obtain a comprehensive description of electrical performance on hetero-contacts devices. We further apply the transfer length method (TLM) on graphene/metal hetero-contacts devices to accurately extract the contact resistance and compare the results with direct metal contact devices. For both Ti and Pd metal contacts, 3.3 times and 4.5 times reduction in contact resistance from hetero-contacts have been achieved, respectively. Moreover, we study the band alignment of graphene/metal hetero-contacts on MoS₂ to provide physical insights into the contact resistance reduction using graphene.