Intact Electrical Contact to Air-Sensitive Atomically Thin Semiconductors and Their Optoelectronic Applications

Two-dimensional semiconductors have been extensively explored with remarkable potential for applications in electronics and optoelectronics, however, high contact resistance and disorders in the monolayer still constrain harnessing their novel optoelectronic properties. There have been a lot of efforts to overcome these challenges such as using semimetal or low temperature metal deposition. Unfortunately, these approaches are not applicable for air-sensitive materials such as MoTe2 or NbSe2, as they require exposing the materials to deposit metal on top. Therefore, degradation is unavoidable unless the materials are completely encapsulated throughout the entire fabrication process. In the monolayer limit, this degradation issue becomes more critical. While the introduction of a protection layer between metal and the monolayer can prevent exposure of the monolayer to the air, it can inadvertently impede charge transfer, resulting in deteriorated performance.<br/>Here, we present a novel technique that enables intact electrical contact to air-sensitive monolayer semiconductors while simultaneously achieving high performance by tackling both two issues. Our approach involves the perfect sealing of the air-sensitive monolayer MoTe2 throughout the process by fluorinated graphene layer. At the same time, fluorine atoms improve the charge transmission between metal and MoTe2 by reducing the interatomic spacing. As a result, monolayer MoTe2 field effect transistor exhibits more than two orders of magnitude improvement in contact performance with excellent ambipolar behavior. By taking advantage of low contact resistance, intrinsic electrical properties of monolayer MoTe2 are comprehensively elucidated. Furthermore, efficient charge transfer of both electrons and holes enables fabricating lateral p-n homojunction. The small band gap (1 .1 eV) of monolayer MoTe2 coupled with its compatibility with silicon holds promising potential for optoelectronic application including photodetector. Moreover, the electrical contact technique introduced in this study can be extended to other air sensitive materials, broadening its applicability.