Due to its high carrier mobility, broadband absorption, and fast response time, the semi-metallic graphene is attractive for optoelectronics. Another two-dimensional semiconducting material molybdenum disulfide (MoS 2) is also known as light- sensitive. Here we show that a large-area and continuous MoS 2 monolayer is achievable using a CVD method and graphene is transferable onto MoS 2. We demonstrate that a photodetector based on the graphene/MoS 2 heterostructure is able to provide a high photogain greater than 10 8. Our experiments show that the electron-hole pairs are produced in the MoS 2 layer after light absorption and subsequently separated across the layers. Contradictory to the expectation based on the conventional built-in electric field model for metal-semiconductor contacts, photoelectrons are injected into the graphene layer rather than trapped in MoS 2 due to the presence of a perpendicular effective electric field caused by the combination of the built-in electric field, the applied electrostatic field, and charged impurities or adsorbates, resulting in a tuneable photoresponsivity.
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