Heterostructures involving layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) are not only fundamentally interesting to explore emerging properties at atomically thin limit, but also technically important to achieve novel optoelectronic devices. However, achieving tunable optoelectronic properties and clarifying interlayer processes (charge transfer, energy transfer) in 2D heterostructures have remained part of the key challenges so far. Here, by fabricating heterostructures of graphene and monolayer TMDCs (n-type MoS2 and p-type WSe2), we demonstrate both electrically and optically tunable responses of the heterostructures, revealing the critical interface processes between graphene and TMDCs. In MoS2/graphene heterostructures, electron transfer from MoS2 to graphene is observed, and gate-tunable interface relaxation induces the electrically controlled photoluminescence (PL), whereas in WSe2/graphene heterostructures, electron transfer from graphene to WSe2 is observed, and the PL is tuned by carrier density, which can be controlled by the gate voltage. The interlayer process can also be modulated by laser intensity, which enables photoinduced doping on graphene and optically tunable electrical characteristics of graphene. Combining the tunable Fermi level of graphene and strong light-matter interaction of monolayer TMDCs, our demonstrations are important for the design of multifunctional and efficient optoelectronic devices with TMDC/graphene heterostructures.
Keywords: charge transfer; electrically tunable; heterostructure; optoelectronic; photoinduced doping; transition metal dichalcogenides.