Two-dimensional large-scale bandgap-tunable monolayer MoS2(1-x)Se2x/graphene heterostructures for phototransistors

Tuning the bandgap of thin-layered two-dimensional transition metal dichalcogenide (2D TMDCs) nanocrystals by controlling their composition or structure is considered to be an important method of tailoring light absorption, electron transition and carrier mobility. However, the large-scale synthesis of TMDs with a tunable bandgap on graphene remains challenging owing to the difficulty in controlling the uniformity of the layer thickness. Herein, we report the large-area synthesis of a uniform monolayer MoS2(1 -x) Se-2x film on a monolayer graphene using low-pressure chemical vapour deposition to realize a 2D heterostructure. The resultant centimetre-scale monolayer MoS2(1 -x) Se-2x film on graphene showed a highly crystalline structure and a tunable bandgap from 1.82 eV to 1.66 eV, which could be controlled by tuning the atomic ratio of S to Se. A phototransistor with the MoS2(1 -x) Se-2x/graphene heterostructure exhibited a high responsivity of 40.64 mA W-1 under light irradiation of 465 nm with good stability up to 50 cycles. A high photocurrent arose from the efficient charge transfer from MoS2(1 -x) Se-2x to graphene with a high carrier mobility based on the good electronic interaction. Thus, the large-scale high-quality bandgap-tunable MoS2(1 -x) Se-2x/graphene heterostructure with controllable structures and electronic properties could be developed and integrated into advanced optoelectronic devices.