van der Waals (vdW) heterojunctions enable arbitrary combinations of different layered semiconductors with unique band structures, offering distinctive band engineering for photonic and optoelectronic devices with new functionalities and superior performance. Here, an interlayer photoresponse of a few-layer MoSe 2 /WSe 2 vdW heterojunction is reported. With proper electrical gating and bias, the heterojunction exhibits highsensitivity photodetection with the operation wavelength extended up to the telecommunication band (i.e. 1550 nm). The photoresponsivity and normalized photocurrent-to-dark current ratio reach up to 127 mA W −1 and 1.9 × 10 4 mW −1 , respectively. The results not only provide a promising solution to realize high-performance vdW telecommunication band photodetectors, but also pave the way for using sub-bandgap engineering of two-dimensional layered materials for photonic and optoelectronic applications.

Bandgap engineering with two-dimensional layered materials based heterostructures provides a new method for designing high-performance broadband photodetectors, modulators and lasers.

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