Broadband Excitonic Near-Infrared Photoresponse at the van der Waals Heterostructure/Metal Interface

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been extensively investigated in photodetection due to their excellent optical and electrical properties. For TMDC monolayers, a large bandgap strongly limits the photoresponse range of photodetection, which can be extended to near-infrared wavelengths by two-photon absorption (TPA). However, it is usually difficult to reach telecom wavelengths, and inevitably results in the inefficiency of devices. Here, we address this issue by means of exciton-based interface engineering. Collaborating with TPA, excitons and interlayer excitons in van der Waals heterostructures can provide more degrees of freedom, including exciton resonance enhancement, working at telecom wavelengths, and broadband response. Moreover, the atomically flat interface of TMDC monolayer (heterostructure)/single-crystalline Ag demonstrates outstanding performance by virtue of high-efficiency conversion from excitons/interlayer excitons to photocarriers, as well as low loss of interface scattering. With an external bias, the broadband response of MoS2/WSe2 heterostructures on single-crystalline Ag can be achieved, with a responsivity of 1.08 mA/W at 1550 nm. Our results open possibilities for 2D semiconductors to realize broadband and sensitive photodetection.