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

Two-dimensional\n(2D) transition metal dichalcogenides (TMDCs) have\nbeen extensively investigated in photodetection due to their excellent\noptical and electrical properties. For TMDC monolayers, a large bandgap\nstrongly limits the photoresponse range of photodetection, which can\nbe extended to near-infrared wavelengths by two-photon absorption\n(TPA). However, it is usually difficult to reach telecom wavelengths,\nand inevitably results in the inefficiency of devices. Here, we address\nthis issue by means of exciton-based interface engineering. Collaborating\nwith TPA, excitons and interlayer excitons in van der Waals heterostructures\ncan provide more degrees of freedom, including exciton resonance enhancement,\nworking at telecom wavelengths, and broadband response. Moreover,\nthe atomically flat interface of TMDC monolayer (heterostructure)/single-crystalline\nAg demonstrates outstanding performance by virtue of high-efficiency\nconversion from excitons/interlayer excitons to photocarriers, as\nwell as low loss of interface scattering. With an external bias, the\nbroadband response of MoS<sub>2</sub>/WSe<sub>2</sub> heterostructures\non single-crystalline Ag can be achieved, with a responsivity of 1.08\nmA/W at 1550 nm. Our results open possibilities for 2D semiconductors\nto realize broadband and sensitive photodetection.