Telecom-Band Waveguide-Integrated MoS₂ Photodetector Assisted by Hot Electrons

We report a waveguide-integrated MoS₂ photodetector operating at the telecom band, which is enabled by hot-electron-assisted photodetection. By integrating few-layer MoS₂ on a silicon nitride waveguide and aligning one of the two Au electrodes on top of the waveguide, the evanescent field of the waveguide mode couples with the Au–MoS₂ junction. Though MoS₂ cannot absorb the telecom-band waveguide mode, the Au electrode could absorb it and generate hot electrons, which transfer to the beneath MoS₂ channel due to the low Au–MoS₂ Schottky barrier and generate considerable photocurrent. A photoresponsivity of 15.7 mA W^–1 at a wavelength of 1550 nm is obtained with a low bias voltage of −0.3 V, which is also moderately uniform over the wide telecom band. A 3 dB dynamic response bandwidth exceeding 1.37 GHz is realized, which is limited by the measurement instrument. The demonstrated MoS₂-based hot-electron photodetector not only outperforms other waveguide-integrated hot-electron photodetectors but also provides a strategy to extend the photodetection spectral range of two-dimensional materials. With the maturity of high-quality large-scale growth and flexible transfer of two-dimensional materials, their hot-electron photodetectors could be integrated on various photonic integrated circuits, including silicon, lithium niobate, polymers, etc.