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.