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.