High-Speed and High-Responsivity Vertical van der Waals Heterostructure Waveguide Photodetector Operating in Telecom Band

Telecom-band waveguide photodetectors have revealed great potential for optical communication, computing, and light detection and ranging. Traditional silicon-based waveguide photodetectors based on bulk materials suffer from lattice and thermal expansion coefficient mismatch, resulting in the degradation of device performance. Recently, two-dimensional MoTe₂ has become an attractive candidate for waveguide photodetectors due to the absence of dangling bonds and strong light-matter interaction. However, the large bandgap and low carrier mobility of MoTe₂ pose an obstacle to achieving high responsivity and large bandwidth in the telecom band. Here, we demonstrate a high-speed and high-responsivity vertical graphene-MoTe₂-graphene heterostructure photodetector. Benefiting from the strain-induced bandgap manipulation, the device exhibits a high responsivity of 20 mA W^-1 in the telecom C-band (∼1550 nm) and a record-high responsivity of 567 mA W^-1 in the telecom O-band (∼1310 nm). On the other hand, the vertical heterostructure minimizes the carrier transit path and promises a high 3 dB bandwidth of 4.81 GHz. Thanks to the comprehensive engineering of the band gap and carrier transition, the demonstrated device achieves a record-high responsivity-bandwidth product. This work demonstrates a high-responsivity and high-speed MoTe₂ photodetector for telecom-band applications.