Mid-infrared waveguide-integrated and photo-thermoelectric graphene photodetector based on germanium-on-silicon platform

Mid-infrared (MIR) photonic integration is desirable in the development of MIR spectroscopy and "lab-on-a-chip" sensing. The germanium-on-silicon (GOS) platform offers a promising solution for MIR photonic integration, extending the operational wavelength to a longer band by eliminating the light-absorbing buried oxide layer. However, MIR photodetectors on the GOS platform remain undeveloped due to the challenging heterogeneous integration of active materials on silicon and inadequate light absorption in the photodetection region. Here, we demonstrate a photo-thermoelectric graphene photodetector on the GOS platform, taking advantage of zero-bias operation and easy heterogeneous integration of graphene. By employing split-gate architecture and plasmonic enhancement to strengthen the light-graphene interaction, we achieve a responsivity of 1.97 V W-1 and noise equivalent power of 2.8 nW Hz(-1/2) at the wavelength of 3.7 mu m. This work enables waveguide-integrated MIR photodetection on the GOS platform for the first time, and it holds great potential for on-chip MIR sensing and imaging applications.