Design of Ge1-xSnx-on-Si waveguide photodetectors featuring high-speed high-sensitivity photodetection in the C- to U-bands

-on-Si waveguide photodetectors for the applications in the C- to U-bands. The GeSn photodetectors have been studied in respect to responsivity, dark current, and bandwidth, with light butt- or evanescent-coupled from an Si waveguide. With the introduction of 4.5% Sn into Ge, the GeSn waveguide PD with evanescent-coupling exhibits high responsivity of 1.25 A/W and 3 dB bandwidth of 123.1 GHz at 1.675 µm. Further increasing the Sn composition cannot improve the absorption in the U-band significantly but does lead to poorer thermal stability and higher dark current. This work suggests a promising avenue for future high-speed high-responsivity photodetection in the C- to U-bands.