High-performance Ge/Si lateral p-i-n waveguide photodetectors for electronic–photonic integrated circuits operating at 1550nm

We report a laterally structured p-i-n thin-film germanium photodetector monolithically integrated on a 220-nm-thick silicon-on-insulator (SOI) waveguide. The photodetector incorporates a grating coupler to efficiently couple 1550-nm optical signals from an optical fiber into the chip. The dimensions of the germanium layer, including its width and thickness, are precisely engineered to maximize responsivity while preserving high-speed operation. Devices featuring germanium absorption regions of varying lengths, ranging from 10.2 to 50.2 micrometers, were fabricated, and their photoelectric properties were systematically characterized. For a device length of 50.2 μm, at a wavelength of 1550 nm and a reverse bias of -3 V, the device exhibits a responsivity exceeding 0.97 A/W, a dark current as low as 93 nA, a 2-dB bandwidth of more than 60 GHz is achieved, and theoretical predictions suggest a 3-dB bandwidth exceeding 100 GHz. This study offers a comprehensive understanding of Ge waveguide photodetectors, fostering high-performance electronic–photonic integrated circuits with implications for telecommunications and beyond.