The 2 μm wavelength band emerges as a promising candidate for the next communication window to enhance the transmission capacity of data. A high-responsivity and high-speed photodetector operating at 2 μm is crucial for the 2-μm-wavelength-band communication system. Here, we present an on-chip waveguide-coupled germanium photodetector with remarkably high responsivity and data-receiving rate, employing subbandgap light absorption and avalanche multiplication. The device is designed with an ingenious and simple asymmetric lateral p-i-n junction structure and fabricated through a standard CMOS process by a commercial factory. It has a responsivity of 3.64 A/W and a maximum bandwidth of 50 GHz at 2 μm wavelength. For the first time, to the best of our knowledge, an optical receiving rate of up to 112 Gbps is demonstrated at 2 μm, verifying its feasibility in a high-speed 2-μm-band communication system. To the best of our knowledge, the proposed device stands out as the fastest photodiode with the highest responsivity among all group III-V and group IV photodetectors working in the 2 μm wavelength band.