For present-day optical communication systems, the commonly used normal-incidence photodetectors suffer from the tradeoff between bandwidth and quantum efficiency. Such a tradeoff is especially adverse for long wavelength communication systems operating at higher data rates. For example, the maximum responsivity for a commercially available 25 Gbps photodetector operating at 1310 nm wavelength is limited to less than 0.8 A/W. In this work, we design and demonstrate a high-speed, backside-incidence, critically-coupled Ge on SOI photodetector operating at 1310 nm while maintaining a high quantum efficiency. Our device is fabricated with RPCVD epitaxy, i-line lithography, silicide contact, and Al metal wire, which are fully compatible with the state-of-art CMOS process technology. With our epitaxial scheme and surface passivation method, a low bulk (surface) dark current density of 13 mA/cm2 (0.79 μA/cm) is measured from a ~ 700 nm thick Ge p-i-n device at -1 V bias. The responsivity at 1310 nm wavelength is measured to be 0.87 A/W, and the 3dB optical bandwidth of a 20 μm diameter device is measured to be 26 GHz. Our high-speed, backside-incidence, critically-coupled Ge on SOI photodetector may serve as a high-performance and low-cost solution for next generation high-speed optical receivers, and its benefit of decoupling bandwidth and quantum efficiency is especially prominent at higher data rates such as 40 Gbps and beyond.