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We investigate the dynamic performance of a Si/SiGe-based impact ionization avalanche transit time photodiode (PD) fabricated on a standard Si substrate that operates at the 830-nm wavelength. The bandwidth-enhancement effect under negative-photoconductance (NPC) operation can greatly relax the internal transit time as well as the tradeoff between the gain and bandwidth performance that characterizes the traditional avalanche PD. Our modeling and measurement results show that the extracted internal resonant frequency increases significantly with the reverse leakage current. By choosing the proper bias voltage in the NPC region, we can simultaneously achieve a wide 3-dB bandwidth (30 GHz), ultrahigh gain-bandwidth product (690 GHz) with a 53.2% external efficiency at unit gain, and clear eye opening at 10 Gb/s.