This study presents a design of the body contact in an 850 nm Si photodiode (PD) fabricated using standard 0.18-\murm m CMOS technology, and presents a systematic investigation of its effects on PD performance. This study confirms a good PD performance within 3 V bias and the establishment of the body current by directly measuring the body current, PD capacitance, and photocurrents. The body current from the biasing body contact was designed to eliminate the slow diffusion photocarriers in the substrate and increase bandwidth. The highest responsivity of 1.2 A/W was obtained from the PD without the body current, with biasing in the avalanche region. Adding the body bias increased the optimal bandwidth from 2.51 to 3.11 GHz, but reduced responsivity. However, the operating bias of the Si PD in the avalanche region was high, making it unsuitable for practical applications. While biasing PD at a low 3 V with a coordinated body bias, a bandwidth of 2.46 GHz was obtained with an acceptable responsivity of 0.1 A/W to allow low-voltage operation.