We systematically investigated the design optimization of an InGaAs/InP modified Uni-Traveling-Carrier Photodiode (MUTC-PD) under high optical power input conditions. Based on internally fabricated experimental devices for a baseline design, we first achieved an excellent match between our experimental and simulation results under low optical power density of 1.4 mW/μm2, demonstrating the accuracy of our simulation model. Based on this model we showed that as optical power injection increases, the intrinsic bandwidth of the MUTC-PD degradation is the primary limitation on its high-speed response. We quantitatively analyzed the fundamental carrier transport physics and key design parameters affecting intrinsic bandwidth degradation under these conditions. In particular cliff layer doping concentration was found to be a very sensitive parameter affecting the MUTC-PD Optical Electrical (OE) intrinsic bandwidth. Based on detailed simulated results, we realized an optimized device design that is capable of achieving a 3 dB bandwidth of approximately 230 GHz at 10 mW/μm2 input optical power density for the first time.