We have studied the response of CMOS com- patible detectors fabricated in a silicon-on-sapphire (SOS) process, operated under short pulse excitation in the blue. These high speed, low capacitance detectors would be suit- able for very precise, surface-normal clock injection with silicon CMOS. We characterize the capacitance of the de- tector structure through a combination of experimental tech- niques and circuit-level and electromagnetic simulations. The transit-time-limited response of the detectors is vali- dated through pump-probe experiments. Detector response times of ∼35 ps have been measured, and devices have ca- pacitance as low as ∼ 4f F.