Low capacitance CMOS silicon photodetectors for optical clock injection

We have studied the response of CMOS compatible 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 suitable for very precise, surface-normal clock injection with silicon CMOS. We characterize the capacitance of the detector structure through a combination of experimental techniques and circuit-level and electromagnetic simulations. The transit-time-limited response of the detectors is validated through pump–probe experiments. Detector response times of ∼35 ps have been measured, and devices have capacitance as low as ∼4 fF.