Photon counting imagers based on high-fill-factor silicon geiger-mode avalanche photodiode arrays

Geiger-mode avalanche photodiodes (APDs) have been used as single-photon-sensitive optical detectors for applications such as lidar imaging, laser spectroscopy, and optical communications. They are biased above the avalanche breakdown voltage, where the absorption of a single photon by the diode can trigger a self-sustaining avalanche discharge that can be digitized to count or time stamp the detection event. This digitization can be done in the pixel, thereby avoiding the readout noise associated with the use of analog circuits such as the charge sensing amplifiers used in CCDs and CMOS active pixel sensors.