Geiger-mode avalanche photodiodes (GMAPDs) are capable of detecting single photons. They can be operated to directly trigger all-digital circuits, so that detection events are digitally counted or time stamped in each pixel. An imager based on an array of GMAPDs therefore has zero readout noise, enabling quantum-limited sensitivity for photon-starved imaging applications. In this review, we discuss devices developed for 3D imaging, wavefront sensing, and passive imaging.
Brian F. Aull, Brian F. Aull,
"Silicon Geiger-mode avalanche photodiode arrays for photon-starved imaging", Proc. SPIE 9492, Advanced Photon Counting Techniques IX, 94920M (13 May 2015); doi: 10.1117/12.2179794; https://doi.org/10.1117/12.2179794