Photon Detection: Avalanche Photodiodes

This lecture explains the behavior of a diode under avalanche conditions, where photons trigger electron-hole pairs leading to an avalanche effect. The lecture covers the generation of multiple electron-hole pairs by a single photon, the concept of excess noise, and the implementation of avalanche photodiodes to detect single photons. It also discusses the challenges of dark count rates and the limitations in photon counting due to thermal generation of electron-hole pairs. Additionally, it explores position-sensitive detectors (PSDs) and quadrant photodiodes for spatial light detection, focusing on their applications in microscopy and atomic force microscopy (AFM) for high-resolution surface imaging.