Stanford EE259 I Photodetection principles (direct vs. coherent), lidar system arch. I 2023 I Lec 17

The video discusses the physics of photo detection and the characteristics of pin semiconductor photodiodes used in lidars. The responsivity of the photodiode, which measures the efficiency of converting photons to electrons, is an important factor. Responsivity is determined by factors such as reflectivity, absorption coefficient, and the fraction of electron-hole pairs that do not recombine. The responsivity is proportional to the quantum efficiency and the wavelength of the incident light. The video also explains the concept of dark current, which is the current that flows through the photodiode in the absence of light. The responsivity and bandwidth of the photodiode are related to its response time. The response time is determined by the charge carrier transit time and the RC time constant of the photodiode. The video also mentions the importance of applying a reverse bias voltage to the device to increase bandwidth.