Photodetectors are devices that convert photons into electrons, i.e., convert optical signals into electrical signals. The physical mechanism of photodetectors is the absorption of photons, which changes the electric properties, such as the generation of a photocurrent in a photoconductor or a photovoltage in a photovoltaic detector. The performance of a photodetector depends on the optical absorption process, the carrier transport, and the interaction with the circuit system.