A photodiode is a semiconductor device with a p-n junction and an intrinsic layer between layers p and n. It produces photocurrent in the generation of electron-hole pairs due to light absorption in the intrinsic region and emptying. The photocurrent generated in this way is proportional to the intensity of the light absorbed
Photodetectors can be classified by their detection mechanism:
Effects or photoelectric effect: photons cause electrons to pass the guide band of a material to the free electrons in a vacuum or gas.
Thermal: the passage of electrons states photons determines the median, then divided into smaller groups and generating heat generating phonons.
Polarization: The photons induce changes in the polarization states of suitable material, which can lead to variations in the refractive index or other polarization effects.
Photochemical: photonics induces a chemical change in a material.
Effects of weak interaction: photons induce side effects, such as photon detectors push or pull gas changes in the Golay cell.
Photodetectors can be used in different configurations. Unique sensors able to detect global light levels. To measure light distribution along a line, a 1-D photodetector matrix, as well as a spectrophotometer or line scanner, can be used. An array of two-dimensional photodetectors can be used as an image sensor to form images from the preceding light pattern.
A photodetector or matrix is typically covered by a lighting window, sometimes with an anti-reflective coating.