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Concept
Photodetector
Summary
Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically
photo detector have a p–n junction that converts light photons into current. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.
Photodetectors can be classified based on their mechanism of operation and device structure. Here are the common classifications:
Photodetectors may be classified by their mechanism for detection:
Photoconductive effect: These detectors work by changing their electrical conductivity when exposed to light. The incident light generates electron-hole pairs in the material, altering its conductivity. Photoconductive detectors are typically made of semiconductors.
Photoemission or photoelectric effect: Photons cause electrons to transition from the conduction band of a material to free electrons in a vacuum or gas.
Thermal: Photons cause electrons to transition to mid-gap states then decay back to lower bands, inducing phonon generation and thus heat.
Polarization: Photons induce changes in polarization states of suitable materials, which may lead to change in index of refraction or other polarization effects.
Photochemical: Photons induce a chemical change in a material.
Weak interaction effects: photons induce secondary effects such as in photon drag detectors or gas pressure changes in Golay cells.
Photodetectors may be used in different configurations. Single sensors may detect overall light levels. A 1-D array of photodetectors, as in a spectrophotometer or a Line scanner, may be used to measure the distribution of light along a line.
Official source
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