The photoelectric effect can be divided into two categories: the external photoelectric effect and the internal photoelectric effect, and the internal photoelectric effect can be divided into the photoconductive effect and the photogenerated volt effect. It refers to the phenomenon that electrons in an object escape from the surface of the object under the illumination of light, resulting in photoelectron emission. The equipment made according to the external photoelectric effect includes photocells, photomultiplier tubes, etc.
The internal photoelectric effect (of semiconductors) refers to the phenomenon that when the light shines on the photosensitive data, the electrons in the valence band absorb the energy of the photons, and then jump to the conduction band through the band gap, so that the electron concentration in the conduction band and the holes in the valence band increase, that is, the electron-hole pairs are excited, so that the resistivity of the semiconductor data changes or the photogenerated electromotive force occurs.
1. Photoconductive effect. When an incident photon enters the surface of a semiconductor, the electron-hole pair occurs when the incident photon is absorbed by the semiconductor, causing its conductivity to change (photoresistor, photodiode, phototriode).
2. Photogenerated volt effect. Illumination causes electromotive force (photocell) to occur at both ends of the PN junction.
Red-limited frequency: The lowest frequency of light required for the photoelectric effect to occur is called the red-limited frequency (also known as cut-off frequency).
Escape work: The minimum amount of energy required for an electron to escape from the surface of the data to overcome the constraints of the nucleus is called the work of escape.
Einstein's equation of the photoelectric effect: photon energy = energy required to remove an electron (work done) + kinetic energy of the emitted electron. The mathematical expression is: Ek = hν-Wo (where Ek indicates the kinetic energy of the escaping photoelectron, Planck constant h=6.626×10ˉ34 J·s, ν denotes the frequency of the incident light, and Wo denotes the work of escape).
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