Photo semiconductors
The term photo semiconductors refers to a group of different types of light-sensitive electronic components based on semiconductor materials . In rare cases the semiconductor materials used in the components are themselves referred to as photo semiconductors.
functionality
If photons (“light particles”) hit a material, they are partially absorbed , reflected or transmitted, depending on the material and the photon energy . With photo semiconductors, the absorption of light in a semiconductor material such as germanium or silicon is used. The light visible to humans is electromagnetic radiation in the spectral range with a photon energy of about 1.66 to 3.26 eV. This means that the energy of visible light is in the range of the energy difference between the valence and conduction bands in semiconductors (see band gap ). Through the absorption of a photon by excitation of an electron from the valence band into the conduction band ( internal photoelectric effect ), additional charge carriers (electrons in the conduction band and holes in the valence band) are available for the transport of electric current. This leads to an increased electrical conductivity of the semiconductor due to the incidence of light ( photoconductivity ).
An additional effect can be achieved in that the light does not fall on an undoped or uniformly doped area, but on the boundary area between two differently doped areas ( pn junction ). In addition to the generation of electron-hole pairs through light absorption, a charge separation also takes place at the junction ( photovoltaic effect ). The resulting electrical potential gradient can be used to generate signals (e.g. photodiode ) or to convert the radiation energy into electrical energy (e.g. solar cell ).
application
The two main areas of application of photo semiconductors are the measurement of optical signals ( radiation detector ) and the conversion of the radiation energy from light into electrical energy. The usable spectral range extends from infrared to visible to ultraviolet light.
Semiconductor radiation detectors include the photoresistor , the photodiode and the phototransistor . They are used, for example, for exposure meters in photo cameras or as light sensors for light barriers. Compared to photodiodes, phototransistors and photoresistors are much more sensitive but also slower. Photodiodes are predominantly used for fast signals and for precision measurements. A large number of sensor elements on a chip are used, for example, in CMOS sensors as image sensors for digital cameras or as a line of photodiodes for optical measuring devices such as spectrophotometers or spectroscopic ellipsometers .
Photo semiconductors such as optocouplers and photothyristors are also used in electrical engineering for the galvanic separation of electrical circuits.
Large-area photodiodes, so-called solar cells , mainly based on silicon, are used to convert light directly into electrical energy .
See also
Individual evidence
- ^ Arnold Willmes: Pocket book chemical substances: elements - inorganics - organic - natural substances - polymers . Harri Deutsch Verlag, 2007, ISBN 978-3-8171-1787-1 , pp. 492 ( limited preview in Google Book search).
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1313.