Semiconductor

1. A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. Semiconductors are tremendously important technologically and economically. Semiconductors are essential materials in all modern electrical devices, from computers to cellular phones to digital audio players. Silicon is the most commercially important semiconductor.

2. Semiconductors are very similar to insulators. The two categories of solids differ only in that insulators have larger band gaps energies that electrons must acquire to be free to flow. In semiconductors at room temperature, just as in insulators, very few electrons gain enough thermal energy to leap the band gap, which is necessary for conduction. For this reason, pure semiconductors and insulators, in the absence of applied fields, have roughly identical electrical properties. The smaller band gaps of semiconductors, however, allow for many other means besides temperature to control their electrical properties.

3. Semiconductors' intrinsic electrical properties are very often permanently modified by introducing impurities, in a process known as doping. Upon the addition of a sufficiently large proportion of dopants, semiconductors conduct electricity nearly as well as metals.

4. In certain semiconductors, when electrons fall from the conduction band to the valence band (the energy levels above and below the band gap), they often emit light. This photoemission process underlies the light emitting diode (LED) and the semiconductor laser, both of which are tremendously important commercially. Conversely, semiconductor absorption of light in photodetectors excites electrons from the valence band to the conduction band, facilitating reception of fiber optic communications, and providing the basis for energy from solar cells.

5. Semiconductors may be elemental materials, such as silicon, compound semiconductors such as gallium arsenide, or alloys, such as silicon germanium or aluminium gallium arsenide.

Notes:

semiconductor	полупроводник
silicon	кремний
insulator	диэлектрик
band gap	запрещенная зона
impurity	примесь
light-emitting diode	светодиод

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