What (who) is diode - definition
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![Structure of a [[vacuum tube]] diode. The filament itself may be the cathode, or more commonly (as shown here) used to heat a separate metal tube which serves as the cathode.](https://commons.wikimedia.org/wiki/Special:FilePath/Diode-english-text.svg?width=200 "Structure of a [[vacuum tube]] diode. The filament itself may be the cathode, or more commonly (as shown here) used to heat a separate metal tube which serves as the cathode.")
![[[Current–voltage characteristic]] of a p–n junction diode showing three regions: '''Breakdown''', '''Reverse''' biased, '''Forward''' biased. The exponential's "knee" is at V<sub>d</sub>. The leveling off region which occurs at larger forward currents is not shown.](https://commons.wikimedia.org/wiki/Special:FilePath/Diode current wiki.png?width=200 "[[Current–voltage characteristic]] of a p–n junction diode showing three regions: '''Breakdown''', '''Reverse''' biased, '''Forward''' biased. The exponential's \"knee\" is at V<sub>d</sub>. The leveling off region which occurs at larger forward currents is not shown.")
![doping]] level, leading to built-in potential of ~0.59V. Observe the different [[quasi Fermi level]]s for conduction band and valence band in n and p regions (red curves).](https://commons.wikimedia.org/wiki/Special:FilePath/PN band.gif?width=200 "doping]] level, leading to built-in potential of ~0.59V. Observe the different [[quasi Fermi level]]s for conduction band and valence band in n and p regions (red curves).")
![envelope demodulator]] circuit.](https://commons.wikimedia.org/wiki/Special:FilePath/Simple envelope detector.svg?width=200 "envelope demodulator]] circuit.")
![[[Light-emitting diode]] (LED)](https://commons.wikimedia.org/wiki/Special:FilePath/LED symbol.svg?width=200 "[[Light-emitting diode]] (LED)")
![Photodiode]]](https://commons.wikimedia.org/wiki/Special:FilePath/Photodiode symbol.svg?width=200 "Photodiode]]")
![Schottky diode]]](https://commons.wikimedia.org/wiki/Special:FilePath/Schottky diode symbol.svg?width=200 "Schottky diode]]")
![[[Transient-voltage-suppression diode]] (TVS)](https://commons.wikimedia.org/wiki/Special:FilePath/Transient voltage suppression diode symbol.svg?width=200 "[[Transient-voltage-suppression diode]] (TVS)")
![[[Tunnel diode]]](https://commons.wikimedia.org/wiki/Special:FilePath/Tunnel diode symbol.svg?width=200 "[[Tunnel diode]]")
![Varicap]]](https://commons.wikimedia.org/wiki/Special:FilePath/Varicap symbol.svg?width=200 "Varicap]]")
![[[Zener diode]]](https://commons.wikimedia.org/wiki/Special:FilePath/Zener diode symbol.svg?width=200 "[[Zener diode]]")
![Typical diode packages in same alignment as diode symbol. Thin bar depicts the [[cathode]].](https://commons.wikimedia.org/wiki/Special:FilePath/Diode pinout en fr.svg?width=200 "Typical diode packages in same alignment as diode symbol. Thin bar depicts the [[cathode]].")
Wikipedia
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance). It has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. It has an exponential current–voltage characteristic. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used.
The obsolete thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate.
Among many uses, diodes are found in rectifiers to convert alternating current (AC) power to direct current (DC), demodulation in radio receivers, and can even be used for logic or as temperature sensors. A common variant of a diode is a light-emitting diode, which is used as electric lighting and status indicators on electronic devices.
