Electronics Engineering: Diode

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A diode is a two-terminal semiconductor device that exhibits nonlinear current-voltage characteristics. The purpose of a diode is to permit current to flow in one direction and to prevent current flow in the opposite direction. The two terminals of a diode are referred to as the anode and the cathode.


When the proper impurities are added in trace amounts, semiconductors display interesting and useful properties. This process is usually referred to as doping. The oldest ancestor of semiconductor devices was the crystal detector that was used in early wireless radios. This device was composed of a single metal wire (often called a "cat's whisker") that would touch against a semiconductor crystal. The result was a rectifying diode that allows current to flow easily in one direction but hinders the flow in the other direction. The rectifying diode had two terminals, but by 1930 vacuum-tube diodes had pretty much replaced the smaller crystal detector. The crystal and "cat's whisker" were abandoned, and would eventually emerge as popular children's toys known as crystal radios.
The development of radar during World War II did a lot to revive the fate of crystal detectors. Though they were temperamental, crystals were better than vacuum-tube diodes at rectifying the high frequencies used by radar. During the war, a lot of effort was invested in improving semiconductors, particularly the silicon and geranium used in crystal detectors. ...
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