ADIODE is a two-terminal, passive, non-linear device that can be used to control voltage and current in a circuit. Some diodes are used primarily to rectify alternating current, some are used as signal detectors and others are used as voltage references or voltage regulators. There are also optical diodes which are used as indicators (light-emitting diodes, or LEDs), signal sources (LEDs and laser diodes) or optical detectors (avalanche photodiodes and PIN diodes). The solar cell is a special type of optical diode which converts light energy directly into electricity and by tonnage is probably the most important use of diodes today. The shape of a diode’s current-voltage relationship determines its specific application, which in today’s solid-state devices depends on the way it is doped during manufacture. There are several classes of diode besides the ‘ordinary’ rectifier, but of these we shall examine only Schottky diodes, Zener diodes and, briefly, light-emitting diodes. Optical signal source and detector diodes are discussed in chapter 25.
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