Diode

A two-terminal electronic component that conducts current more readily in one direction than the other. Its behavior enables rectification, signal control, and voltage regulation.

P–N junction: A boundary between p-type and n-type semiconductor regions, where carrier diffusion creates a depletion region and built-in electric field. Most common diodes use this junction to create their directional current response.
Semiconductor: A material whose electrical conductivity lies between that of a conductor and an insulator and can be controlled by doping, fields, or light. Diodes are built from semiconductors whose conductivity can be engineered by region.
Rectifier: A circuit or device that converts alternating current into unidirectional current. Rectifiers use diode conduction direction to convert AC waveforms into pulsating DC.
Schottky diode: A diode formed by a metal–semiconductor junction, typically characterized by low forward voltage and fast switching. Its junction differs from the p–n structure and suits low-loss, high-speed circuits.
Cat's-whisker detector: An early radio detector using a fine metal wire contacting a semiconductor crystal to rectify radio-frequency signals. It was a practical point-contact diode before semiconductor junctions were understood.
Depletion region: A semiconductor region depleted of mobile charge carriers, containing fixed ionized dopants and an internal electric field. Its width changes with applied voltage, controlling current across a diode junction.
Doping (semiconductor): The intentional addition of impurity atoms to a semiconductor to change its carrier concentration and conductivity. Different dopants create the p-type and n-type regions of a junction diode.
Zener diode: A semiconductor diode designed to operate in reverse breakdown at a specified voltage. Its controlled breakdown makes it useful for voltage references and regulation.
Tunnel diode: A heavily doped semiconductor diode whose quantum tunneling produces a region of negative differential resistance. Its unusual current–voltage curve differs sharply from ordinary rectifying behavior.
Crystal radio: A simple radio receiver that uses a crystal detector and requires no powered amplification. Its detector demonstrates diode rectification in early radio reception.

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