diode

A diode is a two-terminal electronic component that conducts current primarily in one direction. It is usually made from semiconductor materials such as silicon or germanium and relies on a PN junction formed by joining p-type and n-type regions. Diodes are used for rectification, switching, signal demodulation, voltage regulation, and protection in a wide range of circuits.

In operation, forward bias reduces the potential barrier at the PN junction and allows carriers to cross, producing a significant current with a characteristic nonlinear I-V curve. Reverse bias widens the depletion region and suppresses current until a breakdown voltage is reached. The forward voltage drop depends on material and type (for silicon diodes typically about 0.6–0.7 V, germanium around 0.2–0.3 V, and Schottky diodes often 0.15–0.45 V). Reverse leakage is usually small but increases with temperature; some diodes are designed to achieve controlled breakdown for regulation, as in Zener diodes.

Common diode types include the basic PN junction diode; Zener diodes, which regulate voltage by reverse breakdown; Schottky diodes, which have low forward drop and fast switching; light-emitting diodes (LEDs), which emit light when forward biased; and varactor diodes, whose junction capacitance varies with reverse voltage for RF tuning.

Applications span power supplies as rectifiers, demodulators in communications, clamping and protection networks, voltage references, and switching elements in digital circuits. Diodes also enable light sources (LEDs) and optical communications through laser diodes.