Diode, (English: Diode), among electronic components, a device with two electrodes that only allows current to flow in a single direction, and many uses the function of rectification. The varactor diode (Varicap Diode) is used as an electronically tunable capacitor. The current directionality of most diodes is often referred to as the "Rectifying" function. The most common function of a diode is to allow only current to pass in a single direction (called forward bias) and reverse in reverse (called reverse bias). Therefore, the diode can be thought of as an electronic version of the check valve.

 

An early vacuum electronic diode; it is an electronic device that conducts current in one direction. Inside the semiconductor diode, there is a PN junction and two lead terminals. The electronic device has a unidirectional current conductivity according to the direction of the applied voltage. In general, a crystal diode is a p-n junction interface formed by sintering a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of the interface to form a self-built electric field. When the applied voltage is equal to zero, the diffusion current is equal to the drift current caused by the self-built electric field due to the difference in the concentration of the carriers on both sides of the p-n junction, and is in an electric equilibrium state, which is also a diode characteristic in a normal state.

 

Early diodes included "Cat's Whisker Crystals" and vacuum tubes (known as "Thermionic Valves" in the UK). Most of the most common diodes today use semiconductor materials such as silicon or germanium.