In electronics, a diode is a two-terminal electronic component. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube diode (now rarely used except in some high-power technologies) is a vacuum tube with two electrodes: a plate and a cathode.The most common function of a diode is to allow an electric current to pass in one direction (called the diode’s forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extract modulation from radio signals in radio receivers.
Types of Diode
p-n junction DIODE:-
A p-n junction diode is a two terminal device having junction of p-type and n-type materials. This diode is mainly used as a rectifier.
A Zener diode is a special kind of diode which allows current to flow in the forward direction same as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, “Zener knee voltage” or “Zener voltage.” The device was named after Clarence Zener, who discovered this electrical property.A conventional solid-state diode will not allow significant current if it is reverse-biased below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. In case of large forward bias (current in the direction of the arrow), the diode exhibits a voltage drop due to its junction built-in voltage and internal resistance. The amount of the voltage drop depends on the semiconductor material and the doping concentrations.
Light emitting Diode:-
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor.
The meaning of varactor diode is variable capacitance diode.varactor=variable reactor, referring to the voltage varying property of capacitance . We know that holes are majority # charge carriers in P-type semiconductor material and electrons are majority charge carriers in N-type semiconductor material. There is a neutral region (Junction) between these two which do not have any majority carriers. There are two plates in the capacitor between which there is a dielectric material. There in no current carrier in this dielectric material. In. this way, it is cleared that capacitor and diodes both are almost similar in construction, means diode can be used as a similarly, capacitor.