Diodes and Their Types

A diode is an electronic device with two terminals that conduct current primarily in one direction. They feature a low resistance in one direction (ideally zero), and high resistance in the other (ideally infinite). They have a wide range of uses and there are many different types of diodes available. The different properties of these varying diodes allow each one to perform in specialized functions. Below are the most common types of diodes and their uses.

The first type of diode is the avalanche diode. This diode conducts in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. Its name comes from the avalanche effect that occurs when the reverse electric field across the P-N junction creates a wave of ionization, similar to an avalanche, leading to a large current. Diodes of this type are designed to break down at a well-defined reverse voltage without being destroyed. The second type of diode, the Light Emitting Diode (LED) is one of the most common types. LEDs produce light when the diode permits the transfer of electric current between the electrodes. These diodes release energy in the form of light when the diode is turned on and the electrons combine with the holes. The color of light it emits depends on the energy gap of the semiconductor and can produce wavelengths ranging from infrared to near ultraviolet.

The next type, laser diodes, produce coherent light, making them different from an LED. A laser is formed when an LED-like structure is contained within a resonant cavity made by polishing the parallel end faces. Laser diodes are frequently used in optical storage devices as well as high-speed optical communications. Photodiodes have wide, transparent junctions as they operate in reversed bias where minimal amounts of current flow. They are used to detect light and are found in solar cells, photometry, and in optical communications or to generate electricity.

Another type of diode is the Schottky diode, constructed from a metal-to-metal semiconductor contact and featuring a lower forward voltage drop than that of traditional P-N junction diodes. They can be used as a low-loss rectifier, but the reverse leakage current of these diodes is commonly higher than other diodes. Tunnel diodes are similar to the standard P-N junction apart from their doping levels, which are higher and have a more narrow depletion region. Tunneling is an effect that results from quantum mechanical effects as electrons pass through a potential bettier. Tunnel diodes are widely used in microwave applications.

The varicap diode, also known as the varactor diode, is used as a voltage-controlled capacitor with a reverse bias that varies the width of the depletion relative to the voltage across the diodes. Varicap diodes act as capacitors and capacitor plates are formed by the extent of conduction regions as well as the depletion region as the insulating dielectric. The final type of diode, the zener diode, offers a stable reference voltage and can be configured to conduct backwards. Zener diodes are frequently used in conjunction with switching diodes and the two types are connected in series in opposite directions to balance the temperature coefficient to nearly zero. Diodes of this type are primarily used to offer a reference point for voltage in power supplies.

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