Diodes: Types and Applications

Diodes is a two terminal electronic device which allows the flow of current in only one direction and high resistance in opposite direction. The most common diode used currently are p-n junction diode. The diodes are of different types as illustrated below:

• p-n junction Diodes
• Avalanche Diodes
• Zener Diodes
• LED(light emitting diode)
• Photo Diodes
• Sckottky Diodes
• Tunnel Diodes
• Gunn Diodes
• Laser Diodes
• Pin Diodes

p-n junction diode: A pn junction diode is made up of silicon or germanium doped at certain level. Any pentavalent or trivalent impurities can be added to form pn junction diode. It can be either a donor if pentavalent impurities are added or acceptor when trivalent impurities are added. p-n junction diodes are the electronic components that can allow the flow of current in only forward direction and gives 100 percent resistance in reverse direction.

Avalanche Diode: These are the diodes which conducts in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. These are electrically similar to the zener diodes but having a different breakdown mechanism (avalanche effect). 

Zener Diode: These diodes are termed as reverse breakdown diodes because these are mainly used in reverse direction. breakdown occurs at below the breakdown voltage of 5 volts. The zener diodes conduct some minute amount of current (micro amperes) in reverse direction. 

LED: Light emitting diodes are directly made up of gallium arsenide that cross the junction and emit photons when they combine with the majority carrier on the other side. The different voltages corresponds to different colors like 2.1 volts correspond to red and 4 volts corresponds to violet.

Photo Diode: All semiconductors are subject to optical charge carrier generation. A photo diode is used generally to sense light coming from various outlets. So a photo diode is packaged in a material that allows light to pass through. Photo diodes can be used in line following robot, etc.

Sckottky Diode: These diodes have very less forward voltage drop, even lesser than p-n junction diodes. Their voltage drop at forward current of 1mA is at 0.15V to 0.45V, which makes them usefull in voltage clamping applications. They are also used as low loss rectifier.

Tunnel Diode: Tunnel diode or Esaki diode have a region of operation showing negative resistance showing quantum tunneling allowing amplification of signals. These diodes are very fast and can be used in spacecrafts because of their high magnetic field and high radiation environment susceptibility.

Gunn Diode: Gunn diodes are similar to tunnel diodes but these offer negative differential resistance. These diodes are used in high frequency microwave oscillators.

Laser Diode: If a LED is contained in a resonant cavity formed by polishing the parallel end faces a laser can be formed. Laser diodes are used mainly for optical communication.

Pin Diodes: A pin diodes has a central undoped or intrinsic layer forming a p-type or n-type structure. They are used as radio frequency switches and attenuators.These are also used in power electronics.