What is a Avalanche photo diode (APD) ? Advantages and disadvantages.

APD ( Avalanche photo diode):

One of the main working parts of any optical receivers the photo detector . Avalanche photo diode device that transform optical signal to electrical signal.
                         An avalanche photo diode (APD) is a highly sensitive semiconductor electron devices that exploits the photo electric effect to convert light to electricity.

The avalanche photo diode possesses a similar structure to that of the PN or PIN photo diode. An avalanche diode structure similar to that of a Schottky photo diode may also be used but the use of this version is much less common.

The main difference of the avalanche photo diode to other forms of photo diode is that it operates under a high reverse bias condition. This enables avalanche multiplication of the holes and electrons created by the photon / light impact.
  •     In APD an extremely high electric field region is created ~ 3×10 the 5 v cm-1.

Avalanche photo diode advantages and disadvantages


  • Avalanche photo diodes possess a number of advantages and disadvantages. These can be considered in the selection of a suitable photo detector device.

Avalanche photo diode advantages


  • High level of sensitivity as a result of avalanche gain.

Avalanche photo diode disadvantages:


  • Much higher operating voltage may be required.
  • Avalanche photo diode produces a much higher level of noise than a PN photo diode.
  • Avalanche process means that the output is not linear.
The avalanche photo diodes are not as widely used as their PIN counterparts. They are used primarily where the level of gain is of paramount importance, because the high voltages required, combined with a lower reliability means that they are often less convenient to use.

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