7 March 2018

Avalanche photo diode

What is an avalanche photodiode?

An avalanche photodiode is one kind of semiconductor device specially designed to work in the reverse breakdown region. The symbol, of this diode, is actually same to a Zener diode. The avalanche diode comprises two terminals namely anode and cathode. The symbol is alike to the normal diode but with turn edges of the vertical bar that is shown in the following figure.

Avalanche photodiode basics :

An avalanche photodiode is a semiconductor device types of a diode, it looks like as PN photodiode or PIN photodiode. An avalanche photodiode specially designed to work in the reverse breakdown region. In an avalanche photodiode is basically two terminal namely anode and cathode. It is similar or looks like Schottky photodiode. Avalanche multiplication of the holes and electrons created by photon impact.

In this diode when a P-N junction diode is applied with high reverse bias break down can occur by two separate mechanisms direct ionization of the lattice atoms devices, it is a Zener break down and also its is high-velocity carriers causing impact ionization of the lattice atoms called avalanche break down. APD uses has its avalanche break down phenomena for its operation. Here this articles also gives the difference between these two types of a diode; PIN photodiode versus avalanche photodiode.

The avalanche photodiode has its internal gain which increases its responsibility. Shows the figure schematic structure of an APD. By virtue of the doping concentration and physical construction of the N-P  junction, The electric field is high enough to cause of impact ionization.

Under normal operating bias, the I-layer is completely depleted. This is known as reach through condition, hence APDs are also known as reach through APD or reverse APDs.

The avalanche action enables the gain of the diode to be too much increased many times and providing a very much greater level of sensitivity.

APD schematic and variation of E - field across the diode

A breakdown voltage of diode :

The avalanche diode breakdown voltage totally depended on the density of doping. When rising the density of doping will reduce the breakdown voltage of the diode.


Avalanche diode modules :

Avalanche photodiode are available as part of modules which apart from the photodiode also contain additional different electronic components. In particular, there can be a current amplifier integrated into the package, which can not only reduces the number of parts required on a circuit board but also it can also improve the noise performance and results in a better combination of bandwidth and responsivity. Some modules have been specially optimized use for an optical fiber communication system and fiber coupled.

Application of avalanche photodiode :
  • It can be used as white noise generators
  • This diode is more protecting the circuit against unwanted voltages
  • This diode is produced RF noise, they are generally used as noise sources in radio gear
  • It can be also used to generate microwave frequency
For detailed information :

This article also gives the various types of diode listed below: