These photodiodes are helpful where there is a need for sensitive light detection. To provide performance that other photodiode types may not be able to attain, silicon avalanche photodiode is used in various applications. Although the avalanche process has some disadvantages, the avalanche photodiode uses the process to offer additional performance. Given pros and cons, avalanche photodiodes help various niche applications where their features allow them to provide the extra sensitivity that may be needed.

The silicon avalanche photodiode operates under a high reverie bias condition, making it different from other photodiode forms. It has a similar structure to that PIN or PN. As a photon enters the depletion region and creates a whole electron pair, a high electric field pulls these charges away from each other. The charges will create a hole electron pair when their velocity increases to such an extent that they collide with the lattice. Providing a very much greater sensitivity level, the avalanche action enables the gain of the diode to be increased.

For silicon avalanche photodiodes to operate, they require a high reverse bias. Typically, this will be between 100 and 200 volts. As it is found that when higher voltages are applied, the gain levels increase. Where sensitivity is of paramount importance, this can offer a distinct advantage. But obviously, this is at the expense of all the additional circuitry and safety features required for the very high voltages.

Silicon avalanche photodiodes have many advantages and disadvantages.

As a result of avalanche gain., it has a high level of sensitivity.

Fast response time

High performance

There may be a need for a much higher operating voltage.

Avalanche photodiode produces a much higher level of noise than a PN photodiode.

The output is not linear in the avalanche process.

Due to low reliability, it is not widely used.

It has a much higher level of noise.

The silicon avalanche photodiodes are not widely used as their PIN counterparts. Primarily, they are used where the level of gain is of paramount importance. This is because the higher the voltages required, combined with lower reliability.

These applications include receivers in;

Optical fiber

Communications

Imaging

Range finding

High-speed laser scanners like laser microscopy, laser scanners, and optical time domain reflectometers.

the current amplification enormously increases the responsivity. However, the amplification factor and responsivity may vary from device to device because they strongly depend on the reverse voltage. Silicon avalanche photodiodes are hardly suitable for precise low-light powers because their responsivity is not nearly well defined.

Silicon avalanche photodiodes can achieve high detection bandwidth, although there is an inherent trade-off between amplification and bandwidth.

The quantum productivity of a silicon avalanche photodiode is not necessarily high despite the high responsivity. This means that even though other photons trigger an electron avalanche, some of the incident photons do not contribute to the photocurrent. 

With a maximum responsivity occurring around 600nm-800nm, silicon avalanche photodiodes are sensitive in the wavelength area. The multiplication factor of silicon APDs can vary between 50 and 1000 depending on the device and the reverse voltage applied.

Since the large responsivity of a Si APD reduces the impact of electronic noise in the subsequently used photodiode preamplifier, it can help minimize detection noise. Therefore, when electronic noise is a limiting factor, the photodetectors' noise performance with APDs can be better than that of the devices with ordinary p-i-n photodiodes. An increase in amplification factor increases the excess noise factor. Therefore, because the setting minimizes the overall noise, a reverse voltage is often chosen such that the multiplication noise equals the noise of the electronic amplifier.