Which type of diode exhibits impact ionization?

An avalanche photodiode is designed to exploit the phenomenon of impact ionization, which is a critical feature of its operation. In this diode, when a reverse voltage is applied, it reaches a certain threshold that enables the multiplication of charge carriers. This occurs because the high electric field causes the accelerated carriers (electrons or holes) to collide with the lattice atoms of the semiconductor material with enough energy to generate additional electron-hole pairs. As a result, this leads to a cascade effect, significantly amplifying the current generated in response to a single photon.

Avalanche photodiodes are highly sensitive and are often used in applications requiring the detection of weak optical signals, such as in fiber-optic communication and photon counting. Their ability to perform under varying light conditions stems from this impact ionization process, allowing them to effectively convert incoming photons into a measurable electric signal through gain.

In contrast, while standard photodiodes, Schottky diodes, and PIN diodes have their specific operational mechanisms and applications, they do not employ the same impact ionization process that characterizes avalanche photodiodes. Standard photodiodes generate a small current in response to light without significant gain. Schottky diodes, known for their rapid switching capabilities, rely primarily