What is Photodiode ?

Explanation

Photodiode is a p-n junction having photosensitive semiconducting material and is based on the principal of electric conduction from light.

Photo diode is reversed biased as shown in the figure and when light is made to fall, the valence electrons absorb this energy and jump to conduction band leaving a hole in the valence band, so additional electron hole pairs are created in both p and n regions. Thus there is small change in majority carrier concentration and large change in minority carrier concentration. So the reverse current is increased to a large value due to additional minority carriers. Hence with the increase in intensity of incident light the current increases linearly till it becomes saturated.