We all know that photodiodes are widely used in daily life, so do you know where they are mainly used? Let's take a look at it together.

The essence of photodiode: photon → exciting carrier → forming current.

Its core structure (why can it be sensitive to light)

Photodiode is essentially a PN junction (or PIN structure):

P region: many holes.

N region: many electrons

There is a depletion layer in the middle.

This depletion layer is the "photosensitive area", which is very important.

Many high-performance photodiodes use PIN structure with an intrinsic layer (I layer) in the middle: larger photosensitive area, faster response and lower noise.

The real working principle (step by step)

When there is no light

In the reverse bias state (this is the most common usage of photodiode): PN junction is basically non-conductive, only very small, dark current, and the output signal is close to 0.

What happened after the light came in?

When light (visible light, infrared light and ultraviolet light) strikes the depletion layer, photons are absorbed by the semiconductor, resulting in electron-hole pairs, and the built-in electric field in the depletion layer immediately pulls them apart.

The stronger the light, the greater the current.

Light intensity → generated carriers → photocurrent → In a certain range, photocurrent is approximately proportional to light intensity.

The above is the working principle of photodiode. I hope you will have a clear understanding after reading it.