With the help of a neat circuit diagram, explain the working of a photodiode. State its any'two uses.

Explanation

A photodiode is a special type of photodetector used for detecting optical signals. It is a reverse biased `p-n` junction made of photosensitive semiconducting material. It works under reverse bias below the breakdown- voltage.
The conductivity of `p-n` junction photodiode increases with the increase in intensity of light falling of it.
When voltage is less than the breakdown voltage and no light is incident on its junction, the reverse current is extremely small.

When visible light of energy greater than forbidden energy gap is incident on `p-n` junction diode electron-hole pairs starts to move and reverse current starts to flow which increases with increase in intensity of falling light at `p-n` junction.
Uses: `(1)` In photodetection for optical signals.
`(2)` In reading of computers, punch cards.
`(3)` It is used as sensor in remote controlled receivers.