What is Photodiode?
The photo diode is the device which operates in reverse bias.The photo diode has small transparent window that allows light to strike the pn junction.
We know that when reverse biased ,the rectifier diode has a very small leakage of current.The same is true for photodiode.The reverse biased current is produced by thermally generated electron hole pairs in the depletion region which are swept across the pn junction by electric field created by reversing the voltage.
In a rectifier diode the reverse leakage of current increases with temperature due to an increase the number of electron hole pairs.
A photo diode differs from a rectifier diode in that when its pn junction is exposed to light,due to this the reverse current increases with light intensity.When there is no incident light the reverse current is almost negligible and is called the dark current.An increase the amount of light intensity produces an increase in the reverse current.
The photo diode can turn its current ON and OFF in nano seconds. Therefore it is one of the fastest photo detection device.Some other applications of photodiode are:
- Detection for visible and for invisible.
- Automatic switching circuits.
- Logic circuits
- Optical communication equipment
- It is used as variable resistance device controlled by light intensity.