What is Photodiode?
The photodiode is the device that operates in reverse bias. The photodiode has a 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 photodiodes. 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 in the number of electron-hole pairs.
A photodiode differs from a rectifier diode in that when its pn junction is exposed to light, 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 in the amount of light intensity produces an increase in the reverse current.
Read Also: Semiconductor Diode
Uses of Photodiode
The photodiode can turn its current ON and OFF in nanoseconds. Therefore it is one of the fastest photo-detection devices. Some other applications of photodiode are:
- Detection for visible and for invisible.
- Automatic switching circuits.
- Logic circuits
- Optical communication equipment
- It is used as a variable resistance device controlled by light intensity.
- It is used in solar cells or panels.
- it is used in recognition circuits.
- It is used in detection circuits.