What is Photodiode | Working of Photodiode | Usage of Photodiode

Photodiode | Its Working and Usage in Daily Life

What is Photodiode?

Photodiode is an optoelectronic device in which current carriers are generated by photons through photoexcitation. i.e., photoconduction by light.

• A photodiode is a special type P-N junction diode made of photosensitive semiconductor material. In such a diode, a transparent window is made to allow the light of suitable frequency to fall on it.

• It is operated in reverse biased condition and in absence of light, a very small reverse saturation current flow, it is known as Dark current.

• The value of reverse saturation current increases with an increase in the intensity of light.

• A photodiode can turn its current ON and OFF in nanosecond. That’s why photodiode is one of the fastest photodetectors.

Working of Photodiode 

When a light (photon) is incident on the diode, the incident photon is absorbed by a bound electron in the valence band. If photons energy is greater than the forbidden energy gap (E_p≥E_g) (forbidden energy gap means the difference of energy of valence band and conduction band or amount of energy required to jump in conduction band from valence band) then these electrons will jump over the gap into the conduction band, thus a new electron-hole pair is created and this electron is swept toward the N-side and hole swept toward P-side by the reverse bias. This result is an additional current through the diode which we called photocurrent.

Use of Photodiode

• In photodetection for optical signal
• In switching the light ON and OFF
• Light metering
• Counter
• Controlled relay

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