PHOTODIODE
Photodiode is a p-n junction device which is always operated at reversed biased voltage
Construction and Working
· Light is always focussed through a glass lens on the depletion region of the photodiode.
· As the photodiode is reverse biased, depletion region is quite wide and penetrated on both sides of the junction.
· Photons incident on the depletion region will impart their energy to the ions present there and generate electron-hole pairs.
· Number of electron-hole pairs will depend on the intensity of the incident light.
· These electrons and holes will be then attracted towards the positive and negative terminals of the battery.
· Thus, photocurrent is generated.
· Photocurrent generated is directly proportional to the intensity of the incident light.
· ‘Dark current’ is the current flowing through the photodiode in the absence of light. It flows due to minority charge carriers.
Construction and Working
· Light is always focussed through a glass lens on the depletion region of the photodiode.
· As the photodiode is reverse biased, depletion region is quite wide and penetrated on both sides of the junction.
· Photons incident on the depletion region will impart their energy to the ions present there and generate electron-hole pairs.
· Number of electron-hole pairs will depend on the intensity of the incident light.
· These electrons and holes will be then attracted towards the positive and negative terminals of the battery.
· Thus, photocurrent is generated.
· Photocurrent generated is directly proportional to the intensity of the incident light.
· ‘Dark current’ is the current flowing through the photodiode in the absence of light. It flows due to minority charge carriers.
Symbol
Characteristics of Photodiode
Advantages
· High sensitivity
· High speed of operation
Disadvantages
· Dark current increases with increase in temperature
· Poor temperature stability
· External bias is required
· Amplification is required as the output produced is small in magnitude
Application of Photodiode
· Object counting system
· In camera for sensing light
· Fibre Optic receiver
· Light intensity meter
· High sensitivity
· High speed of operation
Disadvantages
· Dark current increases with increase in temperature
· Poor temperature stability
· External bias is required
· Amplification is required as the output produced is small in magnitude
Application of Photodiode
· Object counting system
· In camera for sensing light
· Fibre Optic receiver
· Light intensity meter