3. IMPORTANT DIODES
A]PHOTO DIODE:-
o A photodiode is a PN-junction diode that consumes light energy to produce an
electric current.
o Sometimes it is also called a photo-detector, a light detector, and photo-sensor.
o These diodes are particularly designed to work in reverse bias conditions, it
means that the P-side of the photodiode is associated with the negative
terminal of the battery, and the n-side is connected to the positive terminal of
the battery.
o It works on the principle of photo-electric effect.
o This diode is very sensitive to light so when light falls on the diode it easily
changes light into an electric current. The solar cell is also branded as a large-
area photodiode because it converts solar energy into electric energy.
WORKING PRINCIPLE
1)Absorption Of Light: When
light(photons) strikes the depletion
region of photodiode, it excites the
electrons, creating electron hole
pairs.
2)Seperation of Charge Carriers:
the built in electric field at the P-N
junction separates these carriers.
Electrons move towards the n-
region, and holes move towards the
p-region.
3)Generation Of Current: This
movement of charge carriers creates
a photocurrent that flows through an
external circuit. The intensity of light
affects the amount of current
generated.
4)Low Dark Current: A small
leakage current (called dark current)
exists due to thermally generated
, CONSTRUCTION
1. Material: A photodiode is typically made from semiconductor materials like
silicon (Si), germanium (Ge), or gallium arsenide (GaAs).
2. P-N Junction: The core structure of a photodiode is the P-N junction, which
is formed by joining a p-type semiconductor (with an excess of holes) and an
n-type semiconductor (with an excess of electrons).
3. Depletion Region: The interface between the p-type and n-type regions
creates a depletion region where no free charge carriers exist. This region
plays a crucial role in the photodiode's operation.
4. Light Absorption: The photodiode is designed to absorb light (photons).
When light strikes the junction, it excites electrons, creating electron-hole
pairs.
5. Electric Field: The built-in electric field at the P-N junction separates the
electron-hole pairs, causing the electrons to move toward the n-type side and
holes toward the p type side.
6. Reverse Biasing: Typically, a photodiode operates under reverse bias, which
widens the depletion region and makes the device more sensitive to light. The
photocurrent generated is proportional to the intensity of the incident light.
V-I Characteristics of Photodiodes
A]PHOTO DIODE:-
o A photodiode is a PN-junction diode that consumes light energy to produce an
electric current.
o Sometimes it is also called a photo-detector, a light detector, and photo-sensor.
o These diodes are particularly designed to work in reverse bias conditions, it
means that the P-side of the photodiode is associated with the negative
terminal of the battery, and the n-side is connected to the positive terminal of
the battery.
o It works on the principle of photo-electric effect.
o This diode is very sensitive to light so when light falls on the diode it easily
changes light into an electric current. The solar cell is also branded as a large-
area photodiode because it converts solar energy into electric energy.
WORKING PRINCIPLE
1)Absorption Of Light: When
light(photons) strikes the depletion
region of photodiode, it excites the
electrons, creating electron hole
pairs.
2)Seperation of Charge Carriers:
the built in electric field at the P-N
junction separates these carriers.
Electrons move towards the n-
region, and holes move towards the
p-region.
3)Generation Of Current: This
movement of charge carriers creates
a photocurrent that flows through an
external circuit. The intensity of light
affects the amount of current
generated.
4)Low Dark Current: A small
leakage current (called dark current)
exists due to thermally generated
, CONSTRUCTION
1. Material: A photodiode is typically made from semiconductor materials like
silicon (Si), germanium (Ge), or gallium arsenide (GaAs).
2. P-N Junction: The core structure of a photodiode is the P-N junction, which
is formed by joining a p-type semiconductor (with an excess of holes) and an
n-type semiconductor (with an excess of electrons).
3. Depletion Region: The interface between the p-type and n-type regions
creates a depletion region where no free charge carriers exist. This region
plays a crucial role in the photodiode's operation.
4. Light Absorption: The photodiode is designed to absorb light (photons).
When light strikes the junction, it excites electrons, creating electron-hole
pairs.
5. Electric Field: The built-in electric field at the P-N junction separates the
electron-hole pairs, causing the electrons to move toward the n-type side and
holes toward the p type side.
6. Reverse Biasing: Typically, a photodiode operates under reverse bias, which
widens the depletion region and makes the device more sensitive to light. The
photocurrent generated is proportional to the intensity of the incident light.
V-I Characteristics of Photodiodes
