SEMICONDUCTORS AND ELECTRONIC DEVICES –
MODULE 5
N-TYPE EXTRINSIC SEMICONDUCTOR
• When a small amount of Pentavalent impurity is added to a pure
semiconductor providing a large number of free electrons in it, the extrinsic
semiconductor thus formed is known as n-Type Semiconductor.
• The conduction in the n-type semiconductor is because of the free
electrons denoted by the pentavalent impurity atoms.
• Conduction in N-Type extrinsic semiconductors:
→ In the n-type semiconductor, a large number of free electrons are available
in the conduction band which are donated by the impurity atoms.
→ When a potential difference is applied across this type of semiconductor,
the free electrons are directed towards the positive terminals. It carries an
electric current.
→ As the flow of current through the crystal is constituted by free electrons
which are carriers of the negative charge, therefore, this type of
conductivity is known as negative or n-type conductivity.
→ The electron-hole pairs are formed at room temperature. These holes
which are available in small quantity in the valence band also consists of a
small amount of current.
,P-TYPE EXTRINSIC SEMICONDUCTOR
• The extrinsic p-Type Semiconductor is formed when a trivalent impurity is
added to a pure semiconductor in a small amount, and as a result, a large
number of holes are created in it.
• A large number of holes are provided in the semiconductor material by the
addition of trivalent impurities like Gallium and Indium.
• Conduction in P-type extrinsic semiconductors:
→ In a p-type semiconductor, a large number of holes are created by the
trivalent impurity.
→ When a potential difference is applied across this type of semiconductor
the holes are available in the valence band are directed towards the
negative terminal.
→ As the current flow through the crystal is by holes, which are carriers of
positive charge, therefore, this type of conductivity is known as positive or
p-type conductivity. In a p-type conductivity, the valence electrons move
from one covalent to another.
P-N JUNCTION DIODE
NO APPLIED BIAS (VD = 0)
, → The potential barrier that now exists discourages the diffusion of any more
majority carriers across the junction. However, the potential barrier helps
minority carriers (few free electrons in the P-region and few holes in the N-
region) to drift across the junction.
→ Then an “Equilibrium” or balance will be established when the majority
carriers are equal and both moving in opposite directions, so that the net
result is zero current flowing in the circuit. When this occurs, the junction is
said to be in a state of “Dynamic Equilibrium “.
REVERSE BIAS (VD < 0)
OVERALL PROCESS:
,
MODULE 5
N-TYPE EXTRINSIC SEMICONDUCTOR
• When a small amount of Pentavalent impurity is added to a pure
semiconductor providing a large number of free electrons in it, the extrinsic
semiconductor thus formed is known as n-Type Semiconductor.
• The conduction in the n-type semiconductor is because of the free
electrons denoted by the pentavalent impurity atoms.
• Conduction in N-Type extrinsic semiconductors:
→ In the n-type semiconductor, a large number of free electrons are available
in the conduction band which are donated by the impurity atoms.
→ When a potential difference is applied across this type of semiconductor,
the free electrons are directed towards the positive terminals. It carries an
electric current.
→ As the flow of current through the crystal is constituted by free electrons
which are carriers of the negative charge, therefore, this type of
conductivity is known as negative or n-type conductivity.
→ The electron-hole pairs are formed at room temperature. These holes
which are available in small quantity in the valence band also consists of a
small amount of current.
,P-TYPE EXTRINSIC SEMICONDUCTOR
• The extrinsic p-Type Semiconductor is formed when a trivalent impurity is
added to a pure semiconductor in a small amount, and as a result, a large
number of holes are created in it.
• A large number of holes are provided in the semiconductor material by the
addition of trivalent impurities like Gallium and Indium.
• Conduction in P-type extrinsic semiconductors:
→ In a p-type semiconductor, a large number of holes are created by the
trivalent impurity.
→ When a potential difference is applied across this type of semiconductor
the holes are available in the valence band are directed towards the
negative terminal.
→ As the current flow through the crystal is by holes, which are carriers of
positive charge, therefore, this type of conductivity is known as positive or
p-type conductivity. In a p-type conductivity, the valence electrons move
from one covalent to another.
P-N JUNCTION DIODE
NO APPLIED BIAS (VD = 0)
, → The potential barrier that now exists discourages the diffusion of any more
majority carriers across the junction. However, the potential barrier helps
minority carriers (few free electrons in the P-region and few holes in the N-
region) to drift across the junction.
→ Then an “Equilibrium” or balance will be established when the majority
carriers are equal and both moving in opposite directions, so that the net
result is zero current flowing in the circuit. When this occurs, the junction is
said to be in a state of “Dynamic Equilibrium “.
REVERSE BIAS (VD < 0)
OVERALL PROCESS:
,
