Formation of Depletion layer, Barrier voltage and Biasing in PN junction diode in English

In this video we are going to learn the following topics:
• PN junction diode and its symbol
• Formation of depletion layer
• Barrier voltage
• Biasing of PN junction diode
1.PN JUNCTION DIODE:
• If we join p-type semiconductor with n-type semiconductor such that the crystal structure remains continuous at the boundary, then junction formed in between them is called PN junction.
• And the semiconductor device so formed is called as PN junction diode.
• PN junction diode has two terminals, in p side it has anode and in n side it has cathode
• In symbol of diode, arrow head shows the direction of conventional current.
• In P type semiconductor holes are majority charge carriers and electrons are minority charge carriers.
-In N type semiconductor electrons are majority charge carriers and holes are minority charge carriers.
-Holes and Electrons are mobile charge carriers.
-Positive and negative ions are immobile charge carriers.
2.FORMATION OF DEPLETION LAYER
The majority charge carriers move from higher concentration region to lower concentration region, forming concentration gradient and this process is called as Diffusion. The holes from P region diffuse to N region and the electrons from N region diffuse to P region.
The holes in the P region recombine with electrons in N region and disappear.
Only acceptor ions which are also called as immobile ions are left behind, near the junction.
The electrons in the N region recombine with holes in P region and disappear.
Only Donar ions which are also called as immobile ions are left behind, near the junction.
This process continues.
When sufficient negative charges are accumulated near the junction in P region
Electrons which are coming from N region, experience a repulsive force
Thus diffusion of further charge carriers stops
Similarly,
When sufficient positive charges are accumulated near the junction in N region
Holes which are coming from P region, experience a repulsive force
Thus diffusion of further charge carriers stops.
In equilibrium condition,
There exists a fixed layer of negative and positive ions near the junction, without free electrons or holes
Since this fixed layer is depleted of free electrons and holes
This layer is called as Depletion Layer or Space charge region.
The physical distance from one side to another side of depletion layer is called as Width of Depletion layer.

3.BARRIER VOLTAGE
Due to presence of negative and positively charged ions, an electric potential Vb is established across the junction, called as Junction or barrier potential or cut in voltage.
This voltage acts as barrier to holes and electrons and thus called as barrier voltage
This barrier voltage is 0.7 volts for Silicon and 0.3 volts for Germanium semiconductor

4.BIASING IN PN JUNCTION DIODE
• Forward bias
When p side is connected with positive terminal of the battery and n side is connected with negative terminal of the battery, and large amount of current flows through the junction due to flow of majority charge carriers.
• Reverse bias
When p side is connected with negative terminal of the battery and n side is connected with positive terminal of the battery, and only small leakage current flows through the junction due to flow of minority charge carriers.

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Please watch: "TRANSISTOR, Construction, Biasing in BJT in hindi"
   • TRANSISTOR Construction and Biasing in BJT...  
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