When a p-type semiconductor is joined with an n-type semiconductor, a p-n junction is formed. Electrons from the n-type region diffuse across the junction and combine with holes from the p-type region, forming a depletion layer devoid of charge carriers. The diffusion of charge carriers continues until an electric field is produced that prevents further diffusion. When a voltage is applied across the junction, current can flow as the majority charge carriers are encouraged to diffuse in one direction.

2. CONTENT
INTRODUCTION
DIAGRAM
CHARGE CARRIERS
FORMATION OF DEPLETION LAYER
DIFFUSION CURRENT AND DRIFT CURRENT
CONCLUSION

3. INTRODUCTION
• A P-N junction is a device formed by joining by p-type(doped with B ,Al) with n-
types doped with (P ,As ,Sb) semiconductor and separated by an thin junction is
called p-n junction diode or junction diode.
• The plane dividing the two zones is called junction (plane lies where density of
donors and acceptors is equal)
• The three phenomena takes place at junction
1. Depletion layer
2. Barrier potential
3. Diffusion capacitance

4. DIAGRAM
NOTE :-1. In n type majority charge carries are
electrons.
2. In p type majority charge carries are
holes.

5. CHARGE CARRIERS
In p-n junction
• On the n side, the electrons are the majority carriers, while the holes are
the minority carriers.
• Near the junction is a region having no free charge carriers. This region,
called the depletion layer, behaves as an insulator.
• We can also denote p as a anode and n as a cathode that is
+ve and –ve.

6. FORMATION OF DEPLETION LAYER
• The excess electron in the n region cross the junction and combine with the
excess hole in p region
• N region loses its electron and becomes positively charged.
• And in p region accepts the electrons and becomes negatively charged.
• At last one point ,the migratory action is stopped.

7. DIFFUSION CURRENT AND DRIFT CURRENT
• Diffusion current is due to concentration gradient of charge carriers across the
junction and it is due to majority charge carriers. So it means, diffusion current is
due to movement of holes from p side to n side.
• Movement of electrons and holes to the positive layers and negative layers is
formation of current that current is called drift current.
• The direction of current in diffusion is just opposite of drift.

8. CONCLUSION
• The p-n junction is the basics building block for semiconductor device . understanding of
junction theory serve as the foundation to understanding other semiconductor devices.
• When positive applied to the p side large currents will flow through junction while , when
negative applied virtually no currents flow.
• Modern p n junction are fabricated using planar technology.
• Biasing play vital role in p n semiconductor device.