When a P-type semiconductor is suitably joined to an N-type semiconductor, then resulting arrangement is called P-N junction or P-N junction diode
![2268_pn junction.png](https://www.expertsmind.com/../CMSImages/2268_pn junction.png)
Depletion region: On account of difference in concentration of charge carrier in the two sections of P-N junction, the electrons from N-region diffuse through the junction into P-region and the hole from P region diffuse into N-region.
Due to diffusion, neutrality of both N and P-type semiconductor is disturbed, a layer of negative charged ions appear near the junction in the P-crystal and a layer of positive ions appears near the junction in N-crystal. This layer is called depletion layer
(i) The thickness of depletion layer is 1 micron = 10-6 m.
(ii) Width of depletion layer ∝ 1/Dopping
(iii) Depletion is directly proportional to temperature.
(iv) he P-N junction diode is equivalent to capacitor in which the depletion layer acts as a dielectric.
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![2132_pn junction1.png](https://www.expertsmind.com/../CMSImages/2132_pn junction1.png)
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Potential barrier: The potential difference created across the P-N junction due to the diffusion of electron and holes is called potential barrier.
For Ge vB =0.3v and for silicon vB = 0.7v
On the average the potential barrier in P-N junction is ~ 0.5 V and the width of depletion region ~ 10-6.
So the barrier electric field E = V/d =0.5/10-6 =5 * 105 v/m
Some important graphs:
![1362_pn junction2.png](https://www.expertsmind.com/CMSImages/1362_pn%20junction2.png)
Diffusion and drift current: Because of concentration difference holes/electron try to diffuse from their side to other side. Only these holes/electrons cross the junction, having high kinetic energy. This diffusion results is an electric current from the P-side to the N-side known as diffusion current (idf)
As electron hole pair (because of thermal collisions) is continuously created in the depletion region. These are a regular flow of electrons towards the N-side and of holes towards the P-side. This creates a current from the N-side to the P-side. This current is known as the drift current (idr).
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