JEE Main & Advanced Physics Semiconducting Devices P-N Junction Diode

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

(1) 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 \[\propto \frac{1}{\text{Dopping}}\]

(iii) Depletion is directly proportional to temperature.

(iv) The P-N junction diode is equivalent to capacitor in which the depletion layer acts as a dielectric.

(2) 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   \[{{V}_{B}}=0.3V\]  and for silicon \[{{V}_{B}}=0.7V\] On the average the potential barrier in P-N junction is \[\tilde{\ }0.5\,\,V\] and the width of depletion region \[\tilde{\ }{{10}^{-6}}\,m\]So the barrier electric field \[E=\frac{V}{d}=\frac{0.5}{{{10}^{-6}}}=5\times {{10}^{5}}\,V/m\]

(3) Some important graphs

(4) Diffusion and drift current : Because of concentration difference holes/electron try to diffuse from their side to other side. Only those holes/electrons crosses the junction, which have high kinetic energy. This diffusion results in an electric current from the P-side to the N-side known as diffusion current \[({{i}_{df}})\]

As electron hole pair (because of thermal collisions) are continuously created in the depletion region. There is a regular flow of electrons towards the N-side and of holes towards the P-side. This makes a current from the N-side to the P-side. This current is called the drift current \[({{i}_{dr}})\].