Explain how the depletion layer and barrier potential are formed in pn junction diode ?

Explanation

When a p-type crystal is placed in contact with n-type crystal so as to form one piece, the assembly so obtained is called p-n junction or junction diode or crystal diode. The surface of constant of p and n-type crystals is called junction. In the p-section holes are the majority carriers, while in n-section, the majority carriers are electrons. Due to the high concentration of different type of charge carriers in two sections, holes from p-region diffuse into n-region and electrons from n-region diffuse into p-region. In both cases, when an electron meets a hole, the two cancel the effect of each other and as a result, a thin layer at the junction becomes devoid of charge carriers. This is called depletion layer (Fig). The thickness of the depletion layer is of the order of `10^(-6)m`. Due to the diffusion of holes and electrons, the two sections, of the junction diode no longer remain neutral. The p-section of the junction diode becomes slightly negative, while the n-section is rendered positive. It appears as if some fictitious battery is connected across the junction with its negative pole connected to p-region and positive pole connected to n-region. The potential difference developed across the junction due to migration of majority charge carriers is called potential barrier.