Question

Describe briefly , with the help of a diagram, the role of the two important processes involved in the formation of a pn junction.

Answer 1

The two important process involved in formation of p - n junction:

(i) Diffusion

(ii) Drift

When p and n sides comes in contact then majority carries diffuse from high concentration to low concentration. Electrons flow from n to p junction and combines with holes near the junction. Similarly holes flow from p-side to n side and combine with electrons near the junction. As this happens, region near the junction gets depleted of carriers and gets charged as shown in figure. This diffusion of carriers leads to diffusion current.

The charge in depletion region creates electric field. This electric field leads to flow of minority carriers across depletion region. This is called the drift current.

The diffusion and drift currents are opposite in direction.

In equilibrium, they are equal to each other and p-n junction is formed.