i. The region across the p-n junction where there are no charges is called the depletion layer or the depletion region.
ii. During diffusion of charge carriers across the junction, electrons migrate from the nside to the p-side of the junction. At the same time, holes are transported from p-side to nside of the junction.
iii. As a result, in the p-type region near the junction there are negatively charged acceptor ions, and in the n-type region near the junction there are positively charged donor ions.
iv. The potential barrier thus developed, prevents continuous flow of charges across the junction. A state of electrostatic equilibrium is thus reached across the junction.
v. Free charge carriers cannot be present in a region where there is a potential barrier. This creates the depletion region.
vi. In absence of depletion region, all the majority charge carriers from n-region (i.e., electron) will get transferred to the p-region and will get combined with the holes present in that region. This will result in the decreased efficiency of p-n junction.
vii. Hence, formation of depletion layer across the junction is important to limit the number of majority carriers crossing the junction.