concentration of electrons on ท side while low concentration of electrons on p side. Hence diffusion starts and electrons start moving from ท side towards p side.
Similarly the holes from p-side diffuse across the junction into the n-region.
The initial diffusion is shown in the Fig. 1.14.
1.11.2 Formation of Depletion Region
As holes enter the ท region, they find number of donor atoms. The holes recombine with the donor atoms. As donor atoms accept additional holes, they become positively charged immobile ions. This happens immediately when holes cross the junction hence number of positively charged immobile ions get formed near the junction on ท side.
Atoms on p side are acceptor atoms. The electrons diffusing from ท side to p side recombine with tile acceptor atoms on p side. As acceptor atoms accept additional electrons, they become negatively charged immobile ions. Such large number of negatively charged immobile ions get formed near the junction on p-side. The formation of immobile ions near the junction is shown in the Fig. 1.15.
As more number of holes diffuse on ท side, large positive charge gets accumulated on ท side near the junction. Eventually the diffusing holes which are positively charged,, get repelled due to accumulated positive charge on ท side. And the diffusion of holes stops.
Similarly due to large negative charge accumulated on p side, the diffusing electrons get repelled and eventually the diffusion of electrons also stops.
Thus in thermal equilibrium, in the region near the junction, there exists a wall of negative immobile charges on p side and a wall of positive immobile charges on n-side. In this region, there are no mobile charge carriers. Such a region is depleted of the free mobile charge carriers and hence called depletion region or depletion layer. The depletion region is also called space-charge region. In equilibrium condition, the depletion region