Question

How the depletion layer form

Answer 1

When a p-n junction is formed, some of the free electrons in the n-region diffuse across the junction and combine with holes to form negative ions. In so doing they leave behind positive ions at the donor impurity sites.

Answer 2

In a pn junction diode, p region has holes in majority and n region has electrons in majority.

When these to meet at a junction, the electrons are attracted towards p region and holes are attracted towards n region due to opposite polarity.

This forms a region in the middle of the diode where no ions are present. The electron and hole density remains same here. This region is called the depletion region.