Depletion region is seen in pn junction of a diode.
The region of positive charge and negative charge on either side of the junction is termed as the depletion region.
When the p-type and the n-type materials are held in contact with each other, the junction among them behaves differently from either side of the material alone. The electrons and holes are close to each other at the junction. According to coulomb’s law, there is a force between the negative electrons and the positive holes. When the p-n junction is developed a few electrons from the n-type diffuse through the junction and combines with the holes in the p-side to form negative ions and leaves behind positive ions in the n-side. This results in the formation of the depletion layer, which acts as the barrier and does not allow any further flow of electrons from the n region to the p region.