In a p-n junction diode, majority carriers are holes on p-side and electrons on n-side. Holes, thus diffuse to n-side and electrons to p-side. Thus diffusion causes an excess positive charge in then-region and an excess negative charge in the p-region and an excess negative charge in the p-region near the junction. Thus double layer of charge creates an electric field which exerts a force on the electrons and holes, against their diffusion. Thus electric field becomes strong enough as diffusion proceeds to stop it. In the equilibrium position, there is a barrier, for charge motion with the n-side at a higher potential then the p-side.

The junction region has a very low density of either p or n-type carriers, because of inter diffusion. It is called depletion region. There is a barrier V B associated with it. This is the potential barrier.