How is an electric field across the pn junction created?

An electric field across a pn junction is created when the p-type and n-type semiconductor materials are brought into contact. Electrons from the n-type region diffuse into the p-type region, while holes from the p-type region diffuse into the n-type region. This movement of charge carriers leads to the formation of a depletion region near the junction, where mobile charge carriers are depleted. The resulting separation of charges creates an electric field that points from the n-type region to the p-type region, establishing a potential barrier that affects further charge carrier movement.