Junction voltage
When n- and p-type semiconductors are joined forming a pn-junction, that is the interface between the two types of the semiconductor, a depletion region is created. Over this depletion region, a potential difference or voltage is created, known as barrier voltage or Junction voltage.
The reason for the creation of this junction voltage is this: Electrons in the n-type semiconductor are attracted to holes in the p-type semiconductor. In the same way, holes in the p-type semiconductor are attracted to electrons in the n-type semiconductor. As free electrons cross the junction, the n-type material becomes depleted of electrons near the junction. The same thing happens to the holes in the p-type semiconductor.
An area along the junction known as the depletion region has been created. The electrons that have crossed over to the p side serve as negative potential to repel any further electrons from crossing over. The holes that have moved over to the n side also repel any othe holes from crossing over. The area on the n side of the junction has now a positive charge, while the area on the p side of the junction has a negative charge. These charges exist only in the junction, while overall the diode remains electrically neutral.