p-n junction

The interface between the p-type region and the n-type region of a semiconductor forms a p-n junction. Since the p-region has large number of holes, whereas the n region has large number of electrons (holes and electrons are majority charge carriers in p and n type semiconductors respectively), holes from the p-region and electrons from the n region diffuse to the other side of the junction (due to carrier concentration difference) and recombine, leaving behind the negatively charged ions in the p-region and positively charged ions in the n-region. This results in the formation of a charged region (depletion region) near the interface and a potential barrier (0.7 V for Silicon, 0.4 Volts for Germanium) is developed, which prevent further flow of carriers towards the junction. The schematic diagram and band diagram and symbolic representation of the p-n junction are shown in the figure. The arrow represents the direction of flow of current under forward bias.