A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. The term junction refers to the region where the two types of semiconductor meet. It can be thought of as the border region between the P-type and N-type blocks as shown in the following diagram:
A silicon p-n junction with no applied voltage. The p-n junction possesses some interesting properties which have useful applications in modern electronics. P-doped semiconductor is relatively conductive. The same is true of N-doped semiconductor, but the junction between them is a nonconductor. This nonconducting layer, called the depletion zone, occurs because the electrical charge carriers in doped n-type and p-type silicon (electrons and holes, respectively) attract and eliminate each other in a process called recombination. By manipulating this nonconductive layer, p-n junctions are commonly used as diodes: electrical switches that allow a flow of electricity in one direction but not in the other (opposite) direction. This property is explained in terms of the forward-bias and reverse-bias effects, where the term bias refers to an application of electric voltage to the p-n junction.
Source: CDX Global & Wikipedia - en.wikipedia.org
