what is pn junction

A p-n junction is an interface or boundary between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The p-type side contains an excess of holes, while the n-type side contains an excess of electrons. The p-n junction is created by the process of doping, where impurities are added to the semiconductor material to create regions with an excess of either electrons or holes. The holes from the p-type side diffuse to the n-type side, and the electrons from the n-type side diffuse to the p-type side, creating a diffusion current across the junction. The p-n junction is a fundamental component of semiconductor electronic devices such as diodes, transistors, solar cells, light-emitting diodes (LEDs), and integrated circuits. A diode can be made from a single p-n junction, while a bipolar junction transistor (BJT) consists of two p-n junctions in series.