Semiconductors Junctions

A p–n junction is a combination of two types of semiconductor materials, p-type and n-type, in a single crystal. The "n" (negative) side contains freely-moving electrons, while the "p" (positive) side contains freely-moving electron holes. Connecting the two materials causes creation of a depletion region near the boundary, as the free electrons fill the available holes, which in turn allows electric current to pass through the junction only in one direction. p–n junctions represent the simplest case of a semiconductor electronic device; a p–n junction by itself, when placed in a circuit, is a diode. More complex devices can be created by further combinations of p-type and n-type semiconductors. Transistors such as the BJT, MOSFET, JFET, and IGBT all utilize p–n junctions for operation. Combinations of such semiconductor devices on a single chip allow for the creation of integrated circuits. Solar cells and light-emitting diodes (LEDs) are essentially p–n junctions where the semiconductor materials are chosen, and the component's geometry designed, to maximise the desired effect (light absorption or emission). A Schottky junction is a similar case to a p–n junction, where instead of an n-type semiconductor, a metal directly serves the role of the "negative" charge provider. The invention of the p–n junction is usually attributed to American physicist Russell Ohl of Bell Laboratories in 1939. Two years later (1941), Vadim Lashkaryov reported discovery of p–n junctions in Cu2O and silver sulphide photocells and selenium rectifiers. The modern theory of p–n junctions was elucidated by William Shockley in his classic work Electrons and Holes in Semiconductors (1950).