P-N Junction

When P-type and N-type semiconductors are placed together, the resulting P-N junction behaves differently from either material alone, allowing electric current to flow more easily in one direction. This P-N interface is the basis of a diode. The P-type (positive) side has an excess of holes (positive charge carriers), while the N-type (negative) side has an excess of electrons. At the junction, free electrons near the boundary recombine with holes, creating a potential difference across the junction. This diffusion of electrons and holes near the junction forms positive ions in the N region and negative ions in the P region, establishing the depletion layer. When the P-type is connected to the positive terminal and the N-type to the negative terminal of a power supply, the holes in the P-type region and the electrons in the N-type region are pushed toward the junction, reducing the electric potential across it and allowing electrons to cross. The number of electrons crossing the junction determines the current flow through the diode. The P-N junction is the foundation of many semiconductor devices, including diodes, solar cells, LEDs, transistors and integrated circuits.