p–n junction
A p–n junction is a boundary or interface between two types of semiconductor material, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of electron holes, while the "n" (negative) side contains an excess of electrons. The p-n junction is created by doping, for example by ion implantation, diffusion of dopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant). If two separate pieces of material were used, this would introduce a grain boundary between the semiconductors that would severely inhibit its utility by scattering the electrons and holes.
![Image silicon atoms (Si) enlarged about 45,000,000x.](/Images/godic/202502/03/Silicium-atomes1610.png")
![Figure A. A p–n junction in thermal equilibrium with zero-bias voltage applied. Electron and hole concentration are reported with blue and red lines, respectively. Gray regions are charge-neutral. Light-red zone is positively charged. Light-blue zone is negatively charged. The electric field is shown on the bottom, the electrostatic force on electrons and holes and the direction in which the diffusion tends to move electrons and holes. (The log concentration curves should actually be smoother with slope varying with field strength.)](/Images/godic/202502/03/Pn-junction-equilibrium1610.png")
![Figure B. A p–n junction in thermal equilibrium with zero-bias voltage applied. Under the junction, plots for the charge density, the electric field, and the voltage are reported. (The log concentration curves should actually be smoother, like the voltage.)](/Images/godic/202502/03/Pn-junction-equilibrium-graphs1610.png")
![PN junction operation in forward-bias mode, showing reducing depletion width. The panels show energy band diagram, electric field, and net charge density. Both p and n junctions are doped at a 1e15/cm3 (0.00016C/cm3) doping level, leading to built-in potential of ~0.59 V. Reducing depletion width can be inferred from the shrinking charge profile, as fewer dopants are exposed with increasing forward bias.](/Images/godic/202502/03/PN_band1610.gif")