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. It 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.