Extrinsic semiconductors

The electrical conductivity of an intrinsic (pure) semiconductor is far too low at room temperature to build practical electronic devices out of. The solution is DOPING: deliberately adding a small, carefully controlled amount of a suitable impurity to an intrinsic semiconductor to appreciably increase its conductivity. The resulting doped material is called a doped or EXTRINSIC semiconductor; the added impurity itself is called the DOPANT, and the original, parent atoms of the crystal are called the HOST. The dopant is chosen specifically so that it does not disturb the host's crystal structure -- its atomic size and electronic configuration must be compatible with the host's. …