Dopants

A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance (in very low concentrations) to alter the electrical or optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that were in the crystal lattice of the base material. The crystalline materials are frequently either crystals of a semiconductor such as silicon and germanium for use in solid-state electronics, or transparent crystals for use in the production of various laser types; however, in some cases of the latter, noncrystalline substances such as glass can also be doped with impurities.

In solid-state electronics, using the proper types and amounts of dopants in semiconductors is what produces the p-type semiconductors and n-type semiconductors that are essential for making transistors and diodes.

The addition of a dopant to a semiconductor, known as doping, has the effect of shifting the Fermi levels within the material. This results in a material with predominantly negative (n-type) or positive (p-type) charge carriers depending on the dopant variety. Pure semiconductors that have been altered by the presence of dopants are known as extrinsic semiconductors [See: intrinsic semiconductor]. Dopants are introduced into semiconductors in a variety of techniques: solid sources, gases, spin on liquid, and ion implanting. See ion implantation, surface diffusion, and solid sources footnote.

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