dopants

A dopant is an impurity deliberately introduced into a material to modify its physical properties. In electronics, dopants are used to tailor electrical conductivity by adding charge carriers. The process is central to creating p-type and n-type semiconductors, and to enabling devices such as diodes, transistors, and light-emitting devices.

In semiconductors, dopants substitute host atoms or occupy interstitial sites, altering valence and energy levels. Common n-type dopants for silicon are group V elements such as phosphorus and arsenic; p-type dopants are group III elements such as boron, gallium. The dopant concentration typically ranges from 10^14 to 10^20 per cubic centimeter.

Doping can be achieved by diffusion, ion implantation, or epitaxial growth. Diffusion relies on thermal motion to move dopant atoms; ion implantation uses a beam to place ions with angular precision, usually followed by annealing to repair lattice damage. Activation refers to dopants occupying lattice sites where they donate or accept carriers.

Dopants are not limited to semiconductors. In optical materials, rare-earth ions such as erbium or neodymium are dopants that create laser transitions in glass and crystals. Doped fibers enable optical amplification. In ceramics and gemstones, dopants modify color. In superconductors and magnets, dopants adjust carrier density and ordering phenomena.

Key considerations in doping include solubility limits, defect formation, compensation by counter-dopants, diffusion during processing, and maintaining crystal quality. Dopant profiles—uniform, gradient, or delta-doped layers—control device characteristics. The concept emerged in the early 20th century and expanded with the silicon electronics revolution.