Doped

Doped refers to a material in which a small amount of impurity atoms has been introduced to alter its properties. Most commonly associated with semiconductors, doping tailors electrical conductivity and charge-carrier density; it also affects optical and magnetic properties and can improve mechanical or chemical stability in ceramics and polymers.

In semiconductors, dopants are classified as donors or acceptors. Donor atoms have extra valence electrons that become free carriers, yielding n-type conductivity; acceptors create holes, yielding p-type. Common silicon dopants are phosphorus and arsenic for n-type, boron for p-type. Doped silicon can form p-n junctions essential for diodes and transistors.

Doping methods include diffusion at high temperature, ion implantation, and deposition during growth, such as chemical vapor deposition or molecular beam epitaxy. After introduction, a thermal anneal often activates dopants by moving them to lattice sites. Concentrations typically range from 10^14 to 10^21 atoms per cubic centimeter, depending on material and application.

Beyond silicon, doping is used in other semiconductors, ceramics to adjust ionic conductivity, and conductive polymers to create flexible electronics. Doping can also influence optical properties, such as emission wavelength in lasers and LEDs.

This article focuses on materials science usage. The term doped can also refer, in other contexts, to illicit production or use of substances in sports or medicine, but that is separate from the scientific concept described here.