dopant

A dopant is a substance added in small, controlled amounts to another material to change its properties in a predictable way. In the field of solid-state physics, dopants are impurities that introduce electronic energy levels within the host’s band structure, thereby altering charge-carrier concentrations and behavior.

In semiconductors, dopants are classified as donors or acceptors. Donor dopants add extra electrons and create n-type material, while acceptor dopants create holes and yield p-type material. Common silicon dopants include phosphorus, arsenic and antimony as donors, and boron, aluminum and gallium as acceptors. Doping levels typically range from about 10^14 to 10^18 or 10^19 dopant atoms per cubic centimeter, depending on the device. After incorporation, thermal treatment may activate the dopants, exchanging with lattice sites and becoming electrically active.

Doping is achieved by methods such as diffusion or ion implantation, often followed by annealing to repair lattice damage and activate dopants. The resulting carrier concentration controls device behavior, influencing conductivity, threshold voltages, and switching characteristics in devices like diodes and transistors. Carrier mobility and impurity scattering also affect performance.

Dopants are used beyond electronics as well: rare-earth or transition-metal ions are introduced into crystals and glasses to create lasing, phosphorescent, or color properties; doped ceramics and polymers can show modified mechanical, optical, or electrical traits.

Key considerations include the solubility limit of the dopant in the host, diffusion during processing, compensating defects, and the energy required to ionize dopants. Proper doping enables precise control over material function in a wide range of technologies.