What are intrinsic and extrinsic semiconductors?

Intrinsic semiconductors are pure semiconducting materials, while extrinsic semiconductors are doped with impurities.

Intrinsic semiconductors, such as silicon and germanium, have a perfectly balanced number of electrons and holes, making them poor conductors at room temperature. However, when energy is added to the material, such as through heat or light, electrons can be excited into the conduction band, creating free charge carriers and increasing conductivity.

Extrinsic semiconductors are created by intentionally adding impurities, or dopants, to the pure material. This process is called doping and can be done with elements such as boron or phosphorus. Doping creates an excess of either electrons or holes, increasing conductivity. For example, adding boron to silicon creates p-type semiconductors, where the boron atoms have one less electron than silicon, creating holes. Adding phosphorus creates n-type semiconductors, where the phosphorus atoms have one more electron than silicon, creating excess electrons.

The ability to control conductivity through doping is essential for the creation of modern electronic devices, such as transistors and diodes. By combining p-type and n-type semiconductors, a p-n junction can be created, which allows for the controlled flow of current and the creation of electronic circuits.