How are intrinsic semiconductors different from extrinsic semiconductors?

The primary difference between intrinsic and extrinsic semiconductors lies in their purity and the resulting mechanism of electrical conduction.

Intrinsic Semiconductors

An intrinsic semiconductor is a pure material, such as silicon, that contains negligible impurities. In its crystalline structure, each atom shares its outer electrons to form covalent bonds. At room temperature, electrical conduction is poor because few electrons are free to move. When thermal energy breaks these bonds, it creates an equal number of free electrons and holes—vacancies that act as positive charge carriers.1

Extrinsic Semiconductors

To improve conductivity, manufacturers use doping, which involves intentionally adding specific impurities to the crystal lattice. This creates an extrinsic semiconductor:12

• n-type: Doping with pentavalent atoms (e.g., arsenic or phosphorus) introduces extra electrons that are donated to the conduction band, making electrons the primary charge carriers.12
• p-type: Doping with trivalent atoms (e.g., boron) creates additional holes in the valence band, making these positive sites the primary charge carriers.12

While doping increases overall conductivity, it typically results in a slight decrease in carrier mobility.1