How does doping change the electrical properties of silicon?

Pure crystalline silicon has high electrical resistance at room temperature, making it a poor conductor. Doping—the intentional addition of specific impurities—modifies the silicon crystal lattice to significantly increase its electrical conductivity.123

The type of change depends on the atomic structure of the dopant:

• n-type (negative): When silicon is doped with pentavalent atoms (such as phosphorus or arsenic), which have five outer electrons, four electrons form covalent bonds with neighboring silicon atoms. The fifth electron is left free to conduct current, classifying the material as n-type.32
• p-type (positive): When doped with trivalent atoms (such as boron), which have only three outer electrons, the structure lacks an electron to complete the fourth bond. This creates a "hole," a positively charged vacancy that can migrate through the lattice, classifying the material as p-type.312

By controlling these impurities, engineers can create semiconductors that function as essential electronic components, such as switches that turn current on and off.1