How does doping increase the electrical conductivity of silicon?

Pure crystalline silicon is a poor electrical conductor at room temperature because its electrons are locked into covalent bonds within the crystal lattice. Doping increases conductivity by intentionally introducing specific impurities to create an extrinsic semiconductor, thereby increasing the number of available charge carriers.1234

The process creates two types of semiconductors depending on the dopant used:

• n-type: When silicon is doped with pentavalent atoms (such as arsenic or phosphorus), which have five outer electrons, four electrons form bonds with neighboring silicon atoms. The fifth electron is left as a free conduction electron available to carry current.142
• p-type: When silicon is doped with trivalent atoms (such as boron), which have only three outer electrons, the atom accepts an electron to complete its bonding structure. This creates a vacancy known as a hole, which acts as a mobile, positively charged carrier.142

By increasing the concentration of these free electrons or holes, the material's ability to conduct electric current is significantly enhanced.13