In semiconductor physics, materials can be classified as either intrinsic or extrinsic semiconductors depending on their electrical properties and purity levels.

Intrinsic Semiconductors: Intrinsic semiconductors are pure semiconducting materials that exhibit properties of semiconductors naturally. Examples of intrinsic semiconductors include silicon (Si) and germanium (Ge). These materials have a balanced number of valence electrons and are inherently poor conductors at room temperature.

Extrinsic Semiconductors: Extrinsic semiconductors, on the other hand, are doped semiconductors in which impurities are intentionally added to alter their electrical conductivity. The process of adding impurities to a pure semiconductor is called doping. Doping can be done in two ways: n-doping (adding elements with extra valence electrons) and p-doping (adding elements with fewer valence electrons).

Impurities and Doping: The impurities added during doping introduce new energy levels within the band gap of the semiconductor. These energy levels either donate (for n-doping) or accept (for p-doping) electrons, which leads to an increase in the electron or hole concentration in the semiconductor material. This change in the carrier concentration affects the electrical properties and conductivity of the material.

It is worth noting that intrinsic semiconductors have a very limited range of conductivity, which can be significantly enhanced by doping. This ability to control conductivity is vital in the design and operation of various electronic devices.