Pure or intrinsic semi-conductors: (Ge, Si)

A semiconductor is said intrinsic when it is pure: it contains no impurities and its electrical behaviour depends only on the structure of the material. This behaviour corresponds to a perfect semiconductor, i.e. with no structural defects or chemical impurities. A real semiconductor is never perfectly intrinsic but can sometimes come close, as in the case of pure monocrystalline silicon.

In an intrinsic semiconductor, charge carriers are only created by crystalline defects and thermal excitation. The number of electrons in the conduction band is equal to the number of holes in the valence band.

These semiconductors conduct little or no current unless they are heated to high temperatures.

Remarque

In practice, the intrinsic conductivity of pure undoped semiconductors plays a secondary role. As a rule, the crystals have defects. Very pure crystals are often made conductive by targeted doping with donor or recipient atoms.

he 4 peripheral electrons per atom are shared with neighbouring atoms, creating covalent bonds