Doping

Doping is the process of deliberately altering a semi-Conductor's Conductivity or crystal structure by introducing a small number of impurity atoms into high-purity Semi-conductor crystals. The ratio of impurity to crystal atoms is approximately 1:10⁴ to 1:10⁵.

Atoms with three or five valence electrons are used for doping. If doping is performed with a pentavalent impurity atom, one of the valence electrons is unable to find a binding partner and remains in the crystal structure as a free electron. Using a trivalent atom for doping creates an electron hole in the crystal. This is filled by the adjacent atom. In an n-doped semi-conductor, the free electrons are in the majority and form the current flow. In p-doped semi-conductors, it is the impurities that create the current flow.