N-type semiconductor

From ArticleWorld

N-type semiconductors can be obtained by adding a small amount of a group V element in pure silicon or germanium. The impurity atom or dopant is surrounded by semiconductor atoms. Hence the semiconductor forms four covalent bonds with the dopant and one valence electron from the dopant is left as free electron. Consider, for instance, antimony which is an element of group V and has four valence electrons doped with pure germanium. Four of the five valence electrons are used in covalent bonding with four neighbouring atoms of Germanium. The fifth valence electron is loosely bound and can be easily excited to conduct electricity. A very small level of energy is required to remove this electron form the conduction band; this energy is of the order of 0.05eV.

How conduction takes place

When an electric field is applied to such a doped crystal, the free electrons move towards the positive terminal of the battery. In an n-type semiconductor, the conduction of electricity is thus due to electrons, which are negatively charged carriers. Hence this type of semiconductor is called n-type (negative) semiconductor.

Examples of n-type semiconductor dopants

Elements from the group V like antimony, arsenic, phosphorus, etc are used in n-type semiconductors. These elements are called donors and they donate free (unbounded) electrons.