Engineering Physics

5.11 Distinction between metals, semiconductors and insulators

The differences between metals, semiconductors and insulators can be made based on the availability of number of free electrons that participate in electrical conduction per unit volume when an electric field is applied. These free electrons are called effective electrons. The number of effective electrons per unit volume (N_eff) for a material can be calculated using band theory of solids. According to band theory, the electrons in a solid can possess bands of energies called allowed bands of energies and these electrons may not possess some other bands of energies called forbidden bands of energies. The allowed bands of energies and forbidden bands of energies are present alternatively ...