Distinguished between metal semiconductor and insulation by band theroy
Metal, semiconductor, and insulation are distinguished based on the band theory, which describes the energy levels of electrons in different materials.
In a metal, the valence band (the highest energy band occupied by electrons in a solid) and the conduction band (the next highest energy band) overlap, allowing electrons to move freely between them. This overlapping of energy bands allows metals to conduct electricity efficiently, as the electrons can easily move in response to an applied electric field. The small energy gap between the valence and conduction bands in metals results in high electrical conductivity.
In a semiconductor, there is a small energy gap, known as the band gap, between the valence and conduction bands. This energy gap is typically in the range of 0.1 to 2 eV. At absolute zero temperature, the valence band is completely filled with electrons, and the conduction band is completely empty. However, at room temperature or with the addition of thermal energy, some electrons can acquire enough energy to jump across the band gap and enter the conduction band. This movement of electrons creates mobile charge carriers, allowing semiconductors to conduct electricity to some extent. The conductivity of a semiconductor can be increased by doping it with impurities, which introduces additional energy levels within the band gap.
In an insulator, there is a large energy gap between the valence and conduction bands, typically greater than 3 eV. This large energy gap makes it difficult for electrons to acquire enough energy to jump to the conduction band, resulting in very low conductivity. Insulators are characterized by a high resistance to the flow of electric current due to the lack of mobile charge carriers.
Therefore, the distinction between metal, semiconductor, and insulation is based on the size of the energy gap between the valence and conduction bands, determining the ability of the material to conduct electricity.