valenceconduction

The valence band and conduction band are fundamental concepts in solid-state physics that describe the behavior of electrons in materials, particularly semiconductors and insulators. These bands represent ranges of energy levels that electrons can occupy.

The valence band is the highest energy band that is completely filled with electrons at absolute zero temperature. Electrons in the valence band are typically bound to individual atoms and are not free to move and conduct electricity. When energy is supplied, such as through heat or light, electrons can be excited from the valence band to higher energy levels.

The conduction band is the lowest energy band that is either empty or partially filled with electrons at absolute zero temperature. If electrons gain enough energy to jump from the valence band into the conduction band, they become delocalized and are free to move throughout the material. This movement of free electrons constitutes an electric current.

The energy difference between the top of the valence band and the bottom of the conduction band is known as the band gap. The size of the band gap is a crucial property that determines whether a material is a conductor, semiconductor, or insulator. In conductors, the valence and conduction bands overlap or are very close, allowing electrons to move freely. In semiconductors, there is a moderate band gap, meaning that a certain amount of energy is required to excite electrons into the conduction band. In insulators, the band gap is very large, requiring a significant amount of energy to promote electrons to the conduction band, thus preventing significant electrical conduction.