valensbandets

Valensbandet, or valensbandet in Swedish, is the highest range of energy that electrons occupy in a solid at absolute zero. It is formed by the outermost atomic orbitals that combine in a crystal lattice to create energy bands. In many insulators and semiconductors, the valence band is separated from the next higher band, the conduction band, by a band gap.

At finite temperatures, electrons can be excited from the valence band into the conduction band, leaving behind vacancies or holes in the valence band. Holes behave as positive charge carriers. The distance between the valence-band maximum and the conduction-band minimum, the band gap, largely determines a material’s electrical conductivity and optical properties.

In semiconductors, impurities and defects shift the Fermi level and modify carrier concentrations. In p-type materials, holes in the valence band become the majority carriers; in n-type materials, electrons in the conduction band dominate, though valence-band states contribute to the overall electronic structure through holes.

In metals, the distinction between valence and conduction bands is often less clear because these bands can overlap, allowing free movement of electrons and intrinsic metallic conductivity. The valence-band edge, or valence-band maximum, is important for understanding band alignment, optical transitions, and charge transport in materials used for electronics and optoelectronics.

Overall, the valence band is a central concept in solid-state physics, influencing absorption, emission, and transport properties in semiconductors, photovoltaics, LEDs, and transistors. Its detailed structure depends on crystal configuration, chemical composition, and bonding.