valensbandet

Valensbandet, or the valence band, is a concept in solid-state physics describing the highest range of electron energies in a crystalline solid that can be occupied by electrons at absolute zero. It arises from the overlap and splitting of atomic orbitals of the constituent atoms, forming a band of allowed energies. In most insulators and semiconductors, the valence band is separated from the next higher allowed band, the conduction band, by an energy gap called the band gap. The size of this gap determines whether electrons can be thermally excited into the conduction band, influencing electrical conductivity. In metals, the valence band may overlap with the conduction band, allowing free movement of electrons and intrinsic conductivity without a sizable gap.

At zero temperature the valence band is full and the conduction band is empty. Heating or optical/electrical excitation can promote electrons across the gap into the conduction band, leaving behind holes in the valence band. These holes act as positive charge carriers and contribute to electrical conduction. Doping introduces impurity states: acceptors create holes in the valence band (p-type), donors add electrons to the conduction band (n-type).

The detailed structure of the valence band, including its maxima, curvature, and spin-orbit interactions, depends on crystal structure and chemical composition. In common semiconductors such as silicon and germanium, the valence-band properties influence optical and electronic behavior, including carrier effective masses and mobilities, as well as the temperature dependence of the band gap.

Valence-band concepts are central to many electronic devices, such as diodes, transistors, and solar cells, where control of electron and hole populations enables rectification, amplification, and light-to-electric energy conversion.