bandniveaus

Bandniveaus, or energy bands, describe the allowed energy values electrons may occupy in a crystalline solid as a function of crystal momentum. In a periodic potential, electron states form bands rather than discrete levels; the energy values E(k) for each wavevector k constitute the band structure, and the levels at a given k are the bandniveaus.

Valence bands are the highest occupied bands at zero temperature; conduction bands lie above them and may be empty or partially filled. The energy range between the top of the valence band and the bottom of the conduction band is the band gap. Materials with no band gap overlap bands and behave as metals; those with sizable gaps are insulators, while small gaps yield semiconductors.

Electronic occupation is governed by the Fermi level, the chemical potential; at finite temperature electrons can populate higher bands. Doping, strain, and quantum confinement modify bandniveaus, changing band gaps and effective masses.

Calculations use density functional theory or tight-binding; experiments such as angle-resolved photoemission spectroscopy (ARPES), optical spectroscopy, or scanning tunneling spectroscopy (STS) map E(k) and gaps.

Bandniveaus underpin many electronic and optoelectronic devices, including diodes, transistors, LEDs, and solar cells. In disordered materials, bands broaden into tails and localized states can appear within gaps, affecting transport.