interband

Interband refers to processes or transitions that occur between two energy bands in a solid, most commonly the valence band and the conduction band. Interband transitions involve electrons moving across the band gap and are a central concept in solid-state optics and semiconductor physics.

In optics, interband transitions can produce absorption when photon energy exceeds the band gap and emission when electrons recombine with holes across the gap. This is distinct from intraband processes, which occur within a single band and include free-carrier absorption and plasmonic responses.

The rate of interband transitions is described by quantum-mechanical transition amplitudes and is often treated with Fermi’s golden rule. Momentum conservation may require phonons or defects in indirect-gap materials, and selection rules determine which transitions are allowed or forbidden.

Interband effects are central to many devices and materials. Photovoltaics rely on interband absorption to generate electron-hole pairs, while light-emitting diodes and laser diodes depend on interband radiative recombination to emit light. In materials such as graphene and other two-dimensional systems, interband contributions to optical conductivity shape the absorption spectrum across a broad range of frequencies, often alongside intraband (Drude-like) responses.

Interband tunneling is a related phenomenon in strong electric fields, where electrons tunnel directly from the valence to the conduction band across a narrow band gap. This process is distinct from photon-driven interband transitions but represents a band-to-band, field-assisted transport mechanism.

See also: intraband, band structure, optoelectronics, Zener tunneling.