phononassisted

Phonon-assisted refers to processes in solid-state physics in which phonons, quanta of lattice vibrations, participate to enable or enhance transitions between quantum states. In these processes, coupling between charge carriers and the lattice allows energy and momentum to be conserved in situations where they would otherwise be forbidden or highly unlikely.

One common context is optical transitions in indirect-bandgap materials, where an electron or hole changes momentum by emitting or absorbing a phonon in addition to absorbing or emitting a photon. This enables radiative transitions that would be forbidden by momentum conservation if only a photon were involved. Phonon-assisted transitions also contribute to the temperature dependence of optical spectra, producing characteristic sidebands at phonon energies.

Phonon-assisted processes are also important in electronic transport and tunneling. In nanoscale devices, such as quantum wells, quantum dots, and tunnel junctions, electron tunneling can be aided by phonon emission or absorption, altering current-voltage characteristics and device performance. Nonradiative relaxation and recombination in semiconductors often proceed via phonon-assisted pathways, where electronic energy is transferred to or from the lattice through electron-phonon coupling.

Theoretical treatment of phonon-assisted phenomena typically involves electron-phonon interaction models and perturbation theory, with rates proportional to the electron-phonon coupling strength and phonon occupation numbers. Temperature, material phonon spectra (acoustic and optical modes), and dimensional confinement all influence the likelihood and observable signatures of phonon-assisted processes.

See also: electron-phonon interaction, indirect optical transitions, phonon sidebands, polaron.