Electron–hole pair

An electron–hole pair is a mobile electron and the positively charged vacancy left when an electron is excited from a semiconductor’s valence band into its conduction band.

Valence band: The range of electron energy states in a solid that is filled by electrons at low temperature. The excited electron leaves this band, creating the hole.
Semiconductor: A material whose electrical conductivity lies between that of a conductor and an insulator and can be controlled by doping, light, or fields. Electron–hole pairs are characteristic excitations in these materials.
Photovoltaic effect: The generation of voltage or current in a material when it absorbs light. Separated photogenerated pairs produce electrical power in solar cells.
Carrier lifetime: The average time a nonequilibrium electron or hole persists before recombination or trapping. It determines how long generated pairs can contribute to current.
Electron–hole plasma: A dense collective state of electrons and holes in a semiconductor, where individual bound excitons are screened or destabilized. At high excitation density, many pairs behave collectively rather than independently.
Conduction band: The range of energy states in a solid where electrons can move through the material and conduct electricity. The promoted electron enters this band and becomes mobile.
Electron: A negatively charged elementary particle that occupies quantum states in atoms and solids. The electron is the mobile negative member of the pair.
Photodiode: A semiconductor device that converts incident light into electrical current or voltage. Its signal depends on collecting carriers generated as electron–hole pairs.
Diffusion length: The average distance a nonequilibrium carrier travels by diffusion before recombining. It sets how far a pair’s carriers can move toward collection.
Exciton–polariton: A hybrid quasiparticle formed by strong coupling between an exciton and a photon in a material or optical cavity. It arises when electron–hole binding couples strongly to light.

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