Hålpar

Hålpar, in the context of solid-state physics, refer to pairs consisting of a negatively charged electron in the conduction band and a positively charged hole in the valence band. They arise when a material absorbs energy or when electrons are electrically injected, leaving behind holes. Hålpar can exist as free carriers or form bound states known as excitons, where the Coulomb attraction keeps the electron and hole together.

Formation and behavior of hålpar occur when excitation with light or electrical bias creates electron-hole pairs. In many semiconductors the carriers may be pulled apart by an electric field, contributing to electrical current, while in others the attraction can bind them into excitons. Two common exciton types are Frenkel excitons, typical for organic or molecular crystals with localized charges, and Wannier–Mott excitons, found in inorganic semiconductors with more delocalized charge distributions. The fate of hålpar—whether they separate, bind, or recombine—depends on material properties, temperature, and the surrounding environment.

Recombination of hålpar can be radiative or non-radiative. Radiative recombination emits light and underpins devices such as light-emitting diodes and laser diodes, while non-radiative pathways dissipate energy as heat. In solar cells the dissociation of bound or free hålpar at interfaces is crucial for charge separation and photovoltaic current. Lifetimes for hålpar vary widely, from femtoseconds to nanoseconds, influenced by material quality, defects, and dimensionality.

Measurement and study of hålpar employ spectroscopic techniques such as photoluminescence, transient absorption, and time-resolved spectroscopy to reveal band structure, exciton binding energies, and carrier dynamics. See also electron-hole pair, exciton, and semiconductor.