excitonbindinger

Exciton binding energy, here discussed in the sense of the term excitonbindinger, is the energy required to dissociate a bound electron–hole pair, or exciton, into free charge carriers. An exciton forms when a conduction-band electron and a valence-band hole attract each other through Coulomb interaction, with the interaction strength moderated by the material’s dielectric screening. The magnitude of the binding energy and the spatial extent of the exciton depend on dimensionality, screening, and effective masses.

Two broad categories are typically distinguished. Frenkel excitons are localized to a single molecular unit or lattice site and occur mainly in organic crystals and some molecular solids, with binding energies on the order of hundreds of meV. Wannier–Mott excitons are more delocalized across the crystal and common in inorganic semiconductors; they usually have binding energies ranging from a few meV to a few tens of meV in bulk materials, though larger values appear in wide-bandgap materials.

In two-dimensional materials and quantum-confined systems, exciton binding energies can be substantially larger due to reduced dielectric screening and quantum confinement. For example, monolayer transition metal dichalcogenides commonly exhibit binding energies around several hundred meV up to about 1 eV. In bulk semiconductors, typical values are a few meV (e.g., GaAs around 4 meV, ZnO around 60 meV). Narrowing the dimensionality or decreasing the effective dielectric constant generally increases the binding energy.

The binding energy can be estimated from hydrogenic models using the reduced mass μ and an effective dielectric constant εr, though real materials often require more sophisticated calculations, such as first-principles GW/Bethe–Salpeter approaches. Measurement relies on optical spectroscopy to identify excitonic resonances below the bandgap.