Influence of screening dynamics on excitons in Ga₂O₃ polymorphs

Exciton binding energies E_B measured for α- and β-Ga₂O₃ crystals seem to be not explainable in the Wannier-Mott picture. However, we demonstrate theoretically that including screening dynamics and effective mass anisotropy, reasonable values E_B = 184 meV (α) or 230 meV (β) are derived. Since the binding energies are larger than the phonon frequencies, the exciton formation is so fast that only about 5% of the lattice polarizability contributes to the screening of the electron-hole attraction. Effective dielectric constants possess values between the complete static ones and the electronic high-frequency dielectric constants. They indeed depend on the polymorph.