Nonexponential relaxation dynamics of localized carrier densities in oxide crystals without structural or energetic disorder

A microscopic model for the nonexponential relaxation of localized-charge carrier densities in oxide crystals is derived by taking into account thermally activated diffusive hopping transport and the effect of trap saturation. Thereby it is shown that the relaxation, commonly described by a stretched-exponential function, can be successfully reconstructed without consideration of a structural or energetic disorder. Furthermore, the access to particular microscopic measures such as the lifetime of single hopping events and localized-carrier densities is enabled. The impact of the model approach valid for various complex relaxation processes is demonstrated with the nonexponential relaxation dynamics of optically generated small bound polaron densities experimentally determined in KNbO3 as an example.