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Quantized Auger Recombination of Polaronic Self-trapped Excitons in Bulk Iron Oxide

The Auger recombination in bulk semiconductors can depopulate the charge carriers in a non-radiative way, which, fortunately, only has detrimental impact on optoelectronic device performance under the condition of high carrier density because the restriction arising from concurrent momentum and energy conservation limits the Auger rate. Here, we surprisingly found that the Auger recombination in bulk Fe2O3 films was more efficient than narrow-bandgap high-mobility semiconductors that were supposed to have much higher Auger rate constants than metal oxides. The Auger process in Fe2O3 was ascribed to the Coulombically coupled self-trapped excitons (STEs), which was enhanced by the relaxation of momentum conservation because of the strong spatial localization of these STEs. Furthermore, due to this localization effect the kinetic traces of the STE annihilation for different STE densities exhibited characteristics of quantized Auger recombination, and we demonstrated that these traces could be simultaneously modeled by taking into account the quantized Auger rates.