Photoluminescence in GaAs doping superlattices

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Abstract
The influence of excitation density and excitation energy on the low-temperature photoluminescence spectra of GaAs doping superlattices has been studied in detail. In addition to the strongly tunable luminescence across the indirect gap in real space, which is the specific recombination process in doping superlattices, luminescence lines near the band gap of bulk GaAs, originating from vertical electron-hole recombination processes, are observed. The relative intensities of these vertical luminescence transitions increase at excitation energies close to the bulk band gap and also at high excitation densities. We explain this increase by a simple model based on the classical evaluation of the relaxation kinetics of photoexcited carriers in momentum and real space. The significant result of our investigation is the observation that the luminescence efficiency in GaAs doping superlattices remains constant if the excitation density is varied. Consequently, the relative weight of nonradiative recombination processes is not increasing if the recombination lifetimes are enhanced by several orders of magnitude by lowering the value of the effective gap.