Influence of excitation energy on charged exciton formation in self-assembled InAs single quantum dots

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Abstract
We study the low-temperature photoluminescence (PL) from self-assembled InAs quantum dots as a function of a wide range of external parameters such as excitation power and pump-photon energy. By means of a conventional micro-PL setup we have succeeded in selecting the emission from a single (isolated) quantum dot. The results obtained show dramatic changes in the PL spectra initiated by changes in the pump-photon energy at a fixed excitation power: Two new lines redshifted relative to the ground-state transition appear in PL at certain pump-photon energies. This phenomenon is ascribed to the population of quantum dots with a nonequal amount of electrons and holes which is determined by the excess energies of photogenerated carriers. Based on a comparison of the spectral positions of these two lines with a simple perturbation theory model, these new lines were identified as exciton complexes charged with one and two additional electrons. It is demonstrated that the crucial role of excess energies of photogenerated carriers on the population of quantum dots with a nonequal number of electrons and holes could be used as an effective optical method to create and study charged exciton complexes in zero-dimensional semiconductor nanostructures.