Influence of excitation energy on charged exciton formation in self-assembled InAs single quantum dots - art. no. 085302

We study the low-temperature photoluminescence (PL) from self-assembled InA s 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 (isolate d) quantum dot. The results obtained show dramatic changes in the PL spectr a initiated by changes in the pump-photon energy at a fixed excitation powe r: Two new lines redshifted relative to the ground-state transition appear in PL at certain pump-photon energies. This phenomenon is ascribed to the p opulation of quantum dots with a nonequal amount of electrons and holes whi ch is determined by the excess energies of photogenerated carriers. Based o n a comparison of the spectral positions of these two lines with a simple p erturbation theory model, these new lines were identified as exciton comple xes charged with one and two additional electrons. It is demonstrated that the crucial role of excess energies of photogenerated carriers on the popul ation of quantum dots with a nonequal number of electrons and holes could b e used as an effective optical method to create and study charged exciton c omplexes in zero-dimensional semiconductor nanostructures.