Observation of charged few-particle states in the optical spectra of single semiconductor quantum dots

A detailed discussion of the optical properties of single n-type modulation -doped semiconductor quantum dots is presented. We use the photo-depletion/ back-hopping mechanism to optically control the number of surplus electrons in the dot. Comparison of the experimental data with calculated luminescen ce spectra, obtained within a direct-diagonalization approach for calculati ng electron-hole states, allows the identification of luminescence from the decay of up to fivefold charged excitons. Finally we study the influence o f fluctuating local electric fields, produced by ionized impurities in the surrounding of the dots, on the optical selection rules and on the linewidt h of the emission peaks.