Optical and magneto-optical investigations on single-quantum dots

We report about optical experiments on single self-assembled quantum dots. In power-dependent low-temperature magneto-photoluminescence experiments we have analysed the emission spectra of single dots for increasing exciton o ccupation numbers. Decays from different configurations (up to 4 excitons) lead to a renormalization of the emission lines in the region of the s- and p-shell of the dot. Photoluminescence excitation spectroscopy further allo ws us to explore the absorption properties of a single-quantum dot. Both in terband absorption and comparably strong phonon-assisted absorption via InG aAs and GaAs LO phonons are observed, as well as sequential phonon-assisted biexciton generation followed by sequential biexciton decay. Working towar ds applications of single quantum dots, local charge injection/extraction i nto/from dots is performed on special p-i-n structures via a STM-tip. STM-i nduced luminescence from a single-dot results in single-line emission from the quantum dot ground state under the condition of low injection currents. Reverse operation of such a single quantum dot LED allows in addition for spectrally resolved photocurrent experiments. Characteristic sharp peaks in the STM tip current vs. excitation energy are attributed to resonant quant um dot interband absorption processes. (C) 2001 Elsevier Science B.V. All r ights reserved.