Istituto dei materiali per l'elettronica ed il magnetismo     
Munoz-Matutano G., Gomis J., Alen B., Martinez-Pastor J., Seravalli L., Frigeri P., Franchi S. Modelling of exciton and trion recombination in single quantum dots under selective optical pumping. In: One Day Quantum Dot Meeting (Blackett Laboratory, Imperial College London, 11 Gennaio 2008).
Self-assembled quantum dots (QDs) are potential candidates for single photon sources and quantum logic gates. The trion state has not fine structure splitting and a single charge with well defined spin remains in the QD after radiative recombination. Therefore, of particular importance is either the electrical or optical control of the exciton charge state as a necessary step for the spin manipulation. Photoluminescence (PL) and time resolved PL confocal micro-spectroscopy have been performed in single InAs self-assembled quantum dots emitting at around 970 nm at low temperatures on a low density sample (16.5 QD/Ám2 in average). Given the slow MBE growth used in this sample rate impurities are unintentionally incorporated in the structure. The presence of large number of ionized acceptors at low temperatures gives the possibility to perform selective optical pumping of carriers. This technique has particular interest to study different charged schemes of the QDs. When optical pumping is in the range 1.485-1.505 eV, approximately, the intensity of the trion, X−, is 15-20 times greater than that of the neutral exciton, X. The same ratio is also measured in more restricted energy ranges related to the WL and GaAs excitonic absorption lines. The efficient optical pumping of X− states in our In(Ga)As QDs is possible by the presence of acceptor and donors in the surroundings of the QDs. The light absorption of ionized acceptor impurities produces electrons arriving to the QD, simultaneously with electron-hole pairs captured from the WL, in agreement with similar findings in literature. The results obtained from ÁTRPL transients under X− and X pumping support our conclusion. Our experimental results are in good agreement with numerical simulations coming from a microstate model.
Subject semiconductor quantum dots
Trion and exciton recombination

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