| Abstract: | We use our detailed understanding of the many-carrier confined states of single QDs and the various optical transitions between these states [1] to demonstrate that the charge state of QDs can be controlled almost at will by very weak intensities of light. The light itself is too weak to generate photoluminescence (PL) emission on its own, but its photon energy determines the average charge in the QDs. By changing the light color from red to violet we succeeded in varying the QD charge state from, on average, doubly positively charged to doubly negatively charged, respectively. For a given excitation wavelength, the average charge was different, as judged by the intensity of the emission from various charged exciton states.
All these measurements are favorably compared with a relatively simple rate equation model which takes into account light-induced charging and discharging, spin-conserving and non-conserving relaxations, and optical recombinations [2-3]. The PL spectra are obtained from the steady state solutions of our rate equation model, and the correlation measurements are obtained by setting the initial and final states to the identified polarized emission lines [2]. We succeed in obtaining quantitative agreement between all these measurements using a very small number of adjustable parameters
[1] Y. Benny et al, Phys. Rev. B. 84, 075473, (2011).
[2] D.V. Regelman et al, Phys. Rev. Lett. 87, 257401 (2001).
[3] M. H. Baier et al, Phys. Rev. B. 73, 205321 (2006). |
