Excitation spectroscopy of single quantum dots at tunable positive,   neutral and negative charge states
  We present a comprehensive study of the optical transitions and selection rules of variably charged single self-assembled InAs/GaAs quantum dots. We apply high resolution polarization sensitive photoluminescence excitation spectroscopy to the same quantum dot for three different charge states: neutral and negatively or positively charged by one additional electron or hole. From the detailed analysis of the excitation spectra, a full understanding of the single-carrier energy levels and the interactions between carriers in these levels is extracted for the first time. 
Y. Benny, Y. Kodriano, E. Poem, T. A. Truong, P. M. Petroff, D.   Gershoni
cond-mat.mes-hall quant-ph