Autocorrelation spectroscopy on single ultrathin layers of CdSe/ZnSe: hints for a non-thermal distribution of excitons in quantum islands

Autocorrelation spectroscopy on the basis of thousands of individual near-f ield photoluminescence spectra of single ultrathin CdSe layers at low tempe ratures exhibits a strong positive correlation peak around 18 meV energy wi th a width of 5 meV. Using simulations and experiments as a function of tem perature and laser intensity, we can exclude interpretations along the line s of biexcitons or phonon sidebands. We attribute this feature to the split ting of ground state and an excited state in individual quantum islands. Th is interpretation implies that the potential minima are rather uniform in s ize and that the distribution of excitons is nonthermal.