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-field photoluminescence spectra of single ultrathin CdSe layers at low temperatures exhibits a strong positive correlation peak around 18 meV energy with a width of 5 meV. Using simulations and experiments as a function of temperature and laser intensity, we can exclude interpretations along the lines of biexcitons or phonon sidebands. We attribute this feature to the splitting of ground state and an excited state in individual quantum islands. This interpretation implies that the potential minima are rather uniform in size and that the distribution of excitons is nonthermal.