Time resolved spectroscopy of single quantum dots: Fermi gas of excitons?

Photoluminescence measurements with spatial and temporal resolution are performed on individual GaAs/GaAlAs quantum dots. Already 10 ps after weak, resonant excitation, we observe luminescence which evolves to a spectrum of distinct, narrow lines. With increasing excitation intensity, the spectral weight shifts from the lowest to higher levels but the peak energies hardly change. Our results demonstrate that Coulomb scattering is an important relaxation mechanism and suggest that the interacting electron-hole plasma in quantum dots behaves like an exciton gas obeying Pauli exclusion.