  We have performed near-field spectroscopy and microscopy of the InAs/AlGaAs
quantum-dot-based nanoclusters. It is observed that the photoluminescence
spectra of spatially confined excitons in the nanoclusters is blue-shifted up
to 20 meV as the power density is increased. In particular, the near-field
photoluminescence images have shown that excitons became spatially confined
gradually from lower energy state (1.4150 eV) to higher energy state (1.4392
eV) as the excitation power is increased, which is indicative of the
band-filling effect of semiconductor nanostructures.
