Lateral Coupling of Self-assembled Quantum Dots Studied by Near-field Spectroscopy

Lateral coupling between separate quantum dots has been observed in a system of In0.55Al0.45As self-assembled quantum dots. The experiment was performed by taking photoluminescence excitation (PLE) spectra in the optical near-field at 4.2 K. The high spatial resolution afforded by the near-field technique allows us to resolve individual dots in a density regime where interactions between neighboring dots become apparent. In the PLE spectra, narrow resonances are observed in the emission lines of individual dots. A large fraction of these resonances occur simultaneously in several emission lines, originating from different quantum dots. This is evidence of interdot scattering of carriers, which additional data show to be mediated by localized states at energies below the wetting layer exciton energy. A very rich phonon spectrum generated by the complicated interfaces between barrier and dot material is also evident in the data.