Near-field spectroscopy of a single InGaAs self-assembled quantum dot

Relaxation mechanism of excited carriers in InGaAs-GaAs self-assembled quantum dots has been investigated. Near-field photoluminescence excitation (PLE) spectra show some sharp resonance lines whose energies match those of the LO phonons observed in far-field PLE. The results suggest that the PLE resonant peaks are predominantly due to resonant Raman scattering from phonons. This assignment is consistent with the absence of magnetic field dependence of the resonances. Single dot coherent spectroscopy shows the dephasing time of resonant carriers to be as fast as several tens of picoseconds. This fast dephasing time agrees with the phonon-electron interactions being strong. These results allow better understanding of the carrier relaxation process in InGaAs-GaAs self-assembled quantum dots.