Carrier relaxation and quantum decoherence of excited states in self-assembled quantum dots

We report systematic measurements of photoluminescence excitation spectra and dephasing times (T-2's) on various excited states of hundreds of individual quantum dots (QDs). From the variation of T-2's with the energy separation between excited states and the ground state (E-rel), we identified two distinct regions of E-rel where LO phonon emission and hole relaxation via LA phonon emission play as dominat dephasing mechanisms. We also found a clear evidence of significantly slow energy relaxation in the E-rel range where these phonon emission processes are suppressed due to the reduction of interaction phase space.