Time-resolved photoluminescence spectroscopy of subwetting layer states in InGaAs∕GaAs quantum dot structures

Time-resolved photoluminescence (PL) measurements are carried out for the InGaAs quantum dots (QDs) grown on (001) and (311) oriented GaAs substrates. The detection energies scan the spectral region from the energy of the QD excitonic transition up to the wetting layer absorption edge. A convex-shaped decay of the PL signal in this region gives evidence of carrier relaxation through the continuum states below the wetting layer similar to a diffusion process. Strong dependence of the decay time on the excitation density observed for the QD ground-state PL is consistent with a presented theoretical model.