Time-resolved photoluminescence and carrier dynamics in vertically-coupledself-assembled quantum dots

The relaxation mechanisms of an array of 10 vertically coupled layers of In GaAs/AlGaAs quantum dots were studied by time-resolved photoluminescence. B oth resonant and non-resonant excitation were employed and the photolumines cence (PL) intensity in the non-resonant case is a factor of 200 larger tha n the intensity with resonant excitation. The results obtained in the non-r esonant pumping experiment were analysed with a rate equation model. It was found that the PL decay time increases rapidly with the wavelength of dete ction. Large carrier capture cross-sections [(2.5 +/- 0.9) x 10(-5) cm(3)/s ] were deduced, resulting in a capture time of 1 ps for a carrier concentra tion of 4 x 10(16) cm(-3). A veri fast PL risetime was observed with resona nt pumping, ruling out a phonon bottleneck effect in these samples. The dec ay times at a given wavelength are always shorter for resonant than for non -resonant excitation and their difference increases rapidly with wavelength . This is interpreted in terms of a state filling effect for the non-resona nt case.