Effect of GaAs spacer layer thickness (d GaAs) on carrier capture, and the relaxation process is studied in multi-stacked InAs/GaAs quantum dots by photoluminescence and time-resolved photoluminescence. Auger scattering is the dominating process for carrier relaxation above d GaAs of 15 nm. At d GaAs of 10 nm, the carrier relaxation process is faster due to the combined effect of both single longitudinal optical phonon and Auger scattering resulting in higher photoluminescence intensity. The photoluminescence rise time corresponding to carrier capture and relaxation in quantum dots is longer at 3.06 eV excitation than that at 1.53 eV due to the effect of intervalley scattering in GaAs.

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The dependence of photoluminescence (PL) decay time on the thickness of spacer in InAs/GaAs multistacked QDs (MSQDs) has been studied using time-resolved PL upconversion. The decay time of PL increases with decreasing spacer thickness and indicates that vertical coupling in MSQD is significant. The separation of the two peaks of PL for 30 nm QDs results from excited and ground states indicates that the QDs sizes may be different from those of QDs with 10, 15, and 20 nm spacer thicknesses. The band filling effect is evident in MSQD from the study of time-resolved photoluminescence.1 Introduction InAs/GaAs quantum dots have attracted attentions in the last years for potential applications such as light emitting devices, infrared detector, and in optical communication. The novel structures of the 3-dimensional confinement on carriers also provides as a new pathway to explore physics in nanostructures. Since InAs/GaAs have been demonstrated the emission spectrum covers wavelength of 1.5 and 1.3 µm, which are commonly used in optical fiber communication, research have focused on how to increase the radiative efficiency and to reduce the bandwidth of the emission spectrum. Multistacked QDs structures have been proposed to realize these purposes. It has been shown that multistacked QDs reduce the size distribution of QDs in different layers such that QDs exhibit vertical alignment because of strain relaxation. The gain in MSQD increase drastically as compared to that of a signal layer QDs. Recently, research on multi-stacked InAs/GaAs QDs has focused on the influence of layer thickness and number of layers on the photon emission energy [1,2]. In the present work, we study the impact of the thickness of spacer on the energy shift and carrier relaxation in MSQDs.