The energy relaxation of InN thin films has been studied by ultrafast time-resolved photoluminescence technique. The obtained carrier cooling curves can be explained by carriers releasing excessive energy through the carrier–LO-phonon interaction. The extracted effective phonon emission times decrease as the photoexcited carrier concentration reduces and come close to the theoretical prediction of 23fs at small carrier concentration. The reduction of energy loss rate at high photoexcited carrier density is attributed to the hot phonon effect.

Auger recombination is studied in InN thin films using an ultrafast time-resolved photoluminescence apparatus. The decay rates are analyzed with nonlinear dependence of the photoluminescence intensity on the carrier concentration. The fitted radiative recombination coefficients at a temperature of 35K are consistent with the theoretical prediction. The Auger rates are small at low carrier concentrations but increase quadratically with the carrier concentration. The Auger activation energies of 4.3 and 9.0meV obtained from the temperature-dependent Auger coefficient indicate that Auger recombination is weakly dependent on temperature and is a phonon-assisted process.

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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.