Time-resolved optical characterization of InGaAs/GaAs quantum dots

Abstract

We report on the optical characterization of the strained InGaAs/GaAs quantum dots (QDs). The temperature dependence of the photoluminescence (PL) indicates that the onset energy of the thermal quenching in ∼20-nm-diam QDs is enhanced by a factor of ∼2 as compared to a quantum well (QW), due to the additional confinement. At low temperature, an increased carrier lifetime is observed for the QDs as compared to a reference QW (880 vs 330 ps). The carrier lifetime in the QDs was found to be independent of the temperature for T<30 K. In addition to this different dynamics of the localized excitons, we find that in the steady state PL and PL excitation, there is virtually no overlap between the emission and the absorption energies.

Long luminescence lifetime in self-assembled InGaAs/GaAs quantum dots at room temperature

“…[2][3][4][5] The radiative lifetime of strongly confined excitons in QDs, where the energy separation between the ground state and the first excited exciton state is larger than the thermal energy k B T ͑k B is the Boltzmann constant and T is the temperature͒, should be almost independent of T. However, in real QDs, the radiative lifetime of the ground state excitons is expected to increase with increasing temperature due to the thermal population of optically inactive or poorly active exciton states. [6][7][8] This phenomenon was first observed in InGaAs/GaAs QDs by Wang et al 9 in 1994, in InAs/GaAs QDs by Yu et al 10 in 1996, and by other groups later. 11 They found that the photoluminescence ͑PL͒ radiative lifetime increases first with increasing temperature and then decreases at high temperatures.…”

“…Note that a decrease in the PL decay time at 300 K has been widely reported in the literature. [9][10][11][12][21][22][23] The observation of long PL decay times, even at 300 K, indicates a high quality of our QD sample. The two AlAs layers can suppress the influence of nonradiative centers on the surface and in the substrate.…”

Time-resolved optical characterization of InAs/InGaAs quantum dots emitting at 1.3 μm

“…The constant lifetime value at low temperatures and the subsequent linear increase with temperature has been predicted theoretically 15 and observed before in self-assembled QDs. 16,17 The lateral confinement in the QDs produces nonzero ͑i.e., nonradiative͒ in-plane wave vector k ʈ components in the exciton wave function, thus reducing the radiative emission rate as compared to QWs. 15 As the temperature increases, excited states having larger values of k ʈ become populated, and the radiative rate decreases further.…”

Magnetic field effects on optical and transport properties inInAs∕GaAsquantum dots

“…The temperature-induced reduction of the QD emission intensity at temperatures above 80 K is explained in terms of an increased thermal kick out rate from the dots. 18,19 This statement is supported by PL measurements with below WL excitation, where the carriers are excited directly into the dot. PL performed with below and above WL excitation follows the same general temperature dependence.…”