We demonstrate simultaneous lasing at two well-separated wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, we attribute it to incomplete clamping of the ES population at the GS threshold.

A procedure of InAs/InP quantum dots elaboration emitting at 1.55 μm by gas source molecular beam epitaxy is described. It is based on a modification of the capping layer growth which is deposited in two steps, separated by a growth interruption under phosphorus flux. The main effect of this two step capping layer growth is to reduce the height of the biggest islands and thus to decrease the photoluminescence linewidth of the quantum dots emission line. Transmission electron microscopy and photoluminescence experiments show that quantum dots structure are still present after growth interruption under phosphorus flux and that the photoluminescence linewidth at 1.55 μm is reduced from 120 to 50 meV, thanks to this procedure.

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International audienceInAs quantum-dot (QD) laser structures are grown on (113)B-oriented InP substrate by gas-source molecular-beam epitaxy. Following an optimized growth procedure, a high density of 1.1×1011 cm−2 of uniformly sized QDs is achieved. Broad-area lasers containing three stacked QD layers have been realized and tested. Laser emission on the ground-state transition (λ = 1.59 μm) is obtained at room temperature (RT), at a threshold current density as low as 190 A/cm2. Ground-state modal gain and transparency current density is measured to be 7 cm−1 and 23 A/cm2 per dot layer. Ground-state laser emission is also demonstrated from low temperature (100 K, Jth = 33 A/cm2) to high temperature (350 K), exhibiting an insensitive threshold in the [100, 170] K range, and a 55 K characteristic temperature at RT

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International audienceWe present a comparative study of carrier diffusion in semiconductor heterostructures with different dimensionality [InGaAs quantum wells (QWs), InAs quantum dots (QDs), and disordered InGaNAs QWs (DQWs)]. In order to evaluate the diffusion length in the active region of device structures, we introduce a method based on the measurement of the current-voltage and light-current characteristics in light-emitting diodes where current is injected in an area <1 μm2. By analyzing the scaling behavior of devices with different sizes, we deduce the effective active area, and thus the diffusion length. A strong reduction in the diffusion length is observed going from QWs (Ld≈2.7 μm) to QDs (Ld<100 nm), DQWs being an intermediate case (Ldiff≈0–200 nm depending on the carrier density). These results show that lateral composition fluctuations, either intended or unintended, produce strong carrier localization and significantly affect the carrier profile in a device even at room temperatur

Stacked InAs quantum dots (QDs) grown on InP(113)B are analyzed both experimentally and theoretically in order to study the influence of the electronic vertical coupling between the QD layers. Improved growth conditions enable us to control the optimum QD height of the samples, thus yielding an emission wavelength of our nanostructures at about 1.55μm at room temperature. Three samples containing three QD layers with different vertical spacing are studied. The QD electronic structure is studied by continuous-wave photoluminescence and time-resolved photoluminescence experiments at low temperature. A simplified theoretical model is developed, yielding results consistent with experimental data. This analysis evidences the electronic coupling between the QD layers.

We report the observation of enhanced charge-carrier redistribution in laterally organized and coupled InAs/ InP quantum dots ͑QDs͒. We show that a periodic organization appears in the QD plane for a high in-plane QD density ͑QDD͒. This organization enhances the lateral coupling between the dots, which is evidenced by photoluminescence and magnetophotoluminescence experiments. Electronic inter-QD lateral coupling results in an improved charge-carrier distribution at low temperature, as shown by electroluminescence on high QDD QD lasers. We conclude that the inter-QD tunneling occurs via the tunneling of excited states through the wetting layer, and discuss the prospects of using coupled QDs for improving the quantum efficiency and dynamical properties of QD lasers.