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We report on the growth and characterization of low threshold 1.32-mu m quantum dots (QDs) laser diodes. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). From samples containing multilayer QDs and using the Limited-Area Photoluminescence (LAPL) technique we have shown that the gain of an N-layer structure is higher than N times that of a single layer. This enhancement is attributed to the increase of the quantum dot density in the upper layers and also to the use of the high growth temperature spacer layer. Broad area laser diodes were processed from the grown samples containing three layers of InAs QDs grown directly on GaAs and capped with 4-nm-thick InxGa1-xAs layer. Than measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit between 1.29 and 1.32-mu m which is beyond the strategic telecommunication wavelength. The characteristic temperature is around 80 K and very stable in the hole range of the operating temperature (from 0 to 90 degrees C). The internal quantum efficiency is 53% and the modal gain per QD layer was estimated to be similar to 6 cm(-1). For an infinite cavity length a threshold current density of 8 A/cm(2) per QD layer was obtained. From the calculation of the optical confinement of QDs, we have estimated a material gain of 1979 cm(-1).

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Due to their delta-like density of states, quantum dots (QDs) were expected to improve laser device performances with respect to quantum wells (QWs). Nevertheless, some important drawbacks limit this technology. For instance, QD laser still suffers from a low value of the modal gain, due to the low areal density of QDs, and inhomogeneous broadening, especially when multistacked layers are used. In this paper, we demonstrate that a linear increase of the QD modal gain with the QD layers number, as typically achieved in multi-QW lasers, is possible by a careful control of the Stranski-Krastanov QDs growth and QDs stacking optimization. A low-transparency current density of 10 A/cm(2) per QD layer and a modal gain of 6 cm(-1) per QD layer Were achieved from laser structures containing up to seven QD layers. We demonstrate 10-Gb/s direct modulation (until a temperature of 50 degrees C and high T-0 (110 K) from a single-mode device containing six QD layers.

In this work we present the realization of an experimental setup to measure the absorption spectrum of low planar density active media in nanoscale devices. The experimental technique employs in-plane light transmission through a waveguide embedding the active medium. It has been applied to the investigation of the room temperature optical properties of low density self-assembled InGaAs/GaAs quantum dots (QDs), emitting around 1.3 mu m. A detailed analysis of the obtained spectra showed the occurrence of a Stokes shift which after inspection turned out to be related to the thermally activated carrier migration throughout the QD ensemble.

We have investigated the ultrafast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots emitting at 1.3 mu m by means of time resolved photoluminescence upconversion measurements with a time resolution of about 200 fs. The detection energies scan the spectral region from the energy of the quantum dot excitonic transition up to the barrier layer absorption edge. We found, under high excitation intensity, that the intrinsic electronic states are populated mainly by carriers directly captured from the barrier. (C) 2007 Elsevier Ltd. All rights reserved.

We have investigated the ultra-fast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots (QDs) emitting at 1.3 μm by time resolved photoluminescence (TRPL) upconversion measurements with a time resolution of about 200 fs. Changing the detection energies in the spectral region from the energy of the quantum dots excitonic transition up to the barrier layer absorption edge, we have found that, under high excitation intensity, the intrinsic electronic states are populated mainly by carriers directly captured from the barrier.

Three semiconductor laser structures containing 1, 3 and 5 layers of self organized InAs/InGaAs/GaAs quantum dots (QDs) have been grown by Molecular Beam Epitaxy. Broad area lasers were processed from the grown wafers and tested. These structures show a linear increase of the modal gain with the number of QDs layers with an average modal gain per QDs layer of ∼5 cm–1. A maximum modal gain of 25 cm–1 was obtained at room temperature (RT) from the sample containing 5 layers of QDs. A transparency current density and a low internal loss value of ∼5.5 A/cm2 per QD layer and 1.5 cm–1 were deduced respectively. For an infinite cavity length a minimum threshold current density of ∼9 A/cm2 per QD layer was inferred. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the growth, fabrication and characterization of low threshold laser diodes emitting around 1.3 gim. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). Broad area laser diodes were processed from different samples containing three layers of InAs quantum dots (QDs), and cleaved at different cavity lengths (L c ). Electro-luminescence measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit at 1.32 μm, in the low-absorption spectral window for telecom applications. The characteristic temperature T 0 is in the range 60-77 K and the differential quantum efficiency is 53 %. For an infinite cavity length a threshold current density of 8 A/cm2per QD layer was obtained. Lasing from short-cavity diodes (L c = 750 μm) was also obtained after e-beam evaporation of high-reflection coatings on one edge of the in-plane laser structure.