Search

We show that the epitaxial growth of height-controlled GaAs quantum dots, leading to the reduction of the inhomogeneous emission bandwidth, produces individual nanostructures of peculiar morphology. Besides the height controlled quantum dots, we observe nanodisks formation. Exploiting time resolved and spatially resolved photoluminescence we establish the decoupling between quantum dots and nanodisks and demonstrate the high optical properties of the individual quantum dots, despite the processing steps needed for height control. [ABSTRACT FROM AUTHOR]

The structural and morphological features of bimodal-sized InAs/(In)GaAs quantum dots with density in the low 109 cm-2 range were analyzed with transmission electron microscopy and atomic force microscopy and were related to their optical properties, investigated with photoluminescence and time-resolved photoluminescence. We show that only the family of small quantum dots (QDs) is able to emit narrow photoluminescence peaks characteristic of single-QD spectra; while the behavior of large QDs is attributed to large strain fields that may induce defects affecting their optical properties, decreasing the optical intensity and broadening the homogeneous linewidth. Then, by using a rate-equation model for the exciton recombination dynamics, we show that thermal population of dark states is inhibited in both QD families capped by high In content InGaAs layers. We discuss this behavior in terms of alloy disorder and increased density of point defects in the InGaAs pseudomorphic layer. [ABSTRACT FROM AUTHOR]

We have investigated the temperature dependent recombination dynamics in two bimodally distributed InAs self assembled quantum dots samples. A rate equations model has been implemented to investigate the thermally activated carrier escape mechanism which changes from exciton-like to uncorrelated electron and hole pairs as the quantum dot size varies. For the smaller dots, we find a hot exciton thermal escape process. We evaluated the thermal transfer process between quantum dots by the quantum dot density and carrier escape properties of both samples. [ABSTRACT FROM AUTHOR]

The multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device. [ABSTRACT FROM AUTHOR]

Photoluminescence and time resolved photoluminescence from single metamorphic InAs/GaAs quantum dots (QDs) emitting at 1.3 μm have been measured by means of a novel fibre-based characterization set-up. We demonstrate that the use of a wavelength tunable fibre Bragg grating filter increases the light collection efficiency by more than one order of magnitude as compared to a conventional grating monochromator. We identified single charged exciton and neutral biexciton transitions in the framework of a random population model. The QD recombination dynamics under pulsed excitation can be understood under the weak quantum confinement potential limit and the interaction between carriers at the wetting layer and QD states. [ABSTRACT FROM AUTHOR]

We show that the epitaxial growth of thin layers of AlGaAs on Ge and Si substrates allows to obtain single photon sources by exploiting the sparse and unintentional contamination with acceptors of the AlGaAs. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in quantum dots, but their implementation is by far much easier, since it does not require 3D nucleation. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements. [ABSTRACT FROM AUTHOR]

The article presents research which discussed the properties and growth of low-density InAs/GaAs quantum dot structures through the use of Molecular Beam Epitaxy (MBE). The researchers offered an interesting method to the creation of telecommunication wavelengths single-photon sources. They found that the semiconductor quantum dots (QD) have very low density and their light emission characteristics can be assessed by growth of the dots at low growth rate and high growth temperature.

We investigate the electronic and optical properties of InAs double quantum dots grown on GaAs (001) and laterally aligned along the [110] crystal direction. The emission spectrum has been investigated as a function of a lateral electric field applied along the quantum dot pair mutual axis. The number of confined electrons can be controlled with the external bias, leading to sharp energy shifts which we use to identify the emission from neutral and charged exciton complexes. Quantum tunneling of these electrons is proposed to explain the reversed ordering of the trion emission lines as compared to that of excitons in our system. [ABSTRACT FROM AUTHOR]

We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 108 cm-2 dot density and metamorphic InxGa1-xAs (x=0.15,0.30) confining layers result in emission wavelengths at 1.3 μm. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows. [ABSTRACT FROM AUTHOR]

Highlights • Non-invasive measurement of the zero-delay time in an intensity interferometer. • Non a priori knowledge of the photon distribution is required. • Enhanced Cross-talk from avalanche photodiodes (APD) is used. • Free optics and single mode fiber configurations have been proved. Abstract Measuring photon autocorrelations via a Hanbury-Brown and Twiss (HBT) setup is a widely used experimental technique in quantum optics and is the base for quantum characterizations via Hong-Ou-Mandel interferometry, Bell inequality tests or quantum state tomography. The most common use for HBT measurements is the demonstration of single-photon emission from a quantum emitter. In order to make a definite statement and analyze the coincidence histograms obtained in the experiment, the temporal position of the zero delay time (ZDT) must be accurately known. In many cases, determining the ZDT requires tedious calibration measurements using light sources with known non-trivial photon correlations. Here we report on a non-invasive technique for measuring the ZDT in HBT setups based on avalanche photodiodes (APDs). The technique relies on the deliberate enhancement of optical crosstalk between the APDs. It can be used with any conventional laser source and therefore means a significant improvement for the easy calibration of the ZDT in HBT setups. [ABSTRACT FROM AUTHOR]

The Purcell effect dependence on the excitation power is studied in photonic crystal microcavity lasers embedding InAs/InP quantum wires. In the case of non-lasing modes, the Purcell effect has low dependence on the optical pumping, attributable to an exciton dynamics combining free and localized excitons. In the case of lasing modes, the influence of the stimulated emission makes ambiguous the determination of the Purcell factor. We have found that this ambiguity can be avoided by measuring the dependence of the decay time on the excitation power. These results provide insights in the determination of the Purcell factor in microcavity lasers. [ABSTRACT FROM AUTHOR]

Abstract: We investigate analytically and numerically the dynamics of single mode lasers with periodic ac injection (rocked lasers). Such lasers show phase bistability as the phase of the light emitted by such lasers can lock to either of two values shifted by π. Locking regimes for different lasers are studied showing that the system response is strongly modified in class B lasers due to the influence of relaxation oscillations. [Copyright &y& Elsevier]