Hot phonons and Auger related carrier heating in semiconductor optical amplifiers

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We present detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Samples containing quantum dots of different size were characterized by means of transmission electron microscopy, photoluminescence and photoinduced absorption spectroscopy. Interlevel transitions in the conduction band were identified in the 0.52-0.98 eV range covering the telecommunication wavelength band. The s-p(z), transition ranges from 0.52 e

We have studied systems of asymmetric coupled GaAs V-groove quantum wires p-i-n diodes, in which the electrons and holes are injected into different wires. Despite the use of a 7 nm thick AlGaAs tunnel barrier, and although we demonstrate that holes tunnel more slowly than electrons, we observe a very efficient and fast tunneling between the quantum wires (QWR's). We attribute this to the achievement of a resonance between hole levels in the two QWR's. Photoluminescence excitation experiments are compared w

The peakedness of the density profile in source-free MHD-quiescent L-mode plasmas with lower hybrid current drive is observed to decrease with decreasing peaking of the current profile. For the discharges investigated, which include normal and reversed magnetic shear plasmas, the relationship can be summarized as n(e0)/ congruent to 1.2l(i), where l(i) is the normalized internal inductance. Density profiles are monotonically peaked at negative shear. Since density profiles remain peaked at zero loop v

We analyze the magnitude of degenerate two-photon gain of several quantum wells (QWs) in a resonant microcavity which is pumped off-resonantly by an optical field. A set of coupled phenomenological rate equations for electron-hole pairs and photons is derived. In the framework of this model, we make a realistic prediction of the time-integrated two-photon gain and find that a lambda-cavity containing 11 QWs would give a maximal amplification of similar to 2.3% for a peak,intensity of similar to 80 MW/cm(2).

There is currently both considerable interest in the physics of ELM transport in the scrape-off layer (SOL) and concern over the impact of the ELM power and particle loads on the divertor targets of future fusion reactors. This paper describes some experimental observations of the reaction of target floating potentials and currents during ELMS in TCV, relying principally on fast measurements of these parameters using tile embedded Langmuir probe arrays. Clear evidence is presented for rapid modifications in

Climate changes and global warming are generally associated with the enhanced greenhouse effect, but aerosols can induce a cooling effect and thus regionally mask this warming effect. Unfortunately, the strong variability both in space and in time of the aerosols and thus the difficulty to characterize their global basic properties induce large uncertainties in the predictions of the numerical models. Those uncertainties are as high as the absolute level of the enhanced greenhouse forcing. To solve this pro

InP films have been deposited on amorphous sapphire substrate by means of the metallorganic chemical vapour deposition technique with and without PH3/H-2 plasma preactivation. Polycrystalline materials, having average grain sizes of about 40 nm, which, however, vary according to the growth parameters, were obtained. The structural and compositional disorder strongly influence the optical and electrical properties. The most structurally disordered films present the largest photoluminescence (PL) efficiency a

The nonequilibrium dynamics of a two-dimensional electron-hole gas is studied in the regime of strong and resonant pumping of the exciton resonance. The Coulomb collision rates are consistently determined by taking into account the light-induced coherence of the two-band system that leads to a dressing of the carrier spectral functions. The light dressing dramatically reduces the Coulomb scattering efficiency. Results are presented for Rabi oscillations in the time domain and dynamical Stark splitting in th

We consider an electron-phonon system in two and three dimensions on square, hexagonal, and cubic lattices. The model is a modification of the standard Holstein model where the optical branch is appropriately curved in order to have a reflection positive Hamiltonian. Using infrared bounds together with a recent result on the coexistence of long-range order for electron and phonon fields, we prove that, at sufficiently low temperatures and sufficiently strong electron-phonon coupling, there is a Peierls inst

We performed a spectromicroscopy experiment to find evidence of lateral inhomogeneities in the band bending for the Al/GaS system. Microimages of the interface tuned on the Al 2p con levels revealed localized chemical inhomogeneities in proximity of the edge of the Al overlayer. A careful analysis of the photoemission spectra supports these conclusions and relates the inhomogeneities to band bending variations. The micron-size lateral scale for these features is similar to that of other interfaces. (C) 1999

The fluorescence yield, eta approximate to 0.30, and Lifetime, tau approximate to 52 ps, of recently discovered 'red' polydiacetylene isolated chains [R. Lecuiller, J. Berrehar, C. Lapersonne-Meyer, M. Schott, Phys. Rev. Lett. 80 (1998) 4068] have been measured at 15 K. These values show that the relaxation scheme of the 'red-chain' exciton is very different from that of the usual 'blue chains', and that excited states of A, symmetry are not present in the optical gap of red chains. Moreover, the radiative

A study of the elastic exciton-exciton Coulomb scattering in a semiconductor quantum well is presented, including the interexciton exchange of carriers and the spin degrees of freedom. The theoretical results show that electron-electron and hole-hole exchanges are the dominant mechanisms of interaction, while the classical direct term is negligible. The density-dependent homogeneous linewidth is calculated within the Born approximation and good agreement with the existing experimental data is obtained. Owin

Hot phonons and Auger related carrier heating in semiconductor optical amplifiers

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Spectroscopy of the electron states in self-organized GaN/AlN quantum dots

Electroluminescence and photoluminescence excitation study of asymmetric coupled GaAs/AlxGa1-xAs V-groove quantum wires

Shear and collisionality dependences of particle pinch in JET L-mode plasmas

Feasibility study for degenerate-two-photon gain in a semiconductor microcavity

ELM driven divertor target currents on TCV

Development of the Jungfraujoch multiwavelength lidar system for continuous observations of the aerosol optical properties in the free troposphere

Luminescence study of the disorder in polycrystalline InP thin films

Strongly driven exciton resonances in quantum wells: Light-induced dressing versus Coulomb scattering

Charge density wave and quantum fluctuations in a molecular crystal

A spectromicroscopy study of the Al GaS interface: Evidence of band bending lateral inhomogeneities

Fluorescence quantum yield and lifetime of 'red' polydiacetylene chains isolated in their crystalline monomer matrix

Role of the exchange of carriers in elastic exciton-exciton scattering in quantum wells