Characteristics of InAsP/InGaAsP Edge Emitting Laser Diodes Obtained by Localised Fusion on GaAs Substrates

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Current profile tailoring has been performed by application of electron cyclotron heating (ECH) and electron cyclotron current drive, leading to improved energy confinement in the plasma core of the TCV tokamak. The improved confinement is characterized by a substantial enhancement (H-factor) of the global electron energy confinement time relative to the prediction of the RLW scaling law (Rebut P H et al 1989 Proc. 12th Int. Conf. of Plasma Physics and Controlled Fusion Research (Nice, 1988) vol 2 (Vienna:

Solar blind detectors based on AlGaN grown by Molecular Beam Epitaxy and Metal Organic Vapor Phase Epitaxy have been fabricated and characterized. Metal Semiconductor Metal (MSM) detectors and vertical Schottky detectors have been realized, with a design that allows back side illumination. The growth was optimized in order to improve the layer quality, avoid crack fort-nation, and provide the best detector performance. The technological process was also optimized in order to reduce the dark currents and imp

Microcavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermaliza

A neutron-scattering study of nonsuperconducting La2-xSrxCaCu2O6 (x=0 and 0.2), a bilayer copper oxide without CuO chains, has revealed an unexpected tetragonal-to-orthorhombic transition with a doping dependent transition temperature. The predominant structural modification below the transition is an in-plane shift of the apical oxygen. In the doped sample, the orthorhombic superstructure is strongly disordered, and a glassy state involving both magnetic and structural degrees of freedom develops at low te

Current profile tailoring by electron cyclotron heating (ECH) and current drive (ECCD) is used to improve central electron energy confinement in the TCV tokamak. Counter-ECCD on axis alone achieves this goal in a transient manner only. A stable scenario is obtained by a two-step sequence of err-axis ECH, which stabilizes magnetohydrodynamics modes, and on-axis counter-ECCD, which generates a flat or inverted current profile. This high-confinement regime, with central temperatures up to 9 keV (at a. normaliz

This thesis describes experiments with one-dimensional atomic chains grown by step decoration of vicinal Pt surfaces. The objective of the research was twofold: first, to characterize metal epitaxial growth on stepped substrates; second, to make use of this knowledge to fabricate arrays of monatomic metal wires in order to investigate their electronic and magnetic properties. The first part focuses on molecular beam epitaxy (MBE) of Ag, Cu, Co, and Ni on densely stepped Pt surfaces (one monatomic step every

Third harmonic generation (THG) efficiency is shown to be a greatly enhanced at the onset of inelastic scattering of electrons on optic phonons. Scaling experiments are performed on n-type InP at the pump wave frequency of 9.43 GHz at 80 K. Monte Carlo modeling is employed for scaling the effect to the 3(rd) harmonic frequency of 1 THz. The THG efficiency in n-type GaAs and InP as well as in the wurtzite phase of n-type InN and GaN compound crystals is compared to that in n-type Si. The efficiency maximum i

Experiments with high-power electron cyclotron heating (ECH) and current drive (ECCD) in the TCV tokamak are discussed. Power up to 2.7 MW from six gyrotrons is delivered to the tokamak at the second-harmonic frequency (82.7 GHz) in X-mode. The power is transmitted to the plasma by six independent launchers, each equipped with steerable mirrors that allow a wide variety of injection angles in both the poloidal and toroidal directions. Fully non-inductive operation of the tokamak has been achieved in steady

Microcavity light emitting diodes (MCLEDs) present several interesting features compared to conventional LEDs such as narrow linewidth, improved directionality and high efficiency. We report here on MCLEDs with a top emitting geometry. The MCLED layers were grown using molecular beam epitaxy on GaAs substrates. They consist of a 3-period Be-doped distributed Bragg reflector (DBR) centered at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-periods Si-doped DBR. Different values for

Semiconductor quantum wires (QWRs) are promising structures for optoelectronics applications, since they can provide quantum confinement for charge carriers in two dimensions. The advantage that they offer over conventional quantum wells (QWs) is due to the sharper density of states characteristic of these structures, yielding narrower spectral lines and higher optical gain. However, to exhibit clear confinement characteristics, QWRs must meet stringent requirements in terms of size, uniformity and interfac

We present second-harmonic generation experiments in p-doped asymmetrically stepped quantum wells using the emission of a free-electron laser in the wavelength interval between 13 and 18 mu m. The wells are designed such that the three fewest valence-subbands are about equally spaced. We measured the angular and frequency dependence of the second-harmonic signal excited by intense laser irradiation chosen to be nearly resonant with the transitions between the three lowest valence subbands. We see evidence o

High quality InP/InGaAsP Distributed Bragg Reflectors (DBRs) are a key element in Vertical Cavity Surface Emitting Laser (VCSELs) for long wavelength (1.55 mu m) applications [1-3]. Because of the small index difference between InP and InGaAsP, more than 30 periods are needed to obtain reflectivities above 99 %, which makes it a challenge for the crystal growth technique. In this paper we present the structural and optical characteristics of such DBRs grown by Chemical Beam Epitaxy (CBE) at high growth rate

Characteristics of InAsP/InGaAsP Edge Emitting Laser Diodes Obtained by Localised Fusion on GaAs Substrates

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Control of electron internal transport barriers in TCV

High performance solar blind detectors based on AlGaN grown by MBE and MOCVD

Polariton amplification in semiconductor microcavities

Structural and magnetic instabilities of La2-xSrxCaCu2O6

Long-pulse improved central electron confinement in the TCV tokamak with electron cyclotron heating and current drive

Growth, electronic structure and magnetism of supported metal nanowires

Enhanced third-order nonlinearity in semiconductors giving rise to 1 THz radiation

High-power ECH and fully non-inductive operation with ECCD in the TCV tokamak

High efficiency top-emitting microcavity light-emitting diodes

Formation mechanisms of low-dimensional semiconductor nanostructures grown by OMCVD on nonplanar substrates

Second-harmonic generation involving valence-subband transitions in p-doped GaAs/AlxGa1-xAs quantum wells

Structural and optical characterization of InP/InGaAsP distributed Bragg reflectors grown by CBE