Optical properties of ultrathin GaAs layers embedded in AlxGa1-xAs

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Using a density functional approach, we study structural and electronic properties of the 4H(0001)-SiC/SiO2 interface. Through the sequential use of classical and ab initio simulation methods, we generate an abrupt model structure which describes the transition between crystalline SiC and amorphous SiO2 without showing any coordination defect. The first step in our generation procedure consists in identifying suitable interfacial bonding patterns which account for the bond density reduction across the inter

Cantilever-based detection of ultrasmall forces is of great interest for several applications such as magnetic resonance force miscroscopy (MRFM) where an ultrahigh sensitive cantilever is used to detect magnetic resonance in small ensembles of electron or nuclear spins. Detecting the smallest possible forces requires ultrahigh sensitive cantilevers with low spring constant (k < 0.1 mN/m), resonance frequency f > 1 kHz and high quality factor (Q > 30000 in vacuum). Considerable progress has been made in fab

The case presented in the paper shows how effective measurements can be made to help in the assessment of an important structure in a relatively short time frame using a combination of electronic inclinometers, temperature sensors and hydrostatic leveling. While not directly applicable to all kinds of structures, the methodology presented can certainly be adapted to many situations. It is anticipated that this and similar methods will be developed that will deliver a high quality of information about struct

Microcavity light-emitting diodes (MCLEDs) with top-emitting geometry have been grown by molecular beam epitaxy on GaAs and Si substrates. External quantum efficiencies of up to 10% were obtained for 420 x 420 mu m(2) homoepitaxial devices. The efficiency of 32 x 32 mu m(2) diodes was 4% for homoepitaxial devices and 1% for diodes realized on conformal GaAs-on-Si stripes. Much lower efficiencies were obtained for devices grown directly on GaAs-on-Si seed layers, demonstrating that the conformal epitaxy tech

Wide quantum wells, where the energy spacing between the first two energy levels is lower than the energy of the polar optical phonon, could represent the ideal condition to obtain a population inversion and the production of infrared lasers. On the other hand in these quantum wells the efficiency of carrier-carrier scattering is increasing with the width of the well and can produce a relatively quick relaxation of carriers in the first subband. In this work we present a detailed and systematic joint theore

The electronic states in the conduction and valence bands of quantum wires are studied by means of the effective mass hamiltonian and the Luttinger hamiltonian. The band mixing effects due to the wire geometry are fully taken into account by an accurate finite element solution of the resulting Schrodinger equations. The quantum wire profiles measured by transmission electron microscopy are used. The comparison of theoretical results with photoluminescence excitation spectra of various nanostructures yields

We study the dynamics of the charged and neutral excitons in a modulation-doped GaAs quantum well by time-resolved photoluminescence under a resonant excitation. The radiative lifetime of the charged exciton is found to be surprisingly short, 60 ps. This time is temperature independent between 2 and 10 K, and increases by a factor of 2 at 6 T. We discuss our findings in view of present theories of exciton radiative decay. [S0163-1829(98)03143-9].

A new system, Physilog, for ambulatory monitoring of movement is proposed and its applications in orthopaedic, physiology, angiology and quality of life are presented. Body accelerations were recorded by a portable measuring device. Significant parameters of body motion, namely, movement coordination, temporal parameters, speed, incline, distance covered, kind of physical activity and its duration, are extracted from the subject accelerations in its daily environment. The accuracy of these parameters guaran

We demonstrate a novel all-optical spatial Light modulator capable of megahertz modulation rates. It is based on the quantum-confined Stark effect, but the modulating electric field is entirely photogenerated by strongly asymmetric photocarrier transfer in GaAs/AlAs layers. In a nonoptimized sample, cw optical excitation of approximately 50 W/cm(2) created a 30-kV/cm electric field, inducing a 9-meV exciton red shift at room temperature. Under pulsed excitation the photogenerated electric field can be switc

The electronic properties of amorphous and ion-implanted polycrystalline SnO2 films have been studied using x-ray photoemission spectromicroscopy. First, we analysed the degree of oxidation and the homogeneity of as-deposited films. The SnO and SnO2 phases were identified from their valence band spectra rather than from the Sn 3d core level spectra. Then we studied the damage effects due to the implantation of Pd+ and Ga+ ions in polycrystalline films. The ion bombardment of SnO2 films results in drastic ch

A review of experimental results obtained by different techniques is presented on the problem of zinc diffusion. Zinc diffusion was carried out on Si-doped GaAs (n almost-equal-to 10(18) cm-3) and on multiple quantum well (MQW) structures. The samples were investigated by secondary-ion mass spectroscopy (SIMS), different imaging modes of scanning electron microscopy such as secondary electrons, cathodoluminescence (CL) and electron beam-induced current (EBIC), transmission electron microscopy on a wedge-sha

A procedure for calculating the resonance width of a state degenerate with a continuum is proposed. It is based on a diagonalization of the Hamiltonian on a finite variational basis followed by application of the Fano theory on the resulting eigenstates. The method is first tested on a one-dimensional model that admits an exact solution, and then applied to the problem of the light-hole (LH) exciton in narrow GaAs-Ga(1-x)Al(x)As quantum wells. The resonance width of the LH exciton is found to be of the orde

Optical properties of ultrathin GaAs layers embedded in AlxGa1-xAs

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Structural and electronic properties of an abrupt 4H-SiC(0001)/SiO2 interface model: Classical molecular dynamics simulations and density functional calculations

Combined Al-protection and HF-vapour release process for ultrathin cantilevers

Long-Term Evaluation vs Short-Term Measurements : the Case of the Riddes Bridges

High-efficiency top-emitting microcavity LEDs on GaAs and GaAs Si substrates

Carrier-carrier interaction and fast intersubband scattering in wide GaAs quantum wells

Band-mixing and coupling in single and double quantum wire structures

Charged exciton dynamics in GaAs quantum wells

Motion analysis in clinical practice using ambulatory accelerometry

All-Optical Spatial Light-Modulator with Megahertz Modulation Rates

ESCA Investigation of SnOx Films Used as Gas Sensors

Zinc Diffusion in Gaas and Zinc-Induced Disordering of Gaas Algaas Multiple Quantum-Wells - a Multitechnique Study

Variational Calculation of Fano Linewidth - Application to Excitons in Quantum-Wells