Magneto-optical studies of the correlation between interface microroughness parameters and the photoluminescence line shape in GaAs/Ga0.7Al0.3As quantum wells

In this work we analyze the relation between the interface microroughness and the full width at half maximum (FWHM) of the photoluminescence (PL) spectra for a GaAs/Ga0.7Al0.3As multiple quantum well (QW) system. We show that, in spite of the complex correlation between the microscopic interface-defects parameters and the QW optical properties, the Singh and Bajaj model [Appl. Phys. Lett. 44, 805 (1984)] provides a good quantitative description of the excitonic PL-FWHM. ©1999 The American Physical Society.

Symmetry reduction due to gallium substitution in the garnet Li6.43(2)Ga0.52(3)La2.67(4)Zr2O12

Single-crystal structure refinements on lithium lanthanum zirconate (LLZO; Li7La3Zr2O12) substituted with gallium were successfully carried out in the cubic symmetry space group I [Formula: see text]3d. Gallium was found on two lithium sites as well as on the lanthanum position. Due to the structural distortion of the resulting Li6.43(2)Ga0.52(3)La2.67(4)Zr2O12 (Ga-LLZO) single crystals, a reduction of the LLZO cubic garnet symmetry from Ia[Formula: see text] d to I [Formula: see text]3d was necessary, which could hardly be analysed from X-ray powder diffraction data.

Majority carrier capture cross section determination in the large deep trap concentration cases

A method to determine the thermal cross section of a deep level from capacitance measurements is reported. The results enable us to explain the nonexponential behavior of the capacitance versus capture time when the trap concentration is not negligible with respect to that of the shallow one, and the Debye tail effects are taken into account. A figure of merit for the nonexponential behavior of the capture process is shown and discussed for different situations of doping and applied bias. We have also considered the influence of the position of the trap level"s energy on the nonexponentiality of the capture transient. The experimental results are given for the gold acceptor level in silicon and for the DX center in Al0.55 Ga0.45As, which are in good agreement with the developed theory.

Compositional control of the electrical transport properties in the new series of thiospinels Ga1-xGexV4S8-delta (0 <=x<=1)

A new series of non-stoichiometric sulfides Ga1−xGexV4S8−δ (0≤x≤1; δ≤0.23) has been synthesized at high temperatures by heating stoichiometric mixtures of the elements in sealed quartz tubes. The samples have been characterized by powder X-ray diffraction, SQUID magnetometry and electrical transport-property measurements. Structural analysis reveals that a solid solution is formed throughout this composition range, whilst thermogravimetric data reveal sulfur deficiency of up to 2.9% in the quaternary phases. Magnetic measurements suggest that the ferromagnetic behavior of the end-member phase GaV4S8 is retained at x≤0.7; samples in this composition range showing a marked increase in magnetization at low temperatures. By contrast Ga0.25Ge0.75V4S8−δ appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x≠1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing Ga content, whilst the end-member phase GeV4S8−δ is a p-type semiconductor. The results demonstrate that the physical properties are determined principally by the degree of electron filling of narrow-band states arising from intracluster V–V interactions.

High-energy transitions of shallow magnetodonors in a GaAs/Al0.3Ga0.7As multiple quantum well

The high-energy states of a shallow donor in a GaAs/Ga0.7Al0.3As multiple-quantum-well structure subjected to a magnetic field in the growth direction are studied both theoretically and experimentally. Effects due to higher confinement subbands as well as due to the electron-phonon interaction are investigated. We show that most of the peaks in the infrared photoconductivity spectrum are due to direct transitions from the ground state to the m = +/-1 magnetodonor states associated with the first subband, but transitions to the m = +/-1 states of the third subband are also apparent. The remaining photoconductivity peaks are explained by phonon-assisted impurity transitions.

Diffusion of Zn into GaAs and AlGaAs from isothermal Liquid-phase epitaxy solutions

In this work we present results of zinc diffusion in GaAs using the liquid phase epitaxy technique from liquid solutions of Ga‐As‐Zn and Ga‐As‐Al‐Zn. Using silicon‐doped n‐GaAs substrates, working at a diffusion temperature of 850 °C, and introducing a dopant concentration ranging 1018–1019 cm−3, the most important findings regarding the diffusion properties are as follows: (a) zinc concentration in the solid depends on the square root of zinc atomic fraction in the liquid; (b) the diffusion is dominated by the interstitial‐substitutional process; (c) the diffusivity D varies as about C3 in the form D=2.9×10−67C3.05; (d) aluminum plays the role of the catalyst of the diffusion process, if it is introduced in the liquid solution, since it is found that D varies as (γAsXlAs)−1; (e) the zinc interstitial is mainly doubly ionized (Zn++i); (f) the zinc diffusion coefficient in Al0.85 Ga0.15 As is about four times greater than in GaAs; (g) by means of all these results, it is possible to control zinc diffusion processes in order to obtain optimized depth junctions and doping levels in semiconductor device fabrication.

Top-Hat HELLISH-VCSOA for optical amplification and wavelength conversion for 0.85 to 1.3ìm operation

The Top-Hat hot electron light emission and lasing in semiconductor heterostructure (HELLISH)-vertical cavity semiconductor optical amplifier (VCSOA) is a modified version of a HELLISH-VCSOA device. It has a shorter p-channel and longer n-channel. The device studied in this work consists of a simple GaAs p-i-n junction, containing 11 Ga0.35In0.65 N0.02As0.08/GaAs multiple quantum wells in its intrinsic region; the active region is enclosed between six pairs of GaAs/AlAs top distributed Bragg reflector (DBR) mirrors and 20.5 pairs of AlAs/GaAs bottom DBR mirrors. The operation of the device is based on longitudinal current transport parallel to the layers of the GaAs p-n junction. The device is characterised through I-V-L and by spectral photoluminescence, electroluminescence and electro-photoluminescence measurements. An amplification of about 25 dB is observed at applied voltages of around V = 88 V.

Preliminary temperature accelerated life test (ALT) on lattice mismatched triple-junction concentrator solar cells-on-carriers

A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0.83In0.17As/Ge triple-junction solar cells-on-carrier is being carried out. The solar cells have been tested at three different temperatures: 125, 145 and 165°C and the nominal photo-current condition (500X) is emulated by injecting current in darkness. The final objective of these tests is to evaluate the reliability, warranty period, and failure mechanism of these solar cells in a moderate period of time. Up to now only the test at 165°C has finished. Therefore, we cannot provide complete reliability information, but we have carried out preliminary data and failure analysis with the current results.

The miner's right : a tale of the Australian goldfields /

At end of book: Messrs. Macmillan & Co.'s publications, [6]p; and A classified catalogue of books in general literature published by Macmillan and Co., 48p.

On Finite Element Methods for 2nd order (semi–) periodic Eigenvalue Problems

We deal with a class of elliptic eigenvalue problems (EVPs) on a rectangle Ω ⊂ R^2 , with periodic or semi–periodic boundary conditions (BCs) on ∂Ω. First, for both types of EVPs, we pass to a proper variational formulation which is shown to fit into the general framework of abstract EVPs for symmetric, bounded, strongly coercive bilinear forms in Hilbert spaces, see, e.g., [13, §6.2]. Next, we consider finite element methods (FEMs) without and with numerical quadrature. The aim of the paper is to show that well–known error estimates, established for the finite element approximation of elliptic EVPs with classical BCs, hold for the present types of EVPs too. Some attention is also paid to the computational aspects of the resulting algebraic EVP. Finally, the analysis is illustrated by two non-trivial numerical examples, the exact eigenpairs of which can be determined.

Projectively Solid Sets and an N-dimensional Piccard's Theorem

We discuss functions f : X × Y → Z such that sets of the form f (A × B) have non-empty interiors provided that A and B are non-empty sets of second category and have the Baire property.

Наука и Изкуство: История на взаимно вдъхновение

Science and art are considered as two distinct areas in the spectrum of human activities. Many scientists are inspired by art and many artists embed science in their work. This paper presents a one-year experiment, which started with benchmark tests of a compiler, passed through dynamic systems based on complex numbers and ended as a scientific art exhibition. The paper demonstrates that it is possible to blend science and art in a mutually beneficial way. It also shows how science can inspire the creation of artistic works, as well as how these works can inspire further scientific research.

Supporting and Enhancing Research on Cultural Heritage in France: the PATRIMA Project

In this paper, we first overview the French project on heritage called PATRIMA, launched in 2011 as one of the Projets d'investissement pour l'avenir, a French funding program meant to last for the next ten years. The overall purpose of the PATRIMA project is to promote and fund research on various aspects of heritage presentation and preservation. Such research being interdisciplinary, research groups in history, physics, chemistry, biology and computer science are involved in this project. The PATRIMA consortium involves research groups from universities and from the main museums or cultural heritage institutions in Paris and surroundings. More specifically, the main members of the consortium are the two universities of Cergy-Pontoise and Versailles Saint-Quentin and the following famous museums or cultural institutions: Musée du Louvre, Château de Versailles, Bibliothèque nationale de France, Musée du Quai Branly, Musée Rodin. In the second part of the paper, we focus on two projects funded by PATRIMA named EDOP and Parcours and dealing with data integration. The goal of the EDOP project is to provide users with a data space for the integration of heterogeneous information about heritage; Linked Open Data are considered for an effective access to the corresponding data sources. On the other hand, the Parcours project aims at building an ontology on the terminology about the techniques dealing with restoration and/or conservation. Such an ontology is meant to provide a common terminology to researchers using different databases and different vocabularies.

Solutions of Fractional Diffusion-Wave Equations in Terms of H-functions

MSC 2010: 35R11, 42A38, 26A33, 33E12

Análise da relação entre poupança e investimento para o caso brasileiro, 1996 a 2013

O presente estudo tem por objetivo estimar a relação entre poupança e investimento no curto prazo. Os dados utilizados ficam restritos ao Brasil, no período que varia entre 1996 e 2013. A fim de satisfazer tal finalidade, será estimado um modelo vetor autorregressivo, com base na literatura empírica do modelo Feldstein e Horioka. O resultado obtido indica uma grande mobilidade de capitais para Brasil, em conformidade a não existência de uma relação de precedência temporal (Causalidade de Granger) para as variáveis. Por meio da decomposição da variância é possível inferir também que as variáveis são responsáveis pelas suas próprias variações ao longo do tempo. Ainda, as conclusões obtidas refutam a validade do Enigma Feldstin e Horioka, de que países industrializados teriam uma pequena mobilidade de capitais.