Linear polarization of the photoluminescence of quantum wells

The degree and orientation of the magnetic-field induced linear polarization of the photoluminescence from a wide range of heterostructures containing (Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a function of detection photon energy, applied magnetic field strength and orientation in the quantum well plane. A theoretical description of this effect in terms of an in-plane deformation acting on the valence band states is presented and is verified by comparison with the experimental data. We attempted to identify clues to the microscopic origin of the valence band spin anisotropy and to the mechanisms which actually determine the linear polarization of the PL in the quantum wells subject to the in-plane magnetic field. The conclusions of the present paper apply in full measure to non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain anisotropy.Comment: 21 pages, 10 figure

ÉTUDE DE CENTRES PROFONDS DANS CdTe PAR DES MÉTHODES DE PHOTOCAPACITANCE

Une étude des centres profonds dans CdTe de type n, purifié par fusion de zone, a été menée à l'aide de mesures de photocapacitance utilisant une diode de Schottky Au-CdTe portée à 77 K. L'analyse détaillée des variations temporelles de la capacité permet de séparer les contributions de plusieurs niveaux et de caractériser chacun par sa position, sa section optique efficace et sa concentration. On met ainsi en évidence : 1) un centre comportant deux niveaux : l'un à Ec — 0,58 eV, l'autre à une énergie supérieure avec une concentration de 7,8 x 1011 cm-3, 2) un centre plus profond à Ec — 0,93 eV et une concentration de 5,4 x 1012 cm-3, 3) un niveau entouré d'une barrière de potentiel pour les électrons situé à Ec — 0,54 eV. Ces résultats sont interprétés en termes de centres double donneur et accepteur multiple. Cette assignation soulève le problème intéressant de la correspondance avec les défauts natifs prévus : VTe(ou Cdi) qui serait un donneur double et VCd qui serait un double accepteur.A study of deep centers in zone refined n type CdTe has been conducted by means of photocapacitance measurements performed on a Au-CdTe Schottky diode at the temperature of 77 K. The detailed analysis of the time variations of capacity allows us to separate the contributions of several centers and to determine for each one the level position, the optical cross section and the concentration. In this way we observe the following : 1) a center with two associated levels : one at Ec — 0.58 eV, the other one at a higher energy with a concentration of 7.8 x 1011 cm-3, 2) a deeper center at Ec — 0.93 eV with a concentration of 5.4 x 1012 cm-3, 3) a level surmonted by a potential barrier for electrons, located at Ec — 0.54 eV. These results are interpreted in terms of double donor and multiple acceptor centers. This assignment raises the interesting problem of the connection with the expected native defects : VTe (or Cdi) and VCd which would be a double donor and a double acceptor respectively

EXCHANGE MECHANISM IN SEMIMAGNETIC SEMICONDUCTORS FROM HIGH MAGNETIC FIELD MAGNETIZATION

The analysis of high magnetic field magnetization provides a direct determination of the exchange constants between Mn spins. The study of these values indicate clearly that superexchange is the dominant mechanism for wide gap SMSC, whereas one other type of exchange, probably related to the gap value, is also present in narrow gap SMSC

DESCRIPTION DE DEUX APPAREILS PERMETTANT LE CONTROLE AUTOMATIQUE DES DÉBITS DE LAIT AU COURS DE LA TRAITE A LA MACHINE PREMIERS RÉSULTATS OBTENUS CHEZ LA BREBIS

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APTITUDE A LA TRAITE MÉCANIQUE DES BREBIS DE RACE PRÉALPES DU SUD ET CROISÉES FRISONS × PRÉALPES; ÉTUDE A DIFFÉRENTS STADES DE LA LACTATION

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CONCENTRATION DEPENDENCE OF THE ZEEMAN SPLITTING OF EXCITON IN Zn1-xMnxTe AND Cd1-xMnxTe

Magnetoreflectivity and magnetization measurements were performed in Zn1-xMnxTe and Cd1-xMnxTe for 0.02 ≤x≤0.73 at 4.5 K in fields up to 5.5 T. Zeeman splitting versus average moment per cation is roughly linear for all x, but the slope decreases drastically at high x. A second-order perturbation calculation accounts for this decrease

Fabrication of GaN photonic crystals for 400 nm wavelength

We report on results of the fabrication and the micro-reflectance measurement of GaN photonic crystals. The etching performance of GaN has been studied with a conventional reactive ion etching system and SiCl4 plasma. We obtained an etch rate of 100 nm/min and etching depth of 600 nm for dense GaN pillars. With graphite lattice of 270 run period we observed a high reflection peak in the region of 400 nm wavelengths, depending strongly on the incident light polarization, which is in a good agreement with the theoretical calculation. (C) 2001 Elsevier Science B.V. All rights reserved

Heterostructure of binaries II-VI semiconductors ZnTe and ZnSe / III-V (GaAs, InP, GaSb)

Epitaxial ZnSe, ZnTe and multilayers have been grown on III-V (InP, GaAs and GaSb) substrates by organometallic vapor phase epitaxy. First, the OMVPE growth technique used is described. The microstructural quality of the epilayers was determined by SEM (EDX) and X-Ray diffraction. Mechanichal strain, due firstly to a mismatch between II-VI layers and III-V substrates and secondly to different thermal expansion coefficients is studied. Reflectivity and photoluminescence spectra are presented for one type of material. Growth parameters are identified and problems associated to experimental conditions are discussed

Angular dispersion of photons and phonons in a photonic crystal of selectively grown GaN pyramids containing an InxGa1-xN quantum well structures

Angular-dependent reflection measurements were used to map out the dispersion relations of the resonant Bloch modes, and the angular dispersion of the phonon modes, in a photonic crystal consisting of selectively grown GaN pyramids containing a single InxGa1-xN/GaN quantum well. The dispersion of the photons exhibits strong photonic crystal characteristics, while the mean indium content of the 2 nm thickness InxGa1-xN layer was extracted from the angular dispersion of the phonon modes