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

Raman and photoluminescence of Er3+-doped SnO2 obtained via the sol-gel technique from solutions with distinct pH

Raman and infrared photoluminescence measurements are carried out for Er3+-doped SnO2 pellets (hard-pressed powders) obtained by the sol-gel technique from colloidal suspensions with distinct pH. Raman data indicate that bulk vibration modes are dominating for neutral pH. When the pH is modified, there is an intensity increase of acoustic surface modes. The evaluation of bulk and crystallite surface vibration modes indicates that the contribution of the bulk decreases for pH above the neutral and decreases even further for acid pH, becoming the surface vibration modes as dominating in this case. Infrared photoluminescence data indicate that the intensity of the emission generated from the I-4(13/2) -> I-4(15/2) transition is strongly dependent on the pH of colloidal suspension, which may broaden the emission peaks due to overlapping of Stark levels. (C) 2010 Elsevier B.V. All rights reserved.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Rare earth centers properties and electron trapping in SnO2 thin films produced by sol-gel route

Some very relevant optical. electrical, and structural properties of SnO2 doped with rare-earth ions Er3+ and Eu3+ are presented. Films are produced by the sol-gel-clip coating process, and may be described as a combination of nanoscopic dimension crystallites (about 3-10 nm) with their respective intergrain potential barriers. The Er3+ and Eu3+ ions are expected to act as acceptors in SnO2. which is a natural n-type conductor, inducing a high degree of charge compensation. Electron trapping and emission spectra data are presented and are rather distinct, depending on the location of the rare-earth impurity. This behavior allows the identification of two distinct centers: located either in the SnO2 lattice or segregated at the particles surface. Based on a model for thermally activated cross-section defects, the difference between the capture energy of the photo-excited electron and the intergrain potential barrier is evaluated, leading to distinct values for high and low symmetry sites. A higher distortion in the lattice of undoped SnO2 and SnO2:Eu (1 at.%) was evaluated from Rieuveld refinements of X-ray diffraction data. This was confirmed by Raman spectra, which are associated with the particles size and disorder. By comparing the samples with the same doping concentration, it was found that this disorder is higher in Eu-doped SnO2 than in Er-doped SnO2, which is in agreement with a higher energy for the lattice relaxation in the trapping process by Eu3+ centers. (C) 2008 Elsevier B.V. All rights reserved.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Photoluminescence of Eu(3+) ion in SnO(2) obtained by sol-gel

Photoluminescence data of Eu-doped SnO(2) xerogels are presented, yielding information on the symmetry of Eu(3+) luminescent centers, which can be related to their location in the matrix: at lattice sites, substituting to Sn(4+), or segregated at particles surface. Influence of doping concentration and/or particle size on the photoluminescence spectra obtained by energy transfer from the matrix to Eu(3+) sites is investigated. Results show that a better efficiency in the energy transfer processes is obtained for high symmetry Eu(3+) sites and low doping levels. Emission intensity from (5)D(0) -> (7)F(1) transition increases as the temperature is raised from 10 to 240 K, under excitation at 266 nm laser line, because in this transition the multiphonon emission becomes significant only above 240 K. As an extension of this result, we predict high effectiveness for room temperature operation of Eu-based optical communication devices. X-ray diffraction data show that the impurity excess inhibits particle growth, which may influence the asymmetry ratio of luminescence spectra

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

GaAsSbN/GaAs strained-layer single quantum wells grown on a GaAs substrate by molecular-beam epitaxy with different N concentrations were studied using the photoluminescence (PL) technique in the temperature range from 9 to 296 K. A strong redshift in optical transition energies induced by a small increase in N concentration has been observed in the PL spectra. This effect can be explained by the interaction between a narrow resonant band formed by the N-localized states and the conduction band of the host semiconductor. Excitonic transitions in the quantum wells show a successive red/blue/redshift with increasing temperature in the 2-100 K range. The activation energies of nonradiative channels responsible for a strong thermal quenching are deduced from an Arrhenius plot of the integrated PL intensity. (C) 2003 American Institute of Physics

Optical and structural properties of GaAs/GaInP quantum wells grown by Chemical Beam Epitaxy

In this work we investigated the optical and structural properties of GaAs/GaInP quantum wells (QW) grown by Chemical Beam Epitaxy (CBE). The samples were characterized by photoluminescence (PL), photoluminescence excitation (PLE) and transmission electron microscopy (TEM). Simulations of the quantum well potential profiles, using the Van de Walle-Martin model, supplemented by our experimental results, allowed us to associate the interface properties with the growth procedures. We concluded that a thin GaP layer grown at the interface improves its quality and also that the observed broad emission band in the PL spectrum is related to quaternary Ga1-xIn xAs1-yPy.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Optical properties of remotely doped parabolic quantum wells

This work is intended to report on optical measurements in a parabolic quantum well with a two dimensional-three dimensional electron gas. Photoluminescence results show broad spectra which are related to emission involving several subbands on conduction band with the fundamental level of the valence band. This assumption is based on the behavior of the PL peak position and the full width at half maximum in the function of the incident power intensity. (C) 2002 Elsevier B.V. B.V. All rights reserved

Excitons in undoped AlGaAs/GaAs wide parabolic quantum wells

In this work the electronic structure of undoped AlGaAs/GaAs wide parabolic quantum wells (PQWs) with different well widths (1000 and 3000 ) were investigated by means of photoluminescence (PL) measurements. Due to the particular potential shape, the sample structure confines photocreated carriers with almost three-dimensional characteristics. Our data show that depending on the well width thickness it is possible to observe very narrow structures in the PL spectra, which were ascribed to emissions associated to the recombination of confined 1s-excitons of the parabolic potential wells. From our measurements, the exciton binding energies (of a few meV) were estimated. Besides the exciton emission, we have also observed PL emissions associated to electrons in the excited subbands of the PQWs. © 2010 IOP Publishing Ltd

Many-body effects in wide parabolic AlGaAs quantum wells

Photoluminescence measurements at different temperatures have been performed to investigate the optical response of a two-dimensional electron gas in n-type wide parabolic quantum wells. A series of samples with different well widths in the range of 1000-3000 A was analyzed. Many-body effects, usually observed in the recombination process of a two-dimensional electron gas, appear as a strong enhancement in the photoluminescence spectra at the Fermi level at low temperature only in the thinnest parabolic quantum wells. The suppression of the many-body effect in the thicker quantum wells was attributed to the decrease of the overlap between the wavefunctions of the photocreated holes and the two-dimensional electrons belonging to the highest occupied electron subband. (C) 2007 American Institute of Physics