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Silica-based ZnO-MCM-41 mesoporous nanocomposites with high Zn content (5≤Si/Zn≤50) have been synthesized by a one-pot surfactant-assisted procedure from aqueous solution using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes as inorganic hydrolytic precursors. This preparative technique allows optimization of the dispersion of the ZnO nanodomains in the silica walls. The mesoporous nature of the final materials is confirmed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and N(2) adsorption-desorption isotherms. The ZnO-MCM-41 materials show unimodal pore size distributions without blocking of the pore system even for high Zn content. A careful optical spectroscopic study (using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV-visible spectroscopy) of these materials shows that, irrespective of the Si/Zn ratio, the Zn atoms are organized in well-dispersed, uniform low-defect ZnO nanodomains (radius about 1 nm) and are partially embedded within the silica walls.

Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations of thin wurtzite indium nitride films. Indium nitride is an especially relevant example, due to the technological interest for optoelectronic and solar cell applications in combination with other group III nitrides., J. S. acknowledges financial support from the Spanish Ministry of Science and Innovation by CICYT Grants No. MAT2010-2-129-C02-01 and No. ENE2008-04373, and by Generalitat de Catalunya Grant No. 2009SGR1251. F. J. M. is thankful for the financial support from CICYT projects No. CSD2007-00045 and No. MAT2010-21270-C04-04, and the "Programa de Incentivo a la Investigacion" of the Universidad Politecnica de Valencia through project No. UPV2010-0096. A. H. R. has been supported by CONACyT Mexico under projects No. TAMU-Conacyt and No. J-83247-F. We acknowledge the beam time granted by ESRF.

Photoluminescence excitation (PLE) spectra have been measured for a set of self-assembled InN nanowires (NWs) and a high-crystalline quality InN layer grown by molecular-beam epitaxy. The PLE experimental lineshapes have been reproduced by a self-consistent calculation of the absorption in a cylindrical InN NW. The differences in the PLE spectra can be accounted for the inhomogeneous electron distribution within the NWs caused by a bulk donor concentration $({N}_{D}^{+})$ and a two-dimensional density of ionized surface states $({N}_{ss}^{+})$. For NW radii larger than 30 nm, ${N}_{D}^{+}$ and ${N}_{ss}^{+}$ modify the absorption edge and the lineshape, respectively, and can be determined from the comparison with the experimental data.

The polarization of the emission from a set of highly strained $a$-plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite $c$ axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the $c$ axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been performed to determine the three components of the strain tensor in the active region. Moreover, the experimental results have been compared with the strain values computed by means of a model based on the elastic continuum theory. A high anisotropic compressive in-plane strain has been found, namely, $\ensuremath{-}0.6\mathrm{%}$ and $\ensuremath{-}2.8\mathrm{%}$ along the in-plane directions $[1\overline{1}00]$ and [0001], respectively, for the thickest quantum well. The oscillator strength of the lowest optical transition has been calculated within the framework of a multiband envelope function model for various quantum well widths and strain values. The influence of confinement and strain on the degree of polarization is discussed and compared with experiment considering various sets of material parameters.

InN nanocolumns grown by plasma-assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red-shifted with respect to the PLE onset and both energies were higher than the low temperature band-gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present atthe non-polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the density of free electrons can be somehow controlled by the growth parameters. It was observed that In-BEP and substrate temperature leading to shorter In diffusion lengths diminished the effects of the electron accumulation layer on the optical properties. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on experimental and theoretical studies of the polarization selection rules of the emission of non-polar GaN/AlN self-assembled quantum dots. Time-integrated and time-resolved photoluminescence measurements have been performed to determine the degree of polarization. It is found that the emission of some samples can be predominantly polarized parallel to the wurtzite c axis, in striking difference with the previously reported results for bulk GaN and its heterostructures, in which the emission was preferentially polarized perpendicular to the c axis. Theoretical calculations based on an 8-band k·p model are used to analyze the relative importance of strain, confinement and quantum dot shape on the polarization selection rules. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The room-temperature Raman scattering was measured in ${\text{ZnWO}}_{4}$ up to 45 GPa. We report the pressure dependence of all the Raman-active phonons of the low-pressure wolframite phase. As pressure increases additional Raman peaks appear at 30.6 GPa due to the onset of a reversible structural phase transition to a distorted monoclinic $\ensuremath{\beta}$-fergusonite-type phase. The low-pressure and high-pressure phases coexist from 30.6 to 36.5 GPa. In addition to the Raman measurements we also report ab initio total-energy and lattice-dynamics calculations for the two phases. These calculations helped us to determine the crystalline structure of the high-pressure phase and to assign the observed Raman modes in both the wolframite and $\ensuremath{\beta}$-fergusonite phases. Based upon the ab initio calculations we propose the occurrence of a second phase transition at 57.6 GPa from the $\ensuremath{\beta}$-fergusonite phase to an orthorhombic $Cmca$ phase. The pressure evolution of the lattice parameters and the atomic positions of wolframite ${\text{ZnWO}}_{4}$ are also theoretically calculated, and an equation of state reported.

Raman spectra of aluminum nitride (AlN) under pressure have been measured up to $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, i.e., beyond the onset of the wurtzite-to-rocksalt phase transition around $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The experimental pressure coefficients for all the Raman-active modes of the wurtzite phase are reported and compared to those obtained from ab initio lattice dynamical calculations, as well as to previous experimental and theoretical results. The pressure coefficients of all the Raman-active modes in wurtzite-type semiconductors (AlN, GaN, InN, ZnO, and BeO), as well as the relatively low bulk modulus and phase transition pressure in wurtzite AlN, are discussed in the light of the pressure dependence of the structural crystal anisotropy in wurtzite semiconductors. On pressure release, AlN partially returns to the wurtzite phase below $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ but the presence of a rocksalt phase in AlN was observed at pressures as low as $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, as evidenced by comparing the experimental Raman spectra to calculated one- and two-phonon densities of states of the rocksalt phase.

Publisher Summary This chapter describes quantum dots (QDs) based on group III nitrides (III-N). They are expected to be the active medium of new optoelectronic devices operating at high powers and high temperatures. Besides the well-known advantages of their bulk and quantum well (QW) counterparts, III-N QDs provide strong confinement of carriers in nearly perfect zero-dimensional boxes. Quantum effects provide new degrees of freedom for the design of advanced devices. The chapter reviews the systems of dots that appear spontaneously during epitaxial growth without the need of artificial post-processing and designate them as self-assembled or self-organized QDs regardless of the mechanism responsible for their appearance. It provides a brief overview of the most relevant growth techniques employed for the spontaneous or self-assembled growth of GaN QDs. Special attention will be paid to epitaxial growth categorized into two different modes: Volmer–Weber (VW) mode corresponding to three-dimensional (3D) island growth and Stranski–Krastanov (SK) mode, where the deposition of a strained two-dimensional (2D) wetting layer is followed by elastic relaxation through 3D islanding.

The strain state of $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ quantum dots grown on $6H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ has been investigated as a function of AlN capping thickness by three different techniques. On the one hand, resonant Raman scattering allowed the detection of the ${A}_{1}(\mathrm{LO})$ quasiconfined mode. It was found that its frequency increases with AlN deposition, while its linewidth did not evolve significantly. Available experiments of multiwavelength anomalous diffraction and diffraction anomalous fine structure on the same samples provided the determination of the wurtzite lattice parameters $a$ and $c$ of the quantum dots. A very good agreement is found between resonant Raman scattering and x-ray measurements, especially concerning the in-plane strain state. The results demonstrate the adequacy of Raman scattering, in combination with the deformation potential and biaxial approximations, to determine quantitatively values of strain in GaN quantum dot layers.

We investigate the effects of electron and hole localization in the emission of a GaInNAs/GaAs single quantum well at low temperatures. Photoluminescence measurements varying the excitation density and under magnetic fields up to 14 T have been carried out. The results indicate that electrons are strongly localized in these systems due to small fluctuations in the nitrogen content of the quaternary alloy. The low linear diamagnetic shift of the emission points out the weakness of the Coulomb correlation between electrons and holes and suggests an additional partial localization of the holes.

The growth selectivity and structural quality of GaN nanowires obtained by plasma-assisted molecular beam epitaxy on pre-patterned GaN(0001) templates are investigated by means of non-destructive techniques. Optimum control over the nanowire arrangement and size requires a pitch between the mask apertures below twice the diffusion length of Ga atoms. Lower pitches, however, seem to slightly diminish the structural quality of the material, as revealed by the increase of the Raman peak linewidths. The photoluminescence spectra of the nanowires show a considerable presence of basal plane stacking faults, whose density increases for decreasing nanowire diameter. The capabilities of Kelvin probe force microscopy for imaging these kind of defects are also demonstrated.

We have studied the vibrational properties of $\mathrm{Cu}\mathrm{Al}{\mathrm{O}}_{2}$ by means of Raman scattering in ambient conditions, at low temperature, and also at high pressure. Results are discussed in the framework of an ab initio calculation. Raman active modes have wave numbers ${\ensuremath{\sigma}}_{{E}_{g}}=418.1\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and ${\ensuremath{\sigma}}_{{A}_{1g}}=767.2\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Polarized measurements with single crystals have confirmed their symmetry. We present and discuss the phonon-dispersion curves. Below $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the temperature dependence of the Raman active modes is almost linear, with coefficients $\ensuremath{\partial}{\ensuremath{\sigma}}_{{E}_{g}}∕\ensuremath{\partial}T=(\ensuremath{-}4\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{K}$ and $\ensuremath{\partial}{\ensuremath{\sigma}}_{{A}_{1g}}∕\ensuremath{\partial}T=(\ensuremath{-}1.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{K}$. Most of the temperature shift is associated with thermal expansion. The pressure dependence is given by $\ensuremath{\partial}{\ensuremath{\sigma}}_{{E}_{g}}∕\ensuremath{\partial}P=2.72\ifmmode\pm\else\textpm\fi{}0.07\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{GPa}$ and $\ensuremath{\partial}{\ensuremath{\sigma}}_{{A}_{1g}}∕\ensuremath{\partial}P=4.96\ifmmode\pm\else\textpm\fi{}0.12\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{GPa}$. We observe a reversible phase transition at $34\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, which, as already has been shown to happen in $\mathrm{Cu}\mathrm{Ga}{\mathrm{O}}_{2}$, we relate to the existence of a dynamical instability.

Room-temperature Raman scattering has been measured in lead tungstate up to 17 GPa. We report the pressure dependence of all the Raman modes of the tetragonal scheelite phase PbWO4-I or stolzite, space group I41 /a, which is stable at ambient conditions. Upon compression the Raman spectrum undergoes significant changes around 6.2 GPa due to the onset of a partial structural phase transition to the monoclinic PbWO4-III phase space group P21 /n. Further changes in the spectrum occur at 7.9 GPa, related to a scheelite-to-fergusonite transition. This transition is observed due to the sluggishness and kinetic hindrance of the I → III transition. Consequently, we found the coexistence of the scheelite, PbWO4-III, and fergusonite phases from 7.9 to 9 GPa, and of the last two phases up to 14.6 GPa. We have performed ab initio latticedynamics calculations, which have greatly helped us in assigning the Raman modes of the three phases and discussing their pressure dependence. The Raman modes of the free WO4 molecule are discussed.

The strain state and the deformation profile of GaN quantum dots embedded in AlN have been measured by high resolution electron microscopy, medium energy ion scattering and grazing incidence X-ray diffraction. The results are compared with theoretical calculations, allowing one to conclude that GaN quantum dots experience a non biaxial strain which drastically decreases when going from the basal plane up to the apex of the dots. We also demonstrate that AlN is distorted in the surroundings of the dots, which provides the driving force for vertical correlation of GaN dots when the AlN spacer between successive planes is thin enough.

Self-assembled $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ quantum dots have been investigated by means of Raman scattering. A resonant enhancement of the Raman peaks has been observed when the excitation is tuned above the GaN band-gap energy. The polar mode nature, either quasiconfined or interfacial, has been assigned after comparing with the polar optical modes of spheroidal dots calculated within the framework of the anisotropic dielectric continuum model. The built-in strain of the GaN dots induced a substantial blueshift of the nonpolar ${E}_{2H}$ Raman mode frequency. A theoretical model that analyzes the three-dimensional strain distribution in the quantum dots has been employed for estimating the strain contribution to the frequency shifts of both nonpolar and polar optical modes.

Changes in strain and phonon mode energy in stacks of self-assembled GaN quantum dots embedded in AlN have been studied by means of Raman spectroscopy as a function of the number of periods. The ${E}_{2H}$ phonon modes related to the quantum dots and AlN spacers are clearly resolved, and their energies allow monitoring the state of strain of the dots and AlN spacers simultaneously. The evolution of the measured phonon frequencies and the associated strains are discussed in comparison with theoretical calculations of the inhomogeneous strain distribution in a system of coherent misfitting inclusions.

Medium energy ion scattering (MEIS) has been used to measure at the scale of the monolayer the deformation profile of self-organized GaN quantum dots grown on AlN by molecular-beam epitaxy. The effect of capping the GaN dots by a thin layer of AlN has also been studied. It is shown that GaN dots are partially relaxed in every situation. Capping them with AlN has little effect on the basal plane, as expected, but strongly modifies the strain of the upper part of dots. The experimental results are compared with theoretical calculations, allowing one to conclude that GaN quantum dots experience a nonbiaxial strain, which drastically decreases when going from the basal plane up to the apex of the dots.

The first- and second-order Raman spectra of cubic ZnS $(\ensuremath{\beta}$-ZnS, zinc-blende) are revisited. We consider spectra measured with two laser lines for samples with different isotopic compositions, aiming at a definitive assignment of the observed Raman features and the mechanisms which determine the linewidth of the first order TO and LO Raman phonons. For this purpose, the dependence of the observed spectra on temperature and pressure is investigated. The linewidth of the TO phonons is found to vary strongly with pressure and isotopic masses. Pressure runs, up to 15 GPa, were performed at 16 K and 300 K. Whereas well-defined TO Raman phonons were observed at low temperature in the whole pressure range, at 300 K the TO phonons appear to hybridize strongly with the two-phonon background and lose their identity, especially in the (3--10)-GPa region. The intensity of the TO phonons, which nearly vanishes when measured with a red laser line, is shown to result from a destructive interference of the amplitudes of the band-edge resonance and that of a background of opposite sign. The analysis of these effects is aided by calculations of the densities of one- and two-phonon states performed with the adiabatic bond charge model of the lattice dynamics.

The dynamics of exciton-exciton interaction in quantum wells has been investigated by monitoring the time-resolved resonant secondary emission that follows excitation with linearly and circularly polarized light. Preservation of quantum beating in the cross-polarized emission demonstrates that spin relaxation can take place, for some scattering channels, without total quantum coherence loss. Interexciton electron exchange is the scattering mechanism that explains the persistence of the beating and, since it is sensitive to the fine structure of excitons, the shift by pi in the phase of the beating observed in the experiment.

We have observed that resonant Rayleigh scattering dominates the emission from poly(p-phenylene vinylene) excited with photons at energies below the threshold at which excitonic migration is reduced. The intensity of the resonant emission decays exponentially with a lifetime of up to 450 fs after pulsed excitation. The coherent nature of the emission was confirmed by angular variations in the far-field emission intensity-bright and dark speckles. Persistence of a coherent polarization was demonstrated by coherent control using phase-locked pulses.

The dependence of the ${\mathit{E}}_{0}$ direct gap of Ge, GaAs, and ZnSe on isotopic masses at low temperatures has been investigated. Contributions of the variation of the lattice parameter to the gap shift of the binary compounds have been evaluated by using a volume-dependent lattice dynamics, while local empirical pseudopotential techniques have been employed to calculate gap shifts due to electron-phonon interaction. The dependence of these terms on the lattice-dynamical model and on the q\ensuremath{\rightarrow}0 extrapolation of the pseudopotential form factors has been investigated. The contributions of the optical and acoustical modes to the isotopic shift are analyzed. The results are compared to previous experimental data, in the case of germanium, and to low-temperature reflectance measurements performed as part of this work on GaAs samples with different isotopic gallium composition. Particular attention has been paid to the differences in the effects of changing either the cation or the anion masses. The temperature dependence of the ${\mathit{E}}_{0}$ gap of ZnSe has also been calculated, and reasonable agreement with experiment has been found. \textcopyright{} 1996 The American Physical Society.

We present a study of the emission of GaN∕AlN self-assembled quantum dots grown on a-plane 6H-SiC showing evidence of the suppression of the internal electric field. The strain in dots and barriers is determined by means of Raman scattering and the induced piezoelectric polarizations are estimated. These reveal a compensation of the spontaneous polarization and justify the lack of a quantum confined Stark effect found in the photoluminescence spectra. Strain effects and strong confinement are responsible for the partial depolarization of the emission and its energy dependence.

Raman scattering and photoluminescence (PL) spectroscopy with sub-bandgap excitation has been applied to explore tracing of common impurities (in particular of oxygen) in AlN. Bulk AlN crystals grown by the high temperature sublimation method were studied. PL bands have been observed at around 375 nm and at 560–660 nm and have been attributed to oxygen and to nitrogen vacancy/aluminium excess defects, respectively. The 375 nm UV PL band was found to shift with oxygen concentration. Micro-Raman spectra of the bulk AlN samples were measured in different polarisations. Besides normal Raman modes of AlN the presence of additional vibrational modes was detected. The modes were discussed and tentatively attributed to oxygen and silicon local vibrational modes (LVMs) in AlN.

A systematic study of resonant Rayleigh scattering in semiconductor single quantum wells has been carried out. The dependence of the scattering efficiency on the well width and the temperature has been investigated. The behaviour observed in the resonant Rayleigh spectra can be explained in terms of the confinement of the excitonic states in the plane of the well due to fluctuations in the well width. A microscopic theoretical model for the elastic scattering of light by weakly confined two-dimensional excitonic states has been developed. The Rayleigh scattering efficiency has been calculated to the lowest-order of perturbation theory and the results found to be in good agreement with the experiment.

In the last years, nitride III-V semiconductor alloys attract an increasing amount of attention due to their interesting optical properties and the related potencial for applications in various electronic and optoelectronic devices. The diluted quaternary alloy Ga1−xInxNyAs1−y is a promising material in the field of optical communications, expecting to provide efficient light emitters at the 1.3 and 1.55 μm low loss bands, and being lattice-matched to GaAs, which is desirable because allows to use the technology developed for this binary compound. It is known that N incorporation degrades the optical properties of diluted nitride semiconductor, due to an increasing density of non-radiative centers. In order to remove such defects, post-growth thermal annealing of the sample is necessary. The optical properties of Ga1−xInxNyAs1−y improve considerably after annealing but this also causes a large blueshift of the emission. In this work, we will study by photoluminescence, the optical properties of Ga1−xInxNyAs1−y/GaAs single quantum wells, and the effect of post growth rapid thermal annealing in these properties. The studied samples are 7 nm-thick single quantum wells with y = 0.015 and x varying between 0.2 and 0.3 which undergo post growth rapid thermal annealing at 850 C for 15”. One of this samples also incorporates a GaInAs quantum well with identical In-concentration as the Ga1−xInxNyAs1−y. The photoluminescence (PL) of as-grown and annealed samples, measured as a function of temperature and excitation density, show that Ninduced localized states dominate the emission spectra at low temperature. The localization potential was calculated from the low energy tail of the emission, showing that thermal annealing reduces the localization grade in all these samples. In order to clarify the nature of low temperature emission, PL measurements as a function of the excitation power and under a magnetic field have been carried out. These results confirm that low temperature recombination is not excitonic and involves localized electrons and free holes., Las propiedades físicas de los nitruros semiconductores del grupo III los convierten en excelentes candidatos para la fabricación de variados dispositivos optoelectr ónicos. El nitruro diluido cuaternario Ga1−xInxNyAs1−y en particular, ha suscitado un creciente interés en el área de las comunicaciones ópticas, con miras a la fabricación de emisores y detectores en el rango en el cual las tecnologías de fibras ópticas existentes presentan unas pérdidas mínimas (1.3 y 1.55μm). La ventaja de este material cuaternario es que tiene coincidencia de red con el GaAs, lo que permite aprovechar toda la tecnología desarrollada para la fabricación de este material binario. Es sabido que las propiedades ópticas de los nitruros diluidos se degradan con la incorporación de N, debido a un aumento en la densidad de centros de recombinación no-radiativos. Para eliminar tales defectos, el material es sometido a un tratamiento de recocido térmico después de su fabricación que, además de generar una notable mejora de sus propiedades ópticas, origina un marcado corrimiento de la emisión hacia el azul. En este trabajo, estudiaremos por fotoluminiscencia, las propiedades ópticas de pozos cuánticos de Ga1−xInxNyAs1−y/GaAs, y el efecto que tiene sobre estas el tratamiento de recocido térmico rápido. Las muestras estudiadas son pozos cuánticos sencillos de 7 nm de espesor, con y = 0.015 y x variando entre 0.2 y 0.3. Las muestras fueron sometidas a un recocido térmico rápido a 850 C durante 15”. Una de estas muestras, incorpora además un pozo cuántico de GaInAs con la misma concentración de In que tiene el pozo cuántico de Ga1−xInxNyAs1−y. La PL de las muestras con y sin recocido, medidas en función de la la densidad de excitación y la temperatura, muestran que la emisión de los pozos cuánticos a baja temperatura es dominada por los estados localizados inducidos por el N. Los potenciales de localización fueron calculados a partir del análisis de la asimetría a bajas energías de los espectros de fotoluminiscencia y muestran que el recocido reduce el grado de localización en todas las muestras. Con el ´animo de aclarar la naturaleza de la emisión a baja temperatura, se hicieron medidas de PL bajo campo magnético. Los resultados confirman que la recombinación a baja temperatura no es excitónica y que involucra electrones localizados y huecos libres., 1. Introducción 5, 2. Marco Teórico 9, 3. Proceso experimental, 4. Resultados, Maestría, Magíster en Ciencias de los Materiales

Las propiedades f ́ısicas de los nitruros semiconductores del grupo III los con-vierten en excelentes candidatos para la fabricaci ́on de variados dispositivos op-toelectr ́onicos. El nitruro diluido cuaternario Ga1−xInxNyAs1−yen particular, hasuscitado un creciente inter ́es en el ́area de las comunicaciones ́opticas, con mirasa la fabricaci ́on de emisores y detectores en el rango en el cual las tecnolog ́ıasde fibras ́opticas existentes presentan unas p ́erdidas m ́ınimas (1.3 y 1.55μm). Laventaja de este material cuaternario es que tiene coincidencia de red con el GaAs,lo que permite aprovechar toda la tecnolog ́ıa desarrollada para la fabricaci ́on deeste material binario. Es sabido que las propiedades ́opticas de los nitruros dilui-dos se degradan con la incorporaci ́on de N, debido a un aumento en la densidadde centros de recombinaci ́on no-radiativos. Para eliminar tales defectos, el mate-rial es sometido a un tratamiento de recocido t ́ermico despu ́es de su fabricaci ́onque, adem ́as de generar una notable mejora de sus propiedades ́opticas, origina unmarcado corrimiento de la emisi ́on hacia el azul., 1. Introducción 5 2. Marco Teoríco 9 3. Proceso Experimental 7, Maestría, Magíster en Ciencias de los Materiales