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A dominating donor-acceptor pair (DAP) emission at about 3.27 eV is observed in the photoluminescence and cathodoluminescence spectra of intentionally undoped mass-transport (MT)-grown GaN, while only a weak presence of the DAP emission is recorded in the as-grown hydride vapor phase epitaxial GaN. A comparative study of impurity and native defect incorporation in the as-grown and MT GaN was performed, showing a significant increase of oxygen and empty clusters involving Ga vacancy and oxygen in the MT GaN. Based on the observed results as well as on doping analysis of the structure and kinetic analysis of the emission intensities, we propose an acceptorlike complex, creating a state as a semiclassical potential well near the valence-band top due to the local tensile strain caused by the empty clusters to be responsible for the dominating behavior of the DAP emission. [ABSTRACT FROM AUTHOR]

The temperature dependence of the hole mobilities of Al[SUBx]Ga[SUB1-x]Sb films in the regime 0&les;x&les;0.25 has been examined by Van der Pauw-Hall measurements. The films have been grown by metalorganic chemical vapor deposition on Si-GaAs substrates using TMA1, TMGa, and TMSb precursors. The mobility decreases sharply when a small amount ofA1 in the range 0&les;x&les;0.025 is incorporated into GaSb. The temperature dependence of mobility was analyzed using a model with contributions from various scattering mechanisms. At a low-temperature (<100 K), the mobility decreased due to a contribution from ionized-impurity scattering and in a high-temperature region (> 100 K), the same effect was due to lattice phonon scattering. At 300 and 77 K, the alloy scattering is the most important mechanism in Al[SUBx]Ga[SUB1-x]Sb ternaries, however the temperature dependence of alloy scattering is less pronounced as the temperature decreases. [ABSTRACT FROM AUTHOR]

The grain size for polycrystalline GaN, grown in low-temperature gallium-rich conditions, is shown to be correlated to the oxygen content of the films. Films with lower oxygen content were observed to have larger crystals with an increased tendency to a single-preferred crystal orientation. Elastic recoil detection analysis with heavy ions (i.e., 200 MeV [sup 197] Au ions) was used to determine the composition of the GaN films grown for the study, including the hydrogen, carbon, gallium, nitrogen, and oxygen content. Atomic force microscopy and x-ray diffraction were used to study the sample morphology. From these measurements, the available surface area of the films was found to be sufficient for a significant proportion of the oxygen present in the films to segregate at the grain boundaries. This interpretation is consistent with earlier theoretical studies of the formation and segregation of the V[sub Ga]-(O[sub N])[sub 3] defect complex at dislocation sites in gallium-rich GaN. For this work, however, the defect complex is believed to segregate at the grain boundary of the polycrystalline GaN. [ABSTRACT FROM AUTHOR]

Thick hydride vapor phase epitaxial GaN layers are grown on metalorganic chemical vapor deposited GaN template layers as well as directly on sapphire, with the aim of investigating the effect of the template on the strain relaxation and spatial distribution of free carriers in the overgrown GaN films. Spatially resolved cross-sectional micro-Raman spectroscopy, cathodoluminescence, and transmission electron microscopy show improved crystalline quality for growth on metalorganic chemical vapor deposited GaN templates. The highly doped and highly defective near-substrate layer composed of columnar domains, typically present in hydride vapor phase epitaxial GaN films grown directly on sapphire, is absent in the layers grown on templates. Consequently, this results in elimination of the nonuniformities of free electron distribution, a lower residual free carrier concentration (<10[sup 17]cm[sup -3]), and improved strain relaxation. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the photoluminescence excitation of gallium arsenide/gallium aluminum arsenide multiple-quantum-well structure. Influence of photon recycling on the optical-characteristics-photolumuniscense-excitation spectrum of the structure; Methodology of the study; Results and discussion.

Presents a study which reported results of electrical, optical, electron spin resonance and optically detected magnetic resonance analyses of thermal neutron. Overview of studies on the influence of thermal neutron irradiation on the properties of semiconductors; Application of neutron transmutation doping to gallium phosphide.

Colloidal gold nanoparticles were produced by irradiating a gold disc with a femtosecond laser beam in pure deionized water. Variation of laser fluence between 38 and 330 J/cm2 was used to control the nanoparticle size distribution. The nanoparticles produced were spherically shaped with average diameter between 9 and 10 nm. The effect of ablation time on the nanoparticle production efficiency and size distribution was also studied. [ABSTRACT FROM AUTHOR]

Intra-shell transitions of transition metal and rare earth ions are parity forbidden processes. For Mn2+ ions this is also a spin forbidden process, i.e., light emission should be inefficient. Surprisingly, it has been reported that in nanostructures of ZnMnS the 4T1 to 6A1 intra-shell transition of Mn2+ results in a bright photoluminescence characterized by a short PL decay time. The model of a quantum confined atom was introduced to explain the observed experimental results. It was later claimed that this model is incorrect. Based on the results of our photoluminescence, photoluminescence kinetics, time-resolved photoluminescence, electron spin resonance, and optically detected magnetic resonance investigations, we confirm photoluminescence enhancement and decrease of photoluminescence lifetime and relate these effects to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. This mechanism is active in both bulk and in low-dimensional structures, but is significantly enhanced in nanostructure samples. [ABSTRACT FROM AUTHOR]

AlxGa1-xSb films in the regime 0 ≤ x ≤ 0.30 have been grown by metalorganic chemical vapor deposition on GaAs and GaSb substrates using TMAl, TMGa and TMSb precursors. We report the effects of growth conditions on the optical properties. Samples grown at temperatures of 540°C, 580°C and 600°C and a V/III ratio of 1 have been investigated. The AlxGa1-xSb layers grown at 580°C and 600°C with a V/III ratio of 1 and Al content in the range of 0.5% to 25% were found to exhibit excellent optical quality with a very high optical transmission at energies below the bandgap. The principle photoluminescence features observed are attributed to bound exciton and donor-acceptor transitions with FWHM comparable to the best values reported elsewhere. [ABSTRACT FROM AUTHOR]

Fluorescence labelling has become a technique of increasing importance in modern biotechnology which is increasingly underpinned by advances in materials science. In this paper we describe our contributions to this area. In order to expand the understanding of in vivo fluorescence labelling we carried out the staining of membrane-based structures in effectively secreting Trichoderma reesei using the fluorescent dye FM 4-64 and their confocal microscopy studies. We also describe the observation of efficient fluorescence upconversion in Sm-doped Gd2O3 nanopowders synthesised by the spray pyrolysis method. This result indicates the potential for Sm-doped Gd2O3 to perform as a fluorescent label excited in red, yellow and green and emitting in blue. Finally, we report a simple approach for synthesizing water-soluble CdS nanoparticles by using ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) as a stabilizer. [ABSTRACT FROM AUTHOR]

Scanning cathodoluminescence (CL) spectroscopy and imaging were used to study the effect of post-growth processing on the CL efficiency of metal–organic vapour phase epitaxy-grown Mg-doped GaN. In this work, two treatments, thermal annealing in high-purity gaseous atmospheres (N2, O2 and H2(5%)/N2) and low-energy electron beam irradiation (LEEBI), have been investigated. Post-growth annealing in a H2/N2 atmosphere followed by LEEBI leads to a significant enhancement of the free electron-to-bound Mg-acceptor (e, Mg) CL emission and a reduction of nonradiative centres involving native defects. The presented results demonstrate that the combination of post-growth annealing in a H2/N2 atmosphere and LEEBI dissociation of Mg–H complex acceptors significantly improves the light emitting efficiency of Mg-doped p-type GaN. Conversely, the samples annealed in a N2 or O2 atmosphere exhibit a reduced (e, Mg) emission after both annealing and LEEBI treatment. [ABSTRACT FROM AUTHOR]

AlxGa1−xSb films in the regime 0×0.25 have been grown by metalorganic chemical vapor deposition on GaAs and GaSb substrates using TMAl, TMGa, and TMSb precursors. We report growth conditions and film properties, including the effect of V/III ratio and growth temperature on electrical and optical properties. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. All epilayers grown exhibit p-type behavior. The mobility decreases and the carrier concentration increases sharply when a small amount of Al is incorporated into GaSb. The sharp cutoff and Fabry-Perot oscillations of the transmission spectra of the AlGaSb layers confirm the high quality of the films. The principle photoluminescence features observed are attributed to bound exciton and donor-acceptor transitions with FWHM comparable to the best values reported elsewhere. [ABSTRACT FROM AUTHOR]

We present results of photoluminescence and cathodoluminescence measurements of strained undoped In0.15Ga0.85As/GaAs and In0.15Ga0.85As/Al0.15Ga0.85As quantum well structures, designed to throw light on the current controversy over light-hole band alignment at low In content. We compare these data with theoretical calculations of the confined state energies within the eight band effective mass approximation. Our analysis shows that for In0.15Ga0.85As/GaAs, the observed two transitions are consistent with either type I or type II alignment of the light hole band for band offset ratios within the accepted range. In the case of In0.15Ga0.85As/Al0.15Ga0.85As, however, our results clearly indicate type II alignment for the light hole band. We derive the band offset ratio Q, defined here as Q = δEc/δEg where δEc is the conduction band offset and δEg is the bandgap difference between the quantum well and the barrier in the presence of strain, for the In0.15Ga0.85As/Al0.15Ga0.85As system to be Q = 0.83 and discuss it in the context of the common anion rule. [ABSTRACT FROM AUTHOR]

Stacked self-assembled In0.5Ga0.5As/GaAs quantum dot infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition, with and without silicon dopants in the quantum dot layers, are investigated. The increase of dark currents observed at higher doping levels is attributed to higher defect density leading to stronger sequential resonant tunneling and to lowering of the operating temperature of the device. [ABSTRACT FROM AUTHOR]

We report the observation of efficient fluorescence upconversion in Sm-doped Gd2O3 nanopowders prepared by the spray pyrolysis method. The blue upconversion emission was observed with low-power continuous-wave excitation at 514, 561, 594, and 633 nm and with a pulsed femtosecond at 710 nm, in a laser scanning confocal microscope. This result indicates that Sm-doped Gd2O3 has the potential as a fluorescent label that may be excited in red, yellow, and green with blue emission. [ABSTRACT FROM AUTHOR]

The optical properties of molecular-beam-epitaxy-grown GaN with different Mn-doping levels (5–23×1019 cm-3) were studied by cathodoluminescence (CL) and optical transmission spectroscopy. Transmission measurements at 2 K revealed an absorption peak at 1.414±0.002 eV, which was attributed to an internal 5T2→5E transition of the neutral Mn3+ state. The intensity of this Mn-related transmission peak was found to scale with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm-3 reduced the near band edge emission intensity by around one order of magnitude. A complete quenching of the donor–acceptor-pair band at 3.27 eV and strong decrease of the yellow luminescence centered at 2.2 eV were attributed to a reduced concentration of VGa. In the infrared spectral range of 0.8–1.4 eV three broad, Mn-doping related CL emission bands centered at 1.01±0.02, 1.09±0.02, and 1.25±0.03 eV were observed. Their origin is attributed to deep donor complexes, which are generated as a result of the heavy Mn-doping. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigate photoluminescence from multilayer GaSb self-assembled quantum dots embedded in GaAs grown by metalorganic chemical vapor deposition. The spectra show the emission from quantum dots at about 1.09 eV and from the wetting layer at 1.39 eV. With increasing temperature the wetting layer emission quenches faster than the quantum dot emission. We also observe a decrease of the quantum dot peak energy at temperatures between 50 and 70 K and a peak shift with increasing excitation powers typical of type II structures. A large separation (300 meV) between the photoluminescence peaks from quantum dots and the wetting layer suggests differences in the intermixing at the GaSb/GaAs interface in the structures grown by metalorganic chemical vapor deposition and by molecular-beam epitaxy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical emission properties of mass-transport regions of GaN grown by hydride vapor phase epitaxy are studied by cathodoluminescence imaging and spectroscopy. A strong donor-acceptor pair emission is observed from the mass-transport regions. Spatially resolved cathodoluminescence reveals a strong intensity contrast between the exciton and donor-acceptor bands from mass-transport and nontransport regions. Focused Auger electron and x-ray photoelectron spectroscopies were employed to investigate the impurity incorporation in the different regions. A preferential moderate increase of residual impurity incorporation or redistribution in mass-transport regions is suggested to be responsible for the observed change of the dominant radiative mechanism. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Raman measurements in backscattering configuration are employed to characterize the effect of nitrogen on the structural properties of a GaN[sub x]P[sub 1-x] alloy with x≤3%. The following effects of N incorporation on the vibrational spectra of GaNP are observed. First, frequencies of GaP-like and GaN-like longitudinal optical phonons exhibit strong compositional dependence, due to a combined effect of alloying and biaxial strain. Second, a dramatic quenching of two-phonon Raman scattering and an emergence of zone-edge GaP-like vibrations are observed. These effects are tentatively attributed to a local distortion of the GaNP lattice and/or compositional disorder in the alloy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

© 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Develops a direct method of measuring the shear strain using a laser-based interferometer. Application of the method to the measurement of the d[sub 15] coefficient for wurtzie gallium arsenide (GaN) and aluminum nitride (AlN); Measurement of the value of d[sub 15] for GaN; Value of d[sub 15] for AlN.