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Photoluminescence Measurements (photoluminescence + measurement)
Selected AbstractsLow temperature hydrothermal growth and optical properties of ZnO nanorodsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2009J. H. Yang Abstract Well-faceted hexagonal ZnO nanorods have been synthesized by a simple hydrothermal method at relative low temperature (90°C) without any catalysts or templates. Zinc oxide (ZnO) nanorods were grown in an aqueous solution that contained Zinc chloride (ZnCl2, Aldrich, purity 98%) and ammonia (25%). Most of the ZnO nanorods show the perfect hexagonal cross section and well-faceted top and side surfaces. The diameter of ZnO nanorods decreased with the reaction time prolonging. The samples have been characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurement. XRD pattern confirmed that the as-prepared ZnO was the single-phase wurtzite structure formation. SEM results showed that the samples were rod textures. The surface-related optical properties have been investigated by photoluminescence (PL) spectrum and Raman spectrum. Photoluminescence measurements showed each spectrum consists of a weak band ultraviolet (UV) band and a relatively broad visible light emission peak for the samples grown at different time. It has been found that the green emission in Raman measurement may be related to surface states. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of molecular adsorbates on the structure of electrodeposited nanocrystalline ZnOPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2008T. Loewenstein Abstract Pure ZnO or ZnOEosinY with adsorbed EosinY molecules was deposited electrochemically from aqueous zinc salt solutions on (0001)GaN and (0001)ZnO. X-ray diffraction revealed the deposition of crystalline ZnO in all cases, with almost perfect orientation in the c -direction. Shifts in the peak positions observed for ZnOEosinY were explained by a lattice expansion by 3.6% in the c -direction caused by the strong influence of the EosinY molecules adsorbed during the growth of ZnO. Scanning electron microscopy (SEM) was used to elucidate the film morphology. Photoluminescence measurements served to determine changes in the electronic structure of these nanocrystalline materials. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication of GaN dot structures on Si substrates by droplet epitaxyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Toshiyuki Kondo Abstract Nanosized GaN dot structures were fabricated on Si(111) substrate by droplet epitaxy using an rf plasma MBE system. The size and density of the GaN dots could be controlled by changing the amount of Ga supplied. By reducing the Ga supply, a maximum dot density of 3.3 × 1011 cm,2 was realized. Photoluminescence measurements at room temperature showed band edge emission with negligible yellow luminescence, which indicates a good optical property of GaN dots grown by this technique. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-performance nanoparticle-enhanced tunnel junctions for photonic devicesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010Adam M. Crook Abstract We describe GaAs-based tunnel junctions that are compatible with photonic devices, including long-wavelength vertical-cavity surface-emitting lasers and multi-junction solar cells. Tunneling was enhanced with semimetallic ErAs nanoparticles, particularly when grown at reduced substrate temperatures. Additionally, we present the first direct measurement of the quality of III-V layers grown above ErAs nanoparticles. Photoluminescence measurements indicate that III-V material quality does not degrade when grown above ErAs nanoparticles, despite the mismatch in crystal structures. These findings validate these tunnel junctions as attractive candidates for GaAs-based photonic devices (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Physical properties of quantum-confined europium sulfide nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007M. L. Redígolo Abstract We report the synthesis and the characterization of quantum-confined europium sulphide nanocrystals, which possess intriguing size-dependent optical and magnetic properties. Transmission electron microscopy, X-ray diffraction spectroscopy, and SQUID magnetization measurements provide evidence for the quantum-confinement effects in this monochalcogenide nanomaterial. Photoluminescence measurements indicate a blue-shifted spectrum for the nanocrystals compared with bulk europium sulphide. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self assembly of Eu2O3 nanocrystals and nanoneedlesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007S. Mahajan Abstract The self-assembly of europium oxide (Eu2O3) nanocrystals into anisotropic one dimensional europium hydroxychloride (Eu(OH)2Cl) nanostructures is reported. Eu2O3 nanocrystals, synthesized via colloidal chemistry, form one dimensional structures via a stepwise assembly and growth procedure. Transmission electron microscopy (HR-TEM) reveals the shape and crystal lattice spacing of the nanostructures, whereas X-ray diffraction (XRD) measurements characterize the nanocrystals' crystallinity. Photoluminescence measurements indicate changes in the site location and environment of the Eu3+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Syntheses, Structures and Luminescence Properties of Ln-Coordination Polymers Based on Flexible Thiodiacetic Acid LigandCHINESE JOURNAL OF CHEMISTRY, Issue 8 2009Xiangyang HOU Abstract Two novel lanthanide complexes with the formulas [Ln2(tda)3(H2O)2]n [Ln=Sm (1), Dy (2), H2tda=thiodiacetic acid] have been prepared by using the corresponding lanthanide salt and H2tda under hydrothermal conditions. Single crystal X-ray diffraction studies show that the two compounds are isostructural and present a 2D network based on the 1D metallic chain, in which an edge-sharing dinuclear polyhedral [Ln2O16] was found to be the building unit of the 1D chains. Interestingly, in the network, the tda ligands exhibit two different coordination modes, including the mode La: bis(syn,syn -bridging bidentate, chelating-bridging tridentate), and mode Lb: bis(chelating- bridging tridentate, syn, anti- bridging bidentate). Furthermore, through the tda ligand in modes La and Lb, the 1D metallic chains are cross-linked to generate a 2D network structure with (3,4,5,6)-connected (47·68)(44·66)(45·6)- (46)(43) topology. Photoluminescence measurements indicate that the dysprosium complex is yellow emitters, and the samarium complex shows salmon pink light emission in the solid state at room temperature. [source] Growth and optical characterization of Cd1- xBexSe and Cd1- xMgxSe crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005F. Firszt Abstract Cd1- xBexSe and Cd1- xMgxSe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence and photothermal properties of these materials were investigated. Spectroscopic ellipsometry was applied for determination of the spectral dependence of the complex dielectric function (E) and refractive index n(E) at room temperature in the photon energy range 0.75-6.5 eV for samples with optic axis (c-axis) perpendicular to the air-sample interface. The critical point (CP) parameters for E0 and E1 transitions were determined using a standard excitonic CP function to fit the numerically calculated differential spectra ,2,2/,E2. The dispersion of the refractive index of the alloys was modelled using a Sellmeier-type relation. The values of fundamental and exciton band-gap energies were estimated from the ellipsometric and photoluminescence measurements. The origin of luminescence in Cd1- xBexSe and Cd1- xMgxSe was discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum OxidxeADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Sang-Wan Ryu Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source] The Impact of Interfacial Mixing on Förster Transfer at Conjugated Polymer HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Anthony M. Higgins Abstract Neutron reflectivity and photoluminescence measurements are reported on bilayers of polyfluorene-based conjugated polymers. By using a novel thermal processing procedure it is possible to control the width of the interface between poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene- alt -benzothiadiazole) (F8BT), and measure the impact of interfacial roughness on the resonant energy transfer of excitons at the interface (Förster transfer). It is found that increasing the root mean square (rms) roughness of the F8/F8BT interface over the range of ,1,nm to ,5,nm leads to a greatly enhanced Förster transfer from F8 to F8BT molecules. By comparing photoluminescence measurements with simple calculations it is concluded that the level of enhancement of the F8BT peak at rough interfaces can only be adequately explained if mixing of F8 and F8BT at a molecular level dominates over the interfacial roughness due to thermally excited capillary waves. [source] Hierarchical Shelled ZnO Structures Made of Bunched Nanowire Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007P. Jiang Abstract The size- and morphology-controlled growth of ZnO nanowire (NW) arrays is potentially of interest for the design of advanced catalysts and nanodevices. By adjusting the reaction temperature, shelled structures of ZnO made of bunched ZnO NW arrays are prepared, grown out of metallic Zn microspheres through a wet-chemical route in a closed Teflon reactor. In this process, ZnO NWs are nucleated and subsequently grown into NWs on the surfaces of the microspheres as well as in strong alkali solution under the condition of the pre-existence of zincate (ZnO22,) ions. At a higher temperature (200,°C), three different types of bunched ZnO NW or sub-micrometer rodlike (SMR) aggregates are observed. At room temperature, however, the bunched ZnO NW arrays are found only to occur on the Zn microsphere surface, while double-pyramid-shaped or rhombus-shaped ZnO particles are formed in solution. The ZnO NWs exhibit an ultrathin structure with a length of ca.,,500,nm and a diameter of ca.,10,nm. The phenomenon may be well understood by the temperature-dependent growth process involved in different nucleation sources. A growth mechanism has been proposed in which the degree of ZnO22,saturation in the reaction solution plays a key role in controlling the nucleation and growth of the ZnO NWs or SMRs as well as in oxidizing the metallic Zn microspheres. Based on this consideration, ultrathin ZnO NW cluster arrays on the Zn microspheres are successfully obtained. Raman spectroscopy and photoluminescence measurements of the ultrathin ZnO NW cluster arrays have also been performed. [source] Nanogels of poly(acrylic acid): Uptake and release behavior with fluorescent oligothiophene-labeled bovine serum albuminJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Simona Argentiere Abstract Nanometer-sized poly(acrylic acid) (PAA) hydrogels were synthesized by emulsion polymerization of methyl acrylate and subsequent acidic hydrolysis. The nanohydrogel was characterized by spectroscopic methods (FTIR and 1H-NMR) and scanning probe techniques, and their pH-dependent swelling behavior was studied by dynamic light scattering. To determine the suitability of PAA nanogels as pH-sensitive carriers for biomedical applications, uptake and release of an oligothiophene fluorophore and its albumin conjugated from PAA nanogels were investigated as a function of pH by absorption and photoluminescence measurements. It was observed that uptake and release processes of both the oligothiophene and its conjugate could be controlled by changing the pH of the external solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Optical properties of InN grown on templates with controlled surface polaritiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010Ronny Kirste Abstract The structural and optical properties of InN layers grown on GaN/sapphire templates with controlled Ga-/N-polar surfaces are investigated. Raman spectroscopy and XRD reciprocal space map analysis suggest that the InN layers were grown strain free with a high crystal quality. A line shape analysis of the A1(LO) Raman mode yields to a decreasing carrier concentration for the sample grown on Ga-polar substrate. Low temperature photoluminescence measurements exhibit a shift to lower energies of the luminescence maximum for the sample grown on Ga-polar GaN probably due to a reduced carrier concentration and thus, a decreased Burstein,Moss shift. Following this, we demonstrate that the use of polarity controlled GaN/sapphire substrates leads to unstrained layers with good structural and optical properties. [source] Performance of high-power III-nitride light emitting diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008G. Chen Abstract The performance of III-nitride based high-power light emitting diodes (LEDs) is reviewed. Direct color high-power LEDs with 1 × 1 mm2 chip size in commercial LUXEON® Rebel packages are shown to exhibit external quantum efficiencies at a drive current of 350 mA ranging from ,60% at a peak wavelength of ,420 nm to ,27% at ,525 nm. The short wavelength blue LED emits ,615 mW at 350 mA and >2 W at 1.5 A. The green LED emits ,110 lm at 350 mA and ,270 lm at 1.5 A. Phosphor-conversion white LEDs (1 × 1 mm2 chip size) are demonstrated that emit ,126 lm of white light when driven at 350 mA and 381 lm when driven at 1.5 A (Correlated Color Temperature, CCT , 4700 K). In a similar LED that employs a double heterostructure (DH) insign instead of a multi-quantum well (MQW) active region, the luminous flux increases to 435 lm (CCT , 5000 K) at 1.5 A drive current. Also discussed are experimental techniques that enable the separation of internal quantum efficiency and extraction efficiency. One technique derives the internal quantum efficiency from temperature and excitation-dependent photoluminescence measurements. A second technique relies on variable-temperature electroluminescence measurements and enables the estimation of the extraction efficiency. Both techniques are shown to yield consistent results and indicate that the internal quantum efficiency of short wavelength blue (, , 420 nm) high-power LEDs is as high as 71% even at a drive current of 350 mA. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhanced ultraviolet photoluminescence from V-doped ZnO thin films prepared by a sol,gel processPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007Ling Wei Abstract Undoped and vanadium-doped ZnO thin films were prepared on single-crystalline p-type Si(100) substrates by a sol,gel process and further annealed in an oxygen atmosphere. The influence of vanadium doping on the structural, surface morphological and optical properties of ZnO thin films was investigated by X-ray diffraction, atomic force microscopy and photoluminescence measurements. Both the undoped and V-doped ZnO thin films were of polycrystalline hexagonal wurtzite structure with (002)-preferred orientation. The crystallite size and the root-mean-square roughness of V-doped ZnO are smaller than those of undoped ZnO. Vanadium doping could reduce deep level defects of ZnO and thus strengthen ultraviolet (UV) emission. The peak intensity of UV emission increased with increasing annealing temperature above 400 °C. After annealing at 800 °C, the UV emission for the V-doped ZnO films was largely enhanced, while the visible emission was distinctly weakened. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaAs nanowires grown by MOVPEPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010Jens Bauer Abstract GaAs nanowire (NW) growth was studied by metal-organic vapour phase epitaxy (MOVPE). The vapour,liquid,solid (VLS) mechanism with gold-based alloy particles and the selective-area growth (SAG) mechanism on electron beam lithographically prepared SiNx/GaAs mask structures were applied. A special focus is set on thermodynamic aspects of the VLS process. The alloy particle formation and the influence of MOVPE growth parameters on the growth rate and the GaAs NW morphology are examined. Furthermore, the improvement of the real structure with particular interest on the twin formation is studied. Besides the commonly used continuous VLS growth mode also a pulsed VLS growth mode with alternating precursor supply is reported. Based on photoluminescence measurements the effect of strain in core/shell NW structures is confirmed. For the SAG mechanism the MOVPE growth parameters are determined and the real structure is described. [source] GaN/Al0.5Ga0.5N quantum dots and quantum dashesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Thomas Huault Abstract GaN/Al0.5Ga0.5N nanostructures grown on c -plane sapphire by molecular beam epitaxy using ammonia as N source have been studied. Depending on the ammonia pressure during the two dimensional , three dimensional transition of the GaN layer, the shape of the islands is strongly modified: elongated or isotropic islands are observed, leading to the formation of quantum dashes or quantum dots, respectively. This shape transition is seen as a consequence of a change in surface energy. The change of morphology of the GaN layer is clearly evidenced by photoluminescence measurements, and a large redshift in the emission peak is observed for quantum dashes as compared to quantum dots. An electric field ,3 MV/cm is estimated from the measurements at an excitation power ,20 mW/cm2. Weak photoluminescence quenching between low and room temperature for both QDs and QDashes structures is observed, indicating a strong confinement of carriers into the nanostructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase separation in SiOx films annealed under enhanced hydrostatic pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008G. Yu. Abstract The effect of enhanced hydrostatic pressure (HP, (10,12) × 108 Pa) on thermally stimulated phase decomposition of silicon suboxide layers processed at 450,1000 °C was investigated by infrared spectroscopy and photoluminescence measurements. HP stimulates decomposition of non-stoichiometric SiOx most efficiently at about 450 °C. In spite of enhanced SiOx decomposition, visible photoluminescence appears in HP-treated samples at higher annealing temperatures in comparison to those annealed under ambient pressure (AP, 105 Pa). Contrary to that, application of HP results in essential enhancement of near-infrared emission at lower annealing temperatures as compared to processing under AP. This can be related to pressure-stimulated crystallization of Si inclusions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the way to InGaN quantum dots embedded into monolithic nitride cavitiesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007K. Sebald Abstract We present photoluminescence measurements on single InGaN quantum dots (QDs) grown by metalorganic vapor phase epitaxy, and on monolithicly grown GaN-based quantum well airpost pillar microcavities. The observed sharp emission lines of the quantum dots are characterized by excitation density dependent measurements. The photoluminescence of individual quantum dots can easily be detected for temperatures up to 150 K. The micro-photoluminescence measurements on microcavities reveal three-dimensional confined optical modes which are not seen in the luminescence of the simply planar cavity. The realization of rather temperature stable QDs as well as of nitride based microcavity samples are promising with respect to the intended implementation of QD layers into microcavities. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of photoluminescence of InAs/InP self-assembled quantum wiresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007M. Ruiz-Castillo Abstract This paper investigates the electronic structure of self-assembled InAs quantum wires (QWrs), grown under different conditions by molecular beam epitaxy on InP, by means of photoluminescence measurements under pressure. In samples with regularly distributed QWrs, room pressure photoluminescence spectra consist of a broad band centred at about 0.85 eV, which can be easily de-convoluted in a few Gaussian peaks. In samples with isolated QWrs, photoluminescence spectra exhibit up to four clearly resolved bands. Applying hydrostatic pressure, the whole emission band monotonously shifts towards higher photon energies with pressure coefficients ranging from 72 to 98 meV/GPa. In contrast to InAs quantum dots on GaAs, quantum wires photoluminescence is observed up to 10 GPa, indicating that InAs QWrs are metastable well above pressure at which bulk InAs undergoes a phase transition to the rock-salt phase (7 GPa). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Anisotropic polarization of non-polar GaN quantum dot emissionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009R. Mata Abstract 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) [source] Growth and characterization of isotopic natGa15N by molecular-beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Yong-zhao Yao Abstract Isotopically enriched gallium nitride films, Ga14N and Ga15N, have been fabricated by molecular-beam epitaxy to study the effects of nitrogen atomic mass variation on structures and properties of GaN. The phonon frequency shift due to the isotopic substitution was clearly observed using Raman spectroscopy. The lattice constants of Ga15N differed from those of Ga14N; the unit cell volume of Ga15N was approximately 0.06% less than that of Ga14N. Temperature-dependent photoluminescence measurements revealed that the recombination mechanism in Ga14N and Ga15N was the same in the temperature range of 4-50 K, and the band gap energy difference was Eg15 -Eg14 = 6.0 ± 0.1 meV. This Eg difference is discussed in terms of volume shrinkage and change in phonon-electron interaction due to isotopic substitution. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quantum dots to double concentric quantum ring structures transitionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009S. Bietti Abstract Making use of the droplet,epitaxial technique, we realized a series of GaAs/AlGaAs nanostructured samples, starting from the same initial Ga droplet configuration, in which the nanostructure morphologies are progressively changed, via the As partial pressure provided during the growth, from islands, to single rings and, eventually, to concentric ring structures. We report a detailed characterization of the different structure morphologies, electronic structures and carrier dynamics via AFM and photoluminescence measurements as well as through theoretical simulations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical study of InAs/GaAs quantum dots with two different environmentsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008M. Kaniewska Abstract Unusually complex spectra have been obtained for InAs/GaAs quantum dot (QD) structures when studied as a function of applied bias by deep level transient spectroscopy (DLTS). In spite of their complexity, basic processes for electron escape from the QDs have been recognized. We show that due to the variety of transitions involving direct tunneling and more complex thermal transitions, due to QD size fluctuations, and environmental dependent QD carrier population, measurement conditions have to be carefully suited for characterizing transport properties of the QDs. Additionally, on the basis of results of a comparative study under chosen measurement conditions, we conclude that the states of the InAs QDs shift towards the middle of the energy gap if the QDs are capped with a Ga-rich InGaAs insertion. It explains a red-shift of the emission wavelength that was found by photoluminescence measurements (PL). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Buffer breakdown voltage of AlGaN/GaN HFET on a 4 inch Si(111) substrate grown by MOCVDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Masayuki Iwami Abstract The buffer breakdown voltage and the electron mobility in a two dimensional gas (2DEG) of AlGaN/GaN HFETs on 4 inch Si(111) substrates grown by metalorganic chemical vapor deposition was investigated. The relationship between the electrical properties of HFETs and the crystalline quality of the GaN layer are studied by X-ray diffraction and photoluminescence measurements. The buffer breakdown voltage decreases with an increase in the FWHM of the X-ray (0002) diffraction peak. The electron mobility in a 2DEG decreases with an increase in FWHM of the X-ray (102) diffraction peak. These results indicate that a screw component of the threading dislocations in the GaN layer is a primary source for buffer leakage, and that edge dislocations in the GaN layer have a scattering effect on the 2DEG transport. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Permanent bleaching of F2 color centers in lithium fluoride under UV light illuminationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007M. A. Vincenti Abstract Permanent bleaching of F and F2 color centers in gamma irradiated lithium fluoride crystals has been obtained under low power, CW laser illumination at 244 nm. Optical absorption and photoluminescence measurements reveal a selective change in the concentrations of these kinds of electronic defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bipolariton laser emission from a GaAs microcavityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007L. M. Moreira Abstract Biexciton emission properties were studied in a single GaAs quantum well (QW) semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser like behavior. Very small linewidths were measured, lying below 110 µeV and 150 µeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Varying the pump laser polarization, we were able to show the selection rules for the biexciton particle creation in the quantum well. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoreflectance investigations of energy level structure of InAs quantum dashes embedded in InGaAs/InGaAlAs quantum well grown on InP substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006W. Rudno-Rudzi Abstract Photoreflectance (PR) and photoluminescence measurements have been performed on molecular beam epitaxy grown InAs quantum dashes (QDash) of various sizes, embedded in In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum well (QW), grown on InP substrate. PR response from all relevant parts of the structure, i.e InAs/In0.53Ga0.47As QDashes, InAs/In0.53Ga0.47As/In0.53Ga0.23Al0.24As QW, and In0.53Ga0.23Al0.24As barriers, has been obtained. The lowest energy transition related to the ground state transition in QDashes shifts towards red with the increase in QDash sizes (amount of deposited InAs material) reaching wavelengths longer than for structures without the intermediate QW. The experimental data on the energies of optical transitions combined with the numerical calculation within the effective mass approximation has allowed determining the energy level structure of the entire system, including the values of conduction band offset between InGaAs and InGaAlAs layers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excitons in AgI,oxide particle composites: AgI,SrTiO3PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Fumito Fujishiro Abstract We fabricated (x)AgI,(1,x)SrTiO3 fine particle composites over a wide composition range of 0,100 mol% AgI. It is found that the dispersion of SrTiO3 fine particles enhances the ionic conductivity and (0.6)AgI,(0.4)SrTiO3 has the highest ionic conductivity (1.68 × 10,4 S/cm which is two hundreds times in comparison with that of pristine AgI), for the first time. In order to clarify such ionic conductivity enhanced by dispersing SrTiO3 fine particles into AgI, the photoluminescence measurements were carried out at different temperatures between 10 K and room temperature under different photoexcitation intensities, together with the structural and morphological studies (X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray fluorescence spectroscopy). The spectra consist of free exciton luminescence band and several broad luminescence bands due to the excitons trapped at crystal defects and residual impurities. The free exciton luminescence band almost disappears at x = 0.6, which may suggest the existence of considerable number of non-radiative traps (crystal defects) at the AgI/SrTiO3 particle interfaces. Such crystal defects may act as ionic pathways. The structural and morphological studies confirm the randomly-stacked ,AgI/,AgI heterostructures at the AgI/SrTiO3 particle interfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] n-Al0.75Ga0.25N epilayers for 250 nm emission ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005W. H. Sun Abstract We have developed a unique approach combining migration-enhanced metalorganic chemical vapor deposition (MEMOCVD) high temperature AlN buffer layers and AlGaN/AlN superlattices (SLs) to yield high quality ( HQ) AlGaN layers for 250 nm LEDs. Symmetric/asymmetric X-ray diffraction (XRD) and room temperature photoluminescence measurements were used to study the high-structural and optical quality. The (002) and (114) rocking curve full width at half,maximum (FWHM) of 1.4 µm n-Al0.75Ga0.25N grown over AlGaN/AlN buffer were 143 and 565 arcsec, respectively. Crack-free Al0.75Ga0.25N layers with electron concentration as high as 1 × 1018 cm,3 and Hall mobility about 50 cm2/V.s were successfully grown and used for sub-milliwatt power (0.12 mW at a pulse pump current of 300 mA) 250 nm deep ultraviolet light emitting diodes (UVLEDs). In addition, for comparison, we prepared n-AlGaN only using high temperature AlN without SLs inserted. The experiments show that the AlGaN/AlN SLs inserted play a crucial role in improving structural and optical quality of high Al-composition AlGaN epilayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||