33 CFR 165.1141 - Safety Zone; San Clemente 3 NM Safety Zone, San Clemente Island, CA.

Science.gov (United States)

2010-07-01

...) Location. The following area is a safety zone: All waters of the Pacific Ocean surrounding San Clemente Island, from surface to bottom, extending from the high tide line on the island seaward 3 NM. The zone... 3 NM from the high tide line to 33°02.82′ N, 118°30.65′ W; thence 33°01.29′ N, 118°33.88′ W; thence...

33 CFR 165.554 - Security Zone; Three Mile Island Generating Station, Susquehanna River, Dauphin County...

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Security Zone; Three Mile Island... Areas Fifth Coast Guard District § 165.554 Security Zone; Three Mile Island Generating Station... waters of the Susquehanna River in the vicinity of the Three Mile Island Generating Station bounded by a...

Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN

Energy Technology Data Exchange (ETDEWEB)

Perret, Edith [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland; Xu, Dongwei [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Highland, M. J. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Stephenson, G. B. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Zapol, P. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Fuoss, P. H. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Munkholm, A. [Munkholm Consulting, Mountain View, California 94043, USA; Thompson, Carol [Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA

2017-12-04

Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (1010) m-plane surface. The diffuse scattering is extended in the (0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [1210] and closely spaced along [0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate F and temperature. The island spacing along [0001] observed during the growth of the first monolayer obeys a power-law dependence on growth rate F-n, with an exponent n = 0:25 + 0.02. The results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4.

33 CFR 165.804 - Snake Island, Texas City, Texas; mooring and fleeting of vessels-safety zone.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Snake Island, Texas City, Texas... Guard District § 165.804 Snake Island, Texas City, Texas; mooring and fleeting of vessels—safety zone. (a) The following is a safety zone: (1) The west and northwest shores of Snake Island; (2) The...

The GaN trench gate MOSFET with floating islands: High breakdown voltage and improved BFOM

Science.gov (United States)

Shen, Lingyan; Müller, Stephan; Cheng, Xinhong; Zhang, Dongliang; Zheng, Li; Xu, Dawei; Yu, Yuehui; Meissner, Elke; Erlbacher, Tobias

2018-02-01

A novel GaN trench gate (TG) MOSFET with P-type floating islands (FLI) in drift region, which can suppress the electric field peak at bottom of gate trench during the blocking state and prevent premature breakdown in gate oxide, is proposed and investigated by TCAD simulations. The influence of thickness, position, doping concentration and length of the FLI on breakdown voltage (BV) and specific on-resistance (Ron_sp) is studied, providing useful guidelines for design of this new type of device. Using optimized parameters for the FLI, GaN FLI TG-MOSFET obtains a BV as high as 2464 V with a Ron_sp of 3.0 mΩ cm2. Compared to the conventional GaN TG-MOSFET with the same structure parameters, the Baliga figure of merit (BFOM) is enhanced by 150%, getting closer to theoretical limit for GaN devices.

Intermediate Nucleation State of GaN Growth

Science.gov (United States)

Zheng, L. X.; Xie, M. H.; Tong, S. Y.

2001-03-01

Homoexpitaxial nucleation of GaN during molecular-beam epitaxy is followed by scanning tunneling microcopy (STM). We observe a metastable nucleation state, which manifests as “ghost” islands in STM images. These “ghost” islands can be irreversibly driven into normal islands by continuous STM imaging. It is further established that the “ghost” island formation is related to the presence of excess Ga atoms on the surface: Normal islands are only seen under the N-rich or stoichiometric flux condition, whereas “ghost” islands are observed under Ga-rich conditions. For intermediate excess-Ga coverages, both normal and “ghost” islands are present, however, they show distinctly different sizes, suggesting different nucleation states for the two. A growth model is proposed to account for the formation of metastable, “ghost” islands. Kinetic Monte Carlo simulation is carried out and main features of the surface are reproduced. We acknowledge financial support from HK RGC under grant Nos. 7396/00P, 7142/99P, and 7121/00P.

Effect of vacancies on the structure and properties of Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3}

Energy Technology Data Exchange (ETDEWEB)

Abdul-Jabbar, N. M. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States); Forrest, T. R. [European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex (France); Department of Physics, University of California, Berkeley, California 94720 (United States); Gronsky, R. [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Bourret-Courchesne, E. D. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Wirth, B. D. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)

2015-08-28

Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} belongs to a family of materials with large intrinsic vacancy concentrations that are being actively studied due to their potential for diverse applications that include thermoelectrics and phase-change memory. In this article, the Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} structure is investigated via synchrotron x-ray diffraction, electron microscopy, and x-ray absorption experiments. Diffraction and microscopy measurements showed that the extent of vacancy ordering in Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} is highly dependent on thermal annealing. It is posited that stoichiometric vacancies play a role in local atomic distortions in Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} (based on the fine structure signals in the collected x-ray absorption spectra). The effect of vacancy ordering on Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} material properties is also examined through band gap and Hall effect measurements, which reveal that the Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} band gap redshifts by ≈0.05 eV as the vacancies order and accompanied by gains in charge carrier mobility. The results serve as an encouraging example of altering material properties via intrinsic structural rearrangement as opposed to extrinsic means, such as doping.

33 CFR 165.762 - Security Zone; St. Thomas, U.S. Virgin Islands.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Security Zone; St. Thomas, U.S....762 Security Zone; St. Thomas, U.S. Virgin Islands. (a) Location. Moving and fixed security zones are established 50 yards around all cruise ships entering, departing, moored or anchored in the Port of St. Thomas...

Centrosymmetry vs noncentrosymmetry in La{sub 2}Ga{sub 0.33}SbS{sub 5} and Ce{sub 4}GaSbS{sub 9} based on the interesting size effects of lanthanides: Syntheses, crystal structures, and optical properties

Energy Technology Data Exchange (ETDEWEB)

Zhao, Hua-Jun, E-mail: cszzl772002@yeah.net [Laboratory of Applied Research on the Characteristic Resources in the North of Guizhou Province, School of Chemistry and Chemical Engineering, Zunyi Normal College, Zunyi, Guizhou 563002 (China); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

2016-05-15

Two new quaternary sulfides La{sub 2}Ga{sub 0.33}SbS{sub 5} and Ce{sub 4}GaSbS{sub 9} have been prepared from stoichiometric elements at 1223 K in an evacuated silica tube. Interestingly, La{sub 2}Ga{sub 0.33}SbS{sub 5} crystallizes in the centrosymmetric structure, while Ce{sub 4}GaSbS{sub 9} crystallizes in the noncentrosymmetric structure, which show obvious size effects of lanthanides on the crystal structures of these two compounds. Ce{sub 4}GaSbS{sub 9} belongs to RE{sub 4}GaSbS{sub 9} (RE=Pr, Nd, Sm, Gd–Ho) structure type with a=13.8834(9) Å, b=14.3004(11) Å, c=14.4102(13) Å, V=2861.0(4) Å{sup 3}. The structure features infinite chains of [Ga{sub 2}Sb{sub 2}S{sub 11}{sup 10–}]{sub ∞} propagating along a direction separated by Ce{sup 3+} cations and S{sup 2−} anions. La{sub 2}Ga{sub 0.33}SbS{sub 5} adopts the family of La{sub 4}FeSb{sub 2}S{sub 10}-related structure with a=7.5193(6) Å, c=13.4126(17) Å, V=758.35(13) Å{sup 3}. Its structure is built up from the alternate stacking of La/Sb/S and La/Ga/S 2D building blocks. The La/Sb/S slabs consist of teeter-totter chains of Sb1S{sub 4} seesaws, which are connected via sharing the apexes of μ{sub 4}-S1. Moreover, La1 is positionally disordered with Sb1 and stabilized in a bicapped trigonal prismatic coordination sphere. Between these La/Sb/S slabs, La2S{sub 8} square antiprisms are connected via edge-sharing into 2D building blocks, creating tetrahedral sites partially occupied by the Ga1 atoms. UV/Vis diffuse reflectance spectroscopy study shows that the optical gap of La{sub 2}Ga{sub 0.33}SbS{sub 5} is about 1.76 eV. - Graphical abstract: Two new quaternary sulfides La{sub 2}Ga{sub 0.33}SbS{sub 5} and Ce{sub 4}GaSbS{sub 9} have been prepared by solid-state reactions. Ce{sub 4}GaSbS{sub 9} crystallizes in RE{sub 4}GaSbS{sub 9} (RE=Pr, Nd, Sm, Gd–Ho) structure type, while La{sub 2}Ga{sub 0.33}SbS{sub 5} belongs to the family of La{sub 4}FeSb{sub 2}S{sub 10}-related structure and exhibits an

Size-dependent magnetic properties of FeGaB/Al2O3 multilayer micro-islands

Science.gov (United States)

Wang, X.; Gao, Y.; Chen, H.; Chen, Y.; Liang, X.; Lin, W.; Sun, N. X.

2018-06-01

Recently, micrometer-size patterned magnetic materials have been widely used in MEMS devices. However, the self-demagnetizing action is significantly influencing the performance of the magnetic materials in many MEMS devices. Here, we report an experimental study on the magnetic properties of the patterned micro-scale FeGaB/Al2O3 multilayers. Ferromagnetic hysteresis loop, ferromagnetic resonance (FMR), permeability and domain behavior have been demonstrated by complementary techniques. Magnetic annealing was used to enhance the performance of magnetic multilayers. The comparisons among micro-islands with different sizes in the range of 200 μm ∼ 500 μm as well as full film show a marked influence of size-effect, the exchange coupling effect, and the different domain structures inside the islands.

Er{sub 1.33}Pt{sub 3}Ga{sub 8}: A modulated variant of the Er{sub 4}Pt{sub 9}Al{sub 24}-structure type

Energy Technology Data Exchange (ETDEWEB)

Oswald, Iain W.H. [Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080 (United States); Gourdon, Olivier [Research and Development, ZS Pharma, Coppell, TX 75109 (United States); Bekins, Amy; Evans, Jess [Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, TX 76019 (United States); Treadwell, LaRico J. [Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080 (United States); Chan, Julia Y., E-mail: Julia.Chan@utdallas.edu [Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080 (United States); Macaluso, Robin T., E-mail: robin.macaluso@uta.edu [Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, TX 76019 (United States); Department of Chemistry and Biochemistry, University of Northern Colorado, Greeley, CO 80639 (United States)

2016-10-15

Single crystals of Er{sub 1.33}Pt{sub 3}Ga{sub 8} were synthesized in a molten Ga flux. Er{sub 1.33}Pt{sub 3}Ga{sub 8} can be considered to be a modulated variant of the Er{sub 4}Pt{sub 9}Al{sub 24}-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0β0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er{sub 1.33}Pt{sub 3}Ga{sub 8} shows antiferromagnetic ordering at T{sub N}~5 K. - Graphical abstract: A precession image of the hk0 zone showing weak, periodic, unindexed reflections indicating modulation and representation of the commensurate [ErGa] layer showing the waving modulated occupation. - Highlights: • Single crystals of Er{sub 1.33}Pt{sub 3}Ga{sub 8} were grown from gallium flux. • The structure of Er{sub 1.33}Pt{sub 3}Ga{sub 8} is compared to Er{sub 4}Pt{sub 9}Al{sub 24}. • Structure has been solved in the monoclinic superspace group X2/m(0β0)00 with a commensurate modulated vector q=1/3b*.

33 CFR 334.840 - Waters of Lake Michigan south of Northerly Island at entrance to Burnham Park Yacht Harbor...

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Waters of Lake Michigan south of Northerly Island at entrance to Burnham Park Yacht Harbor, Chicago, Ill.; danger zone adjacent to airport on... Michigan south of Northerly Island at entrance to Burnham Park Yacht Harbor, Chicago, Ill.; danger zone...

33 CFR 334.85 - New York Harbor, adjacent to the Stapleton Naval Station, Staten Island, New York; restricted area.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false New York Harbor, adjacent to the Stapleton Naval Station, Staten Island, New York; restricted area. 334.85 Section 334.85 Navigation and... RESTRICTED AREA REGULATIONS § 334.85 New York Harbor, adjacent to the Stapleton Naval Station, Staten Island...

33 CFR 334.1440 - Pacific Ocean at Kwajalein Atoll, Marshall Islands; missile testing area.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Pacific Ocean at Kwajalein Atoll, Marshall Islands; missile testing area. 334.1440 Section 334.1440 Navigation and Navigable Waters CORPS OF ENGINEERS, DEPARTMENT OF THE ARMY, DEPARTMENT OF DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.1440 Pacific Ocean at Kwajalein...

Degradation mechanisms of optoelectric properties of GaN via highly-charged 209Bi33+ ions irradiation

Science.gov (United States)

Zhang, L. Q.; Zhang, C. H.; Xian, Y. Q.; Liu, J.; Ding, Z. N.; Yan, T. X.; Chen, Y. G.; Su, C. H.; Li, J. Y.; Liu, H. P.

2018-05-01

N-type gallium nitride (GaN) epitaxial layers were subjected to 990-keV Bi33+ ions irradiation to various fluences. Optoelectric properties of the irradiated-GaN specimens were studied by means of Raman scattering and variable temperature photoluminescence (PL) spectroscopy. Raman spectra reveal that both the free-carrier concentration and its mobility generally decrease with a successive increase in ion fluence. Electro-optic mechanisms dominated the electrical transport to a fluence of 1.061 × 1012 Bi33+/cm2. Above this fluence, electrical properties were governed by the deformation potential. The appearance of vacancy-type defects results in an abrupt degradation in electrical transports. Varying temperature photoluminescence (PL) spectra display that all emission lines of 1.061 × 1012 Bi33+/cm2-irradiated specimen present a general remarkable thermal redshift, quenching, and broadening, including donor-bound-exciton peak, yellow luminescence band, and LO-phonon replicas. Moreover, as the temperature rises, a transformation from excitons (donor-acceptor pairs' luminescence) to band-to-band transitions (donor-acceptor combinations) was found, and the shrinkage effect of the band gap dominated the shift of the peak position gradually, especially the temperature increases above 150 K. In contrast to the un-irradiated specimen, a sensitive temperature dependence of all photoluminescence (PL) lines' intensity obtained from 1.061 × 1012 Bi33+/cm2-irradiated specimen was found. Mechanisms underlying were discussed.

Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.

Science.gov (United States)

Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo

2012-02-07

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.

Anisotropic Transport of Electrons in a Novel FET Channel with Chains of InGaAs Nano-Islands Embedded along Quasi-Periodic Multi-Atomic Steps on Vicinal (111)B GaAs

International Nuclear Information System (INIS)

Akiyama, Y.; Kawazu, T.; Noda, T.; Sakaki, H.

2010-01-01

We have studied electron transport in n-AlGaAs/GaAs heterojunction FET channels, in which chains of InGaAs nano-islands are embedded along quasi-periodic steps. By using two samples, conductance G para (V g ) parallel to the steps and G perp (V g ) perpendicular to them were measured at 80 K as functions of gate voltage V g . At sufficiently high V g , G para at 80 K is several times as high as G perp , which manifests the anisotropic two-dimensional transport of electrons. When V g is reduced to -0.7 V, G perp almost vanishes, while Gpara stays sizable unless V g is set below -0.8 V. These results indicate that 'inter-chain' barriers play stronger roles than 'intra-chain' barriers.

Transmission electron microscopy of GaN based, doped semiconductor heterostructures

Energy Technology Data Exchange (ETDEWEB)

Pretorius, A.

2006-07-01

This thesis addresses the analysis of GaN based heterostructures with transmission electron microscopy (TEM). Basic properties of the material of interest are introduced in chapter 2. These include the structural and optical properties as well as an introduction to the growth methods used for the samples analysed in this work. In chapter 3 a brief theoretical treatment of TEM is given. As one main topic of this work is the determination of the In concentration in InGaN islands using strain state analysis, a detailed description of the method is given. Chapter 4 describes the results obtained for pyramidal defects present in metalorganic vapour phase epitaxy grown GaN:Mg with high dopant concentration. Based on the experimental results and the well established knowledge that GaN of inverted polarity is present inside the pyramidal defects, a variety of basal plane inversion domain boundary models was set up. From these models, HRTEM images were simulated using the multislice approach, followed by a quantitative comparison to experimentally obtained HRTEM images. Another focus of this work is the analysis of In{sub x}Ga{sub 1-x}N islands grown on GaN presented in chapter 5. Following a literature survey which describes different methods used to obtain In{sub x}Ga{sub 1-x}N islands, the first topic is the distinction of In{sub x}Ga{sub 1-x}N islands and metal droplets, which can form during growth. This is followed by the experimental results of molecular beam epitaxy and metalorganic vapour phase epitaxy grown In{sub x}Ga{sub 1-x}N island and quantum dot samples. (orig.)

Synthesis of GaAs quantum dots on Si-layers on AlGaAs films grown on GaAs(100) substrates

International Nuclear Information System (INIS)

Mendez-Garcia, V. H.; Zamora-Peredo, L.; Saucedo-Zeni, N.

2002-01-01

In this work we report a novel method for obtaining GaAs quantum dots by molecular beam epitaxy (MBE) on an AlGaAs underlying film. We propose to use a Si monolayer (ML) grown on AlGaAs, in order to induce a 3D nucleation during the GaAs overgrowth. The samples were prepared in a Riber 32P MBE system employing undoped Si-GaAs(100) substrates. First, a 500 nm thick layer of Al x Ga 1-x As was grown with a nominal concentration x=0.35. Several samples were grown in order to analyze the effects of changing the Si interlayer thickness, and the amount of GaAs overgrowth, on the final structures. Previous to the Si-exposure, the AlGaAs presented a (1x3) surface reconstruction which gradually turned to a (3x1) structure when the Si-thickness was 1 ML, as observed in the reflection high-energy electron diffraction (RHEED) patterns. When the GaAs overgrowth started on this surface, transmission RHEED spots appeared and showed a considerable increase in intensity until reaching a maximum. This behavior is typical from a 3D island growth. If the GaAs overgrowth continues, the initial streaky RHEED patterns recovered indicating a 2D-growth. Thus, we prepared a sample stopping the GaAs overgrowth at the time when the diffraction 3D spot reached the maximum intensity, equivalent to 2ML of GaAs. The sample surface was analyzed in air by atomic force microscopy (AFM). Islands of 1.5 nm-height and 20x20 nm of base were clearly observed, these dimensions are suitable for applications in quantum dots. (Authors)

Structure of {sup 33}Mg sheds new light on the N=20 island of inversion

Energy Technology Data Exchange (ETDEWEB)

Kanungo, R., E-mail: ritu@triumf.c [Astronomy and Physics Department, Saint Mary' s University, Halifax, NS B3H 3C3 (Canada); Nociforo, C. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Prochazka, A. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Physics Department, Justus-Liebig University, 35392 Giessen (Germany); Utsuno, Y. [Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Aumann, T. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Boutin, D. [Physics Department, Justus-Liebig University, 35392 Giessen (Germany); Cortina-Gil, D. [Universidad de Santiago de Compostela, E-15706 Santiago de Compostela (Spain); Davids, B. [TRIUMF, Vancouver, BC V6T 2A3 (Canada); Diakaki, M. [National Technical University, Athens (Greece); Farinon, F. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Physics Department, Justus-Liebig University, 35392 Giessen (Germany); Geissel, H. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Gernhaeuser, R. [Physik Dept. E12, Technische Universitaet Muenchen, D-85748 Garching (Germany); Gerl, J. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Janik, R. [Faculty of Mathematics and Physics, Comenius Univ., 84215 Bratislava (Slovakia); Jonson, B. [Fundamental Physics, Chalmers Univ. of Technology, SE 412-916 Goeteborg (Sweden); Kindler, B. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Knoebel, R. [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Physics Dept., Justus-Liebig Univ., 35392 Giessen (Germany); Kruecken, R. [Physik Dept. E12, Technische Univ. Muenchen, D-85748 Garching (Germany); Lantz, M. [Fundamental Physics, Chalmers Univ. of Technology, SE 412-916 Goeteborg (Sweden); Lenske, H. [Physics Dept., Justus-Liebig Univ., 35392 Giessen (Germany)

2010-03-08

The first reaction spectroscopy on the ground state structure of {sup 33}Mg through the measurement of the longitudinal momentum distribution from the one-neutron removal reaction using a C target at 898A MeV is reported. The experiment was performed at the FRS, GSI. The distribution has a relatively narrow width (150+-3 MeV/c (FWHM)) and the one-neutron removal cross-section is 74+-4 mb. An increased contribution from the 2p{sub 3/2} orbital is required to explain the observation showing its lowering compared to existing model predictions. This provides new information regarding the configuration of {sup 33}Mg and the island of inversion.

Polarization-engineered GaN/InGaN/GaN tunnel diodes

International Nuclear Information System (INIS)

Krishnamoorthy, Sriram; Nath, Digbijoy N.; Akyol, Fatih; Park, Pil Sung; Esposto, Michele; Rajan, Siddharth

2010-01-01

We report on the design and demonstration of polarization-engineered GaN/InGaN/GaN tunnel junction diodes with high current density and low tunneling turn-on voltage. Wentzel-Kramers-Brillouin calculations were used to model and design tunnel junctions with narrow band gap InGaN-based barrier layers. N-polar p-GaN/In 0.33 Ga 0.67 N/n-GaN heterostructure tunnel diodes were grown using molecular beam epitaxy. Efficient interband tunneling was achieved close to zero bias with a high current density of 118 A/cm 2 at a reverse bias of 1 V, reaching a maximum current density up to 9.2 kA/cm 2 . These results represent the highest current density reported in III-nitride tunnel junctions and demonstrate the potential of III-nitride tunnel devices for a broad range of optoelectronic and electronic applications.

33 CFR 110.236 - Pacific Ocean off Barbers Point, Island of Oahu, Hawaii: Offshore pipeline terminal anchorages.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Pacific Ocean off Barbers Point... Grounds § 110.236 Pacific Ocean off Barbers Point, Island of Oahu, Hawaii: Offshore pipeline terminal... regulations. (1) No vessels may anchor, moor, or navigate in anchorages A, B, C, or D except: (i) Vessels...

Ecological and physiological parameters of mercury and cesium-137 accumulation in the raccoon

International Nuclear Information System (INIS)

Davis, A.H.

1981-01-01

Raccoons from 4 regions in the southeastern Coastal Plain were evaluated for mercury content. Mercury content of hair when used as an indicator of total body mercury content was significantly different among 3 of the 4 areas: Okefenokee Swamp, Eglin Air Force Base, and Sapelo Island on the Georgia Coast. Raccoons from Echols County Georgia were not significantly different from those of the Okefenokee. Mercury in the liver and kidney was significantly different between Okefenokee and Sapelo. There was a strong correlation between the age of the raccoon and the mercury in hair, with older animals having higher concentrations. This relationship was also valid for most other tissues. There was evidence that mercury content in some tissues was correlated with the season and the body condition of the raccoon. Mercury was not transferred through the placenta to the fetal raccoons. There was a strong relationship of mercury content to raccoon behavioral characteristics. Raccoon body weight was slightly different between the areas studied. Cesium-137 values in raccoons were significantly different between the Okefenokee and Sapelo Island. Cesium-137 content was correlated with raccoon age, body weight, and mercury content. Generally non-detectable levels of chlorinated hydrocarbons and PCB were found in Okefenokee raccoons. Mercury concentrations in crayfish were generally low but probably of importance in the raccoon food chain. The biological half life of mercury in brain, gonad, pancreas, spleen, heart, and lung was approximately 52 days. The half-life of mercury in muscle was 35 days. Mercury content of hair, liver, and kidney decreased at very slow rates, with biological half lives of 229, 108, and 138 days. This was probably due to the role of these tissues in clearance of mercury from the body, and to the molting pattern of raccoon hair

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

Science.gov (United States)

Shirazi-HD, M.; Diaz, R. E.; Nguyen, T.; Jian, J.; Gardner, G. C.; Wang, H.; Manfra, M. J.; Malis, O.

2018-04-01

AlxGa1-xN layers with Al-composition above 0.6 (0.6 < x < 0.9) grown under metal-rich conditions by plasma-assisted molecular beam epitaxy on m-plane GaN miscut towards the -c axis are kinetically unstable. Even under excess Ga flux, the effective growth rate of AlGaN is drastically reduced, likely due to suppression of Ga-N dimer incorporation. The defect structure generated during these growth conditions is studied with energy dispersive x-ray spectroscopy scanning transmission electron microscopy as a function of Al flux. The AlGaN growth results in the formation of thin Al(Ga)N layers with Al-composition higher than expected and lower Al-composition AlGaN islands. The AlGaN islands have a flat top and are elongated along the c-axis (i.e., stripe-like shape). Possible mechanisms for the observed experimental results are discussed. Our data are consistent with a model in which Al-N dimers promote release of Ga-N dimers from the m-plane surface.

TEM characterization of catalyst- and mask-free grown GaN nanorods

International Nuclear Information System (INIS)

Schowalter, M; Aschenbrenner, T; Kruse, C; Hommel, D; Rosenauer, A

2010-01-01

Catalyst- and mask-free grown GaN nanorods have been investigated using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy filtered transmission electron microscopy (EFTEM). The nanorods were grown on nitridated r-plane sapphire substrates in a molecular beam epitaxy reactor. We investigated samples directly after the nitridation and after the overgrowth of the structure with GaN. High resolution transmission electron microscopy (HRTEM) and EFTEM revealed that AlN islands have formed due to nitridation. After overgrowth, the AlN islands could not be observed any more, neither by EFTEM nor by Z-contrast imaging. Instead, a smooth layer consisting of AlGaN was found. The investigation of the overgrown sample revealed that an a-plane GaN layer and GaN nanorods on top of the a-plane GaN have formed. The nanorods reduced from top of the a-plane GaN towards the a-plane GaN/sapphire interface suggesting that the nanorods originate at the AlN islands found after nitridation. However, this could not be shown unambiguously. The number of threading dislocations in the nanorods was very low. The analysis of the epitaxial relationship to the a-plane GaN showed that the nanorods grew along the [000-1] direction, and the [1-100] direction of the rods was parallel to the [0001] direction of the a-plane GaN.

Comparison of trap characteristics between AlGaN/GaN and AlGaN/InGaN/GaN heterostructure by frequency dependent conductance measurement

International Nuclear Information System (INIS)

Chakraborty, Apurba; Biswas, Dhrubes

2015-01-01

Frequency dependent conductance measurement is carried out to observe the trapping effect in AlGaN/InGaN/GaN double heterostructure and compared that with conventional AlGaN/GaN single heterostructure. It is found that the AlGaN/InGaN/GaN diode structure does not show any trapping effect, whereas single heterostructure AlGaN/GaN diode suffers from two kinds of trap energy states in near depletion to higher negative voltage bias region. This conductance behaviour of AlGaN/InGaN/GaN heterostructure is owing to more Fermi energy level shift from trap energy states at AlGaN/InGaN junction compare to single AlGaN/GaN heterostructure and eliminates the trapping effects. Analysis yielded interface trap energy state in AlGaN/GaN is to be with time constant of (33.8–76.5) μs and trap density of (2.38–0.656) × 10 12  eV −1  cm −2 in −3.2 to −4.8 V bias region, whereas for AlGaN/InGaN/GaN structure no interface energy states are found and the extracted surface trap energy concentrations and time constants are (5.87–4.39) ×10 10  eV −1  cm −2 and (17.8–11.3) μs, respectively, in bias range of −0.8–0.0 V

Unbiased Photocatalytic Hydrogen Generation from Pure Water on Stable Ir-treated In 0.33 Ga 0.67 N Nanorods

KAUST Repository

Ebaid, Mohamed; Priante, Davide; Liu, Guangyu; Zhao, Chao; Sharizal Alias, Mohd; Buttner, Ulrich; Khee Ng, Tien; Taylor Isimjan, Tayirjan; Idriss, Hicham; Ooi, Boon S.

2017-01-01

InGaN-based nanostructures have recently been recognized as promising materials for efficient solar hydrogen generation. This is due to their chemical stability, adjustable optoelectronic properties, suitable band edge alignment, and large surface-to-volume ratio. The inherent high density of surface trapping states and the lack of compatible conductive substrates, however, hindered their use as stable photo-catalysts. We have designed, synthesized and tested an efficient photocatalytic system using stable In0.33Ga0.67N-based nanorods (NRs) grown on an all-metal stack substrate (Ti-Mo) for a better electron transfer process. In addition, we have applied a bifunctional ultrathin thiol-based organic surface treatment using 1,2-ethanedithiol (EDT), in which sulfur atoms protected the surface from oxidation. This treatment has dual functions, it passivates the surface (by the removal of dangling bonds) and creates ligands for linking Ir-metal ions as oxygen evolution centers on top of the semiconductor. This treatment when applied to In0.33Ga0.67N NRs resulted in a photo-catalyst that achieved 3.5% solar-to-hydrogen (STH) efficiency, in pure water (pH~7, buffer solution) under simulated one-sun (AM1.5G) illumination and without electrical bias. Over the tested period, a steady increase of the gas evolution rate was observed from which a turnover frequency of 0.23s-1 was calculated. The novel growth of InGaN-based NRs on a metal as well as the versatile surface functionalization techniques (EDT-Ir) have a high potential for making stable photo-catalysts with adjustable band gaps and band edges to harvest sun light.

Unbiased Photocatalytic Hydrogen Generation from Pure Water on Stable Ir-treated In 0.33 Ga 0.67 N Nanorods

KAUST Repository

Ebaid, Mohamed

2017-05-11

InGaN-based nanostructures have recently been recognized as promising materials for efficient solar hydrogen generation. This is due to their chemical stability, adjustable optoelectronic properties, suitable band edge alignment, and large surface-to-volume ratio. The inherent high density of surface trapping states and the lack of compatible conductive substrates, however, hindered their use as stable photo-catalysts. We have designed, synthesized and tested an efficient photocatalytic system using stable In0.33Ga0.67N-based nanorods (NRs) grown on an all-metal stack substrate (Ti-Mo) for a better electron transfer process. In addition, we have applied a bifunctional ultrathin thiol-based organic surface treatment using 1,2-ethanedithiol (EDT), in which sulfur atoms protected the surface from oxidation. This treatment has dual functions, it passivates the surface (by the removal of dangling bonds) and creates ligands for linking Ir-metal ions as oxygen evolution centers on top of the semiconductor. This treatment when applied to In0.33Ga0.67N NRs resulted in a photo-catalyst that achieved 3.5% solar-to-hydrogen (STH) efficiency, in pure water (pH~7, buffer solution) under simulated one-sun (AM1.5G) illumination and without electrical bias. Over the tested period, a steady increase of the gas evolution rate was observed from which a turnover frequency of 0.23s-1 was calculated. The novel growth of InGaN-based NRs on a metal as well as the versatile surface functionalization techniques (EDT-Ir) have a high potential for making stable photo-catalysts with adjustable band gaps and band edges to harvest sun light.

33 CFR 334.40 - Atlantic Ocean in vicinity of Duck Island, Maine, Isles of Shoals; naval aircraft bombing target...

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Atlantic Ocean in vicinity of Duck Island, Maine, Isles of Shoals; naval aircraft bombing target area. 334.40 Section 334.40... Shoals; naval aircraft bombing target area. (a) The danger zone. A circular area with a radius of 500...

33 CFR 165.154 - Safety and Security Zones: Long Island Sound Marine Inspection Zone and Captain of the Port Zone.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Safety and Security Zones: Long... Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) PORTS AND WATERWAYS SAFETY... Areas First Coast Guard District § 165.154 Safety and Security Zones: Long Island Sound Marine...

Quantification of segregation and mass transport in InxGa1-xASGaAs Stranski-Krastanow layers

International Nuclear Information System (INIS)

Rosenauer, A.; Gerthsen, D.; Van Dyck, D.; Arzberger, M.; Boehm, G.; Abstreiter, G.

2001-01-01

We report on transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy measurement of mass transport and segregation in InAs Stranski-Krastanow layers grown on GaAs(001) by molecular beam epitaxy at growth temperatures of 480 and 530 deg. C. Plan-view TEM reveals regularly shaped islands with a density of 7.8x10 10 cm -2 (480 deg. C) and 1.5x10 10 cm -2 (530 deg. C), respectively. Uncapped islands were investigated by strain state analysis of electron wave functions reconstructed from high-resolution TEM images. In-concentration profiles of the islands were obtained by the measurement of lattice-parameter profiles of the islands and the application of finite-element calculations. We find that the islands contain Ga-atoms with a percentage of 50% (480 deg. C) and 67% (530 deg. C). The capped InAs-layers were investigated with PL and TEM. In agreement with TEM, PL indicates a smaller and deeper potential well of the islands grown at 480 deg. C. Concentration profiles of the wetting layers were measured with TEM using the composition evaluation of lattice fringe images method, clearly revealing segregation profiles. The obtained segregation efficiency of In-atoms is 0.77±0.02 (480 deg. C) and 0.82±0.02 (530 deg. C). As an explanation for the strong mass transport of Ga from the substrate to the islands we show that the segregation of In atoms during the growth of the binary InAs can lead to the generation of vacancies in the metal sublattice. The vacancies are filled by Ga-atoms migrating along the surface or by a diffusion of the vacancies from the wetting layer and the islands into the GaAs buffer, leading to a unidirectional diffusion of Ga atoms from the buffer into the Stranski-Krastanow layer

33 CFR 110.50a - Fishers Island Sound, Stonington, Conn.

Science.gov (United States)

2010-07-01

..., Stonington, Conn. An area on the east side of Mason Island bounded as follows: Beginning at the shore line on the easterly side of Mason Island at latitude 41°20′06″; thence due east about 600 feet to latitude 41...′37″; thence due west about 1,000 feet to the shore line on the easterly side of Mason Island at...

Quantum Dots obtained by LPE from under-saturated In-As liquid phases on GaAs substrates

Energy Technology Data Exchange (ETDEWEB)

Ortiz F E; Mishurnyi V; Gorbatchev A; De Anda F [Universidad Autonoma de San Luis Potosi, Instituto de Investigacion en Comunicacion Optica, Av. Karacorum 1470, Col. Lomas 4a Sec., CP 78210San Luis PotosI (Mexico); Prutskij T, E-mail: fcoe_ov@prodigy.net.mx, E-mail: andre@cactus.iico.uaslp.mx [BUAP, Instituto de Ciencias, Apartado Postal 207, 72000, Puebla (Mexico)

2011-01-01

In this work we inform about quantum dots (QD) obtained by Liquid Phase Epitaxy (LPE) on GaAs substrates from under-saturated In-As liquid phases. In our processes, we have prepared saturated In-rich liquid phases by dissolving an InAs wafer at one of the temperatures interval from 450 to 414 C for 60 minutes. The contact between In-As liquid phase and the GaAs substrate was always done at a constant temperature of 444 C for 5 seconds. Thus, the growth temperature for most of the samples was higher than the liquidus temperature. We think that the growth driving force is related to a transient process that occurs when the system is trying to reach equilibrium. Under the atom force microscope (AFM) we have observed nano-islands on the surfaces of the samples obtained from under-saturated liquid phases prepared at 438, 432 and 426 C. The 25 K photoluminescence spectrum shows a peak at a 1.33 eV, in addition to the GaAs related line.

Quantitative assessment of Al-to-N bonding in dilute Al0.33Ga0.67As1-yNy

International Nuclear Information System (INIS)

Wagner, J.; Geppert, T.; Koehler, K.; Ganser, P.; Maier, M.

2003-01-01

A quantitative assessment of the group III-nitrogen bonding in low N-content Al 0.33 Ga 0.67 As 1-y N y with y≤0.04 has been performed, using vibrational mode Raman spectroscopy for the quantitative analysis of local bond formation in combination with energy dispersive x-ray analysis and secondary ion mass spectrometry for chemical analysis. Clear evidence is obtained for the preferential bonding of nitrogen to Al with one nitrogen atom being coordinated to, at the average, 3.4 Al neighbors. This strong preference for Al-to-N bond formation can be understood in terms of the much larger cohesive energy of the Al-N bond compared to the Ga-N chemical bond. In spite of this phase-separation-like formation of local Al-N complexes, the fundamental band gap and the E 1 /E 1 +Δ 1 band gaps show a continuous low-energy and high-energy shift, respectively, upon the addition of nitrogen as already known from dilute GaAsN

Growth modes of InN (000-1) on GaN buffer layers on sapphire

International Nuclear Information System (INIS)

Liu Bing; Kitajima, Takeshi; Chen Dongxue; Leone, Stephen R.

2005-01-01

In this work, using atomic force microscopy and scanning tunneling microscopy, we study the surface morphologies of epitaxial InN films grown by plasma-assisted molecular beam epitaxy with intervening GaN buffer layers on sapphire substrates. On smooth GaN buffer layers, nucleation and evolution of three-dimensional InN islands at various coverages and growth temperatures are investigated. The shapes of the InN islands are observed to be predominantly mesalike with large flat (000-1) tops, which suggests a possible role of indium as a surfactant. Rough GaN buffer layers composed of dense small GaN islands are found to significantly improve uniform InN wetting of the substrates, on which atomically smooth InN films are obtained that show the characteristics of step-flow growth. Scanning tunneling microscopy imaging reveals the defect-mediated surface morphology of smooth InN films, including surface terminations of screw dislocations and a high density of shallow surface pits with depths less than 0.3 nm. The mechanisms of the three-dimensional island size and shape evolution and formation of defects on smooth surfaces are considered

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation

International Nuclear Information System (INIS)

Hwang, Jih-Shang; Liu, Tai-Yan; Chen, Han-Wei; Chattopadhyay, Surjit; Hsu, Geng-Ming; Basilio, Antonio M; Hsu, Yu-Kuei; Tu, Wen-Hsun; Lin, Yan-Gu; Chen, Kuei-Hsien; Li, Chien-Cheng; Wang, Sheng-Bo; Chen, Hsin-Yi; Chen, Li-Chyong

2013-01-01

Enhanced photoelectrochemical (PEC) performances of Ga 2 O 3 and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga 2 O 3 and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga 2 O 3 NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga 2 O 3 . These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga 2 O 3 NWs, or by incorporation of indium to form InGaN NWs. (paper)

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation.

Science.gov (United States)

Hwang, Jih-Shang; Liu, Tai-Yan; Chattopadhyay, Surjit; Hsu, Geng-Ming; Basilio, Antonio M; Chen, Han-Wei; Hsu, Yu-Kuei; Tu, Wen-Hsun; Lin, Yan-Gu; Chen, Kuei-Hsien; Li, Chien-Cheng; Wang, Sheng-Bo; Chen, Hsin-Yi; Chen, Li-Chyong

2013-02-08

Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.

Crystallization kinetics of Ga metallic nano-droplets under As flux

International Nuclear Information System (INIS)

Bietti, S; Somaschini, C; Sanguinetti, S

2013-01-01

We present an experimental investigation of the crystallization dynamics of Ga nano-droplets under As flux. The transformation of the metallic Ga contained in the droplets into a GaAs nano-island proceeds by increasing the size of a tiny ring of GaAs which is formed just after the Ga deposition at the rim of a droplet. The GaAs crystallization rate depends linearly on the liquid–solid interface area. The maximum growth rate is set by the As flux impinging on the droplet, thus showing an efficient As incorporation and transport despite the predicted low solubility of the As in metallic Ga at the crystallization temperatures. (paper)

From $^{27}$Mg to ${33}$Mg transition to the "Island of inversion"

CERN Document Server

Yordanov, Deyan

Since introduced in nuclear physics, the concept of shell structure and magic numbers has governed our understanding of nuclear matter in atomic nuclei close to stability. Nuclear species with a magic number of protons and/or neutrons are known to be more stable and close to spherical in shape. Experimental studies of 30Ne, 31Na and 32Mg, systems with a closed neutron sd shell (N=20), provide evidence for a ground-state deformation in these nuclei. The observed phenomenon is understood as an inversion of the normal spherical ground-state configuration, expected according to the traditional shell model, with deformed states governed by particle-hole excitations over the N=20 shell gap. The properties of nuclei in this Island of inversion are of particular importance for the theoretical modeling of the region. The present doctoral dissertation reports on the first determination of the nuclear ground-state spins and magnetic moments of 31,33Mg, obtained by means of laser spectroscopy in combination with nuclear...

Impact of GaN transition layers in the growth of GaN epitaxial layer on silicon

International Nuclear Information System (INIS)

Zhao Danmei; Zhao Degang; Jiang Desheng; Liu Zongshun; Zhu Jianjun; Chen Ping; Liu Wei; Li Xiang; Shi Ming

2015-01-01

A method for growing GaN epitaxial layer on Si (111) substrate is investigated. Due to the large lattice mismatch between GaN and AlN, GaN grown directly above an AlN buffer layer on the Si substrate turns out to be of poor quality. In this study, a GaN transition layer is grown additionally on the AlN buffer before the GaN epitaxial growth. By changing the growth conditions of the GaN transition layer, we can control the growth and merging of islands and control the transfer time from 3D to 2D growth mode. With this method, the crystalline quality of the GaN epitaxial layer can be improved and the crack density is reduced. Here, we have investigated the impact of a transition layer on the crystalline quality and stress evolution of a GaN epitaxial layer with methods of X-ray diffraction, optical microscopy and in situ reflectivity trace. With the increasing thickness of transition layer, the crack decreases and the crystalline quality is improved. But when the transition layer exceeds a critical thickness, the crystalline quality of the epilayer becomes lower and the crack density increases. (paper)

Use of surfactants to control island size and density

Science.gov (United States)

Merrell, Jason; Liu, Feng; Stringfellow, Gerald B.

2017-08-15

Methods of controlling island size and density on an OMVPE growth film may comprise adding a surfactant at a critical concentration level, allowing a growth phase for a first period of time, and ending the growth phase when desired island size and density are achieved. For example, the island size and density of an OMVPE grown InGaN thin film may be controlled by adding an antimony surfactant at a critical concentration level.

Self-assisted GaAs nanowires with selectable number density on Silicon without oxide layer

International Nuclear Information System (INIS)

Bietti, S; Somaschini, C; Esposito, L; Sanguinetti, S; Frigeri, C; Fedorov, A; Geelhaar, L

2014-01-01

We present the growth of self-assisted GaAs nanowires (NWs) with selectable number density on bare Si(1 1 1), not covered by the silicon oxide. We determine the number density of the NWs by initially self-assembling GaAs islands on whose top a single NW is nucleated. The number density of the initial GaAs base islands can be tuned by droplet epitaxy and the same degree of control is then transferred to the NWs. This procedure is completely performed during a single growth in an ultra-high vacuum environment and requires neither an oxide layer covering the substrate, nor any pre-patterning technique. (paper)

Magnetic properties of (Mn1-xRux)3Ga alloys

International Nuclear Information System (INIS)

Hori, T.; Akimitsu, M.; Miki, H.; Ohoyoama, K.; Yamaguchi, Y.

2002-01-01

We found that the pseudo binary alloys Mn 1-x Ru x 3 Ga, with 0.33≤x≤0.67, have an ordered b.c.c. structure. The lattice constant a is almost constant with respect to x: a=6.000 A for x=0.33 and a=5.992 A for x=0.67. For the alloy with x=0.33, i.e. Mn 2 RuGa, the magnetization is almost saturated in a field of 20 kOe. The saturation magnetization at 4.2 K is 23 emu/g, and the Curie temperature, T C , is 460 K. The T C of (Mn 1-x Ru x ) 3 Ga decreases almost linearly with increasing x, and it vanishes around x=0.67 (MnRu 2 Ga). We also determined atomic and magnetic structures from neutron diffraction experiments. The alloy Mn 2 RuGa (x=0.33) has an ordered structure of CuHg 2 Ti type; the magnetic Mn atoms mainly occupy the 4a (0,0,0) and 4d (3/4,3/4,3/4) sites. We also observed that the magnetic moments of Mn atoms on the 4a and 4d sites are antiparallel to each other; values of the magnetic moment are μ a =4.6 and μ d =3.3 μ B per Mn atom. (orig.)

Determinants of orchid species diversity in world islands

Czech Academy of Sciences Publication Activity Database

Traxmandlová, Iva; Ackerman, J. D.; Tremblay, R. L.; Roberts, D.L.; Štípková, Zuzana; Kindlmann, Pavel

2018-01-01

Roč. 217, č. 1 (2018), s. 12-15 ISSN 0028-646X R&D Projects: GA MŠk(CZ) LO1415; GA ČR GB14-36098G Institutional support: RVO:86652079 Keywords : habitat diversity * island biogeography * latitude * Orchidaceae * species richness * species–area relationship Subject RIV: EF - Botanics OBOR OECD: Plant sciences, botany Impact factor: 7.330, year: 2016

Structure and magnetoresistance of La0.67Ca0.33MnO3 films grown coherently on (001)NdGaO3

International Nuclear Information System (INIS)

Bojkov, Yu.A.; Danilov, V.A.; Bojkov, A.Yu.

2003-01-01

The (001) La 0.67 Ca 0.33 MnO 3 films, 40-120 nm thick, grown through the method of the laser evaporation on the (001)NdGaO 3 , are studied. The crystalline lattice parameters, measured for the La 0.67 Ca 0.33 MnO 3 film in the substrate plane α parallel = 3.851 A and along the normal to its surface α perpendicular = 3.850 A practically coincide with the parameter of the pseudocubic elementary cell of the neodymium gallate. The elementary cell volume in the La 0.67 Ca 0.33 MnO 3 film was insignificantly lesser than the corresponding value for the stoichiometric voluminous samples. The position of the maximum on the specific resistance dependence on the temperature did not depend on the La 0.67 Ca 0.33 MnO 3 film thickness. The maximum values of the negative magnetoresistance (MR ≅ 0.25, H = 0.4 T) for the La 0.67 Ca 0.33 MnO 3 films were observed at the temperatures of 239-244 K [ru

Experimental characterization of true spontaneous emission rate of optically-pumped InGaAs/GaAs quantum-well laser structure

Directory of Open Access Journals (Sweden)

Q.-N. Yu

2017-08-01

Full Text Available In this paper, an experimental approach to acquiring true spontaneous emission rate of optically-pumped InGaAs/GaAs quantum-well laser structure is described. This method is based on a single edge-emitting laser chip with simple sample processing. The photoluminescence spectra are measured at both facets of the edge-emitting device and transformed to the spontaneous emission rate following the theory described here. The unusual double peaks appearing in the spontaneous emission rate spectra are observed for the InGaAs/GaAs quantum-well structure. The result is analyzed in terms of Indium-rich island and Model-Solid theories. The proposed method is suitable for electrically-pumped quantum-well laser structures, as well.

InGaAs/GaAs (110) quantum dot formation via step meandering

Energy Technology Data Exchange (ETDEWEB)

Diez-Merino, Laura; Tejedor, Paloma [Department of Nanostructures and Surfaces, Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049-Madrid (Spain)

2011-07-01

InGaAs (110) semiconductor quantum dots (QDs) offer very promising prospects as a material base for a new generation of high-speed spintronic devices, such as single electron transistors for quantum computing. However, the spontaneous formation of InGaAs QDs is prevented by two-dimensional (2D) layer-by-layer growth on singular GaAs (110) substrates. In this work we have studied, by using atomic force microscopy and photoluminescence spectroscopy (PL), the growth of InGaAs/GaAs QDs on GaAs (110) stepped substrates by molecular beam epitaxy (MBE), and the modification of the adatom incorporation kinetics to surface steps in the presence of chemisorbed atomic hydrogen. The as-grown QDs exhibit lateral dimensions below 100 nm and emission peaks in the 1.35-1.37 eV range. It has been found that a step meandering instability derived from the preferential attachment of In adatoms to [110]-step edges relative to [11n]-type steps plays a key role in the destabilization of 2D growth that leads to 3D mound formation on both conventional and H-terminated vicinal substrates. In the latter case, the driving force for 3D growth via step meandering is enhanced by H-induced upward mass transport in addition to the lower energy cost associated with island formation on H-terminated substrates, which results in a high density array of InGaAs/GaAs dots selectively nucleated on the terrace apices with reduced lateral dimensions and improved PL efficiency relative to those of conventional MBE-grown samples.

InGaAs/GaAs (110) quantum dot formation via step meandering

International Nuclear Information System (INIS)

Diez-Merino, Laura; Tejedor, Paloma

2011-01-01

InGaAs (110) semiconductor quantum dots (QDs) offer very promising prospects as a material base for a new generation of high-speed spintronic devices, such as single electron transistors for quantum computing. However, the spontaneous formation of InGaAs QDs is prevented by two-dimensional (2D) layer-by-layer growth on singular GaAs (110) substrates. In this work we have studied, by using atomic force microscopy and photoluminescence spectroscopy (PL), the growth of InGaAs/GaAs QDs on GaAs (110) stepped substrates by molecular beam epitaxy (MBE), and the modification of the adatom incorporation kinetics to surface steps in the presence of chemisorbed atomic hydrogen. The as-grown QDs exhibit lateral dimensions below 100 nm and emission peaks in the 1.35-1.37 eV range. It has been found that a step meandering instability derived from the preferential attachment of In adatoms to [110]-step edges relative to [11n]-type steps plays a key role in the destabilization of 2D growth that leads to 3D mound formation on both conventional and H-terminated vicinal substrates. In the latter case, the driving force for 3D growth via step meandering is enhanced by H-induced upward mass transport in addition to the lower energy cost associated with island formation on H-terminated substrates, which results in a high density array of InGaAs/GaAs dots selectively nucleated on the terrace apices with reduced lateral dimensions and improved PL efficiency relative to those of conventional MBE-grown samples.

Bartolome Island, Galapagos Stable Oxygen Calibration Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Galapagos Coral Stable Oxygen Calibration Data. Sites: Bartolome Island: 0 deg, 17'S, 90 deg 33' W. Champion Island: 1 deg, 15'S, 90 deg, 05' W. Urvina Bay (Isabela...

Champion Island, Galapagos Stable Oxygen Calibration Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Galapagos Coral Stable Oxygen Calibration Data. Sites: Bartolome Island: 0 deg, 17 min S, 90 deg 33 min W. Champion Island: 1 deg, 15 min S, 90 deg, 05 min W. Urvina...

The sandwich InGaAs/GaAs quantum dot structure for IR photoelectric detectors

International Nuclear Information System (INIS)

Moldavskaya, L. D.; Vostokov, N. V.; Gaponova, D. M.; Danil'tsev, V. M.; Drozdov, M. N.; Drozdov, Yu. N.; Shashkin, V. I.

2008-01-01

A new possibility for growing InAs/GaAs quantum dot heterostructures for infrared photoelectric detectors by metal-organic vapor-phase epitaxy is discussed. The specific features of the technological process are the prolonged time of growth of quantum dots and the alternation of the low-and high-temperature modes of overgrowing the quantum dots with GaAs barrier layers. During overgrowth, large-sized quantum dots are partially dissolved, and the secondary InGaAs quantum well is formed of the material of the dissolved large islands. In this case, a sandwich structure is formed. In this structure, quantum dots are arranged between two thin layers with an increased content of indium, namely, between the wetting InAs layer and the secondary InGaAs layer. The height of the quantum dots depends on the thickness of the GaAs layer grown at a comparatively low temperature. The structures exhibit intraband photoconductivity at a wavelength around 4.5 μm at temperatures up to 200 K. At 90 K, the photosensitivity is 0.5 A/W, and the detectivity is 3 x 10 9 cm Hz 1/2 W -1

33 CFR 110.156 - Randall Bay, Freeport, Long Island, N.Y.

Science.gov (United States)

2010-07-01

... Island, N.Y. 110.156 Section 110.156 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY ANCHORAGES ANCHORAGE REGULATIONS Anchorage Grounds § 110.156 Randall Bay, Freeport, Long Island, N.Y. (a) The anchorage grounds. Southward of a line 312 feet south of and parallel to the south side...

The nucleation of HCl and Cl{sub 2}-based HVPE GaN on mis-oriented sapphire substrates

Energy Technology Data Exchange (ETDEWEB)

Bohnen, Tim; Dreumel, Gerbe W.G. van; Enckevort, Willem J.P. van; Ashraf, Hina; Jong, Aryan E.F. de; Hageman, Paul R.; Vlieg, Elias [IMM, Radboud University, Nijmegen (Netherlands); Weyher, Jan L. [Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw (Poland)

2010-07-15

The nucleation of both classic HCl-based and novel Cl{sub 2{sup -}} based HVPE GaN on mis-oriented sapphire substrates was investigated. The use of Cl{sub 2}in HVPE increases the growth rate by a factor of 4-5 and strongly reduces the parasitic deposition, allowing for the growth of much thicker wafers than HCl-based HVPE. Morphological SEM surface studies of the HCl-based HVPE sample surface show that at 600 C a nanocrystalline layer is deposited on the sapphire. During the subsequent annealing phase, the morphology changes to a {mu}m-sized island structure. During overgrowth at 1080 C, the islands coalesce. Small voids or pinholes are then formed in between the coalescing GaN islands. These pinholes lead to numerous pits on the surface of the GaN at thicknesses of 5 {mu}m. The pits disappear during continued overgrowth and can no longer be found on the surface, when the GaN film reaches a thickness of 45 {mu}m. This particular coalescence mechanism also applies to Cl{sub 2}-based HVPE GaN on sapphire (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Orientation dependence and tension/compression asymmetry of shape memory effect and superelasticity in ferromagnetic Co40Ni33Al27, Co49Ni21Ga30 and Ni54Fe19Ga27 single crystals

International Nuclear Information System (INIS)

Chumlyakov, Y.; Panchenko, E.; Kireeva, I.; Karaman, I.; Sehitoglu, H.; Maier, H.J.; Tverdokhlebova, A.; Ovsyannikov, A.

2008-01-01

In the present study the effects of crystal axis orientation, stress state (tension/compression) and test temperature on shape memory effect and superelasticity of Ni 54 Fe 19 Ga 27 (I), Co 40 Ni 33 Al 27 (II), Co 49 Ni 21 Ga 30 (III) (numbers indicate at.%) single crystals were investigated. The shape memory effect, the start temperature of superelasticity T 1 and the mechanical hysteresis Δσ were found to be dependent on crystal axis orientation and stress state. Superelasticity was observed at T 1 = A f (A f , reverse transformation-finish temperature) in tension/compression for [0 0 1]-oriented Ni-Fe-Ga crystals and in compression for [0 0 1]-oriented Co-Ni-Ga crystals, which all displayed a small mechanical hysteresis (Δσ ≤ 30 MPa). An increase in Δσ of up to 90 MPa in the Co-Ni-Al and the Co-Ni-Ga crystals lead to stabilization of the stress-induced martensite, and an increase in to T 1 = A f + Δ. The maximal value of Δ (75 K) was found in [0 0 1]-oriented Co-Ni-Al crystals in tension. A thermodynamic criterion describing the dependencies of the start temperature of superelasticity T 1 on crystal axis orientation, stress state and the magnitude of mechanical hysteresis is discussed

Cubic AlGaN/GaN structures for device application

Energy Technology Data Exchange (ETDEWEB)

Schoermann, Joerg

2007-05-15

The aim of this work was the growth and the characterization of cubic GaN, cubic AlGaN/GaN heterostructures and cubic AlN/GaN superlattice structures. Reduction of the surface and interface roughness was the key issue to show the potential for the use of cubic nitrides in futur devices. All structures were grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. In situ reflection high energy electron diffraction was first investigated to determine the Ga coverage of c-GaN during growth. Using the intensity of the electron beam as a probe, optimum growth conditions were found when a 1 monolayer coverage is formed at the surface. GaN samples grown under these conditions reveal excellent structural properties. On top of the c-GaN buffer c-AlGaN/GaN single and multiple quantum wells were deposited. The well widths ranged from 2.5 to 7.5 nm. During growth of Al{sub 0.15}Ga{sub 0.85}N/GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. We observed strong room-temperature, ultraviolet photoluminescence at about 3.3 eV with a minimum linewidth of 90 meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson- Schroedinger model calculation. We found that piezoelectric effects are absent in c-III nitrides with a (001) growth direction. Intersubband transition in the wavelength range from 1.6 {mu}m to 2.1 {mu}m was systematically investigated in AlN/GaN superlattices (SL), grown on 100 nm thick c-GaN buffer layers. The SLs consisted of 20 periods of GaN wells with a thickness between 1.5 nm and 2.1 nm and AlN barriers with a thickness of 1.35 nm. The first intersubband transitions were observed in metastable cubic III nitride structures in the range between 1.6 {mu}m and 2.1 {mu}m. (orig.)

Step-flow growth mode instability of N-polar GaN under N-excess

International Nuclear Information System (INIS)

Chèze, C.; Sawicka, M.; Siekacz, M.; Łucznik, B.; Boćkowski, M.; Skierbiszewski, C.; Turski, H.; Cywiński, G.; Smalc-Koziorowska, J.; Weyher, J. L.; Kryśko, M.

2013-01-01

GaN layers were grown on N-polar GaN substrates by plasma-assisted molecular beam epitaxy under different III/V ratios. Ga-rich conditions assure step-flow growth with atomically flat surface covered by doubly-bunched steps, as for Ga-polar GaN. Growth under N-excess however leads to an unstable step-flow morphology. Particularly, for substrates slightly miscut towards , interlacing fingers are covered by atomic steps pinned on both sides by small hexagonal pits. In contrast, a three-dimensional island morphology is observed on the Ga-polar equivalent sample. We attribute this result to lower diffusion barriers on N-polar compared to Ga-polar GaN under N-rich conditions

Phonon deformation potentials of hexagonal GaN studied by biaxial stress modulation

Directory of Open Access Journals (Sweden)

Jun-Yong Lu

2011-09-01

Full Text Available In this work, a biaxial stress modulation method, combining the microfabrication technique, finite element analysis and a weighted averaging process, was developed to study piezospectroscopic behavior of hexagonal GaN films, epitaxially grown by metalorganic chemical vapor deposition on c-sapphire and Si (111 substrates. Adjusting the size of patterned islands, various biaxial stress states could be obtained at the island centers, leading to abundant stress-Raman shift data. With the proposed stress modulation method, the Raman biaxial stress coefficients of E2H and A1 (LO phonons of GaN were determined to be 3.43 cm-1/GPa and 2.34 cm-1/GPa, respectively.

Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors

Energy Technology Data Exchange (ETDEWEB)

Naresh-Kumar, G., E-mail: naresh.gunasekar@strath.ac.uk; Trager-Cowan, C. [Dept of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Vilalta-Clemente, A.; Morales, M.; Ruterana, P. [CIMAP UMR 6252 CNRS-ENSICAEN-CEA-UCBN 14050 Caen Cedex (France); Pandey, S.; Cavallini, A.; Cavalcoli, D. [Dipartimento di Fisica Astronomia, Università di Bologna, 40127 Bologna (Italy); Skuridina, D.; Vogt, P.; Kneissl, M. [Institute of Solid State Physics, Technical University Berlin, 10623 Berlin (Germany); Behmenburg, H.; Giesen, C.; Heuken, M. [AIXTRON SE, Kaiserstr. 98, 52134 Herzogenrath (Germany); Gamarra, P.; Di Forte-Poisson, M. A. [Thales Research and Technology, III-V Lab, 91460 Marcoussis (France); Patriarche, G. [LPN, Route de Nozay, 91460 Marcoussis (France); Vickridge, I. [Institut des NanoSciences, Université Pierre et Marie Curie, 75015 Paris (France)

2014-12-15

We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3μm)/ AlN(100nm)/Al{sub 2}O{sub 3} high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

Multicharacterization approach for studying InAl(GaN/Al(GaN/GaN heterostructures for high electron mobility transistors

Directory of Open Access Journals (Sweden)

G. Naresh-Kumar

2014-12-01

Full Text Available We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(GaN(33nm barrier/Al(GaN(1nm interlayer/GaN(3μm/ AlN(100nm/Al2O3 high electron mobility transistor (HEMT heterostructure grown by metal organic vapor phase epitaxy (MOVPE. In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(GaN interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

Residual thermal desorption studies of Ga adatoms on trenched Si(5 5 12) surface

International Nuclear Information System (INIS)

Kumar, Praveen; Kumar, Mahesh; Shivaprasad, S.M.

2013-01-01

We present here the thermal stability studies of the room temperature adsorbed Ga/Si(5 5 12) interfaces in the monolayer coverage regime, using AES and LEED as in-situ UHV characterization probes. Ga grows in Stranski–Krastanov growth mode at RT on the 2 × 1 reconstructed Si(5 5 12) surface where islands form on top of 2 ML of flat pseudomorphic Ga, yielding a (1 × 1) LEED pattern for coverages of 1.2 ML and above. When this RT adsorbed Ga/Si(5 5 12) interface is annealed at different temperatures, initially the strained Ga adlayers relax by agglomerating into 3D islands on top of a single Ga monolayer with an activation energy of 0.19 eV in the temperature range of 200–300 °C. The remnant Ga monolayer with a sharp (1 × 1) LEED pattern desorbs at temperature >400 °C, yielding the (1 1 2)–6 × 1 and 2 × (3 3 7) sub-monolayer superstructural. Finally at 720 °C Ga completely desorbs from the surface and leaves the clean 2 × 1 reconstructed Si(5 5 12) surface. The studies demonstrate the richness of the atomically trenched high index Si(5 5 12) surface, in obtaining several anisotropic features that can be used as templates to grow self-assembled nanostructures.

Residual thermal desorption studies of Ga adatoms on trenched Si(5 5 12) surface

Energy Technology Data Exchange (ETDEWEB)

Kumar, Praveen [Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India); ISOM, Universidad Politecnia de Madrid, 28040 (Spain); Kumar, Mahesh [Physics and Energy Harvesting Group, National Physical Laboratory, New Delhi 110012 (India); Shivaprasad, S.M., E-mail: smsprasad@jncasr.ac.in [Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)

2013-10-01

We present here the thermal stability studies of the room temperature adsorbed Ga/Si(5 5 12) interfaces in the monolayer coverage regime, using AES and LEED as in-situ UHV characterization probes. Ga grows in Stranski–Krastanov growth mode at RT on the 2 × 1 reconstructed Si(5 5 12) surface where islands form on top of 2 ML of flat pseudomorphic Ga, yielding a (1 × 1) LEED pattern for coverages of 1.2 ML and above. When this RT adsorbed Ga/Si(5 5 12) interface is annealed at different temperatures, initially the strained Ga adlayers relax by agglomerating into 3D islands on top of a single Ga monolayer with an activation energy of 0.19 eV in the temperature range of 200–300 °C. The remnant Ga monolayer with a sharp (1 × 1) LEED pattern desorbs at temperature >400 °C, yielding the (1 1 2)–6 × 1 and 2 × (3 3 7) sub-monolayer superstructural. Finally at 720 °C Ga completely desorbs from the surface and leaves the clean 2 × 1 reconstructed Si(5 5 12) surface. The studies demonstrate the richness of the atomically trenched high index Si(5 5 12) surface, in obtaining several anisotropic features that can be used as templates to grow self-assembled nanostructures.

Strain management of AlGaN-based distributed Bragg reflectors with GaN interlayer grown by metalorganic chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Liu, Yuh-Shiuan; Kao, Tsung-Ting; Mehta, Karan; Jia, Xiao Jia; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D., E-mail: dupuis@gatech.edu [Center for Compound Semiconductors and School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr. NW, Atlanta, Georgia 30332-0250 (United States); Wang, Shuo; Xie, Hongen; Ponce, Fernando A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

2016-08-22

We report the crack-free growth of a 45-pair Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al{sub 0.30}Ga{sub 0.70}N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al{sub 0.04}Ga{sub 0.96}N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N DBR was able to be grown with an atomically smooth surface morphology. Smooth surfaces and sharp interfaces were observed throughout the structure using high-angle annular dark-field imaging in the STEM. The 45-pair AlGaN-based DBR provided a peak reflectivity of 95.4% at λ = 368 nm with a bandwidth of 15 nm.

Hydrogen Generation using non-polar coaxial InGaN/GaN Multiple Quantum Well Structure Formed on Hollow n-GaN Nanowires.

Science.gov (United States)

Park, Ji-Hyeon; Mandal, Arjun; Kang, San; Chatterjee, Uddipta; Kim, Jin Soo; Park, Byung-Guon; Kim, Moon-Deock; Jeong, Kwang-Un; Lee, Cheul-Ro

2016-08-24

This article demonstrates for the first time to the best of our knowledge, the merits of InGaN/GaN multiple quantum wells (MQWs) grown on hollow n-GaN nanowires (NWs) as a plausible alternative for stable photoelectrochemical water splitting and efficient hydrogen generation. These hollow nanowires are achieved by a growth method rather not by conventional etching process. Therefore this approach becomes simplistic yet most effective. We believe relatively low Ga flux during the selective area growth (SAG) aids the hollow nanowire to grow. To compare the optoelectronic properties, simultaneously solid nanowires are also studied. In this present communication, we exhibit that lower thermal conductivity of hollow n-GaN NWs affects the material quality of InGaN/GaN MQWs by limiting In diffusion. As a result of this improvement in material quality and structural properties, photocurrent and photosensitivity are enhanced compared to the structures grown on solid n-GaN NWs. An incident photon-to-current efficiency (IPCE) of around ~33.3% is recorded at 365 nm wavelength for hollow NWs. We believe that multiple reflections of incident light inside the hollow n-GaN NWs assists in producing a larger amount of electron hole pairs in the active region. As a result the rate of hydrogen generation is also increased.

Photoluminescence of Mg-doped m-plane GaN grown by MOCVD on bulk GaN substrates

OpenAIRE

Monemar, Bo; Paskov, Plamen; Pozina, Galia; Hemmingsson, Carl; Bergman, Peder; Lindgren, David; Samuelson, Lars; Ni, Xianfeng; Morkoç, Hadis; Paskova, Tanya; Bi, Zhaoxia; Ohlsson, Jonas

2011-01-01

Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 1018cm-3 to well above 1019 cm-3. The samples were grown with MOCVD at reduced pressure on low defect density m-plane bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9 eV to 3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependenc...

33 CFR 165.151 - Safety Zones; Long Island Sound annual fireworks displays.

Science.gov (United States)

2010-07-01

... annual fireworks displays. 165.151 Section 165.151 Navigation and Navigable Waters COAST GUARD... § 165.151 Safety Zones; Long Island Sound annual fireworks displays. (a) Safety Zones. The following...) Indian Harbor Yacht Club Fireworks Safety Zone. All waters of Long Island Sound off Greenwich CT, within...

Luminescence investigation of Cu(In,Ga)Se{sub 2}solar cells with different Ga-contents grown in a three-stage-process on glass substrate

Energy Technology Data Exchange (ETDEWEB)

Wendt, Kristin; Mueller, Mathias; Hempel, Thomas; Bertram, Frank; Christen, Juergen [Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg (Germany); Abou-Ras, Daniel; Rissom, Thorsten; Unold, Thomas; Schock, Hans-Werner [Helmholtz-Zentrum Berlin for Materials and Energy (Germany)

2011-07-01

A fundamental advantage of Cu(In,Ga)Se{sub 2} (CIGS) alloys as absorber materials in thin-film solar cells is their direct band gap energies which can be varied between 1.04 eV (CuInSe{sub 2}) and 1.68 eV (CuGaSe{sub 2}). Photoluminescence (PL) spectra of complete CIGS solar cells with a systematic variation of the Ga-content in the absorber layer will be presented. The CIGS cells investigated were grown on a Mo back contact sputtered on soda lime glass and have a Ga-concentration ranging over the entire range from CuInSe{sub 2} to CuGaSe{sub 2}. Samples with Ga-contents between 100 % and 33 % show two broad luminescence bands. In contrast, CuInSe{sub 2} exhibits only one broad luminescence band. Each band is composed of two or three different transitions. Varying excitation density over four orders of magnitude results for samples with Ga-content of 0 % and 33 % in a blueshift of the main peak with increasing excitation density. For higher Ga-concentrations, first a blue- and then a redshift of the dominating peak with increasing excitation density is visible. The temperature dependence of the PL spectra is investigated going from 4 K to 300 K.

CpG island protects Rous sarcoma virus-derived vectors integrated into nonpermissive cells from DNA methylation and transcriptional suppression

Czech Academy of Sciences Publication Activity Database

Hejnar, Jiří; Hájková, P.; Plachý, Jiří; Elleder, Daniel; Stepanets, Volodymyr; Svoboda, Jan

2001-01-01

Roč. 98, č. 2 (2001), s. 565-569 ISSN 0027-8424 R&D Projects: GA ČR GA312/97/P082; GA ČR GA312/98/0825 Keywords : CpG island * provirus silencing * DNA methylation Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 10.890, year: 2001

3.3 Ga SHRIMP U-Pb zircon age of a felsic metavolcanic rock from the Mundo Novo greenstone belt in the São Francisco craton, Bahia (NE Brazil)

Science.gov (United States)

Peucat, J. J.; Mascarenhas, J. F.; Barbosa, J. S. F.; de Souza, S. L.; Marinho, M. M.; Fanning, C. M.; Leite, C. M. M.

2002-07-01

Felsic metavolcanics associated with supracrustal rocks provide U-Pb zircon and Sm-Nd TDM ages of approximately 3.3 Ga, which establish an Archean age of the Mundo Novo greenstone belt. A granodioritic gneiss from the Mairi complex, located on the eastern boundary of the Mundo Novo greenstone belt, exhibits a zircon evaporation minimum age of 3.04 Ga and a Nd model age of 3.2 Ga. These results constrain the occurrence of at least three major geological units in this area: the Archean Mundo Novo greenstone belt, the Archean Mairi gneisses, and the adjoining Paleoproterozoic (<2.1 Ga) Jacobina sedimentary basin. The Jacobina basin follows the same trend as the Archean structure, extending southward to the Contendas-Mirante belt, in which a similar Archean-Paleoproterozoic association appears. We postulate that during the Paleoproterozoic in the eastern margin of the Gavião block, these Archean greenstone belts constituted a zone of weakness along which a late-stage orogenic sedimentary basin developed.

Self-Assembled Local Artificial Substrates of GaAs on Si Substrate

Directory of Open Access Journals (Sweden)

Frigeri C

2010-01-01

Full Text Available Abstract We propose a self-assembling procedure for the fabrication of GaAs islands by Droplet Epitaxy on silicon substrate. Controlling substrate temperature and amount of supplied gallium is possible to tune the base size of the islands from 70 up to 250 nm and the density from 107 to 109 cm−2. The islands show a standard deviation of base size distribution below 10% and their shape evolves changing the aspect ratio from 0.3 to 0.5 as size increases. Due to their characteristics, these islands are suitable to be used as local artificial substrates for the integration of III–V quantum nanostructures directly on silicon substrate.

SiO2/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistors

Science.gov (United States)

Watanabe, Kenta; Terashima, Daiki; Nozaki, Mikito; Yamada, Takahiro; Nakazawa, Satoshi; Ishida, Masahiro; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-06-01

Stacked gate dielectrics consisting of wide bandgap SiO2 insulators and thin aluminum oxynitride (AlON) interlayers were systematically investigated in order to improve the performance and reliability of AlGaN/GaN metal–oxide–semiconductor (MOS) devices. A significantly reduced gate leakage current compared with that in a single AlON layer was achieved with these structures, while maintaining the superior thermal stability and electrical properties of the oxynitride/AlGaN interface. Consequently, distinct advantages in terms of the reliability of the gate dielectrics, such as an improved immunity against electron injection and an increased dielectric breakdown field, were demonstrated for AlGaN/GaN MOS capacitors with optimized stacked structures having a 3.3-nm-thick AlON interlayer.

Spatial structure and associations in Pinus canariensis population at the treeline, Pico del Teide, Tenerife, Canary Islands

Czech Academy of Sciences Publication Activity Database

Šrůtek, Miroslav; Doležal, J.; Hara, T.

2002-01-01

Roč. 34, č. 2 (2002), s. 201-210 ISSN 1523-0430 R&D Projects: GA ČR(CZ) GA206/00/1445; GA AV ČR(CZ) KSK6005114 Institutional research plan: CEZ:AV0Z6005908 Keywords : Pinus canariensis * Canary Islands Subject RIV: EF - Botanics Impact factor: 0.964, year: 2002

The core element of a CpG island protects avian sarcoma and leukosis virus-derived vectors from transcriptional silencing

Czech Academy of Sciences Publication Activity Database

Šenigl, Filip; Plachý, Jiří; Hejnar, Jiří

2008-01-01

Roč. 82, č. 16 (2008), s. 7818-7827 ISSN 0022-538X R&D Projects: GA ČR GA204/05/0939; GA ČR GA523/07/1171 Institutional research plan: CEZ:AV0Z50520514 Keywords : anti-methylation protection * retroviral vector * CpG island Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 5.308, year: 2008

Characteristics of InAs/InGaAs/GaAs QDs on GeOI substrates with single-peak 1.3 µm room-temperature emission

International Nuclear Information System (INIS)

Liang, Y Y; Yoon, S F; Loke, W K; Ngo, C Y; Fitzgerald, E A

2012-01-01

GaAs-based quantum dot (QD) systems, especially InAs/InGaAs/GaAs QDs, have demonstrated superior device performances as compared with higher dimensional systems. However, to realize high-speed optical interconnects for Si-based electronics, one will need to grow the QDs on Si substrates. While it is promising to integrate the InAs/InGaAs/GaAs QDs on Si with the use of germanium-on-insulator-on-silicon (GeOI) substrates, reported results exhibit bimodal QD sizes and double emission peaks, i.e. unsatisfactory for realistic applications. In this paper, we showed that with an optimized GaAs buffer, single-peak 1.33 µm room-temperature emission can be obtained from InAs/InGaAs/GaAs QDs on GeOI substrates. (paper)

Band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterostructures measured by X-ray photoemission spectroscopy.

Science.gov (United States)

Sang, Ling; Zhu, Qin Sheng; Yang, Shao Yan; Liu, Gui Peng; Li, Hui Jie; Wei, Hong Yuan; Jiao, Chun Mei; Liu, Shu Man; Wang, Zhan Guo; Zhou, Xiao Wei; Mao, Wei; Hao, Yue; Shen, Bo

2014-01-01

The band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are measured by X-ray photoemission spectroscopy. A large forward-backward asymmetry is observed in the non-polar GaN/AlN and AlN/GaN heterojunctions. The valence-band offsets in the non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are determined to be 1.33 ± 0.16 and 0.73 ± 0.16 eV, respectively. The large valence-band offset difference of 0.6 eV between the non-polar GaN/AlN and AlN/GaN heterojunctions is considered to be due to piezoelectric strain effect in the non-polar heterojunction overlayers.

Initial Stages of GaAs/Au Eutectic Alloy Formation for the Growth of GaAs Nano wires

International Nuclear Information System (INIS)

Rosnita, M.; Yussof, W.; Zuhairi, I.; Zulkafli, O.; Samsudi, S.

2012-01-01

Annealing temperature plays an important role in the formation of an Au-Ga eutectic alloy. The effects of the annealing temperature on gold nanoparticles colloid and substrate surface were studied using AFM, FE-SEM and TEM. At 600 degree Celsius, the layer of gold colloids particle formed an island in the state of molten eutectic alloy and absorbed evaporated metal-organics to formed nano wire (NW) underneath the alloy. Pit formed on the substrate surface due to the chemical reactions during the annealing process have an impact on the direction of growth of the NW. Without annealing, the NW formed vertically on the GaAs (100) surface. The growth direction depends on the original nucleation facets and surface energy when annealed. When annealed, the wire base is large and curved due to the migration of Ga atoms on the substrate surface towards the tip of the wire and the line tension between the substrate surface and gold particle. (author)

Growth-temperature- and thermal-anneal-induced crystalline reorientation of aluminum on GaAs (100) grown by molecular beam epitaxy

International Nuclear Information System (INIS)

Liu, H. F.; Chua, S. J.; Xiang, N.

2007-01-01

The authors investigated the growth of Al thin films on GaAs (100) substrates by molecular beam epitaxy. It is found that the growth at 550 degree sign C results in a texture that consists of (100)Al[010](parallel sign)(100)GaAs[011] and (100)Al[010](parallel sign)(100)GaAs[010] rotated 45 degree sign with respect to each other, while the growth at 300 degree sign C leads to a mixture phase of (100)Al[010](parallel sign)(100)GaAs[011] and (110)Al[001](parallel sign)(100)GaAs[011]. In situ annealing of the Al film grown at 300 degree sign C causes a reorientation of the crystalline from (100)Al[010](parallel sign)(100)GaAs[011] to (110)Al[001](parallel sign)(100)GaAs[011]. The grain sizes of the Al film are increased by the increased growth temperature and in situ annealing; the ratio of the exposed to the covered surface is not changed significantly by changing the growth temperature but decreased by annealing; and the small islands in between the large ones are removed by annealing. These observations are explained based on island migration and coalescence

Structural and optical features of InGaAs quantum dots grown on Si(001) substrates

CERN Document Server

Vdovin, V I; Rzaev, M M; Burbaev, T M

2002-01-01

A multilayer GaAs/SiGe/Si heterostructure with InGaAs quantum dots (QDs) embedded in a GaAs layer was grown by molecular beam epitaxy (MBE) on a Si(001) substrate. A step-graded Si sub 1 sub - sub x Ge sub x (0 <= x <= 1) buffer layer and a GaAs layer with In sub y Ga sub 1 sub sub - sub y As (y approx 0.5) QDs were deposited consecutively in two different MBE systems. The heterostructure exhibits intense photoluminescence in the region of 1.3 mu m at room temperature. Perfect crystal InGaAs islands with height less than 10 nm are the sources of this radiation.

Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy

International Nuclear Information System (INIS)

Chen, Yen-Ting; Araki, Tsutomu; Palisaitis, Justinas; Persson, Per O. Å.; Olof Holtz, Per; Birch, Jens; Chen, Li-Chyong; Chen, Kuei-Hsien; Nanishi, Yasushi

2013-01-01

Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (<35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a “narrow-pass” approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm

Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Chen, Yen-Ting [Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan (China); Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping (Sweden); Araki, Tsutomu [Department of Electrical and Electronic Engineering, Ritsumeikan University, 525-8577 Shiga (Japan); Palisaitis, Justinas; Persson, Per O. Å.; Olof Holtz, Per; Birch, Jens [Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping (Sweden); Chen, Li-Chyong [Center for Condensed Matter Sciences, National Taiwan University, 10617 Taipei, Taiwan (China); Chen, Kuei-Hsien [Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan (China); Center for Condensed Matter Sciences, National Taiwan University, 10617 Taipei, Taiwan (China); Nanishi, Yasushi [Global Innovation Research Organization, Ritsumeikan University, 525-8577 Shiga (Japan)

2013-11-11

Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (<35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a “narrow-pass” approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.

Distributional patterns of endemic, native and alien species along a roadside elevational gradient in Tenerife, Canary Islands

Czech Academy of Sciences Publication Activity Database

Bacaro, G.; Maccherini, S.; Chiarucci, A.; Jentsch, A.; Rocchini, D.; Torri, D.; Gioria, Margherita; Tordoni, E.; Martellos, S.; Altobelli, A.; Otto, R.; Escudero, C. G.; Fernández-Lugo, S.; Fernández-Palacios, J. M.; Arévalo, J. R.

2015-01-01

Roč. 16, č. 2 (2015), s. 223-234 ISSN 1585-8553 R&D Projects: GA ČR GA15-13491S Institutional support: RVO:67985939 Keywords : invasive plants * island invasibility * road disturbance Subject RIV: EH - Ecology, Behaviour Impact factor: 1.019, year: 2015

Enhancement of the 2DEG density in AlGaAs/InGaAs/GaAs P-HEMTs structures grown by MBE on (311)A and (111)A GaAs substrates

International Nuclear Information System (INIS)

Rekaya, S.; Sfaxi, L.; Bouzaiene, L.; Maaref, H.; Bru-Chevallier, C.

2008-01-01

The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al 0.33 Ga 0.7 As/In 0.1 Ga 0.9 As/GaAs have been grown by molecular beam epitaxy (MBE) on (311)A and (111)A GaAs substrates. The epitaxy of strain heterostructure on high index GaAs substrate has led to new growth phenomena, material properties and device applications. The photoluminescence (PL) spectra of the structures have been measured at low temperature. The dominant emission in the PL spectra is due to the recombination from the first electron (e1) subband to the first heavy-hole (hh1) subband (E 11 : e1-hh1). This feature (E 11 ) is a relatively broad peak and has a typical asymmetric line shape. The transformation of the PL spectra in the close vicinity of the Fermi edge (E F ) under different excitation densities gives strong evidence for the Fermi Edge Singularity (FES) existence. The density of the quasi-two-dimensional electron gas (2DEG) determined by PL study (n s PL ), is in sufficient agreement with the values found from Hall measurements n s Hall at 77 K. The results prove an increase of the electron density in sample grown on GaAs (111)A and (311)A rather than in equivalent sample grown on (001) GaAs substrate. This effect is in good agreement with our theoretical prediction, which is based on a self-consistent solution of the coupled Schroedinger and Poisson equations

Seismic activity around and under Krakatau volcano, Sunda Arc: constraints to the source region of island arc volcanics

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

2002-01-01

Roč. 46, č. 3 (2002), s. 545-565 ISSN 0039-3169 R&D Projects: GA ČR GA205/97/0898; GA AV ČR IAA3012002 Institutional research plan: CEZ:AV0Z3012916 Keywords : Krakatau * Sunda Strait seismicity * island arc volcanism * subduction * Wadati-Benioff zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.571, year: 2002

Three dimensional atom probe imaging of GaAsSb quantum rings.

Science.gov (United States)

Beltrán, A M; Marquis, E A; Taboada, A G; Ripalda, J M; García, J M; Molina, S I

2011-07-01

Unambiguous evidence of ring-shaped self-assembled GaSb nanostructures grown by molecular beam epitaxy is presented on the basis of atom-probe tomography reconstructions and dark field transmission electron microscopy imaging. The GaAs capping process causes a strong segregation of Sb out of the center of GaSb quantum dots, leading to the self-assembled GaAs(x)Sb(1-x) quantum rings of 20-30 nm in diameter with x ∼ 0.33. Copyright © 2011 Elsevier B.V. All rights reserved.

Persistent photoconductivity in AlGaN/GaN heterojunction channels caused by the ionization of deep levels in the AlGaN barrier layer

International Nuclear Information System (INIS)

Murayama, H.; Akiyama, Y.; Niwa, R.; Sakashita, H.; Sakaki, H.; Kachi, T.; Sugimoto, M.

2013-01-01

Time-dependent responses of drain current (I d ) in an AlGaN/GaN HEMT under UV (3.3 eV) and red (2.0 eV) light illumination have been studied at 300 K and 250 K. UV illumination enhances I d by about 10 %, indicating that the density of two-dimensional electrons is raised by about 10 12 cm −2 . When UV light is turned off at 300 K, a part of increased I d decays quickly but the other part of increment is persistent, showing a slow decay. At 250 K, the majority of increment remains persistent. It is found that such a persistent increase of I d at 250 K can be partially erased by the illumination of red light. These photo-responses are explained by a simple band-bending model in which deep levels in the AlGaN barrier get positively charged by the UV light, resulting in a parabolic band bending in the AlGaN layer, while some potion of those deep levels are neutralized by the red light

77 FR 22217 - Drawbridge Operation Regulation; Oregon Slough, Hayden Island, OR

Science.gov (United States)

2012-04-13

... DEPARTMENT OF HOMELAND SECURITY Coast Guard 33 CFR Part 117 [Docket No. USCG-2012-0290] Drawbridge Operation Regulation; Oregon Slough, Hayden Island, OR AGENCY: Coast Guard, DHS. ACTION: Notice of temporary..., at Hayden Island, OR. This deviation is necessary to accommodate maintenance of the train signaling...

Suppression of metastable-phase inclusion in N-polar (0001¯) InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy

International Nuclear Information System (INIS)

Shojiki, Kanako; Iwabuchi, Takuya; Kuboya, Shigeyuki; Choi, Jung-Hun; Tanikawa, Tomoyuki; Hanada, Takashi; Katayama, Ryuji; Matsuoka, Takashi; Usami, Noritaka

2015-01-01

The metastable zincblende (ZB) phase in N-polar (0001 ¯ ) (−c-plane) InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy is elucidated by the electron backscatter diffraction measurements. From the comparison between the −c-plane and Ga-polar (0001) (+c-plane), the −c-plane MQWs were found to be suffered from the severe ZB-phase inclusion, while ZB-inclusion is negligible in the +c-plane MQWs grown under the same growth conditions. The ZB-phase inclusion is a hurdle for fabricating the −c-plane light-emitting diodes because the islands with a triangular shape appeared on a surface in the ZB-phase domains. To improve the purity of stable wurtzite (WZ)-phase, the optimum conditions were investigated. The ZB-phase is dramatically eliminated with decreasing the V/III ratio and increasing the growth temperature. To obtain much-higher-quality MQWs, the thinner InGaN wells and the hydrogen introduction during GaN barriers growth were tried. Consequently, MQWs with almost pure WZ phase and with atomically smooth surface have been demonstrated

Three dimensional atom probe imaging of GaAsSb quantum rings

International Nuclear Information System (INIS)

Beltran, A.M.; Marquis, E.A.; Taboada, A.G.; Ripalda, J.M.; Garcia, J.M.; Molina, S.I.

2011-01-01

Unambiguous evidence of ring-shaped self-assembled GaSb nanostructures grown by molecular beam epitaxy is presented on the basis of atom-probe tomography reconstructions and dark field transmission electron microscopy imaging. The GaAs capping process causes a strong segregation of Sb out of the center of GaSb quantum dots, leading to the self-assembled GaAs x Sb 1-x quantum rings of 20-30 nm in diameter with x∼0.33. -- Highlights: → Atom-probe tomography resolves QR morphology of GaSb self-assembled GaSb buried nanostructures. → From atom-probe tomography compositional distribution has been obtained. → Strong segregation and morphological changes are observed with respect to uncapped QR.

On the island biogeography of aliens: a global analysis of the richness of alien plant and bird species on oceanic islands

Czech Academy of Sciences Publication Activity Database

Blackburn, T. M.; Delean, S.; Pyšek, Petr; Cassey, P.

2016-01-01

Roč. 25, č. 7 (2016), s. 859-868 ISSN 1466-822X R&D Projects: GA ČR GB14-36079G Grant - others:AV ČR(CZ) AP1002 Program:Akademická prémie - Praemium Academiae Institutional support: RVO:67985939 Keywords : plants * birds * island invasions Subject RIV: EH - Ecology, Behaviour Impact factor: 6.045, year: 2016

Validation of 68Ge/68Ga generator processing by chemical purification for routine clinical application of 68Ga-DOTATOC

International Nuclear Information System (INIS)

Asti, Mattia; De Pietri, Giovanni; Fraternali, Alessandro; Grassi, Elisa; Sghedoni, Roberto; Fioroni, Federica; Roesch, Frank; Versari, Annibale; Salvo, Diana

2008-01-01

Introduction: Imaging of somatostatin receptor expressing tumours has been greatly enhanced by the use of 68 Ga-DOTATOC and PET/CT. Methods: In this work, a purification method for the 68 Ge/ 68 Ga generator eluate and a method to produce 68 Ga-DOTATOC suitable for clinical use were evaluated. The generator eluate was purified and concentrated on a cation-exchange cartridge in HCl/acetone media. The efficacy of this procedure in eliminating metal impurities from the 68 Ga solution was investigated by ICP-MS. The radiotracer quality was evaluated by radio-TLC, GC and γ-ray spectrometry. Results: 68 Ga-DOTATOC preparations (n=33) were carried out with a mean synthesis yield of 59.3±2.8% (not corrected for decay) and a batch activity ranging from 555 to 296 MBq. The radiochemical and radionuclidic purity were >98% and 99.9999%, respectively. With this purification process, >95% of the Fe(III), Zn(II) and Mn(II) were eliminated from the solution. Conclusions: 68 Ga-DOTATOC produced with this method can be efficiently used in nuclear medicine departments for PET evaluations

33 CFR 334.1160 - San Pablo Bay, Calif.; target practice area, Mare Island Naval Shipyard, Vallejo.

Science.gov (United States)

2010-07-01

... practice area, Mare Island Naval Shipyard, Vallejo. 334.1160 Section 334.1160 Navigation and Navigable... REGULATIONS § 334.1160 San Pablo Bay, Calif.; target practice area, Mare Island Naval Shipyard, Vallejo. (a..., Mare Island Naval Shipyard, Vallejo, California, will conduct target practice in the area at intervals...

Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs

Energy Technology Data Exchange (ETDEWEB)

Timm, R.

2007-12-14

In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast

Analysis of the degradation induced by focused ion Ga3+ beam for the realization of piezoelectric nanostructures

International Nuclear Information System (INIS)

Remiens, D.; Liang, R. H.; Soyer, C.; Deresmes, D.; Troadec, D.; Quignon, S.; Da Costa, A.; Desfeux, R.

2010-01-01

Piezoelectric nanostructures (islands of dimensions in the lateral size range 50-500 nm) have been fabricated by focused Ga 3+ ion beam (FIB) etching on PbZr 0.54 Ti 0.46 O 3 thin films obtained by magnetron sputtering. The degradation induced by the etching process is investigated through the evolution of electromechanical activity measured by means of local piezoelectric hysteresis loops produced by piezoresponse force microscopy. The analysis of surface potential is performed by kelvin force microscopy and the measurement of current-voltage curves is carried out by conducting atomic force microscopy. Two kinds of structures, namely one based on crystallized films and the other based on amorphous ones, were studied. In this latter case, the amorphous films are postannealed after etching to obtain crystallized structure. For the structures based on the crystallized and then etched films, no piezoelectric signal was registered that evidences a serious degradation of material induced by Ga 3+ ion implantation. For the structures based on the films etched in amorphous state and then crystallized, the piezoresponse signal was near to that of the reference films (crystallized and not etched) whatever were the ion dose and the island dimensions. Even for very small lateral size (50 nm), no size effect was observed. The island shapes fabricated by Ga 3+ FIB etching process (islands with less than 50 nm lateral size) show a limitation of FIB processing and electron beam lithography seems to be necessary.

Kinetic Monte Carlo simulations of three-dimensional self-assembled quantum dot islands

International Nuclear Information System (INIS)

Song Xin; Feng Hao; Liu Yu-Min; Yu Zhong-Yuan; Yin Hao-Zhi

2014-01-01

By three-dimensional kinetic Monte Carlo simulations, the effects of the temperature, the flux rate, the total coverage and the interruption time on the distribution and the number of self-assembled InAs/GaAs (001) quantum dot (QD) islands are studied, which shows that a higher temperature, a lower flux rate and a longer growth time correspond to a better island distribution. The relations between the number of islands and the temperature and the flux rate are also successfully simulated. It is observed that for the total coverage lower than 0.5 ML, the number of islands decreases with the temperature increasing and other growth parameters fixed and the number of islands increases with the flux rate increasing when the deposition is lower than 0.6 ML and the other parameters are fixed. (condensed matter: structural, mechanical, and thermal properties)

The ghost of hybridizaion past: niche pre-emption is not the only eplanation of apparent monophyly in island endemics

Czech Academy of Sciences Publication Activity Database

Herben, Tomáš; Suda, Jan; Munclinger, P.

2005-01-01

Roč. 93, - (2005), s. 572-575 ISSN 0022-0477 R&D Projects: GA ČR(CZ) GA206/04/0081 Institutional research plan: CEZ:AV0Z60050516 Keywords : hybridization * Canary Islands * niche preemption Subject RIV: EF - Botanics Impact factor: 4.277, year: 2005

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts

International Nuclear Information System (INIS)

Lü Yuan-Jie; Lin Zhao-Jun; Zhang Yu; Meng Ling-Guo; Cao Zhi-Fang; Luan Chong-Biao; Chen Hong; Wang Zhan-Guo

2011-01-01

Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N 2 ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (I—V) and capacitance—voltage (C—V) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

33 CFR 117.169 - Mare Island Strait and the Napa River.

Science.gov (United States)

2010-07-01

... Strait and the Napa River. (a) The draw of the Mare Island Drawbridge, mile 2.8, at Vallejo shall open on... may contact the City of Vallejo via the same telephone number to schedule drawspan operation. (b) The...

GaN Micromechanical Resonators with Meshed Metal Bottom Electrode.

Science.gov (United States)

Ansari, Azadeh; Liu, Che-Yu; Lin, Chien-Chung; Kuo, Hao-Chung; Ku, Pei-Cheng; Rais-Zadeh, Mina

2015-03-17

This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO₂) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient ( d 33 ) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF₂) etch and therefore eliminating the need for backside lithography and etching.

Direct observation of indium compositional fluctuation in GaInN/GaN multi-quantum wells using an X-ray micro-beam from the 8-GeV storage ring

Energy Technology Data Exchange (ETDEWEB)

Miyajima, Takao; Uemura, Shigeaki; Kudo, Yoshihiro; Fuutagawa, Noriyuki [Materials Laboratories, Sony Corporation, 4-14-1 Asahi-cho, Atsugi, Kanagawa 243-0014 (Japan); Terada, Yasuko [Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)

2008-07-01

We measured the micrometer-scale fluctuation of the indium contents in a 50 {mu}m x 30 {mu}m region of annealed Ga{sub 0.8}In{sub 0.2}N/GaN multi quantum wells by mapping the counts of indium fluorescent X-rays excited by a 1.3 {mu}m x 3.8 {mu}m X-ray micro-beam. The mapping indicates that two distinct regions - indium-rich and indium-poor regions - are formed by the annealing. The indium contents in the island-shaped low-indium regions are 20% less than in the surrounding high-indium region. As the island-shaped low-indium regions clearly coincide with the low-radiative regions as observed by Hg-lamp-excited fluorescent microscopy, we believe that the low-radiative regions are a result not of indium segregation but of the generation of defects such as plane defects. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Nanoscale interfacial engineering to grow Ge on Si as virtual substrates and subsequent integration of GaAs

International Nuclear Information System (INIS)

Leonhardt, Darin; Sheng, Josephine; Cederberg, Jeffrey G.; Li Qiming; Carroll, Malcolm S.; Han, Sang M.

2010-01-01

We have demonstrated the scalability of a process previously dubbed as Ge 'touchdown' on Si to substantially reduce threading dislocations below 10 7 /cm 2 in a Ge film grown on a 2 inch-diameter chemically oxidized Si substrate. This study also elucidates the overall mechanism of the touchdown process. The 1.4 nm thick chemical oxide is first formed by immersing Si substrates in a solution of H 2 O 2 and H 2 SO 4 . Subsequent exposure to Ge flux creates 3 to 7 nm-diameter voids in the oxide at a density greater than 10 11 /cm 2 . Comparison of data taken from many previous studies and ours shows an exponential dependence between oxide thickness and inverse temperature of void formation. Additionally, exposure to a Ge or Si atom flux decreases the temperature at which voids begin to form in the oxide. These results strongly suggest that Ge actively participates in the reaction with SiO 2 in the void formation process. Once voids are created in the oxide under a Ge flux, Ge islands selectively nucleate within the void openings on the newly exposed Si. Island nucleation and growth then compete with the void growth reaction. At substrate temperatures between 823 and 1053 K, nanometer size Ge islands that nucleate within the voids continue to grow and coalesce into a continuous film over the remaining oxide. Coalescence of the Ge islands is believed to result in the creation of stacking faults in the Ge film at a density of 5 x 10 7 /cm 2 . Additionally, coalescence results in films of 3 μm thickness having a root-mean-square roughness of 8 to 10 nm. We have found that polishing the films with dilute H 2 O 2 results in roughness values below 0.5 nm. However, stacking faults originating at the Ge-SiO 2 interface and terminating at the Ge surface are polished at a slightly reduced rate, and show up as 1 to 2 nm raised lines on the polished Ge surface. These lines are then transferred into the subsequent growth morphology of GaAs deposited by metal-organic chemical vapor

Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

Czech Academy of Sciences Publication Activity Database

Elster, Josef; Nedbalová, Linda; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, Jiří

2016-01-01

Roč. 13, č. 2 (2016), s. 535-549 ISSN 1726-4170 R&D Projects: GA MŠk ME 945 Institutional support: RVO:67985939 Keywords : James Ross Island * cyanobacteria * microalgae Subject RIV: EH - Ecology, Behaviour Impact factor: 3.851, year: 2016

Thermodynamic analysis of trimethylgallium decomposition during GaN metal organic vapor phase epitaxy

Science.gov (United States)

Sekiguchi, Kazuki; Shirakawa, Hiroki; Chokawa, Kenta; Araidai, Masaaki; Kangawa, Yoshihiro; Kakimoto, Koichi; Shiraishi, Kenji

2018-04-01

We analyzed the decomposition of Ga(CH3)3 (TMG) during the metal organic vapor phase epitaxy (MOVPE) of GaN on the basis of first-principles calculations and thermodynamic analysis. We performed activation energy calculations of TMG decomposition and determined the main reaction processes of TMG during GaN MOVPE. We found that TMG reacts with the H2 carrier gas and that (CH3)2GaH is generated after the desorption of the methyl group. Next, (CH3)2GaH decomposes into (CH3)GaH2 and this decomposes into GaH3. Finally, GaH3 becomes GaH. In the MOVPE growth of GaN, TMG decomposes into GaH by the successive desorption of its methyl groups. The results presented here concur with recent high-resolution mass spectroscopy results.

Exciton lifetime and spin dynamics in type-I In1−xAlxAs/Ga0.67Al0.33As quantum dots: Photoluminescence and pump-probe experiments

International Nuclear Information System (INIS)

Ben Daly, A.; Bernardot, F.; Barisien, T.; Galopin, E.; Lemaître, A.; Maaref, M.A.; Testelin, C.

2015-01-01

The exciton lifetime and spin relaxation have been studied in self-assembled In 1−x Al x As/Ga 0.67 Al 0.33 As quantum dots (QDs). Time-resolved photoluminescence and resonant pump-probe measurements were performed, at variable temperature and for different QD aluminium compositions. At low temperature, a long exciton-spin relaxation time has been measured, in agreement with the QD zero-dimensional confinement and the quenching of the relaxation mechanisms. The existence of a quasi-2D regime, in sample with a high QD density, has been observed. The importance of thermally-activated processes toward excited states is also evidenced, for QDs with different compositions and sizes. - Highlights: • The exciton lifetime and spin relaxation have been studied in In 1−x Al x As/Ga 0.67 Al 0.33 As quantum dot (QD). • Time-resolved photoluminescence (TRPL) and pump-probe measurements were performed, at variable temperature and for different QD aluminium compositions. • From the PL decay time, several thermal activation processes, related to 0D or 2D regime, or dependending on collective mechanisms. • The importance of thermal activated processes toward excited states is also evidenced, for QD with different compositions and sizes

Improved InGaN/GaN quantum wells on treated GaN template with a Ga-rich GaN interlayer

International Nuclear Information System (INIS)

Fang, Zhilai; Shen, Xiyang; Wu, Zhengyuan; Zhang, Tong-Yi

2015-01-01

Treated GaN template was achieved by in situ droplet epitaxy of a Ga-rich GaN interlayer on the conventional GaN template. InGaN/GaN quantum wells (QWs) were grown on the conventional and treated GaN templates under the same growth conditions and then comprehensively characterized. The indium homogeneity in the InGaN layers and the interface sharpness between InGaN and GaN layers of the InGaN/GaN QWs on the treated GaN template were significantly improved. The emission intensity from the InGaN/GaN QWs on the treated GaN template was enhanced by 20% than that on the conventional GaN template, which was attributed to the strain reduction and the improvement in crystalline quality. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Petrological and geochemical characteristics of Palaeogene low-rank coal on the Faroe Islands: Restricted effects of alteration by basaltic lava flows

Czech Academy of Sciences Publication Activity Database

Kuboušková, S.; Krmíček, Lukáš; Coufalík, Pavel; Pokorný, R.

2016-01-01

Roč. 165, AUG (2016), s. 157-172 ISSN 0166-5162 R&D Projects: GA ČR(CZ) GA13-18482S Institutional support: RVO:68081715 ; RVO:67985831 Keywords : Faroe Island * coal composition * alteration Subject RIV: DB - Geology ; Mineralogy Impact factor: 4.783, year: 2016

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

Czech Academy of Sciences Publication Activity Database

Moscovice, L. R.; Issa, M. H.; Petrželková, Klára Judita; Keuler, N. S.; Snowdon, C. T.; Huffman, M. A.

2007-01-01

Roč. 69, č. 1 (2007), s. 1-16 ISSN 0275-2565 R&D Projects: GA AV ČR KJB600930615 Institutional research plan: CEZ:AV0Z60930519 Keywords : chimpanzee * release site * fecal analyses * fallback food * Rubondo Island Subject RIV: EG - Zoology Impact factor: 1.582, year: 2007

The discrepancies between theory and experiment in the optical emission of monolayer In(Ga)N quantum wells revisited by transmission electron microscopy

Science.gov (United States)

Suski, T.; Schulz, T.; Albrecht, M.; Wang, X. Q.; Gorczyca, I.; Skrobas, K.; Christensen, N. E.; Svane, A.

2014-05-01

Quantitative high resolution transmission electron microscopy studies of intentionally grown 1InN/nGaN short-period superlattices (SLs) were performed. The structures were found to consist of an InxGa1-xN monolayer with an Indium content of x = 0.33 instead of the intended x = 1. Self-consistent calculations of the band structures of 1In0.33Ga0.67N/nGaN SLs were carried out, including a semi-empirical correction for the band gaps. The calculated band gap, Eg, as well as its pressure derivative, dEg/dp, are in very good agreement with the measured photoluminescence energy, EPL, and its pressure derivative, dEPL/dp, for a series of 1In0.33Ga0.67N/nGaN samples with n ranging from 2 to 40. This resolves a discrepancy found earlier between measured and calculated optical emission properties, as those calculations were made with the assumption of a 1InN/nGaN SL composition.

Advanced characterization techniques of nonuniform indium distribution within InGaN/GaN heterostructures grown by MOCVD

International Nuclear Information System (INIS)

Lu, D.; Florescu, D.I.; Lee, D.S.; Ramer, J.C.; Parekh, A.; Merai, V.; Li, S.; Begarney, M.J.; Armour, E.A.; Gardner, J.J.

2005-01-01

Nonuniform indium distribution within InGaN/GaN single quantum well (SQW) structures with nanoscale islands grown by metalorganic chemical vapor deposition (MOCVD) have been characterized by advanced characterization techniques. Robinson backscattered electron (BSE) measurements show cluster-like BSE contrast of high brightness regions, which are not centered at small dark pits in a SQW structure of spiral growth mode. By comparing with the secondary electron (SE) images, the bright cluster areas from the BSE images were found to have higher indium content compared to the surrounding dark areas. Temperature dependant photoluminescence (PL) measurement shows typical ''S-shape'' curve, which shows good correlation with nonuniform indium distribution from BSE measurement. Optical evaluation of the samples show increased PL slope efficiency of the spiral mode SQW, which can be attributed to the presence of Indium inhomogeneities. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Abnormal optical behaviour of InAsSb quantum dots grown on GaAs substrate by molecular beam epitaxy

International Nuclear Information System (INIS)

Rihani, J.; Ben Sedrine, N.; Sallet, V.; Harmand, J.C.; Oueslati, M.; Chtourou, R.

2008-01-01

InAs(Sb) quantum dots (QDs) samples were grown on GaAs (001) substrate by Molecular Beam Epitaxy (MBE). The structural characterization by Atomic Force Microscopy (AFM) of samples shows that InAsSb islands size increases strongly with antimony incorporation in InAs/GaAs QDs and decreases with reducing the growth temperature from 520 deg. C to 490 deg. C. Abnormal optical behaviour was observed in room temperature (RT) photoluminescence (PL) spectra of samples grown at high temperature (520 deg. C). Temperature dependent PL study was investigated and reveals an anomalous evolution of emission peak energy (EPE) of InAsSb islands, well-known as 'S-inverted curve' and attributed to the release of confined carriers from the InAsSb QDs ground states to the InAsSb wetting layer (WL) states. With only decreasing the growth temperature, the S-inverted shape was suppressed indicating a fulfilled 3D-confinement of carriers in the InAsSb/GaAs QD sample

A hybrid niched-island genetic algorithm applied to a nuclear core optimization problem

International Nuclear Information System (INIS)

Pereira, Claudio M.N.A.

2005-01-01

Diversity maintenance is a key-feature in most genetic-based optimization processes. The quest for such characteristic, has been motivating improvements in the original genetic algorithm (GA). The use of multiple populations (called islands) has demonstrating to increase diversity, delaying the genetic drift. Island Genetic Algorithms (IGA) lead to better results, however, the drift is only delayed, but not avoided. An important advantage of this approach is the simplicity and efficiency for parallel processing. Diversity can also be improved by the use of niching techniques. Niched Genetic Algorithms (NGA) are able to avoid the genetic drift, by containing evolution in niches of a single-population GA, however computational cost is increased. In this work it is investigated the use of a hybrid Niched-Island Genetic Algorithm (NIGA) in a nuclear core optimization problem found in literature. Computational experiments demonstrate that it is possible to take advantage of both, performance enhancement due to the parallelism and drift avoidance due to the use of niches. Comparative results shown that the proposed NIGA demonstrated to be more efficient and robust than an IGA and a NGA for solving the proposed optimization problem. (author)

A high-linearity InGaP/GaAs HBT power amplifier for IEEE 802.11a/n

International Nuclear Information System (INIS)

Cui Jie; Chen Lei; Kang Chunlei; Shi Jia; Zhang Xuguang; Ai Baoli; Liu Yi

2013-01-01

A three-stage 4.8–6 GHz monolithic power amplifier (PA) compatible with IEEE 802.11a/n designed based on an advanced 2 μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process is presented. The PA integrates input matching and closed-loop power control circuits on chip. Under 3.3 V DC bias, the amplifier achieves a ∼31 dB small signal gain, excellent wide band input and output matching among overall 1.2 GHz bandwidth, and up to 24.5 dBm linear output power below EVM 3% with IEEE 802.11a 64QAM OFDM input signal. (semiconductor integrated circuits)

Nanoscale interfacial engineering to grow Ge on Si as virtual substrates and subsequent integration of GaAs

Energy Technology Data Exchange (ETDEWEB)

Leonhardt, Darin [Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States); Sheng, Josephine; Cederberg, Jeffrey G.; Li Qiming; Carroll, Malcolm S. [Sandia National Laboratories, Albuquerque, NM 87185 (United States); Han, Sang M., E-mail: meister@unm.ed [Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States)

2010-08-31

We have demonstrated the scalability of a process previously dubbed as Ge 'touchdown' on Si to substantially reduce threading dislocations below 10{sup 7}/cm{sup 2} in a Ge film grown on a 2 inch-diameter chemically oxidized Si substrate. This study also elucidates the overall mechanism of the touchdown process. The 1.4 nm thick chemical oxide is first formed by immersing Si substrates in a solution of H{sub 2}O{sub 2} and H{sub 2}SO{sub 4}. Subsequent exposure to Ge flux creates 3 to 7 nm-diameter voids in the oxide at a density greater than 10{sup 11}/cm{sup 2}. Comparison of data taken from many previous studies and ours shows an exponential dependence between oxide thickness and inverse temperature of void formation. Additionally, exposure to a Ge or Si atom flux decreases the temperature at which voids begin to form in the oxide. These results strongly suggest that Ge actively participates in the reaction with SiO{sub 2} in the void formation process. Once voids are created in the oxide under a Ge flux, Ge islands selectively nucleate within the void openings on the newly exposed Si. Island nucleation and growth then compete with the void growth reaction. At substrate temperatures between 823 and 1053 K, nanometer size Ge islands that nucleate within the voids continue to grow and coalesce into a continuous film over the remaining oxide. Coalescence of the Ge islands is believed to result in the creation of stacking faults in the Ge film at a density of 5 x 10{sup 7}/cm{sup 2}. Additionally, coalescence results in films of 3 {mu}m thickness having a root-mean-square roughness of 8 to 10 nm. We have found that polishing the films with dilute H{sub 2}O{sub 2} results in roughness values below 0.5 nm. However, stacking faults originating at the Ge-SiO{sub 2} interface and terminating at the Ge surface are polished at a slightly reduced rate, and show up as 1 to 2 nm raised lines on the polished Ge surface. These lines are then transferred into the

Physical origin of the incubation time of self-induced GaN nanowires

International Nuclear Information System (INIS)

Consonni, V.; Trampert, A.; Geelhaar, L.; Riechert, H.

2011-01-01

The nucleation process of self-induced GaN nanowires grown by molecular beam epitaxy has been investigated by reflection high-energy electron diffraction measurements. It is found that stable nuclei in the form of spherical cap-shaped islands develop only after an incubation time that is strongly dependent upon the growth conditions. Its evolution with the growth temperature and gallium rate has been described within standard island nucleation theory, revealing a nucleation energy of 4.9 ± 0.1 eV and a very small nucleus critical size. The consideration of the incubation time is critical for the control of the nanowire morphology.

Microbial community dynamics and transformation of vascular plant detritus in two wetland ecosystems

International Nuclear Information System (INIS)

Moran, M.A.

1987-01-01

The microbial ecology of two wetland ecosystems in southeastern Georgia, USA, was studied with respect to microbial community dynamics and microbially-mediated transformations of vascular plant detritus. In the Okefenokee Swamp, biomass of microorganisms in the water column and sediments was generally lower in winter months and higher during spring and summer. Biomass and activity (measured as 14 C-lignocellulose mineralization) differed significantly among five habitats within the Okefenokee, and also among locations within each habitat. Significant heterogeneity in the structure of Okefenokee microbial communities was found at scales from 30 cm to 150 m. In field and laboratory studies of vascular plant decomposition in the Okefenokee and a salt marsh on Sapelo Island, the mathematical model which best describes decomposition kinetics is the decaying coefficient model

Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure

International Nuclear Information System (INIS)

Zhu Qing; Ma Xiao-Hua; Chen Wei-Wei; Hou Bin; Zhu Jie-Jie; Zhang Meng; Chen Li-Xiang; Cao Yan-Rong; Hao Yue

2016-01-01

Deep level transient spectroscopy (DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors (HEMTs) has been widely utilized. The DLTS measurements under different bias conditions are carried out in this paper. Two hole-like traps with active energies of E v + 0.47 eV, and E v + 0.10 eV are observed, which are related to surface states. The electron traps with active energies of E c − 0.56 eV are located in the channel, those with E c − 0.33 eV and E c − 0.88 eV are located in the AlGaN layer. The presence of surface states has a strong influence on the detection of electron traps, especially when the electron traps are low in density. The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state. (paper)

Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

International Nuclear Information System (INIS)

Mahata, Mihir Kumar; Ghosh, Saptarsi; Jana, Sanjay Kumar; Bag, Ankush; Kumar, Rahul; Chakraborty, Apurba; Biswas, Dhrubes; Mukhopadhyay, Partha

2014-01-01

In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al 2 O 3 ) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10 −3 (1 × 10 −3 ), and −1.7 × 10 −3 (2 × 10 −3 ) in GaN layer and 5.1 × 10 −3 (−3.3 × 10 −3 ), and 8.8 × 10 −3 (−1.3 × 10 −3 ) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum

Influence of in-situ deposited SiNx interlayer on crystal quality of GaN epitaxial films

Science.gov (United States)

Fan, Teng; Jia, Wei; Tong, Guangyun; Zhai, Guangmei; Li, Tianbao; Dong, Hailiang; Xu, Bingshe

2018-05-01

GaN epitaxial films with SiNx interlayers were prepared by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The influences of deposition times and locations of SiNx interlayers on crystal quality of GaN epitaxial films were studied. Under the optimal growth time of 120 s for the SiNx interlayer, the dislocation density of GaN film is reduced to 4.05 × 108 cm-2 proved by high resolution X-ray diffraction results. It is found that when the SiNx interlayer deposits on the GaN nucleation islands, the subsequent GaN film has the lowest dislocation density of only 2.89 × 108 cm-2. Moreover, a model is proposed to illustrate the morphological evolution and associated propagation processes of TDs in GaN epi-layers with SiNx interlayers for different deposition times and locations.

On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for InGaN/GaN light-emitting diodes.

Science.gov (United States)

Kyaw, Zabu; Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ju, Zhen Gang; Zhang, Xue Liang; Ji, Yun; Hasanov, Namig; Zhu, Binbin; Lu, Shunpeng; Zhang, Yiping; Sun, Xiao Wei; Demir, Hilmi Volkan

2014-01-13

N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n- GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.

Fast transient current response to switching events in short chains of molecular islands

Czech Academy of Sciences Publication Activity Database

Kalvová, Anděla; Špička, Václav; Velický, B.

2013-01-01

Roč. 26, č. 4 (2013), s. 773-777 ISSN 1557-1939 R&D Projects: GA ČR GAP204/12/0897 Institutional support: RVO:68378271 Keywords : nonequilibrium * molecular islands * initial correlations * transient currents Subject RIV: BE - Theoretical Physics Impact factor: 0.930, year: 2013

Cascade Pumping of 1.9–3.3 μm Type-I Quantum Well GaSb-Based Diode Lasers

International Nuclear Information System (INIS)

Shterengas, Leon; Kipshidze, Gela; Hosoda, Takashi; Liang, Rui; Feng, Tao

2017-01-01

Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in spectral region from 1.9 to 3.3 μm. Coated devices with ~100-μm-wide aperture and 3-mm-long cavity demonstrated continuous wave (CW) output power of 1.96 W near 2 μm, 980 mW near 3 μm, 500 mW near 3.18 μm, and 360 mW near 3.25 μm at room temperature. The corresponding narrow ridge lasers with nearly diffraction limited beams operate in CW regime with tens of mW of output power up to 60 °C. Two step shallow/deep narrow/wide ridge waveguide devices showed lower threshold currents and higher slope efficiencies compared to single step narrow ridge lasers. Laterally coupled DFB lasers mounted epi-up generated above 10 mW of tunable single frequency CW power at 20 °C near 3.22 μm.

Growth of self-assembled (Ga)InAs/GaAs quantum dots and realization of high quality microcavities for experiments in the field of strong exciton photon coupling; Selbstorganisiertes Wachstum von (Ga)InAs/GaAs-Quantenpunkten und Entwicklung von Mikroresonatoren hoechster Guete fuer Experimente zur starken Exziton-Photon-Kopplung

Energy Technology Data Exchange (ETDEWEB)

Loeffler, Andreas

2008-11-05

At the beginning, we improved the three dimensional optical confinement of the micropillars. The quality factor of the pillars could be increased by the use of higher reflectivity mirrors and a matched V/III ratio for the different epitaxial layers. Hence, a record quality factor of about 90000 was achieved for an active micropillar with 26 (30) mirror pairs in the top (bottom) DBR and a diameter of 4 {mu}m. In parallel to this, we made studies on the growth of self-assembled GaInAs quantum dots on GaAs substrates. Here, the nucleation of three dimensional islands as well as their optical properties were object of the investigation. The morphological properties of the dots were analyzed by transmission and scanning electron microscopy, and the optical properties were investigated by photoluminescence and photoreflectance measurements. The optical and particularly the morphological properties of the self-assembled GaInAs quantum dots were essentially improved. Due to a low strain nucleation layer with an indium content of 30 %, the dot density could be reduced to 6-9 x 10{sup 9} cm{sup -2} and their geometric dimensions were increased to typical lengths between 50 and 100 nm and widths of about 30 nm. The lattice mismatch between the quantum dots and the surrounding matrix is decreased due to the reduced indium content. The minimized strain during the dot growth leads to an enhanced migration length of the deposited atoms on the surface. Finally, the obtained findings of the MBE growth of microcavities, their fabrication and the self-assembled island growth of GaInAs on GaAs were used for the realization of further samples. Low strain GaInAs quantum dots were embedded into the microresonators. These structures allowed for the first time the observation of strong coupling between light and matter in a semiconductor. In case of the low strain quantum dots with enlarged dimensions in the strong coupling regime, a vacuum Rabi-splitting of about 140 {mu}eV between the

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

Science.gov (United States)

Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-01-01

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

Directory of Open Access Journals (Sweden)

Hongbo Qin

2017-12-01

Full Text Available For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100 and (111 are isotropic, while the Poisson’s ratio at plane (110 exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals.

Science.gov (United States)

Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-12-12

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol -1 K -1 , respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of

Growth on nonpolar and semipolar GaN: The substrate dilemma

Energy Technology Data Exchange (ETDEWEB)

Wernicke, T.; Weyers, M. [Ferdinand-Braun-Institute, Berlin (Germany); Kneissl, M. [Ferdinand-Braun-Institute, Berlin (Germany); Institute of Solid State Physics, TU Berlin (Germany)

2009-07-01

Growth of nonpolar and semipolar GaN is very promising for achieving green laser diodes (LDs). However, the choice of the substrate is a difficult one: Heteroepitaxial growth on sapphire, SiC, LiAlO{sub 2} yields GaN films with a poor surface quality and high defect densities. On the other hand non- and semipolar bulk GaN substrates provide excellent crystal quality, but are so far only available in very small sizes. In this paper hetero- and homoepitaxial growth is compared. For all heteroepitaxially grown semi- and nonpolar GaN layers threading dislocations (TD) and basal plane stacking faults (BSF) can be found. There are four possible mechanisms for the generation of BSF: Growth of the N-polar basal plane, formation during nucleation at substrate steps, formation at the coalescence front of differently stacked nucleation islands, and generation at planar defects occurring in m-plane GaN on LiAlO{sub 2}. BSF induce surface roughening and are associated with partial dislocations causing nonradiative recombination. Thus they affect the performance of devices. We show that BSFs and TDs can be reduced by epitaxial lateral overgrowth resulting in several micrometer wide defect free areas. However, for LEDs larger defect-free areas are required. GaN layers grown on bulk GaN substrates exhibit a high crystal quality, but show in many cases long-range surface structures with a height of {approx}1{mu}m.

33 CFR 80.1450 - Nawiliwili Harbor, Kauai, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Nawiliwili Harbor, Kauai, HI. 80.1450 Section 80.1450 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1450 Nawiliwili Harbor, Kauai, HI...

33 CFR 80.1470 - Kawaihae Harbor, Hawaii, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Kawaihae Harbor, Hawaii, HI. 80.1470 Section 80.1470 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1470 Kawaihae Harbor, Hawaii, HI...

Demonstration of high mobility and quantum transport in modulation-doped β-(AlxGa1-x)2O3/Ga2O3 heterostructures

Science.gov (United States)

Zhang, Yuewei; Neal, Adam; Xia, Zhanbo; Joishi, Chandan; Johnson, Jared M.; Zheng, Yuanhua; Bajaj, Sanyam; Brenner, Mark; Dorsey, Donald; Chabak, Kelson; Jessen, Gregg; Hwang, Jinwoo; Mou, Shin; Heremans, Joseph P.; Rajan, Siddharth

2018-04-01

In this work, we demonstrate a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O3 interface through modulation doping. Shubnikov-de Haas (SdH) oscillations were observed in the modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure, indicating a high-quality electron channel formed at the heterojunction interface. The formation of the 2DEG channel was further confirmed by the weak temperature dependence of the carrier density, and the peak low temperature mobility was found to be 2790 cm2/Vs, which is significantly higher than that achieved in bulk-doped Beta-phase Gallium Oxide (β-Ga2O3). The observed SdH oscillations allowed for the extraction of the electron effective mass in the (010) plane to be 0.313 ± 0.015 m0 and the quantum scattering time to be 0.33 ps at 3.5 K. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure lays the foundation for future exploration of quantum physical phenomena and semiconductor device technologies based on the β-Ga2O3 material system.

33 CFR 67.01-15 - Classification of structures.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Classification of structures. 67... AIDS TO NAVIGATION AIDS TO NAVIGATION ON ARTIFICIAL ISLANDS AND FIXED STRUCTURES General Requirements § 67.01-15 Classification of structures. (a) When will structures be assigned to a Class? The District...

Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

Energy Technology Data Exchange (ETDEWEB)

Mahata, Mihir Kumar; Ghosh, Saptarsi; Jana, Sanjay Kumar; Bag, Ankush; Kumar, Rahul [Advanced Technology Development Center, Indian Institute of Technology, Kharagpur, 721302 (India); Chakraborty, Apurba; Biswas, Dhrubes [Department of Electronics and Electrical Communication Engineering, Indian Institute of Technology, Kharagpur, 721302 (India); Mukhopadhyay, Partha [Rajendra Mishra School of Engineering Entrepreneurship, Indian Institute of Technology, Kharagpur, 721302 (India)

2014-11-15

In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al{sub 2}O{sub 3}) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10{sup −3}(1 × 10{sup −3}), and −1.7 × 10{sup −3}(2 × 10{sup −3}) in GaN layer and 5.1 × 10{sup −3} (−3.3 × 10{sup −3}), and 8.8 × 10{sup −3}(−1.3 × 10{sup −3}) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

33 CFR 67.20-10 - Sound signal.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Sound signal. 67.20-10 Section 67... AIDS TO NAVIGATION ON ARTIFICIAL ISLANDS AND FIXED STRUCTURES Class âAâ Requirements § 67.20-10 Sound signal. (a) The owner of a Class “A” structure shall: (1) Install a sound signal that has a rated range...

Competition between the In/Ga intermixing and the electronic coupling effects in self-assembled InAs/GaAs double-quantum-dots

Energy Technology Data Exchange (ETDEWEB)

Pocas, Luiz Carlos; Sawata, Marcella Ferraz [Universidade Tecnologica Federal do Parana (UTFPR), Apucarana, PR (Brazil); Lourenco, Sidney Alves [Universidade Tecnologica Federal do Parana (UTFPR), Londrina, PR (Brazil); Laureto, Edson; Duarte, Jose Leonil; Dias, Ivan Frederico Lupiano [Universidade Estadual de Londrina (UEL), PR (Brazil). Dept. de Fisica; Quivy, A.A. [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica

2012-07-01

Full text: The notable progress in the fabrication of low-dimensional semiconductor structures during the last years has made it possible to reduce the effective device dimension from three-dimensional bulk materials, to low dimensional quantum systems, as for example, to quasi-two dimensional quantum well systems and to quasi-zero dimensional quantum dots systems. Semiconductors quantum dots (QDs) have attracted considerable interest from both fundamental and technological point of view and have been extensively studied in aspects involving its structural properties and the electronic structure of the confined charge carriers. These systems have been utilized for applications on optoelectronics devices such as lasers, detectors, photodiodes, solar cells, etc. In despite of its fundamental importance, many aspects of their behavior are still not fully understood including, as for example, carrier capture and escape, optical transitions, effects of the inhomogeneous size and energy distribution, etc. Quantum dots grown by Stranski-Krastanov (SK) technique are self-assembled islands, favored by relaxation of the elastic energy that emerge due to the difference of lattice parameter between the epitaxial layer and the substratum. One of the challenges in growing of QDs by SK is to have control of both size and distribution of the islands in the samples. Recently, the growth of samples with vertically stacked multilayer separated by a layer of another semiconductor material, known as stacked QDs, have shown a vertical alignment of QDs which leads to a better QDs size distribution for the upper layers. The strength of electronic coupling, in the case of vertically stacked QDs, as well as the QDs size distribution, is controlled by thickness of the layers that separate the quantum dots (spacer layers). In this work we present a study from a set of self-assembled stacked InAs/GaAs double-quantum-dots grown on GaAs-(001) substrates by molecular beam epitaxy obtained by SK

33 CFR 80.1460 - Kahului Harbor, Maui, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Kahului Harbor, Maui, HI. 80.1460 Section 80.1460 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1460 Kahului Harbor, Maui, HI. A line drawn...

33 CFR 80.1430 - Kaneohe Bay, Oahu, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Kaneohe Bay, Oahu, HI. 80.1430 Section 80.1430 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1430 Kaneohe Bay, Oahu, HI. A straight line...

33 CFR 80.1440 - Port Allen, Kauai, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Port Allen, Kauai, HI. 80.1440 Section 80.1440 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1440 Port Allen, Kauai, HI. A line drawn from...

33 CFR 80.1420 - Mamala Bay, Oahu, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Mamala Bay, Oahu, HI. 80.1420 Section 80.1420 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1420 Mamala Bay, Oahu, HI. A line drawn from...

33 CFR 80.1480 - Hilo Harbor, Hawaii, HI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Hilo Harbor, Hawaii, HI. 80.1480 Section 80.1480 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1480 Hilo Harbor, Hawaii, HI. A line drawn...

Stranski–Krastanov transition and self-organized structures in low-strained AlInN/GaN multilayer structures

International Nuclear Information System (INIS)

Krost, A; Berger, C; Moser, P; Bläsing, J; Dadgar, A; Hums, C; Hempel, T; Bastek, B; Veit, P; Christen, J

2011-01-01

Low-strained AlInN/GaN multilayers aimed as Bragg mirrors were grown by metal organic vapour phase epitaxy on GaN/Si(1 1 1). In such structures the upper AlInN/GaN interfaces show a considerable roughening on a nanometre scale whereas the lower ones appear flat as evaluated by cross-sectional electron and transmission electron microscopy. The roughening is attributed to a Stranski–Krastanov transition from two-dimensional layer-by-layer to three-dimensional island growth. In addition, a self-organized wavy-like surface morphology on a micrometre scale is observed in such structures which we discuss in terms of Grinfeld instability

GaAsBi/GaAs multi-quantum well LED grown by molecular beam epitaxy using a two-substrate-temperature technique

Science.gov (United States)

Kisan Patil, Pallavi; Luna, Esperanza; Matsuda, Teruyoshi; Yamada, Kohki; Kamiya, Keisuke; Ishikawa, Fumitaro; Shimomura, Satoshi

2017-03-01

We report a GaAs0.96Bi0.04/GaAs multiple quantum well (MQW) light emitting diode (LED) grown by molecular beam epitaxy using a two-substrate-temperature (TST) technique. In particular, the QWs and the barriers in the intrinsic region were grown at the different temperatures of {T}{{GaAsBi}} = 350 °C and {T}{{GaAs}} = 550 ^\\circ {{C}}, respectively. Investigations of the microstructure using transmission electron microscopy (TEM) reveal homogeneous MQWs free of extended defects. Furthermore, the local determination of the Bi distribution profile across the MQWs region using TEM techniques confirm the uniform Bi distribution, while revealing a slightly chemically graded GaAs-on-GaAsBi interface due to Bi surface segregation. Despite this small broadening, we found that Bi segregation is significantly reduced (up to 18% reduction) compared to previous reports on Bi segregation in GaAsBi/GaAs MQWs. Hence, the TST procedure proves as a very efficient method to reduce Bi segregation and thus increase the quality of the layers and interfaces. These improvements positively reflect in the optical properties. Room temperature photoluminescence and electroluminescence (EL) at 1.23 μm emission wavelength are successfully demonstrated using TST MQWs containing less Bi content than in previous reports. Finally, LED fabricated using the present TST technique show current-voltage (I-V) curves with a forward voltage of 3.3 V at an injection current of 130 mA under 1.0 kA cm-2 current excitation. These results not only demonstrate that TST technique provides optical device quality GaAsBi/GaAs MQWs but highlight the relevance of TST-based growth techniques on the fabrication of future heterostructure devices based on dilute bismides.

The isothermal section at 500 deg. C of the Gd-Tb-Ga ternary system

International Nuclear Information System (INIS)

Li, J.Q.; Jian, Y.X.; Ao, W.Q.; Zhuang, Y.H.; He, W.

2006-01-01

Phase equilibria in the Gd-Tb-Ga ternary system at 500 deg. C were investigated by X-ray powder diffraction and differential scanning calorimetry. The binary compounds, Gd 5 Ga 3 , Gd 3 Ga 2 , GdGa, GdGa 2 , Tb 5 Ga 3 , TbGa, TbGa 2 and TbGa 3 have been confirmed at 500 deg. C. No ternary compound was found in this system. The isothermal section of this system at 500 deg. C was constructed. It is composed of 7 single-phase regions, 8 two-phase regions and 2 three-phase regions. Four ternary continuous solid solutions (Gd, Tb), (Gd, Tb) 5 Ga 3 , (Gd, Tb)Ga, (Gd, Tb)Ga 2 were formed in this isothermal section. The maximum solid solubilities of Ga in (Gd, Tb) at 500 deg. C is 5.0 at.%. The homogeneity range of (Gd, Tb)Ga 2 is from 20 to 33.3 at.% Ga in Gd-Ga side but limited in Tb-Ga side. The solid solubilities of Ga in the other phases cannot be detected. The Curie temperatures of the Gd 0.6 Tb 0.4-x Ga x alloys increase from 270 to 298 K as x increases from 0 to 0.03

Geochronological constraints on the evolution of El Hierro (Canary Islands)

Science.gov (United States)

Becerril, Laura; Ubide, Teresa; Sudo, Masafumi; Martí, Joan; Galindo, Inés; Galé, Carlos; Morales, Jose María; Yepes, Jorge; Lago, Marceliano

2016-01-01

New age data have been obtained to time constrain the recent Quaternary volcanism of El Hierro (Canary Islands) and to estimate its recurrence rate. We have carried out 40Ar/39Ar geochronology on samples spanning the entire volcanostratigraphic sequence of the island and 14C geochronology on the most recent eruption on the northeast rift of the island: 2280 ± 30 yr BP. We combine the new absolute data with a revision of published ages onshore, some of which were identified through geomorphological criteria (relative data). We present a revised and updated chronology of volcanism for the last 33 ka that we use to estimate the maximum eruptive recurrence of the island. The number of events per year determined is 9.7 × 10-4 for the emerged part of the island, which means that, as a minimum, one eruption has occurred approximately every 1000 years. This highlights the need of more geochronological data to better constrain the eruptive recurrence of El Hierro.

Lattice Gas Model Based Optimization of Plasma-Surface Processes for GaN-Based Compound Growth

Science.gov (United States)

Nonokawa, Kiyohide; Suzuki, Takuma; Kitamori, Kazutaka; Sawada, Takayuki

2001-10-01

Progress of the epitaxial growth technique for GaN-based compounds makes these materials attractive for applications in high temperature/high-power electronic devices as well as in short-wavelength optoelectronic devices. For MBE growth of GaN epilayer, atomic nitrogen is usually supplied from ECR-plasma while atomic Ga is supplied from conventional K-cell. To grow high-quality epilayer, fundamental knowledge of the detailed atomic process, such as adsorption, surface migration, incorporation, desorption and so forth, is required. We have studied the influence of growth conditions on the flatness of the growth front surface and the growth rate using Monte Carlo simulation based on the lattice gas model. Under the fixed Ga flux condition, the lower the nitrogen flux and/or the higher the growth temperature, the better the flatness of the front surface at the sacrifice of the growth rate of the epilayer. When the nitrogen flux is increased, the growth rate reaches saturation value determined from the Ga flux. At a fixed growth temperature, increasing of nitrogen to Ga flux ratio results in rough surface owing to 3-dimensional island formation. Other characteristics of MBE-GaN growth using ECR-plasma can be well reproduced.

Studies on radionuclide concentration along the Northern Coast of Krusadai Island

International Nuclear Information System (INIS)

Inigo Valan, I.; Stephen, A.; Mathiyarasu, R.; Murthy, S.M.S.; Vijayalakshmi, I.

2014-01-01

Krusadai Island - The Biologist's Paradise, is situated in Gulf of Mannar (GaM) near Rameswaram of Tamilnadu, India. It has been recognized as Ecological sensitive area under Coastal regulation zone notification 1991 because these area act as the breeding zone for a variety of marine species, most of which are consumed by human population. Above all Govt. of India and Govt. of Tamil Nadu jointly declared Gulf of Mannar as Marine National Park under Wildlife (Protection) Act 1972. So it is essential to have a periodic radiological survey in this area in order to check the concentrations of various radionuclide. Apart from this 2004 Tsunami had many devastating effects along the coastal Tamil Nadu. GOM (Especially Rameswaram coast) didn't suffer a lot due to the barricade-like protection given by the island nation Sri Lanka. But reports suggest that northeastern part of the Krusadai Island had noticeable effects due to Tsunami, which interests to study this area. Current study is a preliminary radioactive report on the northern part of the Krusadai Island

Investigation of self-organized quantum dots in InGaN alloys for photovoltaic devices

Energy Technology Data Exchange (ETDEWEB)

Yuan, Jinshe; Wang, Mingyue [Chongqing Normal Univ. (China). Dept. of Physics

2008-07-01

The self-organized quantum dots in InGaN alloys grown by metal organic chemical vapor deposition for photovoltaic devices were investigated using photoluminescence spectra, x-ray diffraction and atomic force microscopy measurements. The AFM view of the alloy shows the island-like microstructure appearing to be composed of granular-crystalline in nanometer scale. By analysis of the PL, it has been found that the narrow 493nm emission peak with 490nm and 487nm shoulder peaks was originated from InGaN self-organized quantum dots, which provide a candidate for realizing high efficiencies photovoltaic devices. (orig.)

Narrow photoluminescence peak from Ge(Si) islands embedded between tensile-strained Si layers

Energy Technology Data Exchange (ETDEWEB)

Shaleev, Mikhail; Novikov, Alexey; Baydakova, Nataliya; Yablonskiy, Artem; Drozdov, Yuriy; Lobanov, Dmitriy; Krasilnik, Zakhary [Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod (Russian Federation); Kuznetsov, Oleg [Physical-Technical Research Institute, Nizhny Novgorod State University, pr. Gagarina 23, 603950 Nizhny Novgorod (Russian Federation)

2011-03-15

The influence of thickness of the strained Si layers, measurement temperature and optical pumping power on width of the photoluminescence line from Ge(Si) self-assembled nanoislands grown on relaxed SiGe/Si(001) buffer layers and embedded between tensile-stained Si layers was studied. This line appears due to the II-type optical transition between the holes localized in islands and the electrons confined in tensile-strained Si layers under and above the islands. The possibility of tuning the photoluminescence line width by changing the strained Si layer thicknesses under and above the islands is showed. The decrease of the photoluminescence line width from Ge(Si) islands down to values comparable with width of the PL line from InAs/GaAs quantum dots was achieved due to the quantum confinement of electrons in thin strained Si layers and taking into account of the higher diffusion-induced smearing of strained Si layer above the islands. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Growth and shape of indium islands on molybdenum at micro-roughened spots created by femtosecond laser pulses

Science.gov (United States)

Ringleb, F.; Eylers, K.; Teubner, Th.; Schramm, H.-P.; Symietz, C.; Bonse, J.; Andree, S.; Heidmann, B.; Schmid, M.; Krüger, J.; Boeck, T.

2017-10-01

Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells.

Ternary gallides RE_4Rh_9Ga_5, RE_5Rh_1_2Ga_7 and RE_7Rh_1_8Ga_1_1 (RE=Y, La-Nd, Sm, Gd, Tb). Intergrowth structures with MgCu_2 and CaCu_5 related slabs

International Nuclear Information System (INIS)

Seidel, Stefan; Rodewald, Ute C.; Poettgen, Rainer; Janka, Oliver

2017-01-01

Fourteen ternary gallides RE_4Rh_9Ga_5, RE_5Rh_1_2Ga_7 and RE_7Rh_1_8Ga_1_1 (RE=Y, La-Nd, Sm, Gd, Tb) were synthesized from the elements by arc-melting, followed by different annealing sequences either in muffle or induction furnaces. The samples were characterized through Guinier powder patterns and the crystal structures of Ce_4Rh_9Ga_5, Ce_5Rh_1_2Ga_7, Ce_7Rh_1_8Ga_1_1, Nd_5Rh_1_0_._4_4_(_4_)Ga_8_._5_6_(_4_), Nd_4Rh_9Ga_5 and Gd_4Rh_9Ga_5 were refined from single crystal X-ray diffractometer data. The new gallides are the n=2, 3 and 5 members of the RE_2_+_n Rh_3_+_3_n Ga_1_+_2_n structure series in the Parthe intergrowth concept. The slabs of these intergrowth structures derive from the cubic Laves phase MgCu_2 (Mg_2Ni_3Si as ternary variant) and CaCu_5 (CeCo_3B_2 as ternary variant). Only the Nd_5Rh_1_0_._4_4_(_4_)Ga_8_._5_6_(_4_) crystal shows Rh/Ga mixing within the Laves type slabs. Magnetic susceptibility measurements reveal Pauli paramagnetism for Y_4Rh_9Ga_5 and Curie-Weiss paramagnetism for Gd_4Rh_9Ga_5 and Tb_4Rh_9Ga_5. Low-temperature data show ferromagnetic ordering at T_C=78.1 (Gd_4Rh_9Ga_5) and 55.8 K (Tb_4Rh_9Ga_5).

33 CFR 110.155 - Port of New York.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Port of New York. 110.155 Section... ANCHORAGE REGULATIONS Anchorage Grounds § 110.155 Port of New York. (a) Long Island Sound—(1) Anchorage No... northwest corner of the crib icebreaker north of the New York Central Railroad Company drawbridge across...

cw argon laser annealing of anodic oxide on GaAs

International Nuclear Information System (INIS)

Chakravarti, S.N.; Das, P.; Webster, R.T.; Bhat, K.N.

1981-01-01

Anodic oxide films (850 +- 50 A thick) grown on n + (100) bulk GaAs were subjected to selective area annealing using a cw argon laser operating at an output power of 1.2 W. Capacitance-voltage (C-V) measurements performed on Al-anodic oxide-GaAs MOS capacitor structures show that laser-annealed capacitor dots have greatly reduced field-induced hysteresis effects in their capacitance-voltage characteristics compared to the unannealed ones. The oxide leakage current also shows a significant improvement: the leakage current magnitude of MOS capacitors in laser-annealed oxide island is over four orders of magnitude less than the oxide region which was not exposed to the laser radiation. Dielectric breakdown measurement indicates that laser-annealed capacitors have considerably higher breakdown voltages, about a factor of 2 higher than the unannealed capacitors

33 CFR 334.1170 - San Pablo Bay, Calif.; gunnery range, Naval Inshore Operations Training Center, Mare Island...

Science.gov (United States)

2010-07-01

... range, Naval Inshore Operations Training Center, Mare Island, Vallejo. 334.1170 Section 334.1170... Operations Training Center, Mare Island, Vallejo. (a) The Danger Zone. A sector in San Pablo Bay delineated..., Vallejo, California, will conduct gunnery practice in the area during the period April 1 through September...

Scintiscanning of lung cancer with 67Ga-citrate

International Nuclear Information System (INIS)

Abe, Mitsunobu; Ohyama, Shiro; Ohtsuka, Hassau; Hoshina, Toshifumi; Takanashi, Shuko

1982-01-01

The clinical value of scintigram with 67 Ga-citrate in 58 patients with primary lung cancer was investigated and discussed. The results are as follows: 1) Positive 67 Ga-scintigram was obtained in 83% of patients with primary lung cancer. The histologically confirmed positive ratios were 74% in adenocarcinoma, 94% in squamous cell carcinoma, 80% in small cell carcinoma and 100% in large cell carcinoma. 2) The positive ratios according to T category of TNM classification was 0% (0/1) in T1, 83% (20/24) in T2 and 85% (28/33) in T3. 3) According to rules for classification of lung cancer (TNM UICC 1978,) T2 cases were divided into two groups. a) In patients with hilar involvements on chest X-ray, positive accumulation to the hilar region was 88% (7/8). b) In patients without the evidence of hilar involvements on chest X-ray, the positive accumulation to the hilar region was 81% (13/16). 4) All cases extending to the mediastinum showed abnormal 67 Ga-citrate accumulation regardless of histological type. 67 Ga-citrate scanning is useful in evaluating the extent of lung cancer, especially with hilar and mediastinal involvements. Therefore 67 Ga-citrate scanning seems to be very useful for planning the radiotherapy for lung cancer. (author)

33 CFR 165.1406 - Safety Zone: Pacific Missile Range Facility (PMRF), Barking Sands, Island of Kauai, Hawaii.

Science.gov (United States)

2010-07-01

... Range Facility (PMRF), Barking Sands, Island of Kauai, Hawaii. 165.1406 Section 165.1406 Navigation and...), Barking Sands, Island of Kauai, Hawaii. (a) Location. The following area is established as a safety zone during launch operations at PMRF, Kauai, Hawaii: The waters bounded by the following coordinates: (22°01...

Efficient InGaP/GaAs DJ solar cell with double back surface field layer

Directory of Open Access Journals (Sweden)

G.P. Mishra

2015-09-01

Full Text Available An effective and optimised BSF layer is an important layer in both single junction and multijunction solar cells. In this work the use of the double layer BSF for top cell with their varied thicknesses is investigated on GaInP/GaAs DJ solar cell using the computational numerical modelling TCAD tool Silvaco ATLAS. The detail photo-generation rates are determined. The major modelling stages are described and the simulation results are validated with published experimental data in order to describe the accuracy of our results produced. For this optimized cell structure, the maximum Jsc = 17.33 mA/cm2, Voc = 2.66 V, and fill factor (FF = 88.67% are obtained under AM1.5G illumination, exhibiting a maximum conversion efficiency of 34.52% (1 sun and 39.15% (1000 suns.

Structural, surface potential and optical studies of AlGaN based double heterostructures irradiated by 120 MeV Si{sup 9+} swift heavy ions

Energy Technology Data Exchange (ETDEWEB)

Arivazhagan, P., E-mail: arivazhaganau2008@gmail.com [Crystal Growth Centre, Anna University, Chennai, 600 025 (India); Ramesh, R.; Balaji, M. [Crystal Growth Centre, Anna University, Chennai, 600 025 (India); Asokan, K. [Inter-University Accelerator Centre (IUAC), New Delhi (India); Baskar, K. [Crystal Growth Centre, Anna University, Chennai, 600 025 (India)

2016-09-15

The Al{sub 0.33}Ga{sub 0.77}N/Al{sub 0.14}Ga{sub 0.86}N based double heterostructure was irradiated using Si{sup 9+} ion at room temperature (RT) and liquid nitrogen temperature (LNT) with four dissimilar ion fluence. The effect of Si{sup 9+} ion irradiation in dislocation densities and in-plane strain of GaN layer were discussed. The in-plane strain values of Al{sub x}Ga{sub 1-x}N layers were calculated from asymmetric reciprocal space mapping (RSM). The surface modification and the variation in phase shift on Al{sub 0.33}Ga{sub 0.77}N surfaces due to the irradiation were measured by Electrostatic Force Microscopy (EFM). The capacitance of the tip-sample system was determined from EFM. The band edge emissions of heterostructures were measured by the room temperature phototluminescence (PL) and the shift in the Al{sub 0.14}Ga{sub 0.86}N active layer emission peaks towards the low energy side at low fluence ion irradiation has been noted. - Highlights: • Effects of Si{sup 9+} ion irradiation on AlGaN double heterostructures were investigated. • Dislocation densities of GaN reduced at liquid nitrogen temperature irradiation. • Variation in phase shift on Al{sub 0.33}Ga{sub 0.77}N surfaces was measured by EFM. • Capacitance per unit area values of AFM tip-sample surface system were calculated. • Si{sup 9+} irradiations play an important role to tune the energy gap in Al{sub 0.14}Ga{sub 0.86}N.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

Science.gov (United States)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Formation of GaAs/AlGaAs and InGaAs/GaAs nanorings by droplet molecular-beam epitaxy

International Nuclear Information System (INIS)

Gong, Z.; Niu, Z.C.; Huang, S.S.; Fang, Z.D.; Sun, B.Q.; Xia, J.B.

2005-01-01

GaAs/AlGaAs lattice-matched nanorings are formed on GaAs (100) substrates by droplet epitaxy. The crucial step in the formation of nanorings is annealing Ga droplets under As flux for proper time. The observed morphologic evolution of Ga droplets during annealing does not support the hypothesis that As atoms preferentially react with Ga around the periphery of the droplets, but somehow relates to a dewetting process similar to that of unstable films. Photoluminescene (PL) test results confirm the quantum-confinement effect of these GaAs nanorings. Using similar methods, we have fabricated InGaAs/GaAs lattice-mismatched rings

Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems

International Nuclear Information System (INIS)

Shen, J; Cha, J J; Song, Y; Lee, M L

2014-01-01

InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems. (paper)

MOVPE grown InGaAs quantum dots of high optical quality as seed layer for low-density InP quantum dots

International Nuclear Information System (INIS)

Richter, D; Hafenbrak, R; Joens, K D; Schulz, W-M; Eichfelder, M; Rossbach, R; Jetter, M; Michler, P

2010-01-01

To achieve a low density of optically active InP-quantum dots we used InGaAs islands embedded in GaAs as a seed layer. First, the structural InGaAs quantum dot properties and the influence of the annealing technique was investigated by atomic force microscope measurements. High-resolution micro-photoluminescence spectra reveal narrow photoluminescence lines, with linewidths down to 11 μeV and fine structure splittings of 25 μeV. Furthermore, using these InGaAs quantum dots as seed layer reduces the InP quantum dot density of optically active quantum dots drastically. InP quantum dot excitonic photoluminescence emission with a linewidth of 140 μeV has been observed.

Reunion island, laboratory of renewable energies

International Nuclear Information System (INIS)

Gateaud, P.

2010-01-01

Hydro-power, biomass fuel, solar photovoltaic and wind power, are the renewable energy sources that Reunion island (Indian Ocean, FR) is developing to manage the security of its electric power system. In 2009, power generation reached 2618 GWh and was ensured at 67% by imported fossil fuels (47% coal and 20% hydrocarbons) and at 33% by renewable energies (20% hydraulic, 20% bagasse and 2% solar, wind and biogas). Total production capacity of the island reaches 625 MW. The average power used is of about 330 MW. Private companies supply 60% of the production and the remaining 40% are supplied by EdF who owns about 330000 clients. The average consumption of a Reunion inhabitant is 1259 kWh per year (2330 kWh/y for a metropolitan French). (J.S.)

Effects of Mg/Ga and V/III source ratios on hole concentration of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy

Science.gov (United States)

Nonoda, Ryohei; Shojiki, Kanako; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Matsuoka, Takashi

2016-05-01

The effects of growth conditions such as Mg/Ga and V/III ratios on the properties of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy were studied. Photoluminescence spectra from Mg-doped GaN depended on Mg/Ga and V/III ratios. For the lightly doped samples, the band-to-acceptor emission was observed at 3.3 eV and its relative intensity decreased with increasing V/III ratio. For the heavily doped samples, the donor-acceptor pair emission was observed at 2.8 eV and its peak intensity monotonically decreased with V/III ratio. The hole concentration was maximum for the Mg/Ga ratio. This is the same tendency as in group-III polar (0001) growth. The V/III ratio also reduced the hole concentration. The higher V/III ratio reduced the concentration of residual donors such as oxygen by substituting nitrogen atoms. The surface became rougher with increasing V/III ratio and the hillock density increased.

Growth of high mobility GaN and AlGaN/GaN high electron mobility transistor structures on 4H-SiC by ammonia molecular-beam epitaxy

International Nuclear Information System (INIS)

Webb, James B.; Tang, H.; Bardwell, J. A.; Coleridge, P.

2001-01-01

Ammonia molecular-beam epitaxy has been used to grow high-quality epilayers of GaN and AlGaN/GaN heterostructure field-effect transistor (HFET) structures on insulating 4H-SiC. The growth process, which used a magnetron sputter epitaxy deposited buffer layer of AlN, has been described previously. Ex situ pretreatment of the SiC substrate was found to be unnecessary. For a single 2.0 μm thick silicon doped epilayer, a room temperature (RT) electron mobility of 500 cm2/Vs was measured at a carrier density of 6.6x10 16 cm -3 . For the HFET structure, a room temperature mobility of 1300 cm2/Vs at a sheet carrier density of 3.3x10 12 cm -2 was observed, increasing to 11000 cm2/Vs at 77 K. The surface morphology of the layers indicated a coalesced mesa structure similar to what we observed for growth on sapphire, but with a lower overall defect density and correspondingly larger grain size. The observation of well-resolved Shubnikov de Haas oscillations at fields as low as 3 T indicated a relatively smooth interface. [copyright] 2001 American Institute of Physics

PHYTOPLANKTON - WET WEIGHT and Other Data from UNKNOWN From Long Island Sound from 19520305 to 19591109 (NODC Accession 9000037)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains two files of nutrient and chlorophyll data for Long Island Sound collected from 1952-59. The data were originally collected by G.A. Riley,...

Synthesis and structures of two isostructural phosphites, Al2(HPO3)3 and Ga2(HPO3)3

International Nuclear Information System (INIS)

Morris, R.E.; Attfield, M.P.; Cheetham, A.K.

1994-01-01

Aluminium hydrogen phosphite, Al 2 (HPO 3 ) 3 , and gallium hydrogen phosphite, Ga 2 (HPO 3 ) 3 , were prepared hydrothermally in Teflon-lined steel autoclaves at 473 K. The compounds are isostructural with Fe 2 (HPO 3 ) 3 . The structures consist of very distorted MO 6 octahedra which share faces to form a dimeric M 2 O 9 unit. These dimers are interlinked by the phosphite groups, which link three different dimers into a three-dimensional arrangement having small proton-lined channels running parallel to the c axis. (orig.)

Structures and energetics of Ga2O3 polymorphs

International Nuclear Information System (INIS)

Yoshioka, S; Hayashi, H; Kuwabara, A; Oba, F; Matsunaga, K; Tanaka, I

2007-01-01

First-principles calculations are made for five Ga 2 O 3 polymorphs. The structure of ε-Ga 2 O 3 with the space group Pna 2 1 (No. 33, orthorhombic), which is sometimes called κ-Ga 2 O 3 in the literature, is consistent with experimental reports. The structure of γ-Ga 2 O 3 is optimized within 14 inequivalent configurations of defective spinel structures. Phonon dispersion curves of four polymorphs are obtained. The volume expansivity, bulk modulus, and specific heat at constant volume are computed as a function of temperature within the quasi-harmonic approximation. The Helmholtz free energies of the polymorphs are thus compared. The expansivity shows a relationship of β<ε<α<δ, while β<ε<δ<α for the bulk modulus. The formation free energies have the tendency β<ε<α<δ<γ at low temperatures. With the increase of temperature, the difference in free energy between the β-phase and the ε-phase becomes smaller. Eventually the ε phase becomes more stable at above 1600 K

Growth of self-assembled (Ga)InAs/GaAs quantum dots and realization of high quality microcavities for experiments in the field of strong exciton photon coupling

International Nuclear Information System (INIS)

Loeffler, Andreas

2008-01-01

At the beginning, we improved the three dimensional optical confinement of the micropillars. The quality factor of the pillars could be increased by the use of higher reflectivity mirrors and a matched V/III ratio for the different epitaxial layers. Hence, a record quality factor of about 90000 was achieved for an active micropillar with 26 (30) mirror pairs in the top (bottom) DBR and a diameter of 4 μm. In parallel to this, we made studies on the growth of self-assembled GaInAs quantum dots on GaAs substrates. Here, the nucleation of three dimensional islands as well as their optical properties were object of the investigation. The morphological properties of the dots were analyzed by transmission and scanning electron microscopy, and the optical properties were investigated by photoluminescence and photoreflectance measurements. The optical and particularly the morphological properties of the self-assembled GaInAs quantum dots were essentially improved. Due to a low strain nucleation layer with an indium content of 30 %, the dot density could be reduced to 6-9 x 10 9 cm -2 and their geometric dimensions were increased to typical lengths between 50 and 100 nm and widths of about 30 nm. The lattice mismatch between the quantum dots and the surrounding matrix is decreased due to the reduced indium content. The minimized strain during the dot growth leads to an enhanced migration length of the deposited atoms on the surface. Finally, the obtained findings of the MBE growth of microcavities, their fabrication and the self-assembled island growth of GaInAs on GaAs were used for the realization of further samples. Low strain GaInAs quantum dots were embedded into the microresonators. These structures allowed for the first time the observation of strong coupling between light and matter in a semiconductor. In case of the low strain quantum dots with enlarged dimensions in the strong coupling regime, a vacuum Rabi-splitting of about 140 μeV between the cavity mode and

The comparative hydrochemistry of two granitic island aquifers. The Isles of Scilly, UK and the Hvaler Islands, Norway

International Nuclear Information System (INIS)

Banks, D.; Reimann, C.; Skarphagen, H.

1998-01-01

A comparative study is presented of granitic groundwaters from the Hvaler Islands, south-eastern Norway (11 samples) and the Scilly Islands, south-western England (10 samples). The islands display similar bulk lithologies (peraluminous S-type, U/Th-enriched granites) and land use, but differing glaciation and hence weathering histories. The groundwater of both groups bears a strong marine signature, although the Hvaler Islands display less marine influence and a greater degree of water-rock interaction. The most interesting hydrochemical dissimilarities concern the health related trace elements Rn, U and F. These display median (and maximum) values of 2510 Bq/l (8520 Bq/l), 15 μg/l (170 μg/l) and 3.3 mg/l (4.4 mg/l), respectively for Hvaler, compared with 140 Bq/l (200 Bq/l), 1.5 μg/l (4 μg/l) and 0.1 mg/l (0.27 mg/l) for Scilly. Commonly employed drinking water limits for these parameters are 500 Bq/l (Norwegian action level), 20 μg/l (Canadian limit) and 1.5 mg/l. The differences in groundwater contents of these elements between Hvaler and Scilly may be ascribed to: (1) differing trace element compositions of the granites and fracture mineralisations; (2) radically differing recent weathering histories; and (3) hydrodynamic factors

Spatial structure and associations in Pinus canariensis population at the treeline, Pico del Teide, Tenerife, Canary Islands

Czech Academy of Sciences Publication Activity Database

Šrůtek, Miroslav; Doležal, J.; Hara, T.

2002-01-01

Roč. 34, č. 2 (2002), s. 201-210 ISSN 1523-0430 R&D Projects: GA AV ČR KSK6005114 Institutional research plan: CEZ:AV0Z6005908 Keywords : Pinus canariensis * Canary Islands Subject RIV: EF - Botanics Impact factor: 0.964, year: 2002

Automated synthesis, characterization and biological evaluation of [{sup 68}Ga]Ga-AMBA, and the synthesis and characterization of {sup nat}Ga-AMBA and [{sup 67}Ga]Ga-AMBA

Energy Technology Data Exchange (ETDEWEB)

Cagnolini, Aldo; Chen Jianqing; Ramos, Kimberly; Marie Skedzielewski, Tina; Lantry, Laura E.; Nunn, Adrian D.; Swenson, Rolf E. [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States); Linder, Karen E., E-mail: karen.e.linder@gmail.co [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States)

2010-12-15

Ga-AMBA (Ga-DO3A-CH{sub 2}CO-G-[4-aminobenzoyl]-QWAVGHLM-NH{sub 2}) is a bombesin-like agonist with high affinity for gastrin releasing peptide receptors (GRP-R). Syntheses for {sup nat}Ga-AMBA, [{sup 67}Ga]Ga-AMBA and [{sup 68}Ga]Ga-AMBA were developed. The preparation of HPLC-purified and Sep-Pak purified [{sup 68}Ga]Ga-AMBA were fully automated, using the built-in radiodetector of the Tracerlab FX F-N synthesizer to monitor fractionated {sup 68}Ge/{sup 68}Ga generator elution and purification. The total synthesis time, including the fractional elution of the generator, was 20 min for Sep-Pak purified material and 40 min for HPLC-purified [{sup 68}Ga]Ga-AMBA. Both [{sup 67}Ga]Ga-AMBA and [{sup 177}Lu]Lu-AMBA showed comparable high affinity for GRP-R in the human prostate cancer cell line PC-3 in vitro (k{sub D}=0.46{+-}0.07; 0.44{+-}0.08 nM), high internalization (78; 77%) and low efflux from cells at 2 h (2.4{+-}0.7; 2.9{+-}1.8%). Biodistribution results in PC-3 tumor-bearing male nude mice showed comparable uptake for [{sup 177}Lu]Lu-, [{sup 111}In]In-, [{sup 67}Ga]Ga- and [{sup 68}Ga]Ga-AMBA.

Strain Balanced AlGaN/GaN/AlGaN nanomembrane HEMTs.

Science.gov (United States)

Chang, Tzu-Hsuan; Xiong, Kanglin; Park, Sung Hyun; Yuan, Ge; Ma, Zhenqiang; Han, Jung

2017-07-25

Single crystal semiconductor nanomembranes (NM) are important in various applications such as heterogeneous integration and flexible devices. This paper reports the fabrication of AlGaN/GaN NMs and NM high electron mobility transistors (HEMT). Electrochemical etching is used to slice off single-crystalline AlGaN/GaN layers while preserving their microstructural quality. A double heterostructure design with a symmetric strain profile is employed to ensure minimal residual strain in freestanding NMs after release. The mobility of the two-dimensional electron gas (2DEG), formed by the AlGaN/GaN heterostructure, is noticeably superior to previously reported values of many other NMs. AlGaN/GaN nanomembrane HEMTs are fabricated on SiO 2 and flexible polymeric substrates. Excellent electrical characteristics, including a high ON/OFF ratio and transconductance, suggest that III-Nitrides nanomembranes are capable of supporting high performance applications.

Spatial distribution of Madeira Island Laurisilva endemic spiders (Arachnida: Araneae)

Science.gov (United States)

2014-01-01

Abstract Madeira island presents a unique spider diversity with a high number of endemic species, many of which are still poorly known. A recent biodiversity survey on the terrestrial arthropods of the native forest, Laurisilva, provided a large set of standardized samples from various patches throughout the island. Out of the fifty two species recorded, approximately 33.3% are Madeiran endemics, many of which had not been collected since their original description. Two new species to science are reported – Ceratinopsis n. sp. and Theridion n. sp. – and the first records of Poeciloneta variegata (Blackwall, 1841) and Tetragnatha intermedia Kulczynski, 1891 are reported for the first time for Madeira island. Considerations on species richness and abundance from different Laurisilva locations are presented, together with distribution maps for endemic species. These results contribute to a better understanding of spider diversity patterns and endemic species distribution in the native forest of Madeira island. PMID:24855443

Quantitative analysis of immobilized penicillinase using enzyme-modified AlGaN/GaN field-effect transistors.

Science.gov (United States)

Müntze, Gesche Mareike; Baur, Barbara; Schäfer, Wladimir; Sasse, Alexander; Howgate, John; Röth, Kai; Eickhoff, Martin

2015-02-15

Penicillinase-modified AlGaN/GaN field-effect transistors (PenFETs) are utilized to systematically investigate the covalently immobilized enzyme penicillinase under different experimental conditions. We demonstrate quantitative evaluation of covalently immobilized penicillinase layers on pH-sensitive field-effect transistors (FETs) using an analytical kinetic PenFET model. This kinetic model is explicitly suited for devices with thin enzyme layers that are not diffusion-limited, as it is the case for the PenFETs discussed here. By means of the kinetic model it was possible to extract the Michaelis constant of covalently immobilized penicillinase as well as relative transport coefficients of the different species associated with the enzymatic reaction which, exempli gratia, give information about the permeability of the enzymatic layer. Based on this analysis we quantify the reproducibility and the stability of the analyzed PenFETs over the course of 33 days as well as the influence of pH and buffer concentration on the properties of the enzymatic layer. Thereby the stability measurements reveal a Michalis constant KM of (67 ± 13)μM while the chronological development of the relative transport coefficients suggests a detachment of physisorbed penicillinase during the first two weeks since production. Our results show that AlGaN/GaN PenFETs prepared by covalent immobilization of a penicillinase enzyme layer present a powerful tool for quantitative analysis of enzyme functionality. Copyright © 2014 Elsevier B.V. All rights reserved.

A 3000 yr paleostorm record from St. Catherines Island, Georgia

Science.gov (United States)

Braun, Erick; Meyer, Brian; Deocampo, Daniel; Kiage, Lawrence M.

2017-09-01

Tropical cyclones (hurricanes in the northern hemisphere) are amongst the most devastating of the world's natural disasters and cause billions of dollars in damage every year. Data on the likelihood of a coastal site being struck by a major hurricane strike can potentially aid in planning and mitigation efforts that could save money and lives. However, forecasting requires data that are currently insufficient for the Georgia Bight. This study provides information to enhance the paleohurricane record by analysis of a 467 cm thick vibracore raised from St. Catherines Island, GA. Sediment geochemistry and foraminiferal assemblages indicate deposits attributable to seven paleohurricane events, five of which were likely major hurricanes when they made landfall on St. Catherines. Magnitudes were estimated by comparison to the overwash deposit left by ;The Sea Islands hurricane of 1893;, a major hurricane recorded by the recent sediment of St. Catherines Island. The St. Catherines record also shows a change in the activity levels on the Georgia coast with two distinct activity regimes over the past 3000 years.

Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia

DEFF Research Database (Denmark)

Johansson, Åke; Waight, Tod Earle; Andersen, Tom

2016-01-01

Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U–Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous...

33 CFR 67.30-1 - Class “C” structures.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Class âCâ structures. 67.30-1... NAVIGATION AIDS TO NAVIGATION ON ARTIFICIAL ISLANDS AND FIXED STRUCTURES Class âCâ Requirements § 67.30-1 Class “C” structures. Class “C” structures shall be the structures erected in an area where Class “C...

33 CFR 67.20-1 - Class “A” structures.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Class âAâ structures. 67.20-1... NAVIGATION AIDS TO NAVIGATION ON ARTIFICIAL ISLANDS AND FIXED STRUCTURES Class âAâ Requirements § 67.20-1 Class “A” structures. Class “A” structures shall be the structures erected in an area where Class “A...

33 CFR 67.25-1 - Class “B” structures.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Class âBâ structures. 67.25-1... NAVIGATION AIDS TO NAVIGATION ON ARTIFICIAL ISLANDS AND FIXED STRUCTURES Class âBâ Requirements § 67.25-1 Class “B” structures. Class “B” structures shall be the structures erected in an area where Class “B...

Genetic diversity of Bactrocera dorsalis (Diptera: Tephritidae) on the Hawaiian islands: Implications for an introduction pathway into California

International Nuclear Information System (INIS)

Barr, Norman B.; Ledezma, Lisa A.; Bartels, David W.; Garza, Daniel; Leblanc, Luc; Jose, Michael San; Rubinoff, Daniel; Geib, Scott M.; Fujita, Brian; Kerr, Peter; Hauser, Martin; Gaimari, Stephen

2015-01-01

Population genetic diversity of the oriental fruit fly, Bactrocera dorsalis (Hendel), on the Hawaiian islands of Oahu, Maui, Kauai, and Hawaii (the Big Island) was estimated using DNA sequences of the mitochondrial cytochrome c oxidase subunit I gene. In total, 932 flies representing 36 sampled sites across the four islands were sequenced for a 1,500-bp fragment of the gene named the C1500 marker. Genetic variation was low on the Hawaiian Islands with >96% of flies having just two haplotypes: C1500- Haplotype 1 (63.2%) or C1500-Haplotype 2 (33.3%). The other 33 flies (3.5%) had haplotypes similar to the two dominant haplotypes. No population structure was detected among the islands or within islands. The two haplotypes were present at similar frequencies at each sample site, suggesting that flies on the various islands can be considered one population. Comparison of the Hawaiian data set to DNA sequences of 165 flies from outbreaks in California between 2006 and 2012 indicates that a single-source introduction pathway of Hawaiian origin cannot explain many of the flies in California. Hawaii, however, could not be excluded as a maternal source for 69 flies. There was no clear geographic association for Hawaiian or non-Hawaiian haplotypes in the Bay Area or Los Angeles Basin over time. This suggests that California experienced multiple, independent introductions from different sources. (author)

Synthesis and properties of γ-Ga2O3-Al2O3 solid solutions

Science.gov (United States)

Afonasenko, T. N.; Leont'eva, N. N.; Talzi, V. P.; Smirnova, N. S.; Savel'eva, G. G.; Shilova, A. V.; Tsyrul'nikov, P. G.

2017-10-01

The textural and structural properties of mixed oxides Ga2O3-Al2O3, obtained via impregnating γ-Al2O3 with a solution of Ga(NO3)3 and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga2O3-Al2O3 up to a Ga2O3 content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga2O3 content exceeds 50 wt %, the β-Ga2O3 phase is observed along with γ-Ga2O3-Al2O3 solid solution. 71Ga and 27Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga2O3-Al2O3.

Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

Science.gov (United States)

Sharma, N; Periasamy, C; Chaturvedi, N

2018-07-01

In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

33 CFR 334.1100 - San Pablo Bay, Carquinez Strait, and Mare Island Strait in vicinity of U.S. Naval Shipyard, Mare...

Science.gov (United States)

2010-07-01

... part of the Navy Yard, Mare Island, south of the causeway between the City of Vallejo and Mare Island... Commander, Mare Island Naval Shipyard, Vallejo, California, shall navigate, anchor or moor in this area. [26...

Atomic-scale structure of irradiated GaN compared to amorphised GaP and GaAs

International Nuclear Information System (INIS)

Ridgway, M.C.; Everett, S.E.; Glover, C.J.; Kluth, S.M.; Kluth, P.; Johannessen, B.; Hussain, Z.S.; Llewellyn, D.J.; Foran, G.J.; Azevedo, G. de M.

2006-01-01

We have compared the atomic-scale structure of ion irradiated GaN to that of amorphised GaP and GaAs. While continuous and homogenous amorphised layers were easily achieved in GaP and GaAs, ion irradiation of GaN yielded both structural and chemical inhomogeneities. Transmission electron microscopy revealed GaN crystallites and N 2 bubbles were interspersed within an amorphous GaN matrix. The crystallite orientation was random relative to the unirradiated epitaxial structure, suggesting their formation was irradiation-induced, while the crystallite fraction was approximately constant for all ion fluences beyond the amorphisation threshold, consistent with a balance between amorphisation and recrystallisation processes. Extended X-ray absorption fine structure measurements at the Ga K-edge showed short-range order was retained in the amorphous phase for all three binary compounds. For ion irradiated GaN, the stoichiometric imbalance due to N 2 bubble formation was not accommodated by Ga-Ga bonding in the amorphous phase or precipitation of metallic Ga but instead by a greater reduction in Ga coordination number

Individual GaN nanowires exhibit strong piezoelectricity in 3D.

Science.gov (United States)

Minary-Jolandan, Majid; Bernal, Rodrigo A; Kuljanishvili, Irma; Parpoil, Victor; Espinosa, Horacio D

2012-02-08

Semiconductor GaN NWs are promising components in next generation nano- and optoelectronic systems. In addition to their direct band gap, they exhibit piezoelectricity, which renders them particularly attractive in energy harvesting applications for self-powered devices. Nanowires are often considered as one-dimensional nanostructures; however, the electromechanical coupling leads to a third rank tensor that for wurtzite crystals (GaN NWs) possesses three independent coefficients, d(33), d(13), and d(15). Therefore, the full piezoelectric characterization of individual GaN NWs requires application of electric fields in different directions and measurements of associated displacements on the order of several picometers. In this Letter, we present an experimental approach based on scanning probe microscopy to directly quantify the three-dimensional piezoelectric response of individual GaN NWs. Experimental results reveal that GaN NWs exhibit strong piezoelectricity in three dimensions, with up to six times the effect in bulk. Based on finite element modeling, this finding has major implication on the design of energy harvesting systems exhibiting unprecedented levels of power density production. The presented method is applicable to other piezoelectric NW materials as well as wires manufactured along different crystallographic orientations. © 2011 American Chemical Society

Tunable band gap in epitaxial ferroelectric Ho(Mn,Ga)O{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Lee, Daesu; Noh, Tae Won, E-mail: twnoh@snu.ac.kr [Center for Correlated Electron Systems, Institute for Basic Science, Seoul 151-742 (Korea, Republic of); Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Choi, Woo Seok [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2016-05-09

Ferroelectrics have recently attracted attention as a new class of materials for use in optical and photovoltaic devices. We studied the electronic properties in epitaxially stabilized ferroelectric hexagonal Ho(Mn{sub 1−x}Ga{sub x})O{sub 3} (x = 0, 0.33, 0.67, and 1) thin films. Our films exhibited systematic changes in electronic structures, such as bandgap and optical transitions, according to the Ga concentration. In particular, the bandgap increased systematically from 1.4 to 3.2 eV, including the visible light region, with increasing Ga concentration from x = 0 to 1. These systematic changes, attributed to lattice parameter variations in epitaxial Ho(Mn{sub 1−x}Ga{sub x})O{sub 3} films, should prove useful for the design of optoelectronic devices based on ferroelectrics.

Shoreline changes in reef islands of the Central Pacific: Takapoto Atoll, Northern Tuamotu, French Polynesia

Science.gov (United States)

Duvat, Virginie K. E.; Pillet, Valentin

2017-04-01

Atoll reef islands are considered highly vulnerable to the impacts of climate change. While accelerated sea-level rise is expected to destabilize reef islands, ocean warming and acidification are considered as major threats to coral reef growth, which is of primary importance for the persistence of islands and of food supply to islanders. Using multi-date aerial imagery, shoreline and island changes between 1969 and 2013 were assessed on Takapoto Atoll, Northern Tuamotu region, in French Polynesia. Results show that over the 44-year study period, 41% of islands were stable in area while 33% expanded and 26% contracted. Island expansion was the dominant mode of change on the leeward side of the atoll. Tropical Cyclone Orama (category 3, 1983) contributed to shoreline and island change on the windward side of the atoll through the reworking of previous storm deposits and the injection of fresh sediments in the island system (with up to 62% of an island's land area being covered with fresh sediments). Human activities contributed significantly to shoreline and island change throughout the atoll through infrastructure construction, the removal of the indigenous vegetation from a number of islets and sediment mining.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

Science.gov (United States)

Anand, M. J.; Ng, G. I.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.; Syamal, B.; Zhou, X.

2015-02-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (ΔVth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 μm), the devices exhibited higher dyn-RDS[ON] degradation but a small ΔVth (˜120 mV). However, at low-EF (Lgd = 5 μm), smaller dyn-RDS[ON] degradation but a larger ΔVth (˜380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔVth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by ID-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

Scintillation characteristic of In, Ga-doped ZnO thin films with different dopant concentrations

International Nuclear Information System (INIS)

Fujimoto, Yutaka; Yanagida, Takayuki; Yokota, Yuui; Chani, Valery; Yoshikawa, Akira; Sekiwa, Hideyuki

2011-01-01

The present study describes the first detailed evaluation of the rise and the decay time of scintillation phenomenon in In 3+ - and Ga 3+ -doped ZnO thin films with different dopant concentrations. In 3+ -(25, 55, and 141 ppm) and Ga 3+ -(33, 67, 333, and 1374 ppm) doped ZnO films were grown by the Liquid Phase Epitaxy (LPE) method. The characterization was performed using the pulse X-ray equipped streak camera system. Both the rise and the decay times were shortened considerably with increasing content of In 3+ and Ga 3+ in the films. However, the scintillation light yield under 241 Am α-ray excitation reduced when concentration of In 3+ and Ga 3+ in the ZnO films was high. (author)

Modulation of transcription factor binding and epigenetic regulation of the MLH1 CpG island and shore by polymorphism rs1800734 in colorectal cancer.

Science.gov (United States)

Savio, Andrea J; Bapat, Bharati

2017-06-03

The MLH1 promoter polymorphism rs1800734 is associated with MLH1 CpG island hypermethylation and expression loss in colorectal cancer (CRC). Conversely, variant rs1800734 is associated with MLH1 shore, but not island, hypomethylation in peripheral blood mononuclear cell DNA. To explore these distinct patterns, MLH1 CpG island and shore methylation was assessed in CRC cell lines stratified by rs1800734 genotype. Cell lines containing the variant A allele demonstrated MLH1 shore hypomethylation compared to wild type (GG). There was significant enrichment of transcription factor AP4 at the MLH1 promoter in GG and GA cell lines, but not the AA cell line, by chromatin immunoprecipitation studies. Preferential binding to the G allele was confirmed by sequencing in the GA cell line. The enhancer-associated histone modification H3K4me1 was enriched at the MLH1 shore; however, H3K27ac was not, indicating the shore is an inactive enhancer. These results demonstrate the role of variant rs1800734 in altering transcription factor binding as well as epigenetics at regions beyond the MLH1 CpG island in which it is located.

Ga2O3 nanowires preparation at atmospheric pressure

Directory of Open Access Journals (Sweden)

Korbutowicz R.

2017-07-01

Full Text Available An attempt has been undertaken to produce gallium oxide nanowires by thermal synthesis from metallic gallium source at atmospheric pressure. Silicon substrates of (1 0 0 and (1 1 1 orientation with and without silicon oxide layers (0.5 μm were used as support. Evaporated thin gold films were deposited on the top of those silicon carriers as a catalytic agent. After thermal treatment by Rapid Thermal Processing RTP (at various temperatures and times, which was applied to make small Au islands with the diameters of about several tens of nanometers, the substrate surfaces were observed by SEM. The Ga2O3 syntheses were made at various conditions: time, temperature and gas mixture were changed. As a result, monoclinic gallium oxide β-Ga2O3 nanostructures with dominant [1 1 1] and [0 0 2] growth directions were grown. The obtained nanostructures of several tens micrometers length were studied by SEM, PL and X-ray methods.

Triple-axis X-ray reciprocal space mapping of In{sub y}Ga{sub 1-y}As thermophotovoltaic diodes grown on (1 0 0) InP substrates

Energy Technology Data Exchange (ETDEWEB)

Dashiell, M.W.; Ehsani, H.; Sander, P.C. [Lockheed Martin Corporation, Schenectady, NY 12301-1072 (United States); Newman, F.D. [Emcore Corporation, Albuquerque, NM 87123 (United States); Wang, C.A. [MIT Lincoln Laboratory, Lexington, MA 02420 (United States); Shellenbarger, Z.A. [Sarnoff Corporation, Princeton NJ, 08543-5300 (United States); Donetski, D.; Gu, N.; Anikeev, S. [Department of Electrical Engineering, State University of New York, Stony Brook, NY 11794-2350 (United States)

2008-09-15

Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of In{sub y}Ga{sub 1-y}As/InP{sub 1-x}As{sub x} thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In{sub 0.53}Ga{sub 0.47}As (E{sub gap}=0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In{sub 0.67}Ga{sub 0.33}As (E{sub gap}=0.6 eV) TPV diodes are grown on three-step InP{sub 1-x}As{sub x} (0Ga{sub 1-y}As TPV active layer and underlying InP{sub 1-x}As{sub x} buffers. Triple-axis X-ray rocking curves about the LMM In{sub 0.67}Ga{sub 0.33}As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In{sub 0.53}Ga{sub 0.47}As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In{sub 0.67}Ga{sub 0.33}As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In{sub 0.67}Ga{sub 0.33}As material compared with the intrinsic recombination processes and/or recombination through native point defects, which would be present in both LMM and LM diode material. However, additional RELP broadening in non-optimized LMM In{sub 0.67}Ga{sub 0.33}As n/p junction diodes does correspond to significant degradation of TPV diode open-circuit voltage and minority carrier lifetime demonstrating that there is correlation between X-ray FWHM and the electronic performance of the LMM TPV diodes. (author)

Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

International Nuclear Information System (INIS)

Liu, H F; Chi, D Z; Liu, W; Guo, S

2016-01-01

High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal–organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [–4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al 2 O 3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings. (paper)

Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

Science.gov (United States)

Liu, H. F.; Liu, W.; Guo, S.; Chi, D. Z.

2016-03-01

High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal-organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [-4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al2O3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings.

Spectroscopic ellipsometry analysis of InGaN/GaN and AlGaN/GaN heterostructures using a parametric dielectric function model

International Nuclear Information System (INIS)

Wagner, J.; Ramakrishnan, A.; Obloh, H.; Kunzer, M.; Koehler, K.; Johs, B.

2000-01-01

Spectroscopic ellipsometry (SE) has been used for the characterization of AlGaN/GaN and InGaN/GaN heterostructures. The resulting pseudodielectric function spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. From this analysis, the dielectric function spectra of GaN, Al x Ga 1-x N (x le 0.16), and In 0.13 Ga 0.87 N were deduced. Further, the dependence of the Al x Ga 1-x N band gap energy on the Al mole fraction was derived and compared with photoluminescence data recorded on the same material. The SE band gap data are compatible with a bowing parameter close to 1 eV for the composition dependence of the Al x Ga 1-x N gap energy. Finally, the parametric dielectric functions have been used to model the pseudodielectric function spectrum of a complete GaN/AlGaN/InGaN LED structure

InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor

International Nuclear Information System (INIS)

Chang, P. C.; Baca, A. G.; Li, N. Y.; Xie, X. M.; Hou, H. Q.; Armour, E.

2000-01-01

We have demonstrated a functional NpN double-heterojunction bipolar transistor (DHBT) using InGaAsN for the base layer. The InGaP/In 0.03 Ga 0.97 As 0.99 N 0.01 /GaAs DHBT has a low V ON of 0.81 V, which is 0.13 V lower than in a InGaP/GaAs heterojunction bipolar transistor (HBT). The lower turn-on voltage is attributed to the smaller band gap (1.20 eV) of metalorganic chemical vapor deposition-grown In 0.03 Ga 0.97 As 0.99 N 0.01 base layer. GaAs is used for the collector; thus the breakdown voltage (BV CEO ) is 10 V, consistent with the BV CEO of InGaP/GaAs HBTs of comparable collector thickness and doping level. To alleviate the current blocking phenomenon caused by the larger conduction band discontinuity between InGaAsN and GaAs, a graded InGaAs layer with δ doping is inserted at the base-collector junction. The improved device has a peak current gain of seven with ideal current-voltage characteristics. (c) 2000 American Institute of Physics

33 CFR 80.1490 - Apra Harbor, U.S. Territory of Guam.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Apra Harbor, U.S. Territory of Guam. 80.1490 Section 80.1490 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1490 Apra Harbor, U...

Methanol sensor for integration with GaP nanowire photocathode

Science.gov (United States)

Novák, J.; Laurenčíková, A.; Hasenohrl, S.; Eliáš, P.; Kováč, J.

2017-05-01

We proposed a new type of the methanol concentration sensor that may be integrated directly to the GaP nanostructured photocathode. Necessary attribute for this design is the possibility to make it compatible with p-type of semiconductor. This condition follows from the fact that photocathodes for the CO2 splitting are exclusively prepared from p-type of semiconductors. Design of methanol sensor emanates from this principle. On the GaP substrate is deposited thin Pt supporting layer (100-200 nm thick).This layer is covered by 500 nm thick Nafion membrane that serves as proton filter. On the top of Nafion layer is deposited top Pt contact layer covered by thin nanostructured Pt layer layer with various thickness (0.5 -5 nm). This nanostructured Pt is formed into small islands. It serves as an absorption layer for methanol. Sensor detection properties were estimated from monitoring of I-V characteristics. They were measured in dark and under various methanol concentrations. Dark current values are in order 10-9 A, and this current increases up to order of microamps for methanol of concentration more than 95%.These measurements proved high sensitivity of the GaP compatible sensor structure. Methanol sensors were realized in form of narrow stripe on the side of the photocathode.

Effect of GaN buffer polarization on electron distribution of AlGaN/GaN heterostructure

International Nuclear Information System (INIS)

He, Xiaoguang; Zhao, Degang; Liu, Wei; Yang, Jing; Li, Xiaojing; Li, Xiang

2016-01-01

The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. A misunderstanding about the 2DEG sheet density expression is clarified. It is predicted by theoretical analysis and validated by self-consistent Schrodinger–Poisson numerical simulation that under the force of GaN polarization, large amounts of electrons will accumulate at the GaN/substrate interface in AlGaN/GaN/substrate HEMT structure. - Highlights: • The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. • Self-consistent Schrodinger–Poisson numerical simulation is used to modulate the AlGaN/GaN/substrate structure. • It is predicted by that large amounts of electrons will accumulate at the GaN/substrate interface.

Effect of GaN buffer polarization on electron distribution of AlGaN/GaN heterostructure

Energy Technology Data Exchange (ETDEWEB)

He, Xiaoguang; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Liu, Wei; Yang, Jing; Li, Xiaojing; Li, Xiang

2016-06-15

The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. A misunderstanding about the 2DEG sheet density expression is clarified. It is predicted by theoretical analysis and validated by self-consistent Schrodinger–Poisson numerical simulation that under the force of GaN polarization, large amounts of electrons will accumulate at the GaN/substrate interface in AlGaN/GaN/substrate HEMT structure. - Highlights: • The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. • Self-consistent Schrodinger–Poisson numerical simulation is used to modulate the AlGaN/GaN/substrate structure. • It is predicted by that large amounts of electrons will accumulate at the GaN/substrate interface.

Soil N mineralization profiles of co-existing woody vegetation islands at the alpine tree line

Czech Academy of Sciences Publication Activity Database

Wang, L.; Godbold, Douglas

2017-01-01

Roč. 136, 5-6 (2017), s. 881-892 ISSN 1612-4669 R&D Projects: GA MŠk(CZ) LO1415 Institutional support: RVO:67179843 Keywords : Tree line * Soil N mineralization * in situ field incubation * Soil N availability * Resin capsule * Woody vegetation islands Subject RIV: DF - Soil Science OBOR OECD: Soil science Impact factor: 2.017, year: 2016

Land-use change and managed aquifer recharge effects on the hydrogeochemistry of two contrasting atoll island aquifers, Roi-Namur Island, Republic of the Marshall Islands

Science.gov (United States)

Hejazian, Mehrdad; Gurdak, Jason J.; Swarzenski, Peter W.; Odigie, Kingsley; Storlazzi, Curt

2017-01-01

Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 x 105 m3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 x 104 m3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using PHREEQC to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a seven-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land-use/land-cover change and

Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

International Nuclear Information System (INIS)

Lee, Sung-Nam; Paek, H.S.; Son, J.K.; Sakong, T.; Yoon, E.; Nam, O.H.; Park, Y.

2006-01-01

We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

AlGaAs/InGaAs/AlGaAs double pulse doped pseudomorphic high electron mobility transistor structures on InGaAs substrates

Science.gov (United States)

Hoke, W. E.; Lyman, P. S.; Mosca, J. J.; McTaggart, R. A.; Lemonias, P. J.; Beaudoin, R. M.; Torabi, A.; Bonner, W. A.; Lent, B.; Chou, L.-J.; Hsieh, K. C.

1997-10-01

Double pulse doped AlGaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistor (PHEMT) structures have been grown on InxGa1-xAs (x=0.025-0.07) substrates using molecular beam epitaxy. A strain compensated, AlGaInAs/GaAs superlattice was used for improved resistivity and breakdown. Excellent electrical and optical properties were obtained for 110-Å-thick InGaAs channel layers with indium concentrations up to 31%. A room temperature mobility of 6860 cm2/V s with 77 K sheet density of 4.0×1012cm-2 was achieved. The InGaAs channel photoluminescence intensity was equivalent to an analogous structure on a GaAs substrate. To reduce strain PHEMT structures with a composite InGaP/AlGaAs Schottky layer were also grown. The structures also exhibited excellent electrical and optical properties. Transmission electron micrographs showed planar channel interfaces for highly strained In0.30Ga0.70As channel layers.

Two new Np--Ga phases: α-NpGa2 and metastable m-NpGa2

International Nuclear Information System (INIS)

Giessen, B.C.; Elliott, R.O.

1976-01-01

Following an earlier study of metastable Np-rich Np--Ga alloys, rapidly quenched Np--Ga alloys with 63 to 80 at. pct. Ga were prepared and studied. Two new NpGa 2 phases, both with an AlB 2 type structure, were found: α-NpGa 2 , with a = 4.246A, c = 4.060A, c/a = 0.956, and m-NpGa 2 , with a = 4.412A, c = 3.642A, c/a = 0.825. While m-NpGa 2 was observed only in very fast quenched (splat cooled) samples and appears to be metastable, α-NpGa 2 is probably an equilibrium phase. In a splat cooled alloy with 75 at. pct. Ga, another, unidentified, metastable phase was observed. Crystal chemical discussions of atomic volumes, interatomic distances and axial ratios are given; the volume difference between the two forms of NpGa 2 is correlated with a valence change of Np

Catalyst and processing effects on metal-assisted chemical etching for the production of highly porous GaN

International Nuclear Information System (INIS)

Geng, Xuewen; Grismer, Dane A; Bohn, Paul W; Duan, Barrett K; Zhao, Liancheng

2013-01-01

Metal-assisted chemical etching is a facile method to produce micro-/nanostructures in the near-surface region of gallium nitride (GaN) and other semiconductors. Detailed studies of the production of porous GaN (PGaN) using different metal catalysts and GaN doping conditions have been performed in order to understand the mechanism by which metal-assisted chemical etching is accomplished in GaN. Patterned catalysts show increasing metal-assisted chemical etching activity to n-GaN in the order Ag < Au < Ir < Pt. In addition, the catalytic behavior of continuous films is compared to discontinuous island films. Continuous metal films strongly shield the surface, hindering metal-assisted chemical etching, an effect which can be overcome by using discontinuous films or increasing the irradiance of the light source. With increasing etch time or irradiance, PGaN morphologies change from uniform porous structures to ridge and valley structures. The doping type plays an important role, with metal-assisted chemical etching activity increasing in the order p-GaN < intrinsic GaN < n-GaN. Both the catalyst identity and the doping type effects are explained by the work functions and the related band offsets that affect the metal-assisted chemical etching process through a combination of different barriers to hole injection and the formation of hole accumulation/depletion layers at the metal–semiconductor interface. (paper)

Investigation and comparison of GaN nanowire nucleation and growth by the catalyst-assisted and self-induced approaches

Energy Technology Data Exchange (ETDEWEB)

Cheze, Caroline

2010-03-04

This work focuses on the nucleation and growth mechanisms of GaN nanowires (NWs) by molecular beam epitaxy (MBE). The two main novelties of this study are the intensive employment of in-situ techniques and the direct comparison of selfinduced and catalyst-induced NWs. On silicon substrates, GaN NWs form in MBE without the use of any external catalyst seed. On sapphire, in contrast, NWs grow under identical conditions only in the presence of Ni seeds. NW nucleation was studied in situ by reflection high-energy electron diffraction (RHEED) in correlation with line-of-sight quadrupole mass spectrometry (QMS). The latter technique allows to monitor the incorporated amount of Ga. For the catalyst-assisted approach, three nucleation stages were identified: first incorporation of Ga into the Ni seeds, second transformation of the seed crystal structure due to Ga accumulation, and last GaN growth under the seeds. The crystalline structure of the seeds during the first two stages is in accord with the Ni-Ga binary phase diagram and evidenced that only Ga incorporates into the Ni particles. GaN forms only after the Ga concentration is larger than the one of Ni. The observation of diffraction patterns generated by the Ni-Ga seed particles during the whole nucleation evidences the solid state of the seeds. Moreover, the QMS study showed that it is not Ga incorporation into Ni but GaN nucleation itself that limits the growth processes. For the self-induced NWs, QMS and RHEED investigations indicate very similar nucleation processes on Si(001) and Si(111) and two nucleation stages were identified. Transmission electron microscopy on samples grown on Si(001) revealed that the first stage is characterized by the competition between the nucleation of crystalline Si{sub x}N{sub y} and GaN. During this stage, the Si surface strongly roughens by the formation of pits and Si mounds. At the same time, very few GaN islands nucleate. During the second stage, the amorphization of the Si

Antisites and anisotropic diffusion in GaAs and GaSb

KAUST Repository

Tahini, H. A.; Bracht, H.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

2013-01-01

The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport

Photoluminescence characterization of GaAs/GaAs0.64P0.19Sb0.17/GaAs heterostructure

International Nuclear Information System (INIS)

Chen, J.Y.; Chen, B.H.; Huang, Y.S.; Chin, Y.C.; Tsai, H.S.; Lin, H.H.; Tiong, K.K.

2013-01-01

Interfacial characteristics of GaAs/GaAs 0.64 P 0.19 Sb 0.17 GaAs heterostructures and emission properties of a quaternary GaAs 0.64 P 0.19 Sb 0.17 layer were studied by excitation-power- and temperature-dependent photoluminescence (PL) measurements. The GaAs-to-GaAsPSb upper interface related emission feature and signals from GaAsPSb and GaAs were observed and characterized. The upper interface related emission peak was attributed to the radiative recombination of spatially separated electron–hole pairs and suggesting the type-II alignment at the GaAs/GaAsPSb interface. The localized excitonic emission feature of GaAsPSb revealed a blueshift due to the saturation effect of localized states and showed a fast thermal-quench with the increase of temperature. The temperature variation of the band edge emission signal of GaAsPSb was found to follow that of GaAs closely. -- Highlights: ► PL characterization of GaAs/GaAsPSb/GaAs heterostructure. ► Type-II alignment at the GaAs/GaAsPSb interface. ► Near-band-edge emission lines of GaAsPSb

GaN-based ultraviolet light-emitting diodes with AlN/GaN/InGaN multiple quantum wells.

Science.gov (United States)

Chang, Hung-Ming; Lai, Wei-Chih; Chen, Wei-Shou; Chang, Shoou-Jinn

2015-04-06

We demonstrate indium gallium nitride/gallium nitride/aluminum nitride (AlN/GaN/InGaN) multi-quantum-well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) to improve light output power. Similar to conventional UV LEDs with AlGaN/InGaN MQWs, UV LEDs with AlN/GaN/InGaN MQWs have forward voltages (V(f)'s) ranging from 3.21 V to 3.29 V at 350 mA. Each emission peak wavelength of AlN/GaN/InGaN MQW UV LEDs presents 350 mA output power greater than that of the corresponding emission peak wavelength of AlGaN/InGaN MQW UV LEDs. The light output power at 350mA of AlN/GaN/InGaN MQWs UV LEDs with 375 nm emission wavelength can reach around 26.7% light output power enhancement in magnitude compared to the AlGaN/InGaN MQWs UV LEDs with same emission wavelength. But 350mA light output power of AlN/GaN/InGaN MQWs UV LEDs with emission wavelength of 395nm could only have light output power enhancement of 2.43% in magnitude compared with the same emission wavelength AlGaN/InGaN MQWs UV LEDs. Moreover, AlN/GaN/InGaN MQWs present better InGaN thickness uniformity, well/barrier interface quality and less large size pits than AlGaN/InGaN MQWs, causing AlN/GaN/InGaN MQW UV LEDs to have less reverse leakage currents at -20 V. Furthermore, AlN/GaN/InGaN MQW UV LEDs have the 2-kV human body mode (HBM) electrostatic discharge (ESD) pass yield of 85%, which is 15% more than the 2-kV HBM ESD pass yield of AlGaN/InGaN MQW UV LEDs of 70%.

Phlebotomine sand flies of edible-nest swiftlet cave of Lang Ga Jiew Island, Chumphon province, Thailand.

Science.gov (United States)

Chittsamart, B; Samruayphol, Suchada; Sungvorayothin, Sangsit; Pothiwat, Ratcharin; Samung, Yudthana; Apiwathnasorn, Chamnarn

2015-09-01

The present study reported for the first time phlebotomine sandfly species inhabiting edible-nest swiftlet cave of the isolated island, based on field collections made during June 2010-May 2011. The insect diversity was relatively lower to that of mainland caves. All species, Phlebotomus stantoni, Sergentomyia anodontis, Sergentomyia bailyi, Sergentomyia gemmea, Sergentomyia hodgsoni and Sergentomyia punjabensis were either endemic island species or native elsewhere in Thailand. Sergentomyia hodgsoni was the most prevalent species accounted for 94.7% and classified as a troglophile species. Seasonal pattern of the phlebotomine abundance and some aspects of their population characteristics were described and discussed. Two ectoparasites, Ornithodorus and Paracimex sp. were also incidentally collected from the swiftlet cave.

Shot noise reduction in the AlGaAs/GaAs- and InGaP/GaAs-based HBTs

Science.gov (United States)

Sakalas, Paulius; Schroeter, Michael; Zampardi, Peter; Zirath, Herbert

2003-05-01

Noise parameters of AlGaAs/GaAs and InGaP/GaAs HBTs were measured in microwave frequency range and modeled using the small-signal equivalent circuit approach. Correlated current noise sources in the base and collector currents with thermal noise in the circuit resistive elements were accounted for by the model and yielded good agreement with the measured data. This enabled an extraction of the different noise source contributions to minimum noise figure (NFmin) in AlGaAs/GaAs and InGaP/GaAs HBTs. Decomposition of the (NFmin) in to the different contributors showed that the main noise sources in investigated HBTs are correlated base and collector current shot noise. The observed minimum of NFmin versus frequency at lower collector current is explained by the reduction of the emitter/base junction shot noise component due to the spike in the emitter/base junction and associated accumulation of the quasi-thermalized electrons forming a space charge, which screens the electron transfer through the barrier. The bias (VCE) increase creates an efficient electric field in collector/base junction, capable of 'washing out' the accumulated charge. Such shot noise reduction in HBTs could be exploited in the LNA for the RF application.

CFD prediction of heat island formation on growing Asian cities. Effect of urbanization in Shanghai; Kyodaikasuru Asia no toshi ni okeru heat island keisei ni kansuru CFD yosoku. Shanghai no toshika ga oyobosu eikyo ni kansuru kento

Energy Technology Data Exchange (ETDEWEB)

Ojima, T.; Murakami, S. [The University of Tokyo, Tokyo (Japan). Institute of Industrial Science; Mitsumoto, K. [Waseda University, Tokyo (Japan). School of Science and Engineering

1997-10-01

Study is conducted of the effect of change in land use and increase in artificial exhaust heat on heat island formation in Shanghai. Concerning the land use distribution in Shanghai, a point sampling survey was conducted in the 1930s using topographic charts, when the area was broken down into building-occupied region, paddy field, bare ground, and waters. In the 1990s, thanks to data from satellites, high-density and low-density urban regions have added. Calculation for Shanghai is performed, based on the rate of increase in Tokyo`s population and data predicted for Shanghai`s population, on the assumption that Shanghai`s population in the 2050s will grow 2.3 times larger than it is in the 1990s. The prediction thus produced indicates that the urban area in Shanghai in the 2050s will be as large as that of the present-day Tokyo that covers a 50km zone. Heat island formation prediction for Shanghai is worked out using computational fluid dynamics (CFD)-aided simulation. According to the prediction, while the maximum temperature in the 1930s was 29.6degC or 4degC higher than in the suburbs, it is 33.2degC or 7.6deg higher in the 1990s, and will be 34.4degC or 8.6degC higher in the 2050s. 16 refs., 11 figs., 1 tab.

Investigation of 'surface donors' in Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructures: Correlation of electrical, structural, and chemical properties

Science.gov (United States)

Ťapajna, M.; Stoklas, R.; Gregušová, D.; Gucmann, F.; Hušeková, K.; Haščík, Š.; Fröhlich, K.; Tóth, L.; Pécz, B.; Brunner, F.; Kuzmík, J.

2017-12-01

III-N surface polarization compensating charge referred here to as 'surface donors' (SD) was analyzed in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) heterojunctions using scaled oxide films grown by metal-organic chemical vapor deposition at 600 °C. We systematically investigated impact of HCl pre-treatment prior to oxide deposition and post-deposition annealing (PDA) at 700 °C. SD density was reduced down to 1.9 × 1013 cm-2 by skipping HCl pre-treatment step as compared to 3.3 × 1013 cm-2 for structures with HCl pre-treatment followed by PDA. The nature and origin of SD was then analyzed based on the correlation between electrical, micro-structural, and chemical properties of the Al2O3/GaN interfaces with different SD density (NSD). From the comparison between distributions of interface traps of MOS heterojunction with different NSD, it is demonstrated that SD cannot be attributed to interface trapped charge. Instead, variation in the integrity of the GaOx interlayer confirmed by X-ray photoelectron spectroscopy is well correlated with NSD, indicating SD may be formed by border traps at the Al2O3/GaOx interface.

Catalytic applications and FTIR investigation of zeolite SSZ-33 after isomorphous substitution

Czech Academy of Sciences Publication Activity Database

Vitvarová, Dana; Kurfiřtová, Lenka; Kubů, Martin; Žilková, Naděžda

2014-01-01

Roč. 194, AUG 2014 (2014), s. 174-182 ISSN 1387-1811 R&D Projects: GA ČR GAP106/11/0819 Institutional support: RVO:61388955 Keywords : SSZ-33 * acidity * toluene alkylation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.453, year: 2014

Growth morphology and structure of bismuth thin films on GaSb(110)

DEFF Research Database (Denmark)

Gemmeren, T. van; Lottermoser, L.; Falkenberg, G.

1998-01-01

Photoelectron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy and surface X-ray diffraction were used to investigate the growth of thin layers of bismuth on GaSb(110). At submonolayer coverages, growth of two-dimensional islands occurs. A uniform (1 x I)-reconstructio...... that the (1 x 1)-phases formed by antimony and bismuth adsorbates on (110) surfaces of other III-V compound semiconductors are also described by the epitaxial continued layer model. (C) 1998 Elsevier Science B.V. All rights reserved....

High breakdown voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN quantum-well electron-blocking layers.

Science.gov (United States)

Lee, Ya-Ju; Yao, Yung-Chi; Huang, Chun-Ying; Lin, Tai-Yuan; Cheng, Li-Lien; Liu, Ching-Yun; Wang, Mei-Tan; Hwang, Jung-Min

2014-01-01

In this paper, we numerically study an enhancement of breakdown voltage in AlGaN/GaN high-electron-mobility transistors (HEMTs) by using the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking layer (EBL) structure. This concept is based on the superior confinement of two-dimensional electron gases (2-DEGs) provided by the QW EBL, resulting in a significant improvement of breakdown voltage and a remarkable suppression of spilling electrons. The electron mobility of 2-DEG is hence enhanced as well. The dependence of thickness and composition of QW EBL on the device breakdown is also evaluated and discussed.

Self-consistent simulation of carrier confinement characteristics in (AlyGa1−yN/AlN)SLs/GaN/(InxGa1−xN/GaN)MQW/GaN heterostructures

International Nuclear Information System (INIS)

Ding Jieqin; Wang Xiaoliang; Xiao Hongling; Wang Cuimei; Yin Haibo; Chen Hong; Feng Chun; Jiang Lijuan

2012-01-01

Highlights: ► We present calculations of carrier confinement characteristics. ► An optimization of In x Ga 1−x N/GaN multiquantum-well (MQW) was made. ► 2DEG sheet carrier density in designed heterostructure is greatly increased. ► Interface roughness and alloy disorder scattering reduced. ► Carrier mobility will be improved in designed heterostructure. - Abstract: We present calculations of carrier confinement characteristics in (Al y Ga 1−y N/AlN)SLs/GaN/(In x Ga 1−x N/GaN)MQW/GaN heterojunction structure in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. An optimization of In x Ga 1−x N/GaN multiquantum-well (MQW) was made firstly including thickness of GaN channel, InGaN, and indium composition of In x Ga 1−x N in order to increase carrier density and mobility, and the influence of pairs of AlGaN/AlN superlattices (SLs) and InGaN/GaN MQWs on structure was discussed. Theoretical calculations clearly indicate that the two-dimensional electron gas (2DEG) sheet carrier density in designed heterostructure is greatly increased due to the enhancing of carrier confinement compared to those in conventional AlGaN/GaN one at the similar Al composition. Furthermore, the calculated carrier distribution shows that carrier mobility will be improved by reducing interface roughness and alloy disorder scattering in designed heterostructure.

AlGaN/GaN double-channel HEMT

International Nuclear Information System (INIS)

Quan Si; Hao Yue; Ma Xiaohua; Zheng Pengtian; Xie Yuanbin

2010-01-01

The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied. (semiconductor devices)

Antisites and anisotropic diffusion in GaAs and GaSb

KAUST Repository

Tahini, H. A.

2013-10-02

The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport. To reconcile the existence of Ga vacancies under Ga-rich conditions, transformation reactions have been proposed. Here, density functional theory is employed to calculate the formation energies of vacancies on both sublattices and the migration energy barriers to overcome the formation of the vacancy-antisite defect. Transformation reactions enhance the vacancy concentration in both materials and migration energy barriers indicate that Ga vacancies will dominate.

AlGaN nanocolumns and AlGaN/GaN/AlGaN nanostructures grown by molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Ristic, J.; Sanchez-Garcia, M.A.; Ulloa, J.M.; Calleja, E. [Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Sanchez-Paramo, J.; Calleja, J.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Jahn, U.; Trampert, A.; Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

2002-12-01

This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E{sub 2} phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

Spatiotemporal patterns of coral disease prevalence on Heron Island, Great Barrier Reef, Australia

Science.gov (United States)

Haapkylä, J.; Melbourne-Thomas, J.; Flavell, M.; Willis, B. L.

2010-12-01

Despite increasing research effort on coral diseases, little is known about factors driving disease dynamics on the Great Barrier Reef (GBR). This is the first study to investigate the temporal patterns of coral disease prevalence and potential drivers of disease around Heron Island, in the southern Capricorn Bunker sector of the GBR. Surveys were conducted in two austral summers and three winters between November 2007 and August 2009 on six sites around the island. Six diseases were detected: brown band syndrome (BrB), growth anomalies (GA), ulcerative white spots (UWS), white syndrome (WS), skeletal eroding band disease (SEB) and black band disease (BBD). The lowest overall mean disease prevalence was 1.87 ± 0.75% (mean ± SE) in November 2007 and the highest 4.22 ± 1.72% in August 2008. There was evidence of seasonality for two diseases: BrB and UWS. This is the first study to report a higher prevalence of BrB in the winter. BrB had a prevalence of 3.29 ± 0.58% in August 2008 and 1.53 ± 0.28% in August 2009, while UWS was the most common syndrome in the summer with a prevalence of 1.12 ± 0.31% in November 2007 and 2.67 ± 0.52% prevalence in January 2008. The prevalence of GAs and SEB did not depend on the season, although the prevalence of GAs increased throughout the study period. WS had a slightly higher prevalence in the summer, but its overall prevalence was low (disease prevalence (12% of Acropora and 3.3% of Montipora species were diseased respectively). These results highlight the correlations between coral disease prevalence, seasonally varying environmental parameters and coral community composition. Given that diseases are likely to reduce the resilience of corals, seasonal patterns in disease prevalence deserve further research.

AlGaN/GaN HEMT structures on ammono bulk GaN substrate

International Nuclear Information System (INIS)

Kruszewski, P; Prystawko, P; Krysko, M; Smalc-Koziorowska, J; Leszczynski, M; Kasalynas, I; Nowakowska-Siwinska, A; Plesiewicz, J; Dwilinski, R; Zajac, M; Kucharski, R

2014-01-01

The work shows a successful fabrication of AlGaN/GaN high electron mobility transistor (HEMT) structures on the bulk GaN substrate grown by ammonothermal method providing an ultralow dislocation density of 10 4  cm −2  and wafers of size up to 2 inches in diameter. The AlGaN layers grown by metalorganic chemical vapor phase epitaxy method demonstrate atomically smooth surface, flat interfaces with reproduced low dislocation density as in the substrate. The test electronic devices—Schottky diodes and transistors—were designed without surface passivation and were successfully fabricated using mask-less laser-based photolithography procedures. The Schottky barrier devices demonstrate exceptionally low reverse currents smaller by a few orders of magnitude in comparison to the Schottky diodes made of AlGaN/GaN HEMT on sapphire substrate. (paper)

Ten unique and charismatic new species of Microgastrinae wasps (Hymenoptera, Braconidae from North America

Directory of Open Access Journals (Sweden)

Jose Fernandez-Triana

2018-01-01

Full Text Available Ten new species within four genera of Microgastrinae parasitoid wasps (Hymenoptera: Braconidae are described from Canada and United States: Diolcogaster ichiroi, Diolcogaster miamensis, Glyptapanteles pseudotsugae, Microgaster archboldensis, Microgaster syntopic, Microplitis altissimus, Microplitis jorgeluisi, Microplitis juanmanueli, Microplitis julioalbertoi, and Microplitis mariamargaritae. The new taxa are significant because they represent the first North American records of a tropical group (species of the basimacula group in Diolcogaster, exemplify interesting ecological cases (niche-based host selection in Glyptapanteles, syntopic species in Microgaster, and showcase unique morphological features and/or altitudinal records (Microplitis. Most of the new species were collected in protected areas or areas with strong research programs (Archbold Biological Station and hammock forests near Miami, Florida; Great Sand Dunes National Park and Preserve, and Mount Evans Wilderness Area, Colorado; Sapelo Island, Georgia; Tonto National Forest, Arizona, and thus are also of value and interest for conservation and research efforts.

Modeling and optimization of a double-well double-barrier GaN/AlGaN/GaN/AlGaN resonant tunneling diode

Science.gov (United States)

Liu, Yang; Gao, Bo; Gong, Min; Shi, Ruiying

2017-06-01

The influence of a GaN layer as a sub-quantum well for an AlGaN/GaN/AlGaN double barrier resonant tunneling diode (RTD) on device performance has been investigated by means of numerical simulation. The introduction of the GaN layer as the sub-quantum well turns the dominant transport mechanism of RTD from the 3D-2D model to the 2D-2D model and increases the energy difference between tunneling energy levels. It can also lower the effective height of the emitter barrier. Consequently, the peak current and peak-to-valley current difference of RTD have been increased. The optimal GaN sub-quantum well parameters are found through analyzing the electrical performance, energy band, and transmission coefficient of RTD with different widths and depths of the GaN sub-quantum well. The most pronounced electrical parameters, a peak current density of 5800 KA/cm2, a peak-to-valley current difference of 1.466 A, and a peak-to-valley current ratio of 6.35, could be achieved by designing RTD with the active region structure of GaN/Al0.2Ga0.8 N/GaN/Al0.2Ga0.8 N (3 nm/1.5 nm/1.5 nm/1.5 nm).

Bipolar characteristics of AlGaN/AlN/GaN/AlGaN double heterojunction structure with AlGaN as buffer layer

International Nuclear Information System (INIS)

Peng, Enchao; Wang, Xiaoliang; Xiao, Hongling; Wang, Cuimei; Yin, Haibo; Chen, Hong; Feng, Chun; Jiang, Lijuan; Hou, Xun; Wang, Zhanguo

2013-01-01

Highlights: •2DEG and 2DHG coexist in the AlGaN/AlN/GaN/AlGaN DH-structure. •The sheet densities of 2DEG and 2DHG vary with buffer Al content and GaN thickness. •The conditions for the disappearance of 2DHG are discussed. •Increasing buffer Al content provides better electron confinement. •Dislocation scattering is reduced in the DH-structure. -- Abstract: This is a theoretical study of AlGaN/AlN/GaN/AlGaN double heterojunction (DH) structure with AlGaN as buffer layer. Our calculation shows that as the buffer Al content increases, though two-dimensional electron gas (2DEG) sheet density decreases, the channel back-barrier caused by polarization-induced electric field in GaN provides better electron confinement. And under certain conditions the DH-structure shows bipolar characteristics, with an additional two-dimensional hole gas (2DHG) formed at GaN/AlGaN interface. The influence of the buffer Al content and GaN channel thickness on the 2DEG and 2DHG sheet densities are investigated, and the conditions for the disappearance of 2DHG are discussed. Also, the mobility inhibited by dislocation scattering is enhanced in DH-structure due to the enhancement of screening effect of the 2DEG

Development and recent activity of the San Andrés landslide on El Hierro, Canary Islands, Spain

Czech Academy of Sciences Publication Activity Database

Klimeš, Jan; Yepes, J.; Becerril, L.; Kusák, Michal; Galindo, I.; Blahůt, Jan

2016-01-01

Roč. 261, MAY 15 (2016), s. 119-131 ISSN 0169-555X R&D Projects: GA MŠk LM2010008 Grant - others: National Geographic Society W244-12 Institutional support: RVO:67985891 Keywords : Deep-seated gravitational slope deformations (DSGSDs) * Landslide monitoring * Creep movements * Canary Islands Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 2.958, year: 2016

ECV profiling of GaAs and GaN HEMT heterostructures

Science.gov (United States)

Yakovlev, G.; Zubkov, V.

2018-03-01

AlGaAs/InGaAs/GaAs and AlGaN/GaN HEMT heterostructures were investigated by means of electrochemical capacitance-voltage technique. A set of test structures were fabricated using various doping techniques: standard doping, δ-doping GaAs pHEMT and nondoping GaN HEMT. The concentration profiles of free charge carriers across the samples were experimentally obtained. The QW filling was analyzed and compared for different mechanisms of emitter doping and 2DEG origins.

Comparison of electrical characteristic between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

International Nuclear Information System (INIS)

Lü Yuan-Jie; Feng Zhi-Hong; Gu Guo-Dong; Dun Shao-Bo; Yin Jia-Yun; Han Ting-Ting; Cai Shu-Jun; Lin Zhao-Jun

2014-01-01

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated. Based on the measured current—voltage and capacitance—voltage curves, the electrical characteristics of AlN/GaN Schottky diode, such as Schottky barrier height, turn-on voltage, reverse breakdown voltage, ideal factor, and the current-transport mechanism, are analyzed and then compared with those of an AlGaN/GaN diode by self-consistently solving Schrödinger's and Poisson's equations. It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes. However, more dislocation defects and a thinner barrier layer for AlN/GaN heterostructure results in a larger tunneling probability, and causes a larger leakage current and lower reverse breakdown voltage, even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an AlGaN/GaN diode. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Influence of AlGaN/GaN superlattice inserted structure on the performance of InGaN/GaN multiple quantum well light emitting diodes

International Nuclear Information System (INIS)

Wang, C.-L.; Tsai, M.-C.; Gong, J.-R.; Liao, W.-T.; Lin, P.-Y.; Yen, K.-Y.; Chang, C.-C.; Lin, H.-Y.; Hwang, S.-K.

2007-01-01

Investigations were conducted to explore the effect of Al 0.3 Ga 0.7 N/GaN short-period superlattice (SPSL)-inserted structures in the GaN under layer on the performance of In 0.2 Ga 0.8 N/GaN multiple quantum well (MQW) light emitting diodes (LEDs). The Al 0.3 Ga 0.7 N/GaN SPSL-inserted LEDs were found to exhibit improved materials and device characteristics including decrements in ideality factor and reverse leakage current. The results of etch pit counts reveal that SPSL-induced threading dislocation density reduction in the SPSL-inserted In 0.2 Ga 0.8 N/GaN MQW LED structures enables the improved LED performance

Growth of GaN layers using Ga2O vapor obtained from Ga and H2O vapor

International Nuclear Information System (INIS)

Sumi, Tomoaki; Taniyama, Yuuki; Takatsu, Hiroaki; Juta, Masami; Kitamoto, Akira; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke; Isemura, Masashi

2015-01-01

In this study, we performed growth of GaN layers using Ga 2 O vapor synthesized from Ga and H 2 O vapor. In this process, we employed H 2 O vapor instead of HCl gas in hydride vapor phase epitaxy (HVPE) to synthesize Ga source gas. In the synthesis reaction of Ga 2 O, a Ga 2 O 3 whisker formed and covered Ga, which impeded the synthesis reaction of Ga 2 O. The formation of the Ga 2 O 3 whisker was suppressed in H 2 ambient at high temperatures. Then, we adopted this process to supply a group III precursor and obtained an epitaxial layer. X-ray diffraction (XRD) measurement revealed that the epitaxial layer was single-crystalline GaN. Growth rate increased linearly with Ga 2 O partial pressure and reached 104 µm/h. (author)

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

International Nuclear Information System (INIS)

Anand, M. J.; Ng, G. I.; Syamal, B.; Zhou, X.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.

2015-01-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-R DS[ON] ) and threshold-voltage shift (ΔV th ) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I DS -V DS ) and drain current (I D ) transients. Different EF was realized with devices of different gate-drain spacing (L gd ) under the same OFF-state stress. Under high-EF (L gd  = 2 μm), the devices exhibited higher dyn-R DS[ON] degradation but a small ΔV th (∼120 mV). However, at low-EF (L gd  = 5 μm), smaller dyn-R DS[ON] degradation but a larger ΔV th (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R DS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔV th . A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I D -transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations

Photoluminescence study of the nitrogen content effect on GaAs/GaAs1-xNx/GaAs/AlGaAs: (Si) quantum well

International Nuclear Information System (INIS)

Hamdouni, A.; Bousbih, F.; Ben bouzid, S.; Aloulou, S.; Harmand, J.C.; Chtourou, R.

2008-01-01

We study the effect of nitrogen content in modulation-doped GaAs/GaAs 1-x N x /GaAs/GaAlAs:(Si) quantum well using low-temperature photoluminescence spectroscopy. The samples were grown on GaAs (001) substrates by molecular-beam epitaxy with different nitrogen compositions. The variation of the nitrogen composition from 0.04% to 0.32% associated to the bi-dimensional electron gas gives a new interaction mode between the nitrogen localized states and the GaAs 1-x N x /GaAs energies levels. The red-shift observed in photoluminescence spectra as function of nitrogen content has been interpreted in the frame of the band anticrossing model

Characteristics study of 2DEG transport properties of AlGaN/GaN and AlGaAs/GaAs-based HEMT

International Nuclear Information System (INIS)

Lenka, T. R.; Panda, A. K.

2011-01-01

Growth of wide bandgap material over narrow bandgap material, results into a two dimensional electron gas (2DEG) at the heterointerface due to the conduction band discontinuity. In this paper the 2DEG transport properties of AlGaN/GaN-based high electron mobility transistor (HEMT) is discussed and its effect on various characteristics such as 2DEG density, C-V characteristics and Sheet resistances for different mole fractions are presented. The obtained results are also compared with AlGaAs/GaAs-based HEMT for the same structural parameter as like AlGaN/GaN-based HEMT. The calculated results of electron sheet concentration as a function of the Al mole fraction are in excellent agreement with some experimental data available in the literature.

Heat Islands

Science.gov (United States)

EPA's Heat Island Effect Site provides information on heat islands, their impacts, mitigation strategies, related research, a directory of heat island reduction initiatives in U.S. communities, and EPA's Heat Island Reduction Program.

Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

Energy Technology Data Exchange (ETDEWEB)

Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May, E-mail: eekmlau@ust.hk [Photonics Technology Center, Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

2015-05-04

We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.

Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May

2015-01-01

We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme

Strain-balanced InGaN/GaN multiple quantum wells

Energy Technology Data Exchange (ETDEWEB)

Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Bharrat, D.; El-Masry, N. A. [Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2014-07-21

InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1−x}N/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1−y}N templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1−x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1−y}N template. Growth of the In{sub y}Ga{sub 1−y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1−y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1−x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1−y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”.

33 CFR 334.220 - Chesapeake Bay, south of Tangier Island, Va.; naval firing range.

Science.gov (United States)

2010-07-01

... ENGINEERS, DEPARTMENT OF THE ARMY, DEPARTMENT OF DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.220 Chesapeake Bay, south of Tangier Island, Va.; naval firing range. (a) The danger zone. Beginning... to latitude 37°45′00″, longitude 76°09′48″; thence to latitude 37°45′00″, longitude 76°08′51″; and...

Ternary gallides RE{sub 4}Rh{sub 9}Ga{sub 5}, RE{sub 5}Rh{sub 12}Ga{sub 7} and RE{sub 7}Rh{sub 18}Ga{sub 11} (RE=Y, La-Nd, Sm, Gd, Tb). Intergrowth structures with MgCu{sub 2} and CaCu{sub 5} related slabs

Energy Technology Data Exchange (ETDEWEB)

Seidel, Stefan; Rodewald, Ute C.; Poettgen, Rainer [Univ. Muenster (Germany). Inst. fuer Anorganische und Analytische Chemie; Janka, Oliver [Univ. Oldenburg (Germany). Inst. fuer Chemie

2017-07-01

Fourteen ternary gallides RE{sub 4}Rh{sub 9}Ga{sub 5}, RE{sub 5}Rh{sub 12}Ga{sub 7} and RE{sub 7}Rh{sub 18}Ga{sub 11} (RE=Y, La-Nd, Sm, Gd, Tb) were synthesized from the elements by arc-melting, followed by different annealing sequences either in muffle or induction furnaces. The samples were characterized through Guinier powder patterns and the crystal structures of Ce{sub 4}Rh{sub 9}Ga{sub 5}, Ce{sub 5}Rh{sub 12}Ga{sub 7}, Ce{sub 7}Rh{sub 18}Ga{sub 11}, Nd{sub 5}Rh{sub 10.44(4)}Ga{sub 8.56(4)}, Nd{sub 4}Rh{sub 9}Ga{sub 5} and Gd{sub 4}Rh{sub 9}Ga{sub 5} were refined from single crystal X-ray diffractometer data. The new gallides are the n=2, 3 and 5 members of the RE{sub 2+n} Rh{sub 3+3n} Ga{sub 1+2n} structure series in the Parthe intergrowth concept. The slabs of these intergrowth structures derive from the cubic Laves phase MgCu{sub 2} (Mg{sub 2}Ni{sub 3}Si as ternary variant) and CaCu{sub 5} (CeCo{sub 3}B{sub 2} as ternary variant). Only the Nd{sub 5}Rh{sub 10.44(4)}Ga{sub 8.56(4)} crystal shows Rh/Ga mixing within the Laves type slabs. Magnetic susceptibility measurements reveal Pauli paramagnetism for Y{sub 4}Rh{sub 9}Ga{sub 5} and Curie-Weiss paramagnetism for Gd{sub 4}Rh{sub 9}Ga{sub 5} and Tb{sub 4}Rh{sub 9}Ga{sub 5}. Low-temperature data show ferromagnetic ordering at T{sub C}=78.1 (Gd{sub 4}Rh{sub 9}Ga{sub 5}) and 55.8 K (Tb{sub 4}Rh{sub 9}Ga{sub 5}).

Persistence of bacterial pathogens, antibiotic resistance genes, and enterococci in tidal creek tributaries.

Science.gov (United States)

Jones, Chance E; Maddox, Anthony; Hurley, Dorset; Barkovskii, Andrei L

2018-05-19

Intertidal creeks form the primary hydrologic link between estuaries and land-based activities on barrier islands. Fecal indicators Enterococcus spp. (Entero1), pathogens Shigella spp. (ipaH), Salmonella spp. (invA), E. coli of EHEC/EPEC groups (eaeA), E. coli of EAEC, EIEC, and UPEC groups (set1B), E. coli of STEC group (stx1); and tetracycline resistance genes (tet(B), tet(C), tet(D), tet(E), tet(K), tet(Q), tet(W), and tet(X); TRG) were detected in the headwater of Oakdale Creek (Sapelo Island, GA) receiving runoffs from Hog Hammock village. Excavation of drainage ditches around the village caused a high increase in the incidence of the above determinants. Water samples were collected from the headwater, transferred to diffusion chambers, submersed in the headwater, saltmarsh, and mouth of the creek; and the determinants were monitored for 3 winter months. With some exceptions, their persistence decreased in order headwater > saltmarsh > mouth. Genes associated with Enterococcus spp. were the most persistent at all the sites, following in the headwater with determinants for Salmonella spp. and E. coli of EAEC, EIEC, and UPEC groups. In the mouth, the most persistent gene was eaeA indicating EHEC, EPEC, and STEC. Tet(B) and tet(C) persisted the longest in headwater and saltmarsh. No TRG persisted after 11 days in the mouth. Most determinants revealed correlations with temperature and pH, and inverse correlations with dissolved oxygen. Decay rates of the above determinants varied in the range of -0.02 to -0.81/day, and were up to 40 folds higher in the saltmarsh and mouth than in the headwater. Our data demonstrated that water parameters could to some extent predict a general trend in the fate of virulence and antibiotic resistance determinants in tidal creek tributaries but strongly suggested that their persistence in these tributaries cannot be predicted from that of enterococci, or extrapolated from one biological contaminant to another. Copyright

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE 581 83 Linköping (Sweden)

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

Spin injection in epitaxial MnGa(111)/GaN(0001) heterostructures

Science.gov (United States)

Zube, Christian; Malindretos, Joerg; Watschke, Lars; Zamani, Reza R.; Disterheft, David; Ulbrich, Rainer G.; Rizzi, Angela; Iza, Michael; Keller, Stacia; DenBaars, Steven P.

2018-01-01

Ferromagnetic MnGa(111) layers were grown on GaN(0001) by molecular beam epitaxy. MnGa/GaN Schottky diodes with a doping level of around n = 7 × 1018 cm-3 were fabricated to achieve single step tunneling across the metal/semiconductor junction. Below the GaN layer, a thin InGaN quantum well served as optical spin detector ("spin-LED"). For electron spin injection from MnGa into GaN and subsequent spin transport through a 45 nm (70 nm) thick GaN layer, we observe a circular polarization of 0.3% (0.2%) in the electroluminescence at 80 K. Interface mixing, spin polarization losses during electrical transport in the GaN layer, and spin relaxation in the InGaN quantum well are discussed in relation with the low value of the optically detected spin polarization.

Island biogeography

DEFF Research Database (Denmark)

Whittaker, Robert James; Fernández-Palacios, José María; Matthews, Thomas J.

2017-01-01

Islands provide classic model biological systems. We review how growing appreciation of geoenvironmental dynamics of marine islands has led to advances in island biogeographic theory accommodating both evolutionary and ecological phenomena. Recognition of distinct island geodynamics permits gener...

Meningiomas: A Comparative Study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for Molecular Imaging in Mice

Science.gov (United States)

Soto-Montenegro, María Luisa; Peña-Zalbidea, Santiago; Mateos-Pérez, Jose María; Oteo, Marta; Romero, Eduardo; Morcillo, Miguel Ángel; Desco, Manuel

2014-01-01

Purpose The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three 68Ga-DOTA-labeled somatostatin analogues (68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE) using PET/CT in a murine model with subcutaneous meningioma xenografts. Methods The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN). 68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L) and tumor-to-muscle (T/M) SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt) was determined. Results Hepatic SUVmax and Vt were significantly higher with 68Ga-DOTANOC than with 68Ga-DOTATOC and 68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between 68Ga-DOTATATE and 68Ga-DOTATOC, both of which had a higher fraction than 68Ga-DOTANOC. The T/M SUV ratio was significantly higher with 68Ga-DOTATATE than with 68Ga-DOTATOC and 68Ga-DOTANOC. The Vt for tumor was higher with 68Ga-DOTATATE than with 68Ga-DOTANOC and relatively similar to that of 68Ga-DOTATOC. Conclusions This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with 68Ga-DOTATATE and 68Ga-DOTATOC, uptake was higher with 68Ga-DOTATATE in the tumor than with 68Ga-DOTANOC and 68Ga-DOTATOC, suggesting a higher diagnostic value of 68Ga-DOTATATE for detecting meningiomas. PMID:25369268

Meningiomas: a comparative study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for molecular imaging in mice.

Directory of Open Access Journals (Sweden)

María Luisa Soto-Montenegro

Full Text Available The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three (68Ga-DOTA-labeled somatostatin analogues ((68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE using PET/CT in a murine model with subcutaneous meningioma xenografts.The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN. (68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L and tumor-to-muscle (T/M SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt was determined.Hepatic SUVmax and Vt were significantly higher with (68Ga-DOTANOC than with (68Ga-DOTATOC and (68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between (68Ga-DOTATATE and (68Ga-DOTATOC, both of which had a higher fraction than (68Ga-DOTANOC. The T/M SUV ratio was significantly higher with (68Ga-DOTATATE than with (68Ga-DOTATOC and (68Ga-DOTANOC. The Vt for tumor was higher with (68Ga-DOTATATE than with (68Ga-DOTANOC and relatively similar to that of (68Ga-DOTATOC.This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with (68Ga-DOTATATE and (68Ga-DOTATOC, uptake was higher with (68Ga-DOTATATE in the tumor than with (68Ga-DOTANOC and (68Ga-DOTATOC, suggesting a higher diagnostic value of (68Ga-DOTATATE for detecting meningiomas.

Tenarife Island, Canary Island Archipelago, Atlantic Ocean

Science.gov (United States)

1991-01-01

Tenarife Island is one of the most volcanically active of the Canary Island archipelago, Atlantic Ocean, just off the NW coast of Africa, (28.5N, 16.5W). The old central caldera, nearly filled in by successive volcanic activity culminating in two stratocones. From those two peaks, a line of smaller cinder cones extend to the point of the island. Extensive gullies dissect the west side of the island and some forests still remain on the east side.

Infant mortality in the Marshall Islands.

Science.gov (United States)

Levy, S J; Booth, H

1988-12-01

Levy and Booth present previously unpublished infant mortality rates for the Marshall Islands. They use an indirect method to estimate infant mortality from the 1973 and 1980 censuses, then apply indirect and direct methods of estimation to data from the Marshall Islands Women's Health Survey of 1985. Comparing the results with estimates of infant mortality obtained from vital registration data enables them to estimate the extent of underregistration of infant deaths. The authors conclude that 1973 census appears to be the most valid information source. Direct estimates from the Women's Health Survey data suggest that infant mortality has increased since 1970-1974, whereas the indirect estimates indicate a decreasing trend in infant mortality rates, converging with the direct estimates in more recent years. In view of increased efforts to improve maternal and child health in the mid-1970s, the decreasing trend is plausible. It is impossible to estimate accurately infant mortality in the Marshall Islands during 1980-1984 from the available data. Estimates based on registration data for 1975-1979 are at least 40% too low. The authors speculate that the estimate of 33 deaths per 1000 live births obtained from registration data for 1984 is 40-50% too low. In round figures, a value of 60 deaths per 1000 may be taken as the final estimate for 1980-1984.

Role of AlGaN/GaN interface traps on negative threshold voltage shift in AlGaN/GaN HEMT

Science.gov (United States)

Malik, Amit; Sharma, Chandan; Laishram, Robert; Bag, Rajesh Kumar; Rawal, Dipendra Singh; Vinayak, Seema; Sharma, Rajesh Kumar

2018-04-01

This article reports negative shift in the threshold-voltage in AlGaN/GaN high electron mobility transistor (HEMT) with application of reverse gate bias stress. The device is biased in strong pinch-off and low drain to source voltage condition for a fixed time duration (reverse gate bias stress), followed by measurement of transfer characteristics. Negative threshold voltage shift after application of reverse gate bias stress indicates the presence of more carriers in channel as compared to the unstressed condition. We propose the presence of AlGaN/GaN interface states to be the reason of negative threshold voltage shift, and developed a process to electrically characterize AlGaN/GaN interface states. We verified the results with Technology Computer Aided Design (TCAD) ATLAS simulation and got a good match with experimental measurements.

Near-surface depletion of antimony during the growth of GaAsSb and GaAs/GaAsSb nanowires

Energy Technology Data Exchange (ETDEWEB)

Kauko, H.; Helvoort, A. T. J. van, E-mail: a.helvoort@ntnu.no [Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim (Norway); Fimland, B. O.; Munshi, A. M. [Department of Electronics and Telecommunications, NTNU, Trondheim (Norway); Grieb, T.; Müller, K.; Rosenauer, A. [Institut für Festkörperphysik, Universität Bremen, Bremen (Germany)

2014-10-14

The near-surface reduction of the Sb mole fraction during the growth of GaAsSb nanowires (NWs) and GaAs NWs with GaAsSb inserts has been studied using quantitative high-angle annular dark field scanning transmission electron microscopy (STEM). A model for diffusion of Sb in the hexagonal NWs was developed and employed in combination with the quantitative STEM analysis. GaAsSb NWs grown by Ga-assisted molecular beam epitaxy (MBE) and GaAs/GaAsSb NWs grown by Ga- and Au-assisted MBE were investigated. At the high temperatures employed in the NW growth, As-Sb exchange at and outward diffusion of Sb towards the surface take place, resulting in reduction of the Sb concentration at and near the surface in the GaAsSb NWs and the GaAsSb inserts. In GaAsSb NWs, an increasing near-surface depletion of Sb was observed towards the bottom of the NW due to longer exposure to the As beam flux. In GaAsSb inserts, an increasing change in the Sb concentration profile was observed with increasing post-insert axial GaAs growth time, resulting from a combined effect of radial GaAs overgrowth and diffusion of Sb. The effect of growth temperature on the diffusion of Sb in the GaAsSb inserts was identified. The consequences of these findings for growth optimization and the optoelectronic properties of GaAsSb are discussed.

AlGaN/GaN High Electron Mobility Transistors with Multi-MgxNy/GaN Buffer

OpenAIRE

Chang, P. C.; Lee, K. H.; Wang, Z. H.; Chang, S. J.

2014-01-01

We report the fabrication of AlGaN/GaN high electron mobility transistors with multi-MgxNy/GaN buffer. Compared with conventional HEMT devices with a low-temperature GaN buffer, smaller gate and source-drain leakage current could be achieved with this new buffer design. Consequently, the electron mobility was larger for the proposed device due to the reduction of defect density and the corresponding improvement of crystalline quality as result of using the multi-MgxNy/GaN buffer.

Reducing Threshold of Multi Quantum Wells InGaN Laser Diode by Using InGaN/GaN Waveguide

Science.gov (United States)

Abdullah, Rafid A.; Ibrahim, Kamarulazizi

2010-07-01

ISE TCAD (Integrated System Engineering Technology Computer Aided Design) software simulation program has been utilized to help study the effect of using InGaN/GaN as a waveguide instead of conventional GaN waveguide for multi quantum wells violet InGaN laser diode (LD). Simulation results indicate that the threshold of the LD has been reduced by using InGaN/GaN waveguide where InGaN/GaN waveguide increases the optical confinement factor which leads to increase the confinement carriers at the active region of the LD.

Thermal stability studies on atomically clean and sulphur passivated InGaAs surfaces

Energy Technology Data Exchange (ETDEWEB)

Chauhan, Lalit; Hughes, Greg [School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9 (Ireland)

2013-03-15

High resolution synchrotron radiation core level photoemission measurements have been used to study the high temperature stability of sulphur passivated InGaAs surfaces and comparisons made with atomically clean surfaces subjected to the same annealing temperatures. Sulphur passivation of clean InGaAs surfaces prepared by the thermal removal of an arsenic capping layer was carried out using an in situ molecular sulphur treatment in ultra high vacuum. The elemental composition of the surfaces of these materials was measured at a series of annealing temperatures up to 530 C. Following a 480 C anneal In:Ga ratio was found to have dropped by 33% on sulphur passivated surface indicating a significant loss of indium, while no drop in indium signal was recorded at this temperature on the atomically InGaAs surface. No significant change in the As surface concentration was measured at this temperature. These results reflect the reduced thermal stability of the sulphur passivated InGaAs compared to the atomically clean surface which has implications for device fabrication. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Carrier confinement effects of InxGa1-xN/GaN multi quantum disks with GaN surface barriers grown in GaN nanorods

Science.gov (United States)

Park, Youngsin; Chan, Christopher C. S.; Taylor, Robert A.; Kim, Nammee; Jo, Yongcheol; Lee, Seung W.; Yang, Woochul; Im, Hyunsik

2018-04-01

Structural and optical properties of InxGa1-xN/GaN multi quantum disks (QDisks) grown on GaN nanorods by molecular beam epitaxy have been investigated by transmission electron microscopy and micro-photoluminescence (PL) spectroscopy. Two types of InGaN QDisks were grown: a pseudo-3D confined InGaN pillar-type QDisks embedded in GaN nanorods; and QDisks in flanged cone type GaN nanorods. The PL emission peak and excitation dependent PL behavior of the pillar-type Qdisks differ greatly from those of the flanged cone type QDisks. Time resolved PL was carried out to probe the differences in charge carrier dynamics. The results suggest that by constraining the formation of InGaN QDisks within the centre of the nanorod, carriers are restricted from migrating to the surface, decreasing the surface recombination at high carrier densities.

Carrier quenching in InGaP/GaAs double heterostructures

Energy Technology Data Exchange (ETDEWEB)

Wells, Nathan P., E-mail: nathan.p.wells@aero.org; Driskell, Travis U.; Hudson, Andrew I.; LaLumondiere, Stephen D.; Lotshaw, William T. [The Aerospace Corporation, Physical Sciences Laboratories, P.O. Box 92957, Los Angeles, California 90009 (United States); Forbes, David V.; Hubbard, Seth M. [NanoPower Research Labs, Rochester Institute of Technology, 156 Lomb Memorial Dr., Rochester, New York 14623 (United States)

2015-08-14

Photoluminescence measurements on a series of GaAs double heterostructures demonstrate a rapid quenching of carriers in the GaAs layer at irradiance levels below 0.1 W/cm{sup 2} in samples with a GaAs-on-InGaP interface. These results indicate the existence of non-radiative defect centers at or near the GaAs-on-InGaP interface, consistent with previous reports showing the intermixing of In and P when free As impinges on the InGaP surface during growth. At low irradiance, these defect centers can lead to sub-ns carrier lifetimes. The defect centers involved in the rapid carrier quenching can be saturated at higher irradiance levels and allow carrier lifetimes to reach hundreds of nanoseconds. To our knowledge, this is the first report of a nearly three orders of magnitude decrease in carrier lifetime at low irradiance in a simple double heterostructure. Carrier quenching occurs at irradiance levels near the integrated Air Mass Zero (AM0) and Air Mass 1.5 (AM1.5) solar irradiance. Additionally, a lower energy photoluminescence band is observed both at room and cryogenic temperatures. The temperature and time dependence of the lower energy luminescence is consistent with the presence of an unintentional InGaAs or InGaAsP quantum well that forms due to compositional mixing at the GaAs-on-InGaP interface. Our results are of general interest to the photovoltaic community as InGaP is commonly used as a window layer in GaAs based solar cells.

Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates

Energy Technology Data Exchange (ETDEWEB)

Yablonsky, A. N., E-mail: yablonsk@ipm.sci-nnov.ru; Morozov, S. V.; Gaponova, D. M.; Aleshkin, V. Ya. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Shengurov, V. G.; Zvonkov, B. N.; Vikhrova, O. V.; Baidus’, N. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Krasil’nik, Z. F. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2016-11-15

We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.

Growth of (20 anti 21)AlGaN, GaN and InGaN by metal organic vapor phase epitaxy

Energy Technology Data Exchange (ETDEWEB)

Ploch, S.; Wernicke, T.; Rass, J.; Pristovsek, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

2012-07-01

Green InGaN-based laser diodes on (20 anti 21)GaN substrates have recently demonstrated performances exceeding those of conventional (0001) oriented devices. However little is known regarding the growth parameters. We have investigated growth of AlGaN, GaN and InGaN on (20 anti 21)GaN substrates by MOVPE. Smooth GaN layers with a rms roughness <0.5 nm were obtained by low growth temperatures and reactor pressures. The layers exhibit undulations along [10 anti 14] similar to the GaN substrate. AlGaN and InGaN layers exhibit an increased surface roughness. Undulation bunching was observed and attributed to reduced adatom surface mobility due to the binding energy of Al and the low growth temperature for InGaN respectively or strain relaxation. AlGaN and InGaN heterostructures on (20 anti 21)GaN relax by layer tilt accompanied by formation of misfit dislocations, due to shear strain of the unit cell. This relaxation mechanism leads to a reduced critical layer thickness of (20 anti 21)AlGaN layers and InGaN multi quantum wells (MQW) in comparison to (0001). PL spectral broadening of 230 meV of (20 anti 21)InGaN single QWs emitting at 415 nm can be reduced by increased growth temperature or increased number of QWs with reduced thickness.

Spectroscopic characterizations of individual single-crystalline GaN nanowires in visible/ultra-violet regime.

Science.gov (United States)

Wu, Chien-Ting; Chu, Ming-Wen; Chen, Li-Chyong; Chen, Kuei-Hsien; Chen, Chun-Wei; Chen, Cheng Hsuan

2010-10-01

Spectroscopic investigations of individual single-crystalline GaN nanowires with a lateral dimensions of approximately 30-90nm were performed using the spatially resolved technique of electron energy-loss spectroscopy in conjunction with scanning transmission electron microscope showing a 2-A electron probe. Positioning the electron probe upon transmission impact and at aloof setup with respect to the nanomaterials, we explored two types of surface modes intrinsic to GaN, surface exciton polaritons at approximately 8.3eV (approximately 150nm) and surface guided modes at 3.88eV (approximately 320nm), which are in visible/ultra-violet spectral regime above GaN bandgap of approximately 3.3eV (approximately 375nm) and difficult to access by conventional optical spectroscopies. The explorations of these electromagnetic resonances might expand the current technical interests in GaN nanomaterials from the visible/UV range below approximately 3.5eV to the spectral regime further beyond.

Exciton binding energy in wurtzite InGaN/GaN quantum wells

International Nuclear Information System (INIS)

Park, Seoung-Hwan; Kim, Jong-Jae; Kim, Hwa-Min

2004-01-01

The internal field and carrier density effects on the exciton binding energies in wurtzite (WZ) InGaN/GaN quantum-well (QW) structures are investigated using the multiband effective-mass theory, and are compared with those obtained from the at-band model and with those of GaN/AlGaN QW structures. The exciton binding energy is significantly reduced with increasing sheet carrier density, suggesting that excitons are nearly bleached at densities around 10 12 cm -2 for both InGaN/GaN and GaN/AlGaN QW structures. With the inclusion of the internal field, the exciton binding energy is substantialy reduced compared to that of the at-band model in the investigated region of the wells. This can be explained by a decrease in the momentum matrix element and an increase in the inverse screening length due to the internal field. The exciton binding energy of the InGaN/GaN structure is smaller than that of the GaN/AlGaN structure because InGaN/GaN structures have a smaller momentum matrix element and a larger inverse screening length than GaN/AlGaN structures.

AlGaN/GaN High Electron Mobility Transistors with Multi-MgxNy/GaN Buffer

Directory of Open Access Journals (Sweden)

P. C. Chang

2014-01-01

Full Text Available We report the fabrication of AlGaN/GaN high electron mobility transistors with multi-MgxNy/GaN buffer. Compared with conventional HEMT devices with a low-temperature GaN buffer, smaller gate and source-drain leakage current could be achieved with this new buffer design. Consequently, the electron mobility was larger for the proposed device due to the reduction of defect density and the corresponding improvement of crystalline quality as result of using the multi-MgxNy/GaN buffer.

InGaAs and GaAsSb strain reducing layers covering InAs/GaAs quantum dots

Czech Academy of Sciences Publication Activity Database

Hospodková, Alice; Hulicius, Eduard; Pangrác, Jiří; Oswald, Jiří; Vyskočil, Jan; Kuldová, Karla; Šimeček, Tomislav; Hazdra, P.; Caha, O.

2010-01-01

Roč. 312, č. 8 (2010), 1383-1387 ISSN 0022-0248 R&D Projects: GA AV ČR IAA100100719; GA ČR GA202/09/0676; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : low dimensional structures * photoluminescence * low-pressure MOVPE * InAs/GaAs quantum dots * semiconducting III/V materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.737, year: 2010

Canary Islands

Science.gov (United States)

1992-01-01

This easterly looking view shows the seven major volcanic islands of the Canary Island chain (28.0N, 16.5W) and offers a unique view of the islands that have become a frequent vacation spot for Europeans. The northwest coastline of Africa, (Morocco and Western Sahara), is visible in the background. Frequently, these islands create an impact on local weather (cloud formations) and ocean currents (island wakes) as seen in this photo.

Systematic study on dynamic atomic layer epitaxy of InN on/in +c-GaN matrix and fabrication of fine-structure InN/GaN quantum wells: Role of high growth temperature

Science.gov (United States)

Yoshikawa, Akihiko; Kusakabe, Kazuhide; Hashimoto, Naoki; Hwang, Eun-Sook; Imai, Daichi; Itoi, Takaomi

2016-12-01

The growth kinetics and properties of nominally 1-ML (monolayer)-thick InN wells on/in +c-GaN matrix fabricated using dynamic atomic layer epitaxy (D-ALEp) by plasma-assisted molecular beam epitaxy were systematically studied, with particular attention given to the effects of growth temperature. Attention was also given to how and where the ˜1-ML-thick InN layers were frozen or embedded on/in the +c-GaN matrix. The D-ALEp of InN on GaN was a two-stage process; in the 1st stage, an "In+N" bilayer/monolayer was formed on the GaN surface, while in the 2nd, this was capped by a GaN barrier layer. Each process was monitored in-situ using spectroscopic ellipsometry. The target growth temperature was above 620 °C and much higher than the upper critical epitaxy temperature of InN (˜500 °C). The "In+N" bilayer/monolayer tended to be an incommensurate phase, and the growth of InN layers was possible only when they were capped with a GaN layer. The InN layers could be coherently inserted into the GaN matrix under self-organizing and self-limiting epitaxy modes. The growth temperature was the most dominant growth parameter on both the growth process and the structure of the InN layers. Reflecting the inherent growth behavior of D-ALEp grown InN on/in +c-GaN at high growth temperature, the embedded InN layers in the GaN matrix were basically not full-ML in coverage, and the thickness of sheet-island-like InN layers was essentially either 1-ML or 2-ML. It was found that these InN layers tended to be frozen at the step edges on the GaN and around screw-type threading dislocations. The InN wells formed type-I band line-up heterostructures with GaN barriers, with exciton localization energies of about 300 and 500 meV at 15 K for the 1-ML and 2-ML InN wells, respectively.

InGaN nanoinclusions in an AlGaN matrix

International Nuclear Information System (INIS)

Sizov, V. S.; Tsatsul'nikov, A. F.; Lundin, V. V.

2008-01-01

GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80-300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.

70Ge, 72Ge, 74Ge, 76Ge(d,3He)69Ga, 71Ga, 73Ga, 75Ga reactions at 26 MeV

International Nuclear Information System (INIS)

Rotbard, G.; La Rana, G.; Vergnes, M.; Berrier, G.; Kalifa, J.; Guilbaut, G.; Tamisier, R.

1978-01-01

The 70 Ge, 72 Ge, 74 Ge, 76 Ge(d, 3 He) 69 Ga, 71 Ga, 73 Ga, 75 Ga reactions have been studied at 26 MeV with 15 keV resolution (F.W.H.M), using the Orsay MP tandem accelerator and a split pole magnetic spectrometer. The spectroscopic factors are determined for 15 levels in 69 Ga and 11 levels in each of the 3 other Ga isotopes. Level schemes are proposed for the practically unknown 73 Ga and 75 Ga. Very simple model wave functions previously proposed for Ge nuclei are seen to reproduce quite well the measured occupation numbers for the proton orbitals. Anomalies in these occupation numbers are observed between Z=31 and 32 and between N=40 and 42, this last one corresponding to the structural transition observed recently in a comparison of the (p,t) and (t,p) reactions. These anomalies could be related to changes in the nuclear shape

Radiative and non-radiative recombination in GaInN/GaN quantum wells; Strahlende und nichtstrahlende Rekombination in GaInN/GaN-Quantenfilmen

Energy Technology Data Exchange (ETDEWEB)

Netzel, C.

2007-02-08

The studies presented in this thesis deal with the occurence of V defectsin GaInN/GaN quantum film structures grown by means of organometallic gas phase epitaxy, and the effects, which have the V defects respectively the GaInN quantum films on the V-defect facets on the emission and recombination properties of the whole GaInN/GaN quantum film structure. The V-defects themselves, inverse pyramidal vacancies with hexagonal base in the semiconductor layers, arise under suitable growth conditions around the percussion violations, which extend in lattice-mismatched growth of GaN on the heterosubstrates sapphire or silicon carbide starting in growth direction through the crystal. If GaInN layers are grown over V-defect dispersed layers on the (1-101) facets of the V defects and the (0001) facets, the growth front of the structure, different growth velocities are present, which lead to differently wide GaInN quantum films on each facets.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

Energy Technology Data Exchange (ETDEWEB)

Anand, M. J., E-mail: anand2@e.ntu.edu.sg, E-mail: eging@ntu.edu.sg; Ng, G. I., E-mail: anand2@e.ntu.edu.sg, E-mail: eging@ntu.edu.sg; Syamal, B.; Zhou, X. [School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C. [Temasek Laboratories@NTU, Nanyang Technological University, 50 Nanyang Drive, Research Techno Plaza, Singapore 637553 (Singapore)

2015-02-23

The influence of electric field (EF) on the dynamic ON-resistance (dyn-R{sub DS[ON]}) and threshold-voltage shift (ΔV{sub th}) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I{sub DS}-V{sub DS}) and drain current (I{sub D}) transients. Different EF was realized with devices of different gate-drain spacing (L{sub gd}) under the same OFF-state stress. Under high-EF (L{sub gd} = 2 μm), the devices exhibited higher dyn-R{sub DS[ON]} degradation but a small ΔV{sub th} (∼120 mV). However, at low-EF (L{sub gd} = 5 μm), smaller dyn-R{sub DS[ON]} degradation but a larger ΔV{sub th} (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R{sub DS[ON]} degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔV{sub th}. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I{sub D}-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

Land-use change and managed aquifer recharge effects on the hydrogeochemistry of two contrasting atoll island aquifers, Roi-Namur Island, Republic of the Marshall Islands

International Nuclear Information System (INIS)

Hejazian, Mehrdad; Gurdak, Jason J.; Swarzenski, Peter; Odigie, Kingsley O.; Storlazzi, Curt D.

2017-01-01

Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 × 10"5 m"3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 × 10"4 m"3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using PHREEQC to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a six-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land

Ohmic contacts to n+-GaN capped AlGaN/AlN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Wang Liang; Mohammed, Fitih M.; Ofuonye, Benedict; Adesida, Ilesanmi

2007-01-01

Investigations of Ti/Al/Mo/Au Ohmic contact formation, premetallization plasma treatment effects, and interfacial reactions for n + -GaN capped AlGaN/AlN/GaN heterostructures are presented. Ti thickness played an important role in determining contact performance. Transmission electron microscopy studies confirmed that thick Ti layer was necessary to fully consume the GaN cap and the top of AlGaN to enable a higher tunneling current flow. A direct correlation of plasma treatment conditions with I-V linearity, current level, and contact performance was established. The plasma-affected region is believed to extend over 20 nm into the AlGaN and GaN

InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers.

Science.gov (United States)

Lv, Wenbin; Wang, Lai; Wang, Jiaxing; Hao, Zhibiao; Luo, Yi

2012-11-07

InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm.

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

International Nuclear Information System (INIS)

Choi, Yunju; Kim, Yangsoo; Ahn, Kwang-Soon; Kim, Hyunsoo

2014-01-01

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10 −3 , 4.3 × 10 −4 , and 1.1 × 10 −3 Ω cm 2 for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N 2 ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

Energy Technology Data Exchange (ETDEWEB)

Choi, Yunju [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Kim, Yangsoo [Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Ahn, Kwang-Soon, E-mail: kstheory@ynu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 712-749 (Korea, Republic of); Kim, Hyunsoo, E-mail: hskim7@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

2014-10-30

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10{sup −3}, 4.3 × 10{sup −4}, and 1.1 × 10{sup −3} Ω cm{sup 2} for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N{sub 2} ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples.

78 FR 74009 - Safety Zone; Nike Fireworks, Upper New York Bay, Ellis Island, NY

Science.gov (United States)

2013-12-10

... DEPARTMENT OF HOMELAND SECURITY Coast Guard 33 CFR Part 165 [Docket No. USCG-2013-0962] Safety Zone; Nike Fireworks, Upper New York Bay, Ellis Island, NY AGENCY: Coast Guard, DHS. ACTION: Notice of... published in the Federal Register on November 9, 2011 (76 FR 69614). [[Page 74010

Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures

Energy Technology Data Exchange (ETDEWEB)

Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre [Laboratoire Charles Coulomb – UMR 5221, CNRS and University Montpellier, Case courier 074, 34095 Montpellier Cedex 5 (France); Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe [CRHEA-CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, rue Bernard Gregory, 06560 Valbonne (France)

2015-09-21

We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.

Computational study of GaAs1-xNx and GaN1-yAsy alloys and arsenic impurities in GaN

International Nuclear Information System (INIS)

Laaksonen, K; Komsa, H-P; Arola, E; Rantala, T T; Nieminen, R M

2006-01-01

We have studied the structural and electronic properties of As-rich GaAs 1-x N x and N-rich GaN 1-y As y alloys in a large composition range using first-principles methods. We have systematically investigated the effect of the impurity atom configuration near both GaAs and GaN sides of the concentration range on the total energies, lattice constants and bandgaps. The N (As) atoms, replacing substitutionally As (N) atoms in GaAs (GaN), cause the surrounding Ga atoms to relax inwards (outwards), making the Ga-N (Ga-As) bond length about 15% shorter (longer) than the corresponding Ga-As (Ga-N) bond length in GaAs (GaN). The total energies of the relaxed alloy supercells and the bandgaps experience large fluctuations within different configurations and these fluctuations grow stronger if the impurity concentration is increased. Substituting As atoms with N in GaAs induces modifications near the conduction band minimum, while substituting N atoms with As in GaN modifies the states near the valence band maximum. Both lead to bandgap reduction, which is at first rapid but later slows down. The relative size of the fluctuations is much larger in the case of GaAs 1-x N x alloys. We have also looked into the question of which substitutional site (Ga or N) As occupies in GaN. We find that under Ga-rich conditions arsenic prefers the substitutional N site over the Ga site within a large range of Fermi level values

Achievement of normally-off AlGaN/GaN high-electron mobility transistor with p-NiO{sub x} capping layer by sputtering and post-annealing

Energy Technology Data Exchange (ETDEWEB)

Huang, Shyh-Jer [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan (China); Chou, Cheng-Wei, E-mail: j2222222229@gmail.com [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan (China); Su, Yan-Kuin, E-mail: yksu@mail.ncku.edu.tw [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan (China); Lin, Jyun-Hao; Yu, Hsin-Chieh; Chen, De-Long [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan (China); Ruan, Jian-Long [National Chung-Shan Institute of Science and Technology, Taoyuan, Taiwan (China)

2017-04-15

Highlights: • A technique to fabricate normally off GaN-based high-electron mobility transistor (HEMT) by sputtering and post-annealing p-NiO{sub x} capping layer. • The V{sub th} shifts from −3 V in the conventional transistor to 0.33 V, and on/off current ratio became 10{sup 7}. • The reverse gate leakage current is 10{sup −9} A/mm, and the off-state drain-leakage current is 10{sup −8} A/mm. • The V{sub th} hysteresis is extremely small at about 33 mV. - Abstract: In this paper, we present a technique to fabricate normally off GaN-based high-electron mobility transistor (HEMT) by sputtering and post-annealing p-NiO{sub x} capping layer. The p-NiO{sub x} layer is produced by sputtering at room temperature and post-annealing at 500 °C for 30 min in pure O{sub 2} environment to achieve high hole concentration. The V{sub th} shifts from −3 V in the conventional transistor to 0.33 V, and on/off current ratio became 10{sup 7}. The forward and reverse gate breakdown increase from 3.5 V and −78 V to 10 V and −198 V, respectively. The reverse gate leakage current is 10{sup −9} A/mm, and the off-state drain-leakage current is 10{sup −8} A/mm. The V{sub th} hysteresis is extremely small at about 33 mV. We also investigate the mechanism that increases hole concentration of p-NiO{sub x} after annealing in oxygen environment resulted from the change of Ni{sup 2+} to Ni{sup 3+} and the surge of (111)-orientation.

Nanomaterial disordering in AlGaN/GaN UV LED structures

International Nuclear Information System (INIS)

Shabunina, E I; Levinshtein, M E; Kulagina, M M; Petrov, V N; Ratnikov, V V; Smirnova, I N; Troshkov, S I; Shmidt, N M; Kurin, S Yu; Makarov, Yu N; Chernyakov, A E; Usikov, A S; Helava, H

2015-01-01

Multifractal analysis was applied to characterize quantitatively nanostructural disordering in HVPE-grown AlGaN/GaN UV LED structures. A higher level of leakage currents shunting the active region of LEDs by an extended defect system is correlated with higher values of multifractal parameters (MFs). As a result, the concentration of injected carriers participating in radiative recombination in the active region is reduced. MFs and the conductivity of quasi-ohmic shunts localized in an extended defect system are higher in AlGaN/GaN structures than in InGaN/GaN structures. It is one of the reasons behind the low external quantum efficiency of AlGaN/GaN UV LEDs. (paper)

The influence of growth temperature and input V/III ratio on the initial nucleation and material properties of InN on GaN by MOCVD

International Nuclear Information System (INIS)

Wang, H; Jiang, D S; Zhu, J J; Zhao, D G; Liu, Z S; Wang, Y T; Zhang, S M; Yang, H

2009-01-01

The effects of growth temperature and V/III ratio on the InN initial nucleation of islands on the GaN (0 0 0 1) surface were investigated. It is found that InN nuclei density increases with decreasing growth temperature between 375 and 525 °C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters of less than 100 nm, whereas at elevated temperatures the InN islands can grow larger and well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. At a given growth temperature of 500 °C, a controllable density and size of separated InN islands can be achieved by adjusting the V/III ratio. The larger islands lead to fewer defects when they are coalesced. Comparatively, the electrical properties of the films grown under higher V/III ratio are improved

Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

Energy Technology Data Exchange (ETDEWEB)

Yang, Lin' an, E-mail: layang@xidian.edu.cn; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)

2016-04-28

Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al{sub 0.15}Ga{sub 0.85}N emitter barrier and a 1.7-nm-thick Al{sub 0.25}Ga{sub 0.75}N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al{sub 0.2}Ga{sub 0.8}N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In{sub 0.03}Ga{sub 0.97}N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

Molecular and morphological characterization of Xiphinema chambersi population from live oak in Jekyll Island, Georgia, with comments on morphometric variations

Science.gov (United States)

Zafar A Handoo; Lynn K. Carta; Andrea M. Skantar; Sergei A. Subbotin; Stephen W. Fraedrich

2016-01-01

A population of Xiphinema chambersi from the root zone around live oak (Quercus virginiana Mill.) trees on Jekyll Island, GA, is described using both morphological and molecular tools and compared with descriptions of type specimens. Initially, because of a few morphological differences, this nematode was thought to represent...

White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

Science.gov (United States)

Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

2015-04-06

Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

Arrays of ZnO/CuInxGa1−xSe2 nanocables with tunable shell composition for efficient photovoltaics

International Nuclear Information System (INIS)

Akram, Muhammad Aftab; Javed, Sofia; Xu, Jun; Mujahid, Mohammad; Lee, Chun-Sing

2015-01-01

Arrays of one-dimensional (1D) nanostructure are receiving much attention for their optoelectronic and photovoltaic applications due to their advantages in light absorption, charge separation, and transportation. In this work, arrays of ZnO/CuIn x Ga 1−x Se 2 core/shell nanocables with tunable shell compositions over the full range of 0 ≤ x ≤ 1 have been controllably synthesized. Chemical conversions of ZnO nanorods to a series of ZnO-based nanocables, including ZnO/ZnSe, ZnO/CuSe, ZnO/CuSe/In x Ga 1−x , ZnO/CuSe/(In x Ga 1−x ) 2 Se 3 , and ZnO/CuIn x Ga 1−x Se 2 , are well designed and successfully achieved. Composition-dependent influences of the CuIn x Ga 1−x Se 2 shells on photovoltaic performance are investigated. It is found that the increase in indium content (x) leads to an increase in short-circuit current density (J SC ) but a decrease in open-circuit voltage (V OC ) for the ZnO/CuIn x Ga 1−x Se 2 nanocable solar cells. An array of ZnO/CuIn 0.67 Ga 0.33 Se 2 nanocables with a length of ∼1 μm and a shell thickness of ∼10 nm exhibits a bandgap of 1.20 eV, and yields a maximum power conversion efficiency of 1.74% under AM 1.5 G illumination at an intensity of 100 mW/cm 2 . It dramatically surpasses that (0.22%) of the ZnO/CuIn 0.67 Ga 0.33 Se 2 planar thin-film device. Our work reveals that 1D nanoarray allows efficient photovoltaics without using toxic CdS buffer layer

Molecular and morphological characterization of Xiphinema chambersi population from live oak in Jekyll Island, Georgia, with comments on morphometric variations

Science.gov (United States)

Zafar A. Handoo; Lynn K. Carta; Andrea M. Skantar; Sergei A. Subbotin; Stephen Fraedrich

2016-01-01

A population of Xiphinema chambersi from the root zone around live oak (Quercus virginiana Mill.) trees on Jekyll Island, GA, is described using both morphological and molecular tools and compared with descriptions of type specimens. Initially, because of a few morphological differences, this nematode was thought to represent an undescribed species. However, on further...

Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

Science.gov (United States)

Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Shih, Hong-An; Nakazawa, Satoshi; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-06-01

The impacts of inserting ultrathin oxides into insulator/AlGaN interfaces on their electrical properties were investigated to develop advanced AlGaN/GaN metal–oxide–semiconductor (MOS) gate stacks. For this purpose, the initial thermal oxidation of AlGaN surfaces in oxygen ambient was systematically studied by synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and atomic force microscopy (AFM). Our physical characterizations revealed that, when compared with GaN surfaces, aluminum addition promotes the initial oxidation of AlGaN surfaces at temperatures of around 400 °C, followed by smaller grain growth above 850 °C. Electrical measurements of AlGaN/GaN MOS capacitors also showed that, although excessive oxidation treatment of AlGaN surfaces over around 700 °C has an adverse effect, interface passivation with the initial oxidation of the AlGaN surfaces at temperatures ranging from 400 to 500 °C was proven to be beneficial for fabricating high-quality AlGaN/GaN MOS gate stacks.

AlGaN/GaN high electron mobility transistors with a low sub-threshold swing on free-standing GaN wafer

Directory of Open Access Journals (Sweden)

Xinke Liu

2017-09-01

Full Text Available This paper reported AlGaN/GaN high electron mobility transistors (HEMTs with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD on free-standing GaN, small full-width hall maximum (FWHM of 42.9 arcsec for (0002 GaN XRD peaks and ultralow dislocation density (∼104-105 cm-2 were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (∼60 mV/decade, low hysteresis of 54 mV, and high peak electron mobility μeff of ∼1456 cm2V-1s-1. Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaN HEMTs are promising candidate for next generation high power device applications.

Enhanced Thermionic Emission and Low 1/f Noise in Exfoliated Graphene/GaN Schottky Barrier Diode.

Science.gov (United States)

Kumar, Ashutosh; Kashid, Ranjit; Ghosh, Arindam; Kumar, Vikram; Singh, Rajendra

2016-03-01

Temperature-dependent electrical transport characteristics of exfoliated graphene/GaN Schottky diodes are investigated and compared with conventional Ni/GaN Schottky diodes. The ideality factor of graphene/GaN and Ni/GaN diodes are measured to be 1.33 and 1.51, respectively, which is suggestive of comparatively higher thermionic emission current in graphene/GaN diode. The barrier height values for graphene/GaN diode obtained using thermionic emission model and Richardson plots are found to be 0.60 and 0.72 eV, respectively, which are higher than predicted barrier height ∼0.40 eV as per the Schottky-Mott model. The higher barrier height is attributed to hole doping of graphene due to graphene-Au interaction which shifts the Fermi level in graphene by ∼0.3 eV. The magnitude of flicker noise of graphene/GaN Schottky diode increases up to 175 K followed by its decrease at higher temperatures. This indicates that diffusion currents and barrier inhomogeneities dominate the electronic transport at lower and higher temperatures, respectively. The exfoliated graphene/GaN diode is found to have lower level of barrier inhomogeneities than conventional Ni/GaN diode, as well as earlier reported graphene/GaN diode fabricated using chemical vapor deposited graphene. The lesser barrier inhomogeneities in graphene/GaN diode results in lower flicker noise by 2 orders of magnitude as compared to Ni/GaN diode. Enhanced thermionic emission current, lower level of inhomogeneities, and reduced flicker noise suggests that graphene-GaN Schottky diodes may have the underlying trend for replacing metal-GaN Schottky diodes.

Structure, magnetism, and interface properties of epitactical thin Fe and FePt films on GaAs(001) substrates; Struktur, Magnetismus und Grenzflaecheneigenschaften epitaktischer duenner Fe- und FePt-Filme auf GaAs(001)-Substraten

Energy Technology Data Exchange (ETDEWEB)

Schuster, Ellen Ursula

2007-12-17

The research in this thesis is focused on the study of the Fe spin structure and interface magnetism of thin epitaxial Fe layers or epitaxial FePt alloy films with chemical L1{sub 0} order on GaAs(001) surfaces. The main method of investigation was isotope-specific conversion electron Moessbauer spectroscopy (CEMS) combined with the {sup 57}Fe probe-layer technique in the temperature range of 4.2-300 K. The film structure was studied using electron diffraction (RHEED) and X-ray diffraction (XRD). The chemical order parameter S determined by XRD was found to increase with rising growth temperature, T{sub S}, to a maximum value of 0.71, until long range order is destroyed at T{sub S}>350 C by alloying with the substrate. As an important result a linear correlation between short-range order (revealed by the relative spectral area of the L1{sub 0} phase) and long-range order S was observed. The observed perpendicular Fe spin texture, characterized by the mean tilting angle left angle {theta} right angle of the Fe spins (relative to the film normal direction), was found to correlate with the L1{sub 0} phase content and with S. Furthermore, epitaxial Fe(001) films on GaAs(001)-(4 x 6) and on GaAs(001)-LED surfaces were grown successfully. In the initial stage of Fe film growth non-monotonous behavior of the in-plane lattice parameter was observed by RHEED. The magnetic hyperfine field distributions P(B{sub hf}) at the Fe/GaAs interface extracted from CEMS spectra for T{sub S}=-140 C or room temperature (RT) were found to be very similar. The observed large mean hyperfine fields of left angle B{sub hf} right angle {approx}25-27 T at the interface indicate the presence of high average Fe moments of 1.7-1.8 {mu}{sub B}. Nonmagnetic interface layers either can be excluded (Fe/GaAs) or are very thin (0.5 ML,Fe/GaAs-LED). Owing to its island structure an ultrathin (1.9 ML thick) uncoated Fe(001) film on GaAs(001)-(4 x 6) shows superparamagnetism with a blocking temperature of

Investigation of room-temperature wafer bonded GaInP/GaAs/InGaAsP triple-junction solar cells

Energy Technology Data Exchange (ETDEWEB)

Yang, Wen-xian; Dai, Pan; Ji, Lian; Tan, Ming; Wu, Yuan-yuan [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Uchida, Shiro [Department of Mechanical Science and Engineering Faculty of Engineering, Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba 275-0016 (Japan); Lu, Shu-long, E-mail: sllu2008@sinano.ac.cn [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Yang, Hui [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China)

2016-12-15

Highlights: • High quality InGaAsP material with a bandgap of 1.0 eV was grown by MBE. • Room-temperature wafer-bonded GaInP/GaAs/InGaAsP SCs were fabricated. • An efficiency of 30.3% of wafer-bonded triple-junction SCs was obtained. - Abstract: We report on the fabrication of III–V compound semiconductor multi-junction solar cells using the room-temperature wafer bonding technique. GaInP/GaAs dual-junction solar cells on GaAs substrate and InGaAsP single junction solar cell on InP substrate were separately grown by all-solid state molecular beam epitaxy (MBE). The two cells were then bonded to a triple-junction solar cell at room-temperature. A conversion efficiency of 30.3% of GaInP/GaAs/InGaAsP wafer-bonded solar cell was obtained at 1-sun condition under the AM1.5G solar simulator. The result suggests that the room-temperature wafer bonding technique and MBE technique have a great potential to improve the performance of multi-junction solar cell.

GaAsSb/InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates

International Nuclear Information System (INIS)

Klem, J. F.; Blum, O.; Kurtz, S. R.; Fritz, I. J.; Choquette, K. D.

2000-01-01

We have investigated the properties of GaAsSb/InGaAs type-II bilayer quantum-well structures grown by molecular-beam epitaxy for use in long-wavelength lasers on GaAs substrates. Structures with layer strains and thicknesses designed to be thermodynamically stable against dislocation formation exhibit room-temperature photoluminescence at wavelengths as long as 1.43 μm. The photoluminescence emission wavelength is significantly affected by growth temperature and the sequence of layer growth (InGaAs/GaAsSb versus GaAsSb/InGaAs), suggesting that Sb and/or In segregation results in nonideal interfaces under certain growth conditions. At low-injection currents, double-heterostructure lasers with GaAsSb/InGaAs bilayer quantum-well active regions display electroluminescence at wavelengths comparable to those obtained in photoluminescence, but at higher currents the electroluminescence shifts to shorter wavelengths. Lasers have been obtained with threshold current densities of 120 A/cm2 at 1.17 μm, and 2.1 kA/cm2 at 1.21 μm. (c) 2000 American Vacuum Society

Multidecadal shoreline changes of atoll islands in the Marshall Islands

Science.gov (United States)

Ford, M.

2012-12-01

Atoll islands are considered highly vulnerable to the impacts of continued sea level rise. One of the most commonly predicted outcomes of continued sea level rise is widespread and chronic shoreline erosion. Despite the widespread implications of predicted erosion, the decadal scale changes of atoll island shorelines are poorly resolved. The Marshall Islands is one of only four countries where the majority of inhabited land is comprised of reef and atoll islands. Consisting of 29 atolls and 5 mid-ocean reef islands, the Marshall Islands are considered highly vulnerable to the impacts of sea level rise. A detailed analysis of shoreline change on over 300 islands on 10 atolls was undertaken using historic aerial photos (1945-1978) and modern high resolution satellite imagery (2004-2012). Results highlight the complex and dynamic nature of atoll islands, with significant shifts in shoreline position observed over the period of analysis. Results suggest shoreline accretion is the dominant mode of change on the islands studied, often associated with a net increase in vegetated island area. However, considerable inter- and intra-atoll variability exists with regards to shoreline stability. Findings are discussed with respect to island morphodynamics and potential hazard mitigation and planning responses within atoll settings.

Gold free contacts to AlGaN/GaN heterostructures

NARCIS (Netherlands)

Hajlasz, Marcin

2018-01-01

Transistors and diodes based on AlGaN/GaN are suitable candidates for high-voltage and high-speed electronics due to the GaN material properties such as wide bandgap, large breakdown field, high electron saturation velocity and good thermal conductivity. When thin AlGaN layer is grown epitaxially on

Clinical evaluation of 67Ga gut accumulation in 67Ga scintigraphy

International Nuclear Information System (INIS)

Kobayashi, Hidetoshi; Ohno, Akiko; Watanabe, Youichi; Ishigaki, Takeo.

1994-01-01

Accumulation of 67 Ga in gut was evaluated in 67 Ga scintigraphy retrospectively in 30 patients (32 examinations). TIBC and UIBC were examined in all patients on the day when their scintigraphies were performed. Blood transfusion or Fe administration 2 months before 67 Ga scintigraphies were not carried out in any patient. Fifty percents (6/12) of male, and 40% (8/20) of female patients showed 67 Ga accumulation in gut. There was significant correlation between 67 Ga accumulation in gut and low ion-saturation ratio for transferrin. Excretion of 67 Ga bound with transferrin from liver was thought to be an important factor of 67 ga accumulation in gut. (author)

Surface segregation of InGaAs films by the evolution of reflection high-energy electron diffraction patterns

International Nuclear Information System (INIS)

Zhou Xun; Luo Zi-Jiang; Guo Xiang; Zhang Bi-Chan; Shang Lin-Tao; Zhou Qing; Deng Chao-Yong; Ding Zhao

2012-01-01

Surface segregation is studied via the evolution of reflection high-energy electron diffraction (RHEED) patterns under different values of As 4 BEP for InGaAs films. When the As 4 BEP is set to be zero, the RHEED pattern keeps a 4×3/(n × 3) structure with increasing temperature, and surface segregation takes place until 470 °C. The RHEED pattern develops into a metal-rich (4 × 2) structure as temperature increases to 495 °C. The reason for this is that surface segregation makes the In inside the InGaAs film climb to its surface. With the temperature increasing up to 515 °C, the RHEED pattern turns into a GaAs(2 × 4) structure due to In desorption. While the As 4 BEP comes up to a specific value (1.33 × 10 -4 Pa−1.33 × 10 -3 Pa), the surface temperature can delay the segregation and desorption. We find that As 4 BEP has a big influence on surface desorption, while surface segregation is more strongly dependent on temperature than surface desorption. (condensed matter: structural, mechanical, and thermal properties)

Characterization of GaN/AlGaN epitaxial layers grown

Indian Academy of Sciences (India)

GaN and AlGaN epitaxial layers are grown by a metalorganic chemical vapour deposition (MOCVD) system. The crystalline quality of these epitaxially grown layers is studied by different characterization techniques. PL measurements indicate band edge emission peak at 363.8 nm and 312 nm for GaN and AlGaN layers ...

Study of GaN nanorods converted from β-Ga2O3

Science.gov (United States)

Li, Yuewen; Xiong, Zening; Zhang, Dongdong; Xiu, Xiangqian; Liu, Duo; Wang, Shuang; Hua, Xuemei; Xie, Zili; Tao, Tao; Liu, Bin; Chen, Peng; Zhang, Rong; Zheng, Youdou

2018-05-01

We report here high-quality β-Ga2O3 nanorods (NRs) grown on sapphire substrates by hydrothermal method. Ammoniating the β-Ga2O3 NRs results in strain-free wurtzite gallium nitride (GaN) NRs. It was shown by XRD and Raman spectroscopy that β-Ga2O3 was partially converted to GaN/β-Ga2O3 at 1000 °C and then completely converted to GaN NRs at 1050 °C, as confirmed by high-resolution transmission electron microscopy (HRTEM). There is no band-edge emission of β-Ga2O3 in the cathodoluminescence spectrum, and only a deep-level broad emission observed at 3.68-3.73 eV. The band edge emission (3.39 eV) of GaN NRs converted from β-Ga2O3 can also be observed.

Magnetic anisotropy and anisotropic magnetoresistance of (Ga,Mn)As Layers on (113)A GaAs

Energy Technology Data Exchange (ETDEWEB)

Donhauser, Daniela; Dreher, Lukas; Daeubler, Joachim; Glunk, Michael; Rapp, Christoph; Schoch, Wladimir; Sauer, Rolf; Limmer, Wolfgang [Institut fuer Halbleiterphysik, Universitaet Ulm (Germany)

2009-07-01

We study the magnetic anisotropy and the anisotropic magnetoresistance of compressively strained (Ga,Mn)As films with various Mn concentrations, grown on (113)A-oriented GaAs substrates. High-resolution x-ray diffraction (HRXRD) studies reveal a monoclinic symmetry of the distorted (113)A layers in agreement with an explicit calculation of the strain tensor. Based on this result, general expressions for the resistivity tensor and the free energy of single-crystalline ferromagnets are derived from a series expansion with respect to the magnetization orientation, including terms up to the fourth order. With these expressions we are able to model the measured angular dependences of our magnetotransport data with the assumption of a single ferromagnetic domain model. In order to quantitatively derive the resistivity and anisotropy parameters the longitudinal and transverse resistivities are experimentally studied for magnetic fields rotated within the (113), (33 anti 2), and (anti 110) plane at various field strengths. It turned out that some of the resistivity parameters significantly depend on the strength of the external magnetic field. Furthermore we found that the layers exhibit a uniaxial anisotropy along the [001] crystallographic axis, which can be theoretically explained based on the explicit form of the strain tensor.

Foundation Investigation for Ground Based Radar Project-Kwajalein Island, Marshall Islands

Science.gov (United States)

1990-04-01

iL_ COPY MISCELLANEOUS PAPER GL-90-5 i iFOUNDATION INVESTIGATION FOR GROUND BASED RADAR PROJECT--KWAJALEIN ISLAND, MARSHALL ISLANDS by Donald E...C!assification) Foundatioa Investigation for Ground Based Radar Project -- Kwajalein Island, Marshall Islands 12. PERSONAL AUTHOR(S) Yule, Donald E...investigation for the Ground Based Radar Project -- Kwajalein Island, Marshall Islands , are presented.- eophysical tests comprised of surface refrac- tion

Source identification of soil mercury in the Spanish islands.

Science.gov (United States)

Rodríguez Martín, José Antonio; Carbonell, Gregoria; Nanos, Nikos; Gutiérrez, Carmen

2013-02-01

This study spatially analysed the relation between mercury (Hg) content in soil and Hg in rock fragment for the purpose of assessing natural soil Hg contribution compared with Hg from human inputs. We present the Hg content of 318 soil and rock fragment samples from 11 islands distributed into two Spanish archipelagos (the volcanic Canary Islands [Canaries] and the Mediterranean Balearic [Balearic] islands). Assumedly both are located far enough away from continental Hg sources to be able to minimise the effects of diffuse pollution. Physical and chemical soil properties were also specified for the samples. Hg contents were significantly greater in the Balearic limestone soils (61 μg kg(-1)) than in the volcanic soils of the Canaries (33 μg kg(-1)). Hg levels were also greater in topsoil than in rocky fragments, especially on the Balearics. The soil-to-rock ratios varied between 1 and 30. Interestingly, the highest topsoil-to-rock Hg ratio (>16 ×) was found in the vicinity of a coal-fired power plant in Majorca, whereas no similar areas in the Canary archipelago were identified.

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates

Science.gov (United States)

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-01

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates.

Science.gov (United States)

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-02

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

Investigation of the current collapse induced in InGaN back barrier AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Wan Xiaojia; Wang Xiaoliang; Xiao Hongling; Feng Chun; Jiang Lijuan; Qu Shenqi; Wang Zhanguo; Hou Xun

2013-01-01

Current collapses were studied, which were observed in AlGaN/GaN high electron mobility transistors (HEMTs) with and without InGaN back barrier (BB) as a result of short-term bias stress. More serious drain current collapses were observed in InGaN BB AlGaN/GaN HEMTs compared with the traditional HEMTs. The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse. The surface states may be the primary mechanism of the origination of current collapse in AlGaN/GaN HEMTs for short-term direct current stress. (semiconductor devices)

Investigation of the GaN-on-GaAs interface for vertical power device applications

International Nuclear Information System (INIS)

Möreke, Janina; Uren, Michael J.; Kuball, Martin; Novikov, Sergei V.; Foxon, C. Thomas; Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J.; Haigh, Sarah J.; Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain

2014-01-01

GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

Investigation of the GaN-on-GaAs interface for vertical power device applications

Energy Technology Data Exchange (ETDEWEB)

Möreke, Janina, E-mail: janina.moereke@bristol.ac.uk; Uren, Michael J.; Kuball, Martin [H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Novikov, Sergei V.; Foxon, C. Thomas [Department of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Haigh, Sarah J. [Super STEM Laboratory, STFC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD (United Kingdom); School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain [School of Engineering, University of Glasgow, Rankine Bldg, Oakfield Avenue, Glasgow G12 8LT (United Kingdom)

2014-07-07

GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

Nanoselective area growth and characterization of dislocation-free InGaN nanopyramids on AlN buffered Si(111) templates

Energy Technology Data Exchange (ETDEWEB)

Sundaram, S.; El Gmili, Y. [CNRS, UMI 2958 Georgia Tech-CNRS, 2 Rue Marconi, 57070 Metz (France); Puybaret, R.; Li, X.; Bonanno, P. L.; Voss, P. L.; Ougazzaden, A., E-mail: abdallah.ougazzaden@georgiatech-metz.fr [CNRS, UMI 2958 Georgia Tech-CNRS, 2 Rue Marconi, 57070 Metz (France); School of Electrical and Computer Engineering, Georgia Institute of Technology, GT Lorraine, 57070 Metz (France); Pantzas, K.; Patriarche, G. [CNRS, UPR LPN, Route de Nozay, 91460 Marcoussis (France); Salvestrini, J. P. [Universite de Lorraine, Centrale Supelec, LMOPS, EA 4423, 2 rue E. Belin, 57070 Metz (France)

2015-09-14

We report the metal organic chemical vapor deposition growth of dislocation-free 100 nm thick hexagonal InGaN nanopyramid arrays with up to 33% of indium content by nano-selective area growth on patterned AlN/Si (111) substrates. InGaN grown on SiO{sub 2} patterned templates exhibit high selectivity. Their single crystal structure is confirmed by scanning transmission electron microscope combined with an energy dispersive X-ray analysis, which also reveals the absence of threading dislocations in the InGaN nanopyramids due to elastic strain relaxation mechanisms. Cathodoluminescence measurements on a single InGaN nanopyramid clearly show an improvement of the optical properties when compared to planar InGaN grown under the same conditions. The good structural, morphological, and optical quality of the InGaN nanostructures grown on AlN/Si indicates that the nano-selective area growth technology is attractive for the realization of site-controlled indium-rich InGaN nanostructure-based devices and can also be transferred to other highly mismatched substrates.

Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

International Nuclear Information System (INIS)

Harmatha, Ladislav; Ľubica, Stuchlíková; Juraj, Racko; Juraj, Marek; Juraj, Pecháček; Peter, Benko; Michal, Nemec; Juraj, Breza

2014-01-01

Highlights: • Dependences of CV characteristics of the AlGaN/GaN structure on frequency and temperature variations. • Identification of electrical activity of defects by capacitance DLTS. • Simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure. - Abstract: The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al 2 O 3 substrate by Low-Pressure Metal–Organic Vapour-Phase Epitaxy (LP-MOVPE). Dependences of the capacitance–voltage (CV) characteristics on the frequency of the measuring signal allow analysing the properties of the 2D electron gas (2DEG) at the AlGaN/GaN heterojunction. Exact location of the hetero-interface below the surface (20 nm) was determined from the concentration profile. Temperature variations of the CV curves reveal the influence of bulk defects in GaN and of the traps at the AlGaN/GaN interface. Electrical activity of these defects was characterized by capacitance Deep Level Transient Fourier Spectroscopy (DLTFS). Experimental results of CV measurements were supported by simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure in dependence on the influence of the concentration of donor-like traps in GaN and of the temperature upon the CV curves

Anomalous disorder-related phenomena in InGaN/GaN multiple quantum well heterosystems

International Nuclear Information System (INIS)

Hu, Y.-J.; Huang, Y.-W.; Fang, C.-H.; Wang, J.-C.; Chen, Y.-F.; Nee, T.-E.

2010-01-01

The influences of InGaN/GaN multiple quantum well (MQW) heterostructures with InGaN/GaN and GaN barriers on carrier confinement were investigated. The degree of disordering over a broad range of temperatures from 20 to 300 K was considered. The optical and electrical properties were strongly influenced by structural and compositional disordering of the InGaN/GaN MQW heterostructures. To compare the degree of disordering we examined the temperature dependence of the luminescence spectra and electrical conductance contingent on the Berthelot-type mechanisms in the InGaN/GaN MQW heterostructures. We further considered carrier transport in the InGaN/GaN disordered systems, probability of carrier tunneling, and activation energy of the transport mechanism for devices with InGaN/GaN and GaN barriers. The optical properties of InGaN/GaN disordered heterosystems can be interpreted from the features of the absorption spectra. The anomalous temperature-dependent characteristics of the disordered InGaN/GaN MQW structures were attributable to the enhancement of the exciton confinement.

Ga and Pt NMR study of UPtGa sub 5 and UNiGa sub 5

CERN Document Server

Kato, H; Tokunaga, Y; Tokiwa, Y; Ikeda, S; Onuki, Y; Kambe, S; Walstedt, R E

2003-01-01

Ga and Pt NMR measurements have been carried out for two isomorphs compounds, UPtGa sub 5 and UNiGa sub 5 , which exhibit different magnetic structures below T sub N. Knight shift K measurements in the paramagnetic region are reported here. The transferred hyperfine coupling constants at Ga and Pt sites are determined. The temperature independent part K sub 0 of K, which probes the conduction electron polarization at the ligand site, has been successfully evaluated. A nearly identical conduction electron structure in the paramagnetic region is suggested for these two compounds. The origin of the different magnetic structures is discussed.

AlGaN/GaN heterostructures with an AlGaN layer grown directly on reactive-ion-etched GaN showing a high electron mobility (>1300 cm2 V-1 s-1)

Science.gov (United States)

Yamamoto, Akio; Makino, Shinya; Kanatani, Keito; Kuzuhara, Masaaki

2018-04-01

In this study, the metal-organic-vapor-phase-epitaxial growth behavior and electrical properties of AlGaN/GaN structures prepared by the growth of an AlGaN layer on a reactive-ion-etched (RIE) GaN surface without regrown GaN layers were investigated. The annealing of RIE-GaN surfaces in NH3 + H2 atmosphere, employed immediately before AlGaN growth, was a key process in obtaining a clean GaN surface for AlGaN growth, that is, in obtaining an electron mobility as high as 1350 cm2 V-1 s-1 in a fabricated AlGaN/RIE-GaN structure. High-electron-mobility transistors (HEMTs) were successfully fabricated with AlGaN/RIE-GaN wafers. With decreasing density of dotlike defects observed on the surfaces of AlGaN/RIE-GaN wafers, both two-dimensional electron gas properties of AlGaN/RIE-GaN structures and DC characteristics of HEMTs were markedly improved. Since dotlike defect density was markedly dependent on RIE lot, rather than on growth lot, surface contaminations of GaN during RIE were believed to be responsible for the formation of dotlike defects and, therefore, for the inferior electrical properties.

Durability testing of the high-capacity GA-4/GA-9 trailer

International Nuclear Information System (INIS)

Zimmer, A.; Lyon, T.

1995-01-01

GA designed trailers to transport the GA-4 and GA-9 LWT from-reactor spent nuclear fuel shipping casks. GA designed and fabricated the GA-9 trailer to ANSI N14.30 requirements and is now performing a durability test at the AlliedSignal Automotive Proving Grounds. The trailer, simulated cask and tractor. The test program objective is to evaluate and improve, as necessary, the trailer's durability, reliability and performance

Efficiency enhancement of InGaN/GaN light-emitting diodes with pin-doped GaN quantum barrier

International Nuclear Information System (INIS)

Sirkeli, Vadim P; Al-Daffaie, Shihab; Oprea, Ion; Küppers, Franko; Hartnagel, Hans L; Yilmazoglu, Oktay; Ong, Duu Sheng

2017-01-01

Blue InGaN/GaN light-emitting diodes with undoped, heavily Si-doped, Si delta-doped, heavily Mg-doped, Mg delta-doped, and Mg–Si pin-doped GaN barrier are investigated numerically. The simulation results demonstrate that the Mg–Si pin-doping in the GaN barrier effectively reduces the polarization-induced electric field between the InGaN well and the GaN barrier in the multiple quantum well, suppresses the quantum-confined Stark effect, and enhances the hole injection and electron confinement in the active region. For this light-emitting diode (LED) device structure, we found that the turn-on voltage is 2.8 V, peak light emission is at 415.3 nm, and internal quantum efficiency is 85.9% at 100 A cm −2 . It is established that the LED device with Mg–Si pin-doping in the GaN barrier has significantly improved efficiency and optical output power performance, and lower efficiency droop up to 400 A cm −2 compared with LED device structures with undoped or Si(Mg)-doped GaN barrier. (paper)

Growth and characterization of Ga(As,N) and (In,Ga)(As,N)

International Nuclear Information System (INIS)

Mussler, G.

2005-01-01

This dissertation deals with the MBE growth and characterization of Ga(As,N) and (In,Ga)(As,N). The work commences with the optimization of the Ga(As,N) growth. Owing to a large miscibility gap of GaN in GaAs, the incorporation of nitrogen into GaAs causes a structural degradation that is dependent on the substrate temperature, the nitrogen concentration, and the quantum well thickness. Another problem related to the growth of Ga(As,N) are point defects that have a detrimental influence on optical properties. A thermal treatment of Ga(As,N) reduces the concentration of these point defects. This leads to a substantial improvement of optical properties. We will show that nitrogen split interstitials that incorporate into gallium and arsenic vacancies may be attributed to these point defects. A thermal treatment of Ga(As,N) at high temperatures, on the contrary, results in a creation of extended defects which are detrimental to optical properties. We show that the temperature of the thermal treatment that yields the highest photoluminescence intensity is nitrogen concentration-dependent. The growth of (In,Ga)(As,N) is similar with respect to Ga(As,N). Again, one has to face a high miscibility gap of (In,Ga)N in (In,Ga)As that results in a structural degradation. A thermal treatment of (In,Ga)(As,N) is also beneficial for improving optical properties. We show that a thermal treatment of (In,Ga)As results in an indium diffusion that is suppressed by the incorporation of nitrogen. The characterization of (In,Ga)(As,N) edge emitting lasers shows emission at wavelengths up to 1366 nm. With higher nitrogen concentrations, there is a strong increase of the threshold current density and a decrease of the output power

Groove-type channel enhancement-mode AlGaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

International Nuclear Information System (INIS)

Duan Xiao-Ling; Zhang Jin-Cheng; Xiao Ming; Zhao Yi; Ning Jing; Hao Yue

2016-01-01

A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor (GTCE-HEMT) with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 mS/mm, and subthreshold slope of 85 mV/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage ( V B ) is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode (D-mode) polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits. (paper)

Large exchange bias induced by polycrystalline Mn3Ga antiferromagnetic films with controlled layer thickness

Science.gov (United States)

Wu, Haokaifeng; Sudoh, Iori; Xu, Ruihan; Si, Wenshuo; Vaz, C. A. F.; Kim, Jun-young; Vallejo-Fernandez, Gonzalo; Hirohata, Atsufumi

2018-05-01

Polycrystalline Mn3Ga layers with thickness in the range from 6–20 nm were deposited at room temperature by a high target utilisation sputtering. To investigate the onset of exchange-bias, a ferromagnetic Co0.6Fe0.4 layer (3.3–9 nm thick) capped with 5 nm Ta, were subsequently deposited. X-ray diffraction measurements confirm the presence of Mn3Ga (0 0 0 2) and (0 0 0 4) peaks characteristic of the D019 antiferromagnetic structure. The 6 nm thick Mn3Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The blocking temperature is found to decrease with increasing Mn3Ga thickness. These results in combination with x-ray reflectivity measurements confirm that the quality of the Mn3Ga/Co0.6Fe0.4 interface controls the exchange bias, with the sharp interface with the 6-nm-thick Mn3Ga inducing the largest exchange bias. The magneto-crystalline anisotropy for 6 nm thick Mn3Ga thin film sample is calculated to be . Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics.

P- and N-type implantation doping of GaN with Ca and O

International Nuclear Information System (INIS)

Zolper, J.C.; Wilson, R.G.; Pearton, S.J.

1996-01-01

III-N photonic devices have made great advances in recent years following the demonstration of doping of GaN p-type with Mg and n-type with Si. However, the deep ionization energy level of Mg in GaN (∼ 160 meV) limits the ionized of acceptors at room temperature to less than 1.0% of the substitutional Mg. With this in mind, the authors used ion implantation to characterize the ionization level of Ca in GaN since Ca had been suggested by Strite to be a shallow acceptor in GaN. Ca-implanted GaN converted from n-to-p type after a 1,100 C activation anneal. Variable temperature Hall measurements give an ionization level at 169 meV. Although this level is equivalent to that of Mg, Ca-implantation may have advantages (shallower projected range and less straggle for a given energy) than Mg for electronic devices. In particular, the authors report the first GaN device using ion implantation doping. This is a GaN junction field effect transistor (JFET) which employed Ca-implantation. A 1.7 microm JFET had a transconductance of 7 mS/mm, a saturation current at 0 V gate bias of 33 mA/mm, a f t of 2.7 GHz, and a f max of 9.4 GHz. O-implantation was also studied and shown to create a shallow donor level (∼ 25 meV) that is similar to Si. SIMS profiles of as-implanted and annealed samples showed no measurable redistribution of either Ca or O in GaN at 1,125 C

Strain-compensated (Ga,In)N/(Al,Ga)N/GaN multiple quantum wells for improved yellow/amber light emission

Energy Technology Data Exchange (ETDEWEB)

Lekhal, K.; Damilano, B., E-mail: bd@crhea.cnrs.fr; De Mierry, P.; Vennéguès, P. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Valbonne 06560 (France); Ngo, H. T.; Rosales, D.; Gil, B. [Laboratoire Charles Coulomb, CNRS-INP-UMR 5221, Université Montpellier 2, F-34095 Montpellier (France); Hussain, S. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Valbonne 06560 (France); Université de Nice Sophia Antipolis, Parc Valrose, 28 av. Valrose, 06108 Nice cedex 2 (France)

2015-04-06

Yellow/amber (570–600 nm) emitting In{sub x}Ga{sub 1−x}N/Al{sub y}Ga{sub 1−y}N/GaN multiple quantum wells (QWs) have been grown by metal organic chemical vapor deposition on GaN-on- sapphire templates. When the (Al,Ga)N thickness of the barrier increases, the room temperature photoluminescence is red-shifted while its yield increases. This is attributed to an increase of the QW internal electric field and an improvement of the material quality due to the compensation of the compressive strain of the In{sub x}Ga{sub 1−x}N QWs by the Al{sub y}Ga{sub 1−y}N layers, respectively.

First-principle natural band alignment of GaN / dilute-As GaNAs alloy

Directory of Open Access Journals (Sweden)

Chee-Keong Tan

2015-01-01

Full Text Available Density functional theory (DFT calculations with the local density approximation (LDA functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

Magnetic properties of the tetragonal RCuGa{sub 3} (R=Pr, Nd and Gd) single crystals

Energy Technology Data Exchange (ETDEWEB)

Nagalakshmi, R., E-mail: nagaphys@yahoo.com [Department of Physics, National Institute of Technology, Tiruchirappalli 6200015 (India); Kulkarni, Ruta; Dhar, S.K.; Thamizhavel, A. [DCMPMS, Tata Institute of Fundamental Research, Mumbai 400005 (India); Krishnakumar, V. [Department of Physics, Periyar University, Salem 636011 (India); Reiffers, Marian; Čurlík, Ivan [Institute of Experimental Physics, Watsonova 47, SK-040 01 Kosice (Slovakia); Department of Physics, University of Presov, 17 Novembra 1, SK-080 01 (Slovakia); Hagemann, Hans; Lovy, Dominique [Department of Physical Chemistry, University of Geneva, Geneva (Switzerland); Nallamuthu, S. [Department of Physics, National Institute of Technology, Tiruchirappalli 6200015 (India)

2015-07-15

Single crystals of tetragonal RCuGa{sub 3} (R=La, Pr, Nd and Gd), with BaNiSn{sub 3} type structure (space group I4 mm), have been grown by high temperature solution growth technique using Ga as flux. Their magnetic properties were determined by heat capacity and the measurement of magnetization and electrical resistivity along [100] and [001] directions. Except LaCuGa{sub 3}, the compounds order magnetically. PrCuGa{sub 3} undergoes a ferromagnetic transition with Curie temperature of 4.6 K. NdCuGa{sub 3} shows a bulk magnetic transition at 3.3 K. The data on GdCuGa{sub 3} indicate combined characteristics of spin glass and antiferromagnetic behavior at low temperatures. From the Schottky heat capacity data the crystal electric field level energy spectra have been determined. Further we have performed temperature dependent measurements of electron spin resonance (ESR) on GdCuGa{sub 3} between 11 K and room temperature. The ESR data indicate an enhancement of magnetic fluctuations associated with spin reorientation and both homogeneous and inhomogeneous thermal broadening of the linewidth. - Highlights: • RCuGa{sub 3} (R=La, Pr, Nd and Gd) single crystals were grown by flux technique. • The compounds exhibit long range magnetic ordering. • Crystal electric field levels have been derived from Schottky heat capacity. • Electron spin resonance (ESR) studies of GdCuGa{sub 3} are also discussed.

Tuning high frequency magnetic properties and damping of FeGa, FeGaN and FeGaB thin films

Directory of Open Access Journals (Sweden)

Derang Cao

2017-11-01

Full Text Available A series of FeGa, FeGaN and FeGaB films with varied oblique angles were deposited by sputtering method on silicon substrates, respectively. The microstructure, soft magnetism, microwave properties, and damping factor for the films were investigated. The FeGa films showed a poor high frequency magnetic property due to the large stress itself. The grain size of FeGa films was reduced by the additional N element, while the structure of FeGa films was changed from the polycrystalline to amorphous phase by the involved B element. As a result, N content can effectively improve the magnetic softness of FeGa film, but their high frequency magnetic properties were still poor both when the N2/Ar flow rate ratio is 2% and 5% during the deposition. The additional B content significantly led to the excellent magnetic softness and the self-biased ferromagnetic resonance frequency of 1.83 GHz for FeGaB film. The dampings of FeGa films were adjusted by the additional N and B contents from 0.218 to 0.139 and 0.023, respectively. The combination of these properties for FeGa films are helpful for the development of magnetostrictive microwave devices.

A hole modulator for InGaN/GaN light-emitting diodes

Science.gov (United States)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

2015-02-01

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ˜332 meV to ˜294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.

Ga originated kink-and-tail Zn diffusion profiles in InGaAsP and InGaAlAs alloys during MOVPE regrowth

Science.gov (United States)

Kitatani, T.; Okamoto, K.; Uchida, K.; Tanaka, S.

2017-12-01

We investigated the diffusion characteristics of Zn in ternary and quaternary alloys of InGaAsP and InGaAlAs, which are important materials in long-wavelength optical communication devices. The measured Zn diffusion profiles of InGaAs, InGaAsP, and InGaAlAs showed kink-and-tail shapes in which Zn concentration fell abruptly at first and then decreased slowly, whereas those of InP and InAlAs showed only abrupt decreases. Thus, only Ga-containing alloys had tail-like profiles. Since this tail was well described by the group-V vacancy related defect model, we deduced that its mechanism is closely related with group-V vacancies in Ga-related bonds such as GaP or GaAs. Furthermore, we demonstrated the possibility that many more group-V vacancies originated from GaP bonds than from GaAs bonds, indicating the difficulty in crystal growth of high quality alloys that have GaP components.

InGaN/GaN quantum well improved by in situ SiN{sub x} pretreatment of GaN template

Energy Technology Data Exchange (ETDEWEB)

Huang, Demeng; Wu, Zhengyuan; Fang, Zhilai [Department of Physics, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Xiamen University (China)

2016-12-15

In situ SiN{sub x} pretreatment was employed to modify the growth behavior and optical properties of InGaN/GaN quantum wells (QWs). With moderate SiN{sub x} pretreatment surface smoothness of InGaN/GaN QWs was improved and attributed to enhanced layer growth by Ga surfactant effect. Significant increase of photoluminescence peak intensity and relatively uniform and bright cathodoluminescence images were observed, which were attributed to the improvement in crystalline quality and strain reduction for the InGaN/GaN QWs with moderate SiN{sub x} pretreatment. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Fabrication of p-type porous GaN on silicon and epitaxial GaN

OpenAIRE

Bilousov, Oleksandr V.; Geaney, Hugh; Carvajal, Joan J.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Giguere, A.; Drouin, D.; Diaz, Francesc; Aguilo, Magdalena; O'Dwyer, Colm

2013-01-01

Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurem...

AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

Energy Technology Data Exchange (ETDEWEB)

Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Anaya Calvo, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Stoffels, S.; Marcon, D. [IMEC, Kapeldreef 75, B3001 Leuven (Belgium)

2013-11-11

AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

Island in an island – The suggestions for transportation improvement plan for Haidian Island, Haikou, Hainan

Directory of Open Access Journals (Sweden)

Sia Rosalind Juo Ling

2017-01-01

Full Text Available Haidian Island, which situated at the Northern part of Haikou City of Hainan Province, is an island within a city. Haidian Island is unique in term of it's development which centered around an university, the Hainan University, besides some others important landmarks, such as Haikou city hospital, Baishamen municipal park, Golf Driving Range etc. All commercials, residential, recreational activities etc are planned to serve Hainan University in particular. The study, taking ‘Haidian Island Area Development Control Plan’ as case study, would like to look into the importance of transportation and traffic planning. The study used observation, site investigation and traffic study methods to gather data needed. Firstly the study analyzed the current state of transportation system for Haidian Island in accordance to the Island Development Control plan and Haikou master plan and identified the problems. Then, the study made some recommendations for these problems. The study highlighted the important of non-motorized, cycling and walking as the main transportation system for an education-based island and as supportive to domestic tourism activities found. The transportation planning suggested by the study took ‘green and low-carbon’ approaches considered the role of University as the core activity in the island.

Characteristics of AlGaN/GaN/AlGaN double heterojunction HEMTs with an improved breakdown voltage

International Nuclear Information System (INIS)

Ma Juncai; Zhang Jincheng; Xue Junshuai; Lin Zhiyu; Liu Ziyang; Xue Xiaoyong; Ma Xiaohua; Hao Yue

2012-01-01

We studied the performance of AlGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with an AlGaN buffer layer, which leads to a higher potential barrier at the backside of the two-dimensional electron gas channel and better carrier confinement. This, remarkably, reduces the drain leakage current and improves the device breakdown voltage. The breakdown voltage of AlGaN/GaN double heterojunction HEMTs (∼100 V) was significantly improved compared to that of conventional AlGaN/GaN HEMTs (∼50 V) for the device with gate dimensions of 0.5 × 100 μm and a gate—drain distance of 1 μm. The DH-HEMTs also demonstrated a maximum output power of 7.78 W/mm, a maximum power-added efficiency of 62.3% and a linear gain of 23 dB at the drain supply voltage of 35 V at 4 GHz. (semiconductor devices)

Microstructure of (Ga,Mn)As/GaAs digital ferromagnetic heterostructures

International Nuclear Information System (INIS)

Kong, X.; Trampert, A.; Guo, X.X.; Kolovos-Vellianitis, D.; Daeweritz, L.; Ploog, K.H.

2005-01-01

We report on the microstructure of (Ga,Mn)As digital ferromagnetic heterostructures grown on GaAs (001) substrates by low-temperature molecular-beam epitaxy. The Mn concentration and the As 4 /Ga beam equivalent pressure (BEP) ratio are varied in the samples containing periods of Mn sheets separated by thin GaAs spacer layers. Transmission electron microscopy studies reveal that decreasing the Mn doping concentration and reducing the BEP ratio lead to smaller composition fluctuations of Mn and more homogeneous (Ga,Mn)As layers with abrupt interfaces. Planar defects are found as the dominant defect in these heterostructures and their density is related to the magnitude of the composition fluctuation. These defects show a noticeable anisotropy in the morphologic distribution parallel to the orthogonal [110] and [110] direction. Along the [110] direction, they are stacking faults, which are preferentially formed in V-shaped pairs and nucleate at the interfaces between (Ga,Mn)As and GaAs layers. Along the [110] direction, the planar defects are isolated thin twin lamellae. The character of the planar defects and their configuration are analyzed in detail

Diffuse scattering from the liquid-vapor interfaces of dilute Bi:Ga, Tl:Ga, and Pb:Ga alloys

International Nuclear Information System (INIS)

Li Dongxu; Jiang Xu; Rice, Stuart A.; Lin Binhua; Meron, Mati

2005-01-01

As part of a study of the in-plane wave-vector (q xy ) dependence of the effective Hamiltonian for the liquid-vapor interface, H(q), the wave-vector dependences of diffuse x-ray scattering from the liquid-vapor interfaces of dilute alloys of Bi in Ga, Tl in Ga, and Pb in Ga have been measured. In these dilute alloys the solute component segregates as a monolayer that forms the outermost stratum of the liquid-vapor interfaces, and the density distribution along the normal to the interface is stratified. Over the temperature ranges that the alloy interfaces were studied, the Tl and Pb monolayers exhibit both crystalline and liquid phases while the Bi monolayer is always liquid. The diffuse scattering from the liquid-vapor interfaces of these alloys displays interesting differences with that from the liquid-vapor interface of pure Ga. The presence of a segregated monolayer of solute in the liquid-vapor interface of the alloy appears to slightly suppress the fluctuations in an intermediate wave-vector range in a fashion that preserves the validity of the macroscopic capillary wave model to smaller wavelengths than in pure liquid Ga, and there is an increase in diffuse scattering when the Tl and Pb monolayers melt. The surface intrinsic roughness from fitting the wave-vector dependence of surface tension is 5.0 pm for the Tl:Ga alloy and 1.4 pm for the Bi:Ga alloy. Also, a mode of excitation that contributes to diffuse scattering from the liquid-vapor interface of Pb in Ga, but does not contribute to diffuse scattering from the liquid-vapor interface of Ga, has been identified. It is proposed that this mode corresponds to the separation of the Pb and Ga layers in the regime 1 nm -1 ≤q xy ≤10 nm -1

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires.

Science.gov (United States)

Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T; Martinez, Julio A

2016-01-08

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

Idiosyncratic responses to climate-driven forest fragmentation and marine incursions in reed frogs from Central Africa and the Gulf of Guinea Islands

Czech Academy of Sciences Publication Activity Database

Bell, R. C.; Parra, J. L.; Badjedjea, G.; Barej, M. F.; Blackburn, D. C.; Burger, M.; Channing, A.; Dehling, J. M.; Greenbaum, E.; Gvoždík, Václav; Kielgast, J.; Kusamba, C.; Lötters, S.; McLaughlin, P. J.; Nagy, Z. T.; Rödel, M.-O.; Portik, D. M.; Stuart, B. L.; VanDerWal, J.; Zassi-Boulou, A.-G.; Zamudio, K. R.

2017-01-01

Roč. 26, č. 19 (2017), s. 5223-5244 ISSN 0962-1083 R&D Projects: GA ČR GJ15-13415Y Institutional support: RVO:68081766 Keywords : climatic refugia * ecological niche modelling * Hyperolius * land-bridge island * lineage divergence * riverine barriers Subject RIV: EH - Ecology, Behaviour OBOR OECD: Ecology Impact factor: 6.086, year: 2016

A hole modulator for InGaN/GaN light-emitting diodes

International Nuclear Information System (INIS)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

2015-01-01

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm 2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs

From Schottky to Ohmic graphene contacts to AlGaN/GaN heterostructures: Role of the AlGaN layer microstructure

International Nuclear Information System (INIS)

Fisichella, G.; Greco, G.; Roccaforte, F.; Giannazzo, F.

2014-01-01

The electrical behaviour of graphene (Gr) contacts to Al x Ga 1−x N/GaN heterostructures has been investigated, focusing, in particular, on the impact of the AlGaN microstructure on the current transport at Gr/AlGaN interface. Two Al 0.25 Ga 0.75 N/GaN heterostructures with very different quality in terms of surface roughness and defectivity, as evaluated by atomic force microscopy (AFM) and transmission electron microscopy, were compared in this study, i.e., a uniform and defect-free sample and a sample with a high density of typical V-defects, which locally cause a reduction of the AlGaN thickness. Nanoscale resolution current voltage (I-V) measurements by an Au coated conductive AFM tip were carried out at several positions both on the bare and Gr-coated AlGaN surfaces. Rectifying contacts were found onto both bare AlGaN surfaces, but with a more inhomogeneous and lower Schottky barrier height (Φ B  ≈ 0.6 eV) for AlGaN with V-defects, with respect to the case of the uniform AlGaN (Φ B  ≈ 0.9 eV). Instead, very different electrical behaviours were observed in the presence of the Gr interlayer between the Au tip and AlGaN, i.e., a Schottky contact with reduced barrier height (Φ B ≈ 0.4 eV) for the uniform AlGaN and an Ohmic contact for the AlGaN with V-defects. Interestingly, excellent lateral uniformity of the local I-V characteristics was found in both cases and can be ascribed to an averaging effect of the Gr electrode over the AlGaN interfacial inhomogeneities. Due to the locally reduced AlGaN layer thickness, V defect act as preferential current paths from Gr to the 2DEG and can account for the peculiar Ohmic behaviour of Gr contacts on defective AlGaN

Gas sensing with AlGaN/GaN 2DEG channels

NARCIS (Netherlands)

Offermans, P.; Vitushinsky, R.; Crego-Calama, M.; Brongersma, S.H.

2011-01-01

AlGaN/GaN shows great promise as a generic platform for (bio-)chemical sensing because of its robustness and intrinsic sensitivity to surface charge or dipoles. Here, we employ the two-dimensional electron gas (2DEG) formed at the interface of AlGaN/GaN layers grown on Si substrates for the

First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

Energy Technology Data Exchange (ETDEWEB)

Schulthess, T C [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Svane, A [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States)

2007-04-23

We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments.

First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

International Nuclear Information System (INIS)

Schulthess, T C; Temmerman, W M; Szotek, Z; Svane, A; Petit, L

2007-01-01

We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments

Gallium-containing Heusler phases ScRh{sub 2}Ga, ScPd{sub 2}Ga, TmRh{sub 2}Ga and LuRh{sub 2}Ga. Magnetic and solid state NMR-spectroscopic characterization

Energy Technology Data Exchange (ETDEWEB)

Heletta, Lukas; Seidel, Stefan; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Benndorf, Christopher [Leipzig Univ. (Germany). Inst. fuer Mineralogie, Kristallographie und Materialwissenschaften; Eckert, Hellmut [Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; Sao Paulo Univ., Sao Carlos (Brazil). Inst. of Physics

2017-10-01

The gallium-containing Heusler phases ScRh{sub 2}Ga, ScPd{sub 2}Ga, TmRh{sub 2}Ga and LuRh{sub 2}Ga have been synthesized by arc-melting of the elements followed by different annealing sequences to improve phase purity. The samples have been studied by powder X-ray diffraction. The structures of Lu{sub 0.97}Rh{sub 2}Ga{sub 1.03} (Fm3m, a=632.94(5) pm, wR2=0.0590, 46 F{sup 2} values, seven variables) and Sc{sub 0.88}Rh{sub 2}Ga{sub 1.12} (a=618.91(4) pm, wR2=0.0284, 44 F{sup 2} values, six variables) have been refined from single crystal X-ray diffractometer data. Both gallides show structural disorder through Lu/Ga and Sc/Ga mixing. Temperature dependent magnetic susceptibility measurements showed Pauli paramagnetism for ScRh{sub 2}Ga, ScPd{sub 2}Ga, and LuRh{sub 2}Ga and Curie-Weiss paramagnetism for TmRh{sub 2}Ga. {sup 45}Sc and {sup 71}Ga solid state MAS NMR spectroscopic investigations of the Sc containing compounds confirmed the site mixing effects typically observed for Heusler phases. The data indicate that the effect of mixed Sc/Ga occupancy is significantly stronger in ScRh{sub 2}Ga than in ScPd{sub 2}Ga.

Burner Rig Hot Corrosion of a Single Crystal Ni-48Al-Ti-Hf-Ga Alloy

Science.gov (United States)

Nesbitt, James A.; Darolia, Ram; Cuy, Michael D.

1998-01-01

The hot corrosion resistance of a single crystal Ni-48Al-1Ti-0.5Hf-0.2Ga alloy was examined in a Mach 0.3 burner rig at 900 C for 300 hours. The combustion chamber was doped with 2 ppmw synthetic sea salt. The hot corrosion attack produced a random mound morphology on the surface. Microstructurally, the hot corrosion attack appeared to initiate with oxide-filled pits which were often broad and shallow. At an intermediate stage, the pits increased in size to incorporate unoxidized Ni islands in the corrosion product. The rampant attack stage, which was observed only at sharp sample corners, was characterized by rapid inward growth of alumina in finger-like protrusions incorporating significant amounts of Al-depleted Ni islands. Aluminum consumption in the oxide fingers resulted in the growth of a gamma' layer ahead of the advancing oxide fingers.

Burner rig hot corrosion of a single crystal Ni-48Al-Ti-Hf-Ga alloy

Energy Technology Data Exchange (ETDEWEB)

Nesbitt, J.A.; Darolia, R.; Cuy, M.D.

1999-07-01

The hot corrosion resistance of a single crystal Ni-48Al-1Ti-0.5Hf-0.2Ga alloy was examined in a Mach 0.3 burner rig at 900 C for 300 hours. The combustion chamber was doped with 2 ppmw synthetic sea salt. The hot corrosion attack produced a random mound morphology on the surface. Microstructurally, the hot corrosion attack appeared to initiate with oxide-filled pits which were often broad and shallow. At an intermediate stage, the pits increased in size to incorporate unoxidized Ni islands in the corrosion product. The rampant attack stage, which was observed only at sharp sample corners, was characterized by rapid inward growth of alumina in finger-like protrusions incorporating significant amounts of Al-depleted Ni islands. Aluminum consumption in the oxide fingers resulted in the growth of a {gamma}{prime} layer ahead of the advancing oxide fingers.

Ga-Ga bonding and tunnel framework in the new Zintl phase Ba{sub 3}Ga{sub 4}Sb{sub 5}

Energy Technology Data Exchange (ETDEWEB)

Park, S -M; Kim, S -J; Kanatzidis, M G

2003-11-01

A new Zintl phase Ba{sub 3}Ga{sub 4}Sb{sub 5} was obtained from the reaction of Ba and Sb in excess Ga flux at 1000 deg. C, and its structure was determined with single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group Pnma (No. 62) with a=13.248(3) A, b=4.5085(9) A, c=24.374(5) A and Z=4. Ba{sub 3}Ga{sub 4}Sb{sub 5} has a three-dimensional [Ga{sub 4}Sb{sub 5}]{sup 6-} framework featuring large tunnels running along the b-axis and accommodating the Ba ions. The structure also has small tube-like tunnels of pentagonal and rhombic cross-sections. The structure contains ethane-like dimeric Sb{sub 3}Ga-GaSb{sub 3} units and GaSb{sub 4} tetrahedra that are connected to form 12- and 14-membered tunnels. Band structure calculations confirm that the material is a semiconductor and indicate that the structure is stabilized by strong Ga-Ga covalent bonding interactions.

Islands and non-islands in native and heritage Korean

Directory of Open Access Journals (Sweden)

Boyoung eKim

2016-02-01

Full Text Available To a large extent, island phenomena are cross-linguistically invariable, but English and Korean present some striking differences in this domain. English has wh-movement and Korean does not, and while both languages show sensitivity to wh-islands, only English has island effects for adjunct clauses. Given this complex set of differences, one might expect Korean/English bilinguals, and especially heritage Korean speakers (i.e. early bilinguals whose L2 became their dominant language during childhood to be different from native speakers, since heritage speakers have had more limited exposure to Korean, may have had incomplete acquisition and/or attrition, and may show significant transfer effects from the L2. Here we examine islands in heritage speakers of Korean in the U.S. Through a series of four formal acceptability experiments comparing these heritage speakers with native speakers residing in Korea, we show that the two groups are remarkably similar. Both show clear evidence for wh-islands and an equally clear lack of adjunct island effects. Given the very different linguistic environment that the heritage speakers have had since early childhood, this result lends support to the idea that island phenomena are largely immune to environmental influences and stem from deeper properties of the processor and/or grammar. Similarly, it casts some doubt on recent proposals that islands are learned from the input.

Class renormalization: islands around islands

International Nuclear Information System (INIS)

Meiss, J.D.

1986-01-01

An orbit of 'class' is one that rotates about a periodic orbit of one lower class with definite frequency. This contrasts to the 'level' of a periodic orbit which is the number of elements in its continued fraction expansion. Level renormalization is conventionally used to study the structure of quasi-periodic orbits. The scaling structure of periodic orbits encircling other periodic orbits in area preserving maps is discussed here. Fixed points corresponding to the accumulation of p/q bifurcations are found and scaling exponents determined. Fixed points for q > 2 correspond to self-similar islands around islands. Frequencies of the island boundary circles at the fixed points are obtained. Importance of this scaling for the motion of particles in stochastic regions is emphasized. (author)

III-V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration

Science.gov (United States)

Cariou, Romain; Benick, Jan; Feldmann, Frank; Höhn, Oliver; Hauser, Hubert; Beutel, Paul; Razek, Nasser; Wimplinger, Markus; Bläsi, Benedikt; Lackner, David; Hermle, Martin; Siefer, Gerald; Glunz, Stefan W.; Bett, Andreas W.; Dimroth, Frank

2018-04-01

Silicon dominates the photovoltaic industry but the conversion efficiency of silicon single-junction solar cells is intrinsically constrained to 29.4%, and practically limited to around 27%. It is possible to overcome this limit by combining silicon with high-bandgap materials, such as III-V semiconductors, in a multi-junction device. Significant challenges associated with this material combination have hindered the development of highly efficient III-V/Si solar cells. Here, we demonstrate a III-V/Si cell reaching similar performances to standard III-V/Ge triple-junction solar cells. This device is fabricated using wafer bonding to permanently join a GaInP/GaAs top cell with a silicon bottom cell. The key issues of III-V/Si interface recombination and silicon's weak absorption are addressed using poly-silicon/SiOx passivating contacts and a novel rear-side diffraction grating for the silicon bottom cell. With these combined features, we demonstrate a two-terminal GaInP/GaAs//Si solar cell reaching a 1-sun AM1.5G conversion efficiency of 33.3%.

Barrier layer engineering: Performance evaluation of E-mode InGaN/AlGaN/GaN HEMT

Science.gov (United States)

Majumdar, Shubhankar; Das, S.; Biswas, D.

2015-08-01

Impact on DC characteristics of InGaN/AlGaN/GaN HEMT due to variation in the hetero-structure parameters i.e. molar fraction of Al and thickness of AlGaN barrier layer is presented in this paper. Gate controllability over the channel is dependent on barrier layer thickness, and molar fraction has an impact on band offset and 2DEG, which further affects the current. HEMT device that is simulated in SILVACO has InGaN cap layer of 2 nm thickness with 15% In molar fraction, variation of Al percentage and thickness of the AlGaN barrier layer are taken as 15-45% and 5-20nm, respectively. A tremendous change in threshold voltage (Vth), maximum transconductance (Gmmax) and subthreshold swing is found due to variation in hetero-structure parameter of barrier layer and the values are typically 1.3-0.1 V, 0.6-0.44 S/mm and 75-135 mV/dec respectively.

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

International Nuclear Information System (INIS)

Song, Erdong; Martinez, Julio A; Li, Qiming; Pan, Wei; Wang, George T; Swartzentruber, Brian

2016-01-01

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power. (paper)

Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

International Nuclear Information System (INIS)

Gao, Qingxue; Liu, Rong; Xiao, Hongdi; Cao, Dezhong; Liu, Jianqiang; Ma, Jin

2016-01-01

Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

Energy Technology Data Exchange (ETDEWEB)

Gao, Qingxue [School of Physics, Shandong University, Jinan, 250100 (China); Liu, Rong [Department of Fundamental Theories, Shandong Institute of Physical Education and Sports, Jinan 250063 (China); Xiao, Hongdi, E-mail: hdxiao@sdu.edu.cn [School of Physics, Shandong University, Jinan, 250100 (China); Cao, Dezhong; Liu, Jianqiang; Ma, Jin [School of Physics, Shandong University, Jinan, 250100 (China)

2016-11-30

Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

Investigation of GaN LED with Be-implanted Mg-doped GaN layer

International Nuclear Information System (INIS)

Huang, H.-W.; Kao, C.C.; Chu, J.T.; Kuo, H.C.; Wang, S.C.; Yu, C.C.; Lin, C.F.

2004-01-01

We report the electrical and optical characteristics of GaN light emitting diode (LED) with beryllium (Be) implanted Mg-doped GaN layer. The p-type layer of Be-implanted GaN LED showed a higher hole carrier concentration of 2.3 x 10 18 cm -3 and low specific contact resistance value of 2.0 x 10 -4 Ωcm 2 than as-grown p-GaN LED samples without Be-implantation. The Be-implanted GaN LEDs with InGaN/GaN MQW show slightly lower light output (about 10%) than the as-grown GaN LEDs, caused by the high RTA temperature annealing process

Mixed conductivity in La(Ga,Mg,NbO3-δ Perovskites

Directory of Open Access Journals (Sweden)

Marques, F. M. B.

1999-12-01

Full Text Available Solid-solution formation has been found in the perovskite-type system LaGa0.85-xMg0.15(Nb0.33Mg0.66xO3-δ (x = 0 - 0.20. Increasing dopant concentration leads to lower oxygen ionic conductivity and, at temperatures above 1000 K, higher p-type electronic conductivity. Oxygen-ion transference numbers in air were determined to vary in the range 0.78 to 0.96, decreasing with increasing x and temperature. Thermal expansion coefficients of ceramic samples of LaGa0.85-xMg0.15(Nb0.33Mg0.66xO3-δ were calculated in a temperature range of 300 to 1100 K to be essentially independent of composition, varying in the range (10.0 ± 0.2 x 10-6 K-1. Values of the activation energy for the total electrical conductivity in air are 104-106 kJ/mol in the temperature range 670 - 1000 K and 67 - 76 kJ/mol in the temperature range 1000 - 1200 K. The method of synthesis was found to affect both the symmetry of the perovskite unit cell and phase composition. The presence of second phases led to a dramatic decrease in conductivity.Se ha encontrado la formación de una solución sólida en el sistema LaGa0.85-xMg0.15(Nb0.33Mg0.66xO3-δ (x = 0 - 0.20. Un aumento de la concentración de dopante lleva a una menor conductividad iónica de oxígeno y a temperaturas superiores a 1000 K, una mayor conductividad electrónica de tipo p. El número de transferencia del ión oxígeno en aire fue determinado y varía en el rango 0.78 a 0.96 disminuyendo con el aumento de x y de la temperatura. El coeficiente de expansión térmico de las muestras cerámicas de LaGa0.85-xMg0.15(Nb0.33Mg0.66xO3-δ fue calculado en el rango de temperatura de 300 a 1100 k siendo independiente de la composición, y variando en el rango (10.0 ± 0.2 x 10-6 K-1. Los valores de la energía de activación para la conductividad eléctrica total en aire son 104-106 KJ/mol en el rango de temperatura 670-1000 K y 67-76 kJ/mol en el rango de temperaturas 1000-1200 K. Se encontró que el método de síntesis afecta

Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates

International Nuclear Information System (INIS)

Pérez-Tomás, A.; Fontserè, A.; Llobet, J.; Placidi, M.; Rennesson, S.; Chenot, S.; Moreno, J. C.; Cordier, Y.; Baron, N.

2013-01-01

The vertical bulk (drain-bulk) current (I db ) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental I db (25–300 °C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (E a ), the (soft or destructive) vertical breakdown voltage (V B ), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (E a = 0.35 eV at T = 25–300 °C; V B = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E a = 2.5 eV at T > 265 °C; V B > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E a = 0.35 eV at T > 150 °C; V B = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.

Fabrication and improved photoelectrochemical properties of a transferred GaN-based thin film with InGaN/GaN layers.

Science.gov (United States)

Cao, Dezhong; Xiao, Hongdi; Gao, Qingxue; Yang, Xiaokun; Luan, Caina; Mao, Hongzhi; Liu, Jianqiang; Liu, Xiangdong

2017-08-17

Herein, a lift-off mesoporous GaN-based thin film, which consisted of a strong phase-separated InGaN/GaN layer and an n-GaN layer, was fabricated via an electrochemical etching method in a hydrofluoric acid (HF) solution for the first time and then transferred onto quartz or n-Si substrates, acting as photoanodes during photoelectrochemical (PEC) water splitting in a 1 M NaCl aqueous solution. Compared to the as-grown GaN-based film, the transferred GaN-based thin films possess higher and blue-shifted light emission, presumably resulting from an increase in the surface area and stress relaxation in the InGaN/GaN layer embedded on the mesoporous n-GaN. The properties such as (i) high photoconversion efficiency, (ii) low turn-on voltage (-0.79 V versus Ag/AgCl), and (iii) outstanding stability enable the transferred films to have excellent PEC water splitting ability. Furthermore, as compared to the film transferred onto the quartz substrate, the film transferred onto the n-Si substrate exhibits higher photoconversion efficiency (2.99% at -0.10 V) due to holes (h + ) in the mesoporous n-GaN layer that originate from the n-Si substrate.

One-step rapid synthesis of ultrafine γ-Ga2O3 nanocrystals by microwave hydrothermal method in ammonium hydroxide medium

Science.gov (United States)

Cui, Lu; Wang, Hong; Xin, Baifu; Mao, Guijie

2017-10-01

Ultrafine nanocrystals of γ-gallium oxide (γ-Ga2O3) were rapidly synthesized via microwave hydrothermal method at 140 °C, in which Ga(NO3)3 was used as the gallium source and urea was the precipitant. The samples were characterized by X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), transmission electron microscopy (TEM), nitrogen physisorption and photoluminescence spectroscopy (PL). The crystallite size of ultrafine spinel γ-Ga2O3 was in the range from 4 to 5 nm and the optical bandgap was 4.61 eV. To improve the crystallinity, the ultrafine γ-Ga2O3 nanocrystals were calcined at 300-700 °C further. The ultrafine γ-Ga2O3 calcined at 500 °C (calcined-γ-Ga2O3) still remained the metastable γ-phase with relatively high crystallinity and the crystallite size around 5-7 nm. Photocatalytic performances of the synthesized samples were also evaluated by the degradation of rhodamine B (RhB). Results revealed that the ultrafine γ-Ga2O3 and the calcined-γ-Ga2O3 samples exhibited high photocatalytic efficiencies of 68.2 and 90.7%, respectively.

Alkylation of phenols and acylation 2-methoxynaphthalene over SSZ-33, SSZ-35 and SSZ-42 zeolites

Czech Academy of Sciences Publication Activity Database

Vitvarová, Dana; Lupínková, Lenka; Kubů, Martin

2015-01-01

Roč. 210, JUL 2015 (2015), s. 133-141 ISSN 1387-1811 R&D Projects: GA ČR GAP106/11/0819 Institutional support: RVO:61388955 Keywords : phenol alkylation * 2-methoxynaphthalene acylation * SSZ-33 Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.349, year: 2015

An Ultra-Efficient Nonlinear Platform: AlGaAs-On-Insulator

DEFF Research Database (Denmark)

Pu, Minhao; Ottaviano, Luisa; Semenova, Elizaveta

The combination of nonlinear and integrated photonics enables applications including optical signal processing, multi-wavelength lasers, metrology, spectroscopy, and quantum information science. Silicon-on-insulator (SOI) has emerged as a promising platform [1, 2] due to its high material...... nonlinearity and its compatibility with the CMOS industry. However, silicon suffers two-photon absorption (TPA) in the telecommunication wavelength band around 1.55 µm, which hampers its applications. Different platforms have been proposed to avoid TPA in the telecom wavelength range such as Si3N4 and Hydex [3...... a nonlinear index (n2) on the order of 10−17 W/m2 and a high refractive index (n ≈3.3), a large transparency window (from near- to mid-infrared), and the ability to engineer the material bandgap to mitigate TPA [5]. In this presentation, we introduce AlGaAson-insulator (AlGaAsOI) platform which combines both...

Sub-monolayer Deposited InGaAs/GaAs Quantum Dot Heterostructures and Lasers

DEFF Research Database (Denmark)

Xu, Zhangcheng

2004-01-01

deposition, the deposition of a short-period InAs/GaAs superlattice on GaAs (100) surface with an InAs effective thickness of less than 1 monolayer (ML), results in the formatioin of nanometer scale (In,Ga)As QDs of a non-SK class.In this thesis, the SML InGaAs/GaAs QDs are formed by 10 cycles of alternate......The fabrication, characterization and exploitation of self-assembled quantum dot (QD) heterostructures have attracted much attention not only in basic research, but also by the promising device applications such as QD lasers. The Stranski-Krastanow (SK) growth and the submonolayer (SML) deposition...... deposition of 0.5 ML InAs and 2.5 MLGaAs. The growth, structure, and optical properties of SML InGaAs/GaAs QD heterostructures are investigated in detail. SML InGaAs/GaAs QD lasers lasing even at room temperature have been successfully realized. The gain properties of SML InGaAs QD lasers are studied...

Tectonic Model of Bali Island Inferred from GPS Data

OpenAIRE

Cecep Sulaeman; Sri Hidayati; Amalfi Omang; Imam Catur Priambodo

2018-01-01

DOI: 10.17014/ijog.5.1.81-91Seven periods of GPS campaign have been conducted for three years since March 2013 - October 2015 on fourteen GPS sites across Bali Island. The GAMIT/GLOBK 10.6 version was used to compute data with respect for thirteen reference sites of International Terrestrial Reference Frame (ITRF) 2008 surrounding Bali. The result shows that horizontal displacement varies between 1.93 and 22.53 mm/yr dominantly northeastward. Vertical displacement ranges at -184.34 to 33.79 m...

Energy Transition Initiative: Island Energy Snapshot - Antigua and Barbuda; NREL (National Renewable Energy Laboratory)

Energy Technology Data Exchange (ETDEWEB)

None

2015-05-20

This profile provides a snapshot of the energy landscape of Antigua and Barbuda, an independent nation in the Leeward Islands in the eastern Caribbean Sea. Antigua and Barbuda’s utility rates are approximately $0.37 U.S. dollars (USD) per kilowatt-hour (kWh), which is above the Caribbean regional average of $0.33 USD/kWh.

Energy Transition Initiative: Island Energy Snapshot - Trinidad and Tobago; NREL (National Renewable Energy Laboratory)

Energy Technology Data Exchange (ETDEWEB)

None

2015-05-20

This profile provides a snapshot of the energy landscape of Trinidad and Tobago, a two-island nation located off the coast of Venezuela. Trinidad and Tobago’s electricity rates are some of the lowest in the Caribbean at approximately $0.04 per kilowatt-hour (kWh), well below the regional average of $0.33/kWh.

Self-diffusion in 69Ga121Sb/71Ga123Sb isotope heterostructures

Science.gov (United States)

Bracht, H.; Nicols, S. P.; Haller, E. E.; Silveira, J. P.; Briones, F.

2001-05-01

Gallium and antimony self-diffusion experiments have been performed in undoped 69Ga121Sb/71Ga123Sb isotope heterostructures at temperatures between 571 and 708 °C under Sb- and Ga-rich ambients. Ga and Sb profiles measured with secondary ion mass spectrometry reveal that Ga diffuses faster than Sb by several orders of magnitude. This strongly suggests that the two self-atom species diffuse independently on their own sublattices. Experimental results lead us to conclude that Ga and Sb diffusion are mediated by Ga vacancies and Sb interstitials, respectively, and not by the formation of a triple defect proposed earlier by Weiler and Mehrer [Philos. Mag. A 49, 309 (1984)]. The extremely slow diffusion of Sb up to the melting temperature of GaSb is proposed to be a consequence of amphoteric transformations between native point defects which suppress the formation of those native defects which control Sb diffusion. Preliminary experiments exploring the effect of Zn indiffusion at 550 °C on Ga and Sb diffusion reveal an enhanced intermixing of the Ga isotope layers compared to undoped GaSb. However, under the same conditions the diffusion of Sb was not significantly affected.

77 FR 51912 - Safety Zone; Tom Lyons Productions Fireworks, Long Island Sound, Sands Point, NY

Science.gov (United States)

2012-08-28

... DEPARTMENT OF HOMELAND SECURITY Coast Guard 33 CFR Part 165 [Docket Number USCG-2012-0618] RIN 1625-AA00 Safety Zone; Tom Lyons Productions Fireworks, Long Island Sound, Sands Point, NY AGENCY.... 165.T01-0618 to read as follows: Sec. 165.T01-0618 Safety Zone; Tom Lyons Productions Fireworks, Long...

AlGaN-Based Solar-Blind Schottky Photodetectors Fabricated on AlN/Sapphire Template

International Nuclear Information System (INIS)

Li-Wen, Sang; Zhi-Xin, Qin; Long-Bin, Cen; Bo, Shen; Guo-Yi, Zhang; Shu-Ping, Li; Hang-Yang, Chen; Da-Yi, Liu; Jun-Yong, Kang; Cai-Jing, Cheng; Hong-Yan, Zhao; Zheng-Xiong, Lu; Jia-Xin, Ding; Lan, Zhao; Jun-Jie, Si; Wei-Guo, Sun

2008-01-01

We report AlGaN-based back-illuminated solar-blind Schottky-type ultraviolet photodetectors with the cutoff-wavelength from 280nm to 292nm without bias. The devices show low dark current of 2.1 × 10 −6 A/cm 2 at the reverse bias of 5 V. The specific detectivity D* is estimated to be 3.3 × 10 12 cmHz 1/2 W −1 . To guarantee the performance of the photodetectors, the optimization of AlGaN growth and annealing condition for Schottky contacts were performed. The results show that high-temperature annealing method for Ni/Pt Schottky contacts is effective for the reduction of leakage current

Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

Directory of Open Access Journals (Sweden)

Nigamananda Samal

2010-02-01

Full Text Available An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW on GaAs by molecular beam epitaxy (MBE are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM of ~60 meV in room temperature (RT photoluminescence (PL indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

Self-organized formation of GaSb/GaAs quantum rings.

Science.gov (United States)

Timm, R; Eisele, H; Lenz, A; Ivanova, L; Balakrishnan, G; Huffaker, D L; Dähne, M

2008-12-19

Ring-shaped GaSb/GaAs quantum dots, grown by molecular beam epitaxy, were studied using cross-sectional scanning tunneling microscopy. These quantum rings have an outer shape of a truncated pyramid with baselengths around 15 nm and heights of about 2 nm but are characterized by a clear central opening extending over about 40% of the outer baselength. They form spontaneously during the growth and subsequent continuous capping of GaSb/GaAs quantum dots due to the large strain and substantial As-for-Sb exchange reactions leading to strong Sb segregation.

32 CFR 33.33 - Supplies.

Science.gov (United States)

2010-07-01

...) Disposition. If there is a residual inventory of unused supplies exceeding $5,000 in total aggregate fair... 32 National Defense 1 2010-07-01 2010-07-01 false Supplies. 33.33 Section 33.33 National Defense... Requirements Changes, Property, and Subawards § 33.33 Supplies. (a) Title. Title to supplies acquired under a...

Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Science.gov (United States)

Hu, Hongpo; Zhou, Shengjun; Liu, Xingtong; Gao, Yilin; Gui, Chengqun; Liu, Sheng

2017-03-01

We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL. The threading dislocation (TD) densities in GaN-based UV LEDs with GaN/AlGaN/sputtered AlN NLs were determined by high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM), which revealed that the TD density in UV LED with AlGaN NL was the highest, whereas that in UV LED with sputtered AlN NL was the lowest. The light output power (LOP) of UV LED with AlGaN NL was 18.2% higher than that of UV LED with GaN NL owing to a decrease in the absorption of 375 nm UV light in the AlGaN NL with a larger bandgap. Using a sputtered AlN NL instead of the AlGaN NL, the LOP of UV LED was further enhanced by 11.3%, which is attributed to reduced TD density in InGaN/AlInGaN active region. In the sputtered AlN thickness range of 10-25 nm, the LOP of UV LED with 15-nm-thick sputtered AlN NL was the highest, revealing that optimum thickness of the sputtered AlN NL is around 15 nm.

Energetics of Mg incorporation at GaN(0001) and GaN(0001¯) surfaces

Science.gov (United States)

Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

2006-04-01

By using density functional calculations in the generalized gradient approximation, we investigate the energetics of Mg adsorption and incorporation at GaN(0001) and GaN(0001¯) surfaces under various Ga and Mg coverage conditions as well as in presence of light or electron beam-induced electronic excitation. We find significant differences in Mg incorporation between Ga- and N-polar surfaces. Mg incorporation is easier at the Ga-polar surface, but high Mg coverages are found to cause important distortions which locally change the polarity from Ga to N polar. At the N-rich and moderately Ga-rich GaN(0001) surface, 0.25 ML of Mg substituting Ga in the top bilayer strongly reduce the surface diffusion barriers of Ga and N adatoms, in agreement with the surfactant effect observed in experiments. As the Mg coverage exceeds 0.5 ML, partial incorporation in the subsurface region (second bilayer) becomes favorable. A surface structure with 0.5 ML of incorporated Mg in the top bilayer and 0.25 ML in the second bilayer is found to be stable over a wide range of Ga chemical potential. At the Ga bilayer-terminated GaN(0001) surface, corresponding to Ga-rich conditions, configurations where Mg is incorporated in the interface region between the metallic Ga bilayer and the underlying GaN bilayer appear to be favored. At the N-polar surface, Mg is not incorporated under N-rich or moderately Ga-rich conditions, whereas incorporation in the adlayer may take place under Ga-rich conditions. In the presence of light or electron beam induced excitation, energy differences between Mg incorporated at the surface and in deeper layers are reduced so that the tendency toward surface segregation is also reduced.

Hexagonal (wurtzite) GaN inclusions as a defect in cubic (zinc-blende) GaN

International Nuclear Information System (INIS)

Zainal, N.; Novikov, S.V.; Akimov, A.V.; Staddon, C.R.; Foxon, C.T.; Kent, A.J.

2012-01-01

The dependence of the hexagonal fraction with thickness in MBE-grown bulk cubic (c-) GaN epilayer is presented in this paper. A number of c-GaN epilayers with different thicknesses were characterized via PL and XRD measurements. From the PL spectra, the signal due to h-GaN inclusions increases as the thickness of the c-GaN increases. On the contrary, in the XRD diffractogram, c-GaN shows a dominant signal at all thicknesses, and only a weak peak at ∼35° is observed in the diffractogram, implying the existence of a small amount of h-GaN in the c-GaN layer. The best quality of c-GaN is observed in the first 10 μm of GaN on the top of GaAs substrate. Even though the hexagonal content increases with the thickness, the average content remains below 20% in c-GaN layers up to 50 μm thick. The surface morphology of thick c-GaN is also presented.

Comparison of MOVPE grown GaAs, InGaAs and GaAsSb covering layers for different InAs/GaAs quantum dot applications

Czech Academy of Sciences Publication Activity Database

Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Hulicius, Eduard

2017-01-01

Roč. 464, Apr (2017), s. 59-63 ISSN 0022-0248 R&D Projects: GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : MOVPE * quantum dot * strain reducing layer * InAs * GaAsSb * InGaAs Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

Band gaps of wurtzite Sc{sub x}Ga{sub 1−x}N alloys

Energy Technology Data Exchange (ETDEWEB)

Tsui, H. C. L.; Moram, M. A. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Goff, L. E. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Rhode, S. K. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Pereira, S. [CICECO and Dept. Physics, Universidade de Aveiro, 3810-193 Aveiro (Portugal); Beere, H. E.; Farrer, I.; Nicoll, C. A.; Ritchie, D. A. [Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2015-03-30

Optical transmittance measurements on epitaxial, phase-pure, wurtzite-structure Sc{sub x}Ga{sub 1−x}N films with 0 ≤ x ≤ 0.26 showed that their direct optical band gaps increased from 3.33 eV to 3.89 eV with increasing x, in agreement with theory. These films contained I{sub 1}- and I{sub 2}-type stacking faults. However, the direct optical band gaps decreased from 3.37 eV to 3.26 eV for Sc{sub x}Ga{sub 1−x}N films, which additionally contained nanoscale lamellar inclusions of the zinc-blende phase, as revealed by aberration-corrected scanning transmission electron microscopy. Therefore, we conclude that the apparent reduction in Sc{sub x}Ga{sub 1−x}N band gaps with increasing x is an artefact resulting from the presence of nanoscale zinc-blende inclusions.

Comb-drive GaN micro-mirror on a GaN-on-silicon platform

International Nuclear Information System (INIS)

Wang, Yongjin; Sasaki, Takashi; Wu, Tong; Hu, Fangren; Hane, Kazuhiro

2011-01-01

We report here a double-sided process for the fabrication of a comb-drive GaN micro-mirror on a GaN-on-silicon platform. A silicon substrate is first patterned from the backside and removed by deep reactive ion etching, resulting in totally suspended GaN slabs. GaN microstructures including the torsion bars, movable combs and mirror plate are then defined on a freestanding GaN slab by the backside alignment technique and generated by fast atom beam etching with Cl 2 gas. Although the fabricated comb-drive GaN micro-mirrors are deflected by the residual stress in GaN thin films, they can operate on a high resistivity silicon substrate without introducing any additional isolation layer. The optical rotation angles are experimentally characterized in the rotation experiments. This work opens the possibility of producing GaN optical micro-electro-mechanical-system (MEMS) devices on a GaN-on-silicon platform.

Improved AlGaN/GaN HEMTs Grown on Si Substrates Using Stacked AlGaN/AlN Interlayer by MOCVD

International Nuclear Information System (INIS)

Wang Yong; Yu Nai-Sen; Li Ming; Lau Kei-May

2011-01-01

AlGaN/GaN high electron mobility transistors (HEMTs) are grown on 2-inch Si (111) substrates by MOCVD. The stacked AlGaN/AlN interlayer with different AlGaN thickness and indium surfactant doped is designed and optimized to relieve the tensile stress during GaN epitaxial growth. The top 1.0μm GaN buffer layer grown on the optimized AlGaN/AlN interlayer shows a crack-free and shining surface. The XRD results show that GaN(002) FWHM is 480 arcsec and GaN(102) FWHM is 900 arcsec. The AGaN/GaN HEMTs with optimized and non-optimized AlGaN/AlN interlayer are grown and processed for comparison and the dc and rf characteristics are characterized. For the dc characteristics of the device with optimized AlGaN/AlN interlayer, maximum drain current density I dss of 737mA/mm, peak transconductance G m of 185mS/mm, drain leakage current density I ds of 1.7μA/mm, gate leakage current density I gs of 24.8 μA/mm and off-state breakdown voltage V BR of 67 V are achieved with L g /W g /L gs /L gd = 1/10/1/1 μm. For the small signal rf characteristics of the device with optimized AlGaN/AlN interlayer, current gain cutoff frequency f T of 8.3 GHz and power gain cutoff frequency f max of 19.9 GHz are achieved with L g /W g /L gs /L gd = 1/100/1/1 μm. Furthermore, the best rf performance with f T of 14.5 GHz and f max of 37.3 GHz is achieved with a reduced gate length of 0.7μm. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

Science.gov (United States)

Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

2016-06-01

Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

Aspects of the ecology of feral cats on Dassen Island, South Africa ...

African Journals Online (AJOL)

Numbers of feral cats on Dassen Island (33°25'S/18°06'E) increased from 20–25 in May 1979 to 37–50 in June 1980. Kittens were born in eight months of the year with birth peaks in October-November and in January. Mean litter size was 2,7 and 80% of kittens born between August 1979 and January 1980 survived until ...

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

International Nuclear Information System (INIS)

Neumann, L.; Gerlach, J.W.; Rauschenbach, B.

2012-01-01

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700 °C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25 eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5 × 10 13 and 2 × 10 14 at. cm −2 s −1 . The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio. - Highlights: ► Ultra-thin epitaxial GaN films prepared by hyperthermal ion-beam assisted deposition. ► Surface structure and topography studied during and after initial growth stages. ► Growth mode dependent on nitrogen ion to gallium atom flux ratio. ► Change from three-dimensional to two-dimensional growth for Ga-rich growth conditions.

Tuppiap Qeqertaa (Tobias Island): a newly discovered island off northeast Greenland

DEFF Research Database (Denmark)

Bennike, O.; Mikkelsen, N.; Forsberg, René

2006-01-01

The small island of Tuppiap Qeqertaa, formerly known as Tobias circle divide or Tobias Island, is situated 80 km off the northeast Greenland coast. The island was discovered in 1993 and is approximately 2 km long and 1.5 km wide. Most of the island is covered by an ice cap that rises to 35 in abo...

Impact ionization of excitons in electric field of GaN and quantum wells of GaN/AlGaN

International Nuclear Information System (INIS)

Nel'son, D.K.; Yakobson, M.A.; Kagan, V.D.; Gil, B.; Grandjean, N.; Beaumont, B.; Massier, J.; Gibart, P.

2001-01-01

The effect of the exciton states impact ionization in the GaN exploit films and in the GaN/AlGaN structures with quantum wells is studied. The study was carried out through the optical method, based on the exciton photoluminescence quenching by applying the electric field. It is established that in the process of the electrons relaxation by energy and pulse the scattering on the admixtures prevails over the scattering on the acoustic phonons. The average length of the hot electrons free run is evaluated. The average length of the hot electrons free run in the GaN/AlGaN wells proved to be by the value order higher than in the GaN epitaxial films, which is conditioned by decrease in the probability of the electrons scattering in the two-dimensional case [ru

Localized deep levels in AlxGa1−xN epitaxial films with various Al compositions

International Nuclear Information System (INIS)

Shi Li-Yang; Shen Bo; Wang Ping; Yan Jian-Chang; Wang Jun-Xi

2014-01-01

By using high-temperature deep-level transient spectroscopy (HT-DLTS) and other electrical measurement techniques, localized deep levels in n-type Al x Ga 1−x N epitaxial films with various Al compositions (x = 0, 0.14, 0.24, 0.33, and 0.43) have been investigated. It is found that there are three distinct deep levels in Al x Ga 1−x N films, whose level position with respect to the conduction band increases as Al composition increases. The dominant defect level with the activation energy deeper than 1.0 eV below the conduction band closely follows the Fermi level stabilization energy, indicating that its origin may be related to the defect complex, including the anti-site defects and divacancies in Al x Ga 1−x N films. (condensed matter: structural, mechanical, and thermal properties)

Self-diffusion in 69Ga121Sb/71Ga123Sb isotope heterostructures

OpenAIRE

Bracht, H.; Nicols, S. P.; Haller, E. E.; Silveira, Juan Pedro; Briones Fernández-Pola, Fernando

2001-01-01

Gallium and antimony self-diffusion experiments have been performed in undoped 69Ga121Sb/71Ga123Sb isotope heterostructures at temperatures between 571 and 708 °C under Sb- and Ga-rich ambients. Ga and Sb profiles measured with secondary ion mass spectrometry reveal that Ga diffuses faster than Sb by several orders of magnitude. This strongly suggests that the two self-atom species diffuse independently on their own sublattices. Experimental results lead us to conclude that Ga and Sb diffusio...

Photocurrent characteristics of metal–AlGaN/GaN Schottky-on-heterojunction diodes induced by GaN interband excitation

Science.gov (United States)

Tang, Xi; Li, Baikui; Chen, Kevin J.; Wang, Jiannong

2018-05-01

The photocurrent characteristics of metal–AlGaN/GaN Schottky-on-heterojunction diodes were investigated. When the photon energy of incident light was larger than the bandgap of GaN but smaller than that of AlGaN, the alternating-current (ac) photocurrent measured using lock-in techniques increased with the chopper frequency. Analyzing the generation and flow processes of photocarriers revealed that the photocurrent induced by GaN interband excitation featured a transient behavior, and its direction reversed when the light excitation was removed. The abnormal dependence of the measured ac photocurrent magnitude on the chopper frequency was explained considering the detection principles of a lock-in amplifier.

Diomede Islands, Bering Straight

Science.gov (United States)

2008-01-01

The Diomede Islands consisting of the western island Big Diomede (also known as Imaqliq, Nunarbuk or Ratmanov Island), and the eastern island Little Diomede (also known as Krusenstern Island or Inaliq), are two rocky islands located in the middle of the Bering Strait between Russia and Alaska. The islands are separated by an international border and the International Date Line which is approximately 1.5 km from each island; you can look from Alaska into tomorrow in Russia. At the closest land approach between the United States, which controls Little Diomede, and Russia, which controls Big Diomede, they are 3 km apart. Little Diomede Island constitutes the Alaskan City of Diomede, while Big Diomede Island is Russia's easternmost point. The first European to reach the islands was the Russian explorer Semyon Dezhnev in 1648. The text of the 1867 treaty finalizing the sale of Alaska uses the islands to designate the border between the two nations. The image was acquired July 8, 2000, covers an area of 13.5 x 10.8 km, and is located at 65.8 degrees north latitude, 169 degrees west longitude. The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

Sociodemographic Factors Influencing Island Food Consumption in the Pacific Islander Health Study

OpenAIRE

Baumhofer, Nicole Kau'i

2016-01-01

This dissertation explores the relationships between island food consumption, sociodemographic variables, and cardiovascular risk using data from the Pacific Islander Health Study (PIHS). Chapter 1 explores the associations between self-reported level of island food consumption and key covariates. Island food consumption was modeled using Poisson regression and adjusted for demographic, socioeconomic, and cultural characteristics. Increased Pacific Island cultural affinity was the strongest p...

Paradise Islands? Island States and Environmental Performance

Directory of Open Access Journals (Sweden)

Sverker C. Jagers

2016-03-01

Full Text Available Island states have been shown to outperform continental states on a number of large-scale coordination-related outcomes, such as levels of democracy and institutional quality. The argument developed and tested in this article contends that the same kind of logic may apply to islands’ environmental performance, too. However, the empirical analysis shows mixed results. Among the 105 environmental outcomes that we analyzed, being an island only has a positive impact on 20 of them. For example, island states tend to outcompete continental states with respect to several indicators related to water quality but not in aspects related to biodiversity, protected areas, or environmental regulations. In addition, the causal factors previously suggested to make islands outperform continental states in terms of coordination have weak explanatory power in predicting islands’ environmental performance. We conclude the paper by discussing how these interesting findings can be further explored.

Interface States in AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors

International Nuclear Information System (INIS)

Feng Qian; Du Kai; Li Yu-Kun; Shi Peng; Feng Qing

2013-01-01

Frequency-dependent capacitance and conductance measurements are performed on AlGaN/GaN high electron mobility transistors (HEMTs) and NbAlO/AlGaN/GaN metal-insulator-semiconductor HEMTs (MISHEMTs) to extract density and time constants of the trap states at NbAlO/AlGaN interface and gate/AlGaN interface with the gate-voltage biased into the accumulation region and that at the AlGaN/GaN interface with the gate-voltage biased into the depletion region in different circuit models. The measurement results indicate that the trap density at NbAlO/AlGaN interface is about one order lower than that at gate/AlGaN interface while the trap density at AlGaN/GaN interface is in the same order, so the NbAlO film can passivate the AlGaN surface effectively, which is consistent with the current collapse results

Influence of annealing condition and multicycle AlGaAs/GaAs structures on the Al0.26Ga0.74As surface morphology

International Nuclear Information System (INIS)

Wei, Wenzhe; Wang, Yi; Guo, Xiang; Luo, Zijiang; Zhao, Zhen; Zhou, Haiyue; Ding, Zhao

2015-01-01

Highlights: • STM study on the change of AlGaAs surface morphology with varying annealing conditions. • Interesting phenomenon that the subsequent sample has more surface roughness than the previous samples do. A physical model was proposed to explain why the multi-runs growth can increase surface roughness. • The annealing conditions of AlGaAs/GaAs surface were proposed. - Abstract: The influence of annealing temperature, As 4 beam equivalent pressure and multi-runs growth on AlGaAs/GaAs structures was investigated. The real space ultrahigh vacuum scanning tunneling microscopy images showed that AlGaAs/GaAs surface morphology greatly depends on annealing conditions and initial state of surface. The reasons of the surface phenomenon are proposed, and a physical model was proposed to explain why the multi-runs growth structures can increase AlGaAs surface roughness. The reasonable preparation conditions for AlGaAs/GaAs structures were proposed

Temperature Dependence of the Energy Band Diagram of AlGaN/GaN Heterostructure

Directory of Open Access Journals (Sweden)

Yanli Liu

2018-01-01

Full Text Available Temperature dependence of the energy band diagram of AlGaN/GaN heterostructure was investigated by theoretical calculation and experiment. Through solving Schrodinger and Poisson equations self-consistently by using the Silvaco Atlas software, the energy band diagram with varying temperature was calculated. The results indicate that the conduction band offset of AlGaN/GaN heterostructure decreases with increasing temperature in the range of 7 K to 200 K, which means that the depth of quantum well at AlGaN/GaN interface becomes shallower and the confinement of that on two-dimensional electron gas reduces. The theoretical calculation results are verified by the investigation of temperature dependent photoluminescence of AlGaN/GaN heterostructure. This work provides important theoretical and experimental basis for the performance degradation of AlGaN/GaN HEMT with increasing temperature.

Characterization of modulation doped pseudomorphic AlGaAs/InGaAs/GaAs HEMT structures by electron beam electroreflectance and photoluminescence

International Nuclear Information System (INIS)

Herman, M.A.; Ward, I.D.; Kopf, R.F.; Pearton, S.J.; Jones, E.D.

1990-01-01

The authors have investigated the optical transitions present in MBE-grown modulation doped pseudomorphic Al x Ga 1-x As/In y Ga 1-y As/GaAs HEMT structures of 120 Angstrom InGaAs thickness, y values 0 to 0.28, and x values 0.20 to 0.30. From both 300K electron beam electroreflectance (EBER) and 4K photoluminescence (PL) measurements the authors observe transitions from the InGaAs strained quantum well layer. The intensity and lineshape of the InGaAs transition in both optical spectra are affected by processing temperatures, and provides an indication of the quality of the HEMT

Defining Population Health Vulnerability Following an Extreme Weather Event in an Urban Pacific Island Environment: Honiara, Solomon Islands

Science.gov (United States)

Natuzzi, Eileen S.; Joshua, Cynthia; Shortus, Matthew; Reubin, Reginald; Dalipanda, Tenneth; Ferran, Karen; Aumua, Audrey; Brodine, Stephanie

2016-01-01

Extreme weather events are common and increasing in intensity in the southwestern Pacific region. Health impacts from cyclones and tropical storms cause acute injuries and infectious disease outbreaks. Defining population vulnerability to extreme weather events by examining a recent flood in Honiara, Solomon Islands, can help stakeholders and policymakers adapt development to reduce future threats. The acute and subacute health impacts following the April 2014 floods were defined using data obtained from hospitals and clinics, the Ministry of Health and in-country World Health Organization office in Honiara. Geographical information system (GIS) was used to assess morbidity and mortality, and vulnerability of the health system infrastructure and households in Honiara. The April flash floods were responsible for 21 acute deaths, 33 injuries, and a diarrhea outbreak that affected 8,584 people with 10 pediatric deaths. A GIS vulnerability assessment of the location of the health system infrastructure and households relative to rivers and the coastline identified 75% of the health infrastructure and over 29% of Honiara's population as vulnerable to future hydrological events. Honiara, Solomon Islands, is a rapidly growing, highly vulnerable urban Pacific Island environment. Evaluation of the mortality and morbidity from the April 2014 floods as well as the infectious disease outbreaks that followed allows public health specialists and policy makers to understand the health system and populations vulnerability to future shocks. Understanding the negative impacts natural disaster have on people living in urban Pacific environments will help the government as well as development partners in crafting resilient adaptation development. PMID:27091867

Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

International Nuclear Information System (INIS)

Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

2010-01-01

Molecular-Beam Epitaxy growth of multiple In 0.4 Ga 0.6 As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4 Ga 0.6 As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4 Ga 0.6 As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

Science.gov (United States)

Zheng, Nan; Ahrenkiel, S. Phillip

2017-07-01

Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and lattice images.

Formation of columnar (In,Ga)As quantum dots on GaAs(100)

International Nuclear Information System (INIS)

He, J.; Noetzel, R.; Offermans, P.; Koenraad, P.M.; Gong, Q.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

2004-01-01

Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced

Compositional and structural characterisation of GaSb and GaInSb

International Nuclear Information System (INIS)

Corregidor, V.; Alves, E.; Alves, L.C.; Barradas, N.P.; Duffar, Th.; Franco, N.; Marques, C.; Mitric, A.

2005-01-01

Low band gap III-V semiconductors are researched for applications in thermophotovoltaic technology. GaSb crystal is often used as a substrate. Ga 1-x In x Sb is also a promising substrate material, because its lattice parameters can be adjusted by controlling x. We used a new method to synthesise GaSb and GaInSb, in which a high frequency alternate magnetic field is used to heat, to melt and to mix the elements. We present a compositional and structural characterisation of the materials using a combination of complementary techniques. Rutherford backscattering was used to determine accurately the composition of the GaSb. With proton induced X-ray emission in conjunction with a 3 x 3 μm 2 micro-beam we studied the homogeneity of the samples. Structural analysis and phase identification were done with X-ray diffraction. The results for GaSb show a homogeneous composition while the GaInSb samples were found to be strongly heterogeneous at the end of the ingot. The ingots produced are competitive feed material, when compared to other growth techniques, to be used in a second step for the production of good quality ternary crystals

Atmospheric pressure-MOVPE growth of GaSb/GaAs quantum dots

Science.gov (United States)

Tile, Ngcali; Ahia, Chinedu C.; Olivier, Jaco; Botha, Johannes Reinhardt

2018-04-01

This study focuses on the growth of GaSb/GaAs quantum dots (QD) using an atmospheric pressure MOVPE system. For the best uncapped dots, the average dot height, base diameter and density are 5 nm, 45 nm and 4.5×1010 cm-2, respectively. Capping of GaSb QDs at high temperatures caused flattening and formation of thin inhomogeneous GaSb layer inside GaAs resulting in no obvious QD PL peak. Capping at low temperatures lead to the formation of dot-like features and a wetting layer (WL) with distinct PL peaks for QD and WL at 1097 nm and 983 nm respectively. Some of the dot-like features had voids. An increase in excitation power caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending leading to triangular potential wells, typical of type-II alignment between GaAs and strained GaSb. Variable temperature PL measurements of the QD sample showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the temperature increased.

Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions

NARCIS (Netherlands)

Wittmann, B.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.

2008-01-01

The resonant circular photogalvanic effect is observed in wurtzite (0001)-oriented GaN low-dimensional structures excited by infrared radiation. The current is induced by angular-momentum transfer of photons to the photoexcited electrons at resonant intersubband optical transitions in a GaN/AlGaN

High resolution x-ray diffraction analyses of GaN/LiGaO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Matyi, R.J. [Department of Materials Science and Engineering University of Wisconsin, Madison, WI (United States); Doolittle, W.A.; Brown, A.S. [School of Electrical and Computer Engineering Georgia Institute of Technology, Atlanta, GA (United States)

1999-05-21

Lithium gallate (LiGaO{sub 2}) is gaining increasing attention as a potential substrate for the growth of the important semiconductor GaN. In order to better understand this material we have performed high-resolution double- and triple-axis x-ray diffraction analyses of both the starting LiGaO{sub 2} and GaN/LiGaO{sub 2} following epitaxial growth. A high-resolution triple-axis reciprocal space map of the substrate showed a sharp, well-defined crystal truncation rod and a symmetric streak of intensity perpendicular to q{sub 002}, suggesting high structural quality with mosaic spread. Triple-axis scans following GaN growth showed (1) the development of isotropic diffuse scatter around the LiGaO{sub 2} (002) reflection, (2) the presence of a semi-continuous intensity streak between the LiGaO{sub 2} (002) and GaN (0002) reflections, and (3) a compact pattern of diffuse scatter around the GaN (0002) reflection that becomes increasingly anisotropic as the growth temperature is increased. These results suggest that LiGaO{sub 2} permits the epitaxial growth of GaN with structural quality that may be superior to that observed when growth is performed on SiC or Al{sub 2}O{sub 3}. (author)

Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

Science.gov (United States)

Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

2008-12-01

Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

Fermi edge singularity evidence from photoluminescence spectroscopy of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs grown on (3 1 1)A GaAs substrates

International Nuclear Information System (INIS)

Rekaya, S.; Sfaxi, L.; Bru-Chevallier, C.; Maaref, H.

2011-01-01

InGaAs/AlGaAs/GaAs pseudomorphic high electron mobility transistor (P-HEMT) structures were grown by Molecular Beam Epitaxy (MBE) on (3 1 1)A GaAs substrates with different well widths, and studied by photoluminescence (PL) spectroscopy as a function of temperature and excitation density. The PL spectra are dominated by one or two spectral bands, corresponding, respectively, to one or two populated electron sub-bands in the InGaAs quantum well. An enhancement of PL intensity at the Fermi level energy (E F ) in the high-energy tail of the PL peak is clearly observed and associated with the Fermi edge singularity (FES). This is practically detected at the same energy for all samples, in contrast with energy transitions in the InGaAs channel, which are shifted to lower energy with increasing channel thickness. PL spectra at low temperature and low excitation density are used to optically determine the density of the two-dimensional electron gas (2DEG) in the InGaAs channel for different thicknesses. The results show an enhancement of the 2DEG density when the well width increases, in good agreement with our previous theoretical study.

Spin dynamics in GaAs and (110)-GaAs heterostructures; Spindynamik in GaAs und (110)-GaAs-Heterostrukturen

Energy Technology Data Exchange (ETDEWEB)

Oertel, Stefan

2012-07-01

This thesis investigates the spin dynamics in both bulk GaAs and (llO)GaAs heterostructures using time- and polarization-resolved photoluminescence spectroscopy. In bulk GaAs the spin relaxation t ime is measured for the first time in the high temperature regime from 280 K to 400 K and is compared to numerical calculations. The numerical calculations are based on the spin relaxation theory of the Dyakonov-Perel mechanism effected by momentum scattering with polar optical phonons and electron-electron scattering and are in good agreement with the experimental results. Measurements of the dependence on the electron density serve to determine the energy dependent proportional factor between the electron density and the effective electron-electron scattering time. Also in bulk GaAs the interaction between the electron spin system and the nuclear spin system is investigated. The measured electron Lande g-factor under the influence of the nuclear magnetic field is used as an indicator to monitor the temporal evolution of the nuclear magnetic field under sustained dynamic nuclear polarization. Measurements with polarization modulated excitation enable the determination of the relevant time scale at which dynamic nuclear polarization takes place. Furthermore, the temporal evolution of the measured electron Lande g-factor shows the complex interplay of the dynamic nuclear polarization, the nuclear spin diffusion and the nuclear spin relaxation. In symmetric (110)-GaAs quantum wells the dependence of the inplane anisotropy of the electron Lande g-factor on the quantum well thickness is determined experimentally. The measurements are in very good agreement with calculations based upon k . p-theory and reveal a maximum of the anisotropy at maximum carrier localization in the quantum well. The origin of the anisotropy that is not present in symmetric (001) quantum wells is qualitatively described by means of a simplified model based on fourth-order perturbation theory. A

Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

International Nuclear Information System (INIS)

Zhong Guohua; Zhang Kang; He Fan; Ma Xuhang; Lu Lanlan; Liu Zhuang; Yang Chunlei

2012-01-01

Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce-Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin-orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.

GaAsP on GaP top solar cells

Science.gov (United States)

Mcneely, J. B.; Negley, G. H.; Barnett, A. M.

1985-01-01

GaAsP on GaP top solar cells as an attachment to silicon bottom solar cells are being developed. The GaAsP on GaP system offers several advantages for this top solar cell. The most important is that the gallium phosphide substrate provides a rugged, transparent mechanical substrate which does not have to be removed or thinned during processing. Additional advantages are that: (1) gallium phosphide is more oxidation resistant than the III-V aluminum compounds, (2) a range of energy band gaps higher than 1.75 eV is readily available for system efficiency optimization, (3) reliable ohmic contact technology is available from the light-emitting diode industry, and (4) the system readily lends itself to graded band gap structures for additional increases in efficiency.

Microarray applications to understand the impact of exposure to environmental contaminants in wild dolphins (Tursiops truncatus).

Science.gov (United States)

Mancia, Annalaura; Abelli, Luigi; Kucklick, John R; Rowles, Teresa K; Wells, Randall S; Balmer, Brian C; Hohn, Aleta A; Baatz, John E; Ryan, James C

2015-02-01

It is increasingly common to monitor the marine environment and establish geographic trends of environmental contamination by measuring contaminant levels in animals from higher trophic levels. The health of an ecosystem is largely reflected in the health of its inhabitants. As an apex predator, the common bottlenose dolphin (Tursiops truncatus) can reflect the health of near shore marine ecosystems, and reflect coastal threats that pose risk to human health, such as legacy contaminants or marine toxins, e.g. polychlorinated biphenyls (PCBs) and brevetoxins. Major advances in the understanding of dolphin biology and the unique adaptations of these animals in response to the marine environment are being made as a result of the development of cell-lines for use in in vitro experiments, the production of monoclonal antibodies to recognize dolphin proteins, the development of dolphin DNA microarrays to measure global gene expression and the sequencing of the dolphin genome. These advances may play a central role in understanding the complex and specialized biology of the dolphin with regard to how this species responds to an array of environmental insults. This work presents the creation, characterization and application of a new molecular tool to better understand the complex and unique biology of the common bottlenose dolphin and its response to environmental stress and infection. A dolphin oligo microarray representing 24,418 unigene sequences was developed and used to analyze blood samples collected from 69 dolphins during capture-release health assessments at five geographic locations (Beaufort, NC, Sarasota Bay, FL, Saint Joseph Bay, FL, Sapelo Island, GA and Brunswick, GA). The microarray was validated and tested for its ability to: 1) distinguish male from female dolphins; 2) differentiate dolphins inhabiting different geographic locations (Atlantic coasts vs the Gulf of Mexico); and 3) study in detail dolphins resident in one site, the Georgia coast, known to

Investigation of GaN-based light emitting diodes with nano-hole patterned sapphire substrate (NHPSS) by nano-imprint lithography

International Nuclear Information System (INIS)

Huang, H.W.; Lin, C.H.; Huang, J.K.; Lee, K.Y.; Lin, C.F.; Yu, C.C.; Tsai, J.Y.; Hsueh, R.; Kuo, H.C.; Wang, S.C.

2009-01-01

In this paper, gallium-nitride (GaN)-based light-emitting diodes (LEDs) with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated and investigated. At an injection current of 20 mA, the LED with NHPSS increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.33, and the wall-plug efficiency is 30% higher at 20 mA indicating that the LED with NHPSS had larger light extraction efficiency. In addition, by examining the radiation patterns, the LED with NHPSS shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography.

Characterization of GaN/AlGaN epitaxial layers grown by ...

Indian Academy of Sciences (India)

GaN and AlGaN epitaxial layers are grown by a metalorganic chemical ... reported by introducing annealing of the GaN layer in nitrogen [5], Fe doping [6], .... [2] Y F Wu, S M Wood, R P Smith, S Sheppard, S T Allen, P Parikh and J Milligan,.

Radiative and non-radiative recombination in GaInN/GaN quantum wells

International Nuclear Information System (INIS)

Netzel, C.

2007-01-01

The studies presented in this thesis deal with the occurence of V defectsin GaInN/GaN quantum film structures grown by means of organometallic gas phase epitaxy, and the effects, which have the V defects respectively the GaInN quantum films on the V-defect facets on the emission and recombination properties of the whole GaInN/GaN quantum film structure. The V-defects themselves, inverse pyramidal vacancies with hexagonal base in the semiconductor layers, arise under suitable growth conditions around the percussion violations, which extend in lattice-mismatched growth of GaN on the heterosubstrates sapphire or silicon carbide starting in growth direction through the crystal. If GaInN layers are grown over V-defect dispersed layers on the (1-101) facets of the V defects and the (0001) facets, the growth front of the structure, different growth velocities are present, which lead to differently wide GaInN quantum films on each facets

Two-dimensional electron gas in AlGaN/GaN heterostructures

International Nuclear Information System (INIS)

Li, J.Z.; Lin, J.Y.; Jiang, H.X.; Khan, M.A.; Chen, Q.

1997-01-01

The formation of a two-dimensional electron gas (2DEG) system by an AlGaN/GaN heterostructure has been further confirmed by measuring its electrical properties. The effect of persistent photoconductivity (PPC) has been observed and its unique features have been utilized to study the properties of 2DEG formed by the AlGaN/GaN heterointerface. Sharp electronic transitions from the first to the second subbands in the 2DEG channel have been observed by monitoring the 2DEG carrier mobility as a function of carrier concentration through the use of PPC. These results are expected to have significant implications on field-effect transistor and high electron mobility transistor applications based on the GaN system. copyright 1997 American Vacuum Society

Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

Energy Technology Data Exchange (ETDEWEB)