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Sample records for river augusta ga

  1. 76 FR 18497 - Television Broadcasting Services; Augusta, GA

    Science.gov (United States)

    2011-04-04

    ... FEDERAL COMMUNICATIONS COMMISSION 47 CFR Part 73 [MB Docket No. 11-54, RM-11624; DA 11-499] Television Broadcasting Services; Augusta, GA AGENCY: Federal Communications Commission. ACTION: Proposed... 73 Television. Federal Communications Commission. Barbara A. Kreisman, Chief, Video Division, Media...

  2. 77 FR 55141 - Safety Zone, ESI Ironman 70.3 Augusta Triathlon, Savannah River; Augusta, GA

    Science.gov (United States)

    2012-09-07

    ... Environmental Health Risks and Safety Risks. This rule is not an economically significant rule and does not create an environmental risk to health or risk to safety that may disproportionately affect children. 11... zone unless authorized by the Captain of the Port Savannah or a designated representative. DATES: This...

  3. 33 CFR 110.179 - Skidaway River, Isle of Hope, Ga.

    Science.gov (United States)

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Skidaway River, Isle of Hope, Ga. 110.179 Section 110.179 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY ANCHORAGES ANCHORAGE REGULATIONS Anchorage Grounds § 110.179 Skidaway River, Isle of Hope, Ga. (a) The...

  4. Chemical constituents of Gustavia Augusta L. (Lecythidaceae)

    International Nuclear Information System (INIS)

    Souza, Afonso Duarte Leao de; Rocha, Arnaldo F. Imbiriba da; Pinheiro, Maria Lucia Belem; Andrade, Carlos Humberto de S.; Galotta, Ana Lucia de A. Queiroz; Santos, Maria do Perpetuo Socorro S. dos

    2001-01-01

    The Gustavia augusta is used in the folk medicine against leishmaniasis and showed anti-inflammatory action. The phyto chemical studies of the plant stem bark have led to the isolation of (22E)-stigmasta-7,22-dien-3β-ol, 24(α(S)-ethyl-5α-colesta-7, trans-22-dien-3-one, D-friedoolean-14-en-3β-ol, D-friedoolean-14-en-3-one and D-friedoolean-14-en-3α-ol along with stigmasterol, α-amyrin, β-amyrin, lupeol, 3α-hydroxy-lupeol and betulinic acid. The structures of these compounds were identified by IR, GC/M S, 1 H and 1 3 C NMR spectral analysis and comparison with literature data. (author)

  5. Severe Weather Guide - Mediterranean Ports. 4. Augusta Bay

    Science.gov (United States)

    1988-03-01

    the year. The track o-f strong extratropical storms has moved northward and poses little tiireat to Augusta Bay. Sea breezes are daily occurrences...as temperatures, begin to moderate. Extratropi cal systems begin to transit Europe as the storm track moves southward in advance of the winter...SUB-GROUP 18. SUBJECT TERMS {Continue on reverse if necessary and identify by block number) Storm haven Mediterranean meteorology Augusta Bay

  6. Chemical constituents of Gustavia Augusta L. (Lecythidaceae); Constituintes quimicos de Gustavia Augusta L. (Lecythidaceae)

    Energy Technology Data Exchange (ETDEWEB)

    Souza, Afonso Duarte Leao de; Rocha, Arnaldo F. Imbiriba da; Pinheiro, Maria Lucia Belem; Andrade, Carlos Humberto de S.; Galotta, Ana Lucia de A. Queiroz; Santos, Maria do Perpetuo Socorro S. dos [Amazonas Univ., Manaus, AM (Brazil). Dept. de Quimica]. E-mail: afonsodlsouza@yahoo.com.br

    2001-08-01

    The Gustavia augusta is used in the folk medicine against leishmaniasis and showed anti-inflammatory action. The phyto chemical studies of the plant stem bark have led to the isolation of (22E)-stigmasta-7,22-dien-3{beta}-ol, 24{alpha}(S)-ethyl-5{alpha}-colesta-7, trans-22-dien-3-one, D-friedoolean-14-en-3{beta}-ol, D-friedoolean-14-en-3-one and D-friedoolean-14-en-3{alpha}-ol along with stigmasterol, {alpha}-amyrin, {beta}-amyrin, lupeol, 3{alpha}-hydroxy-lupeol and betulinic acid. The structures of these compounds were identified by IR, GC/M S, {sup 1} H and {sup 1} {sup 3} C NMR spectral analysis and comparison with literature data. (author)

  7. La figura de Diocleciano en la Historia Augusta

    Directory of Open Access Journals (Sweden)

    Isabel MORENO FERRERO

    2009-11-01

    Full Text Available Uno de los principales problemas que la Historia Augusta tiene hoy, todavía, planteados, a pesar de los esfuerzos realizados por resolverlo, es el del verdadero momento de composición de las vidas. Desde este punto de vista el nombre de Diocleciano, junto al de Constantino, ha ocupado un lugar preferente en la discusión de los investigadores e, incluso dentro del intento de definición que la Historia Augusta parece hacer de un ideal de optimus princeps, se ha sugerido que es él, junto a la Tetrarquía, el auténtico destinatario de las alabanzas que la colección dedica a distintos emperadores.

  8. Una producción de lucernas en Asturica Augusta

    Directory of Open Access Journals (Sweden)

    María Teresa AMARÉ TAFALLA

    2009-12-01

    Full Text Available RESUMEN: En este estudio se da a conocer y se analiza una producción local de lucernas registrada en Asturica Augusta (Astorga, León con un conjunto de moldes y lámparas, valorado como de gran interés por su carácter exclusivo en la Península Ibérica. Los ejemplares se examinan en sus aspectos técnicos (deficiente factura, formales (Dressel-Lamboglia, 5C, decorativos (sin ornamentación, Victoria, máscara teatral y epigráficos (firmas VIR1LLI0 F, SIL0[-} y S para concluir estableciendo su cronología (segunda mitad del siglo I y siglo II de la Era y difusión (estrictamente local.ABSTRACT: This study records and analyses a local production of lamps in Asturica Augusta (Astorga in the province of León, Spain, with regard to a find of moulds and of lamps, wich is seen as of great interest, since it is unique in the Iberian Peninsula. The finds are considered from a number of viewpoints: technique (poor finish, form (Dressel- Lamboglia, 5C, decoration (no ornamentation, Victory, and theatrical mask and epigraphy (signatures VIRILL10 F, SIL0[-~}, and S. In conclusion a chronology is established for them (second half of the first century A.D. and second century A.D. and their spread is determined (strictly local.

  9. 76 FR 62298 - Special Local Regulations; Line of Sail Marine Parade, East River and Brunswick River, Brunswick, GA

    Science.gov (United States)

    2011-10-07

    ...-AA08 Special Local Regulations; Line of Sail Marine Parade, East River and Brunswick River, Brunswick... during the Line of Sail Marine Parade on Saturday, October 8, 2011. The marine parade will consist of... did not receive notice of the Line of Sail Marine Parade with sufficient time to publish an NPRM or to...

  10. 75 FR 61460 - Avondale Mills Inc.; Augusta Canal Authority; Notice of Application for Transfer of License, and...

    Science.gov (United States)

    2010-10-05

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Project No. 5044-015] Avondale Mills... and Motions To Intervene September 24, 2010. On September 13, 2010, Avondale Mills Inc. (transferor... Mill Project No. 5044, located on the Augusta Canal in the City of Augusta, Richmond County, Georgia...

  11. [Evaluation of mercury exposure in populations living near the industrial Augusta Bay (Sicily Region, Southern Italy)].

    Science.gov (United States)

    Bonsignore, Maria; Andolfi, Nunzia; Quinci, Enza Maria; Madeddu, Anselmo; Tisano, Francesco; Ingallinella, Vincenzo; Castorina, Maria; Sprovieri, Mario

    2016-01-01

    OBIETTIVI: valutare e quantificare l'esposizione umana al mercurio (Hg) ed esplorare i fattori chiave che influenzano la contaminazione nelle popolazioni residenti in prossimità della Rada di Augusta, un'area a elevato rischio ambientale a causa degli effetti degli sversamenti incontrollati di Hg da parte di uno dei più grandi impianti cloro-soda d'Europa. DISEGNO: un campione di residenti nei comuni di Augusta, Priolo e Melilli (Sicilia orientale) è stato selezionato per lo studio di biomonitoraggio umano. Un questionario dettagliato è stato somministrato a ogni partecipante per raccogliere informazioni anagrafiche sulle abitudini di vita e alimentari. I livelli di Hg in sangue e capelli, usati come traccianti di esposizione a metilmercurio, sono stati messi in relazione al consumo di pesce locale. Il contenuto di Hg nelle urine è stato utilizzato per esplorare eventuali esposizioni atmosferiche a Hg inorganico. Una regressione lineare multivariata è stata applicata con l'obiettivo di esplorare i fattori che influenzano l'esposizione umana al Hg. L'approccio tossicocinetico è stato impiegato al fine di calcolare la dose settimanale provvisoria tollerabile ( provisional tolerable weekly intake, PTWI) e di predire le concentrazioni di Hg attese nel sangue degli individui con una dieta alimentare basata esclusivamente su pesce locale. 224 individui residenti nei comuni di Augusta, Melilli e Priolo. RISULTATI: eccessi di Hg sono stati misurati nel sangue e nei capelli del campione considerato. I più alti livelli sono stati rilevati ad Augusta, dove anche il consumo di pesce locale risulta maggiore. I valori di dose settimanale tollerabile provvisoria (PTWI) calcolati eccedono, nella maggior parte dei casi, le raccomandazioni internazionali, specialmente nei residenti ad Augusta. CONCLUSIONI: gli elevati livelli di Hg registrati nei campioni di sangue e capelli derivano, con ogni probabilità, dal consumo di pesce locale. Rispetto ad Augusta, gli individui di

  12. Praise Through Letters: Panegyrical Strategies in Eusebius' Vita Constantini and the Historia Augusta

    NARCIS (Netherlands)

    Burgersdijk, D.W.P.

    2013-01-01

    Departing from the progress in Constantinian studies in the last few decades, in this article the collection of imperial biographies called the Historia Augusta (HA) is reconsidered as an anti-Constantinian scripture. After all, the HA, as a literary product, is presented to the reader as a

  13. Complete nucleotide sequence of pGA45, a 140,698-bp incFIIY plasmid encoding blaIMI-3-mediated carbapenem resistance, from river sediment

    Directory of Open Access Journals (Sweden)

    Bingjun eDang

    2016-02-01

    Full Text Available Plasmid pGA45 was isolated from the sediment of Haihe River using E. coli CV601 (gfp-tagged as recipients and indigenous bacteria from sediment as donors. This plasmid confers reduced susceptibility to imipenem which belongs to carbapenem group. Plasmid pGA45 was fully sequenced on an Illumina HiSeq 2000 sequencing system. The complete sequence of plasmid pGA45 was 140,698 bp in length with an average G+C content of 52.03%. Sequence analysis shows that pGA45 belongs to incFIIY group and harbors a backbone region shares high homology and gene synteny to several other incF plasmids including pNDM1_EC14653, pYDC644, pNDM-Ec1GN574, pRJF866, pKOX_NDM1 and pP10164-NDM. In addition to the backbone region, plasmid pGA45 harbors two notable features including one blaIMI-3-containing region and one type VI secretion system region. The blaIMI-3-containing region is responsible for bacteria carbapenem resistance and the type VI secretion system region is probably involved in bacteria virulence, respectively. Plasmid pGA45 represents the first complete nucleotide sequence of the blaIMI-harboring plasmid from environment sample and the sequencing of this plasmid provided insight into the architecture used for the dissemination of blaIMI carbapenemase genes.

  14. Concentrations and distributions of metals associated with dissolved organic matter from the Suwannee River (GA, USA)

    Science.gov (United States)

    Kuhn, M. Keshia; Neubauer, Elisabeth; Hofmann, Thilo; von der Kammer, Frank; Aiken, George R.; Maurice, Patricia A.

    2015-01-01

    Concentrations and distributions of metals in Suwannee River (SR) raw filtered surface water (RFSW) and dissolved organic matter (DOM) processed by reverse osmosis (RO), XAD-8 resin (for humic and fulvic acids [FA]), and XAD-4 resin (for “transphilic” acids) were analyzed by asymmetrical flow field-flow fractionation (AsFlFFF). SR samples were compared with DOM samples from Nelson's Creek (NLC), a wetland-draining stream in northern Michigan; previous International Humic Substances Society (IHSS) FA and RO samples from the SR; and an XAD-8 sample from Lake Fryxell (LF), Antarctica. Despite application of cation exchange during sample processing, all XAD and RO samples contained substantial metal concentrations. AsFlFFF fractograms allowed metal distributions to be characterized as a function of DOM component molecular weight (MW). In SR RFSW, Fe, Al, and Cu were primarily associated with intermediate to higher than average MW DOM components. SR RO, XAD-8, and XAD-4 samples from May 2012 showed similar MW trends for Fe and Al but Cu tended to associate more with lower MW DOM. LF DOM had abundant Cu and Zn, perhaps due to amine groups that should be present due to its primarily algal origins. None of the fractograms showed obvious evidence for mineral nanoparticles, although some very small mineral nanoparticles might have been present at trace concentrations. This research suggests that AsFlFFF is important for understanding how metals are distributed in different DOM samples (including IHSS samples), which may be key to metal reactivity and bioavailability.

  15. Tracing mercury pathways in Augusta Bay (southern Italy) by total concentration and isotope determination

    International Nuclear Information System (INIS)

    Bonsignore, M.; Tamburrino, S.; Oliveri, E.; Marchetti, A.; Durante, C.; Berni, A.; Quinci, E.; Sprovieri, M.

    2015-01-01

    The mercury (Hg) pollution of sediments is the main carrier of Hg for the biota and, subsequently, for the local fish consumers in Augusta Bay area (SE Sicily, Italy), a coastal marine system affected by relevant sewage from an important chlor-alkali factory. This relationship was revealed by the determination of Mass Dependent (MDF) and Mass Independent Fractionation (MIF) of Hg isotopes in sediment, fish and human hair samples. Sediments showed MDF but no MIF, while fish showed MIF, possibly due to photochemical reduction in the water column and depending on the feeding habitat of the species. Benthic and demersal fish exhibited MDF similar to that of sediments in which anthropogenic Hg was deposited, while pelagic organisms evidenced higher MDF and MIF due to photoreduction. Human hair showed high values of δ 202 Hg (offset of +2.2‰ with respect to the consumed fish) and Δ 199 Hg, both associated to fish consumption. - Highlights: • We report the Hg isotope ratios of sediments, fish and human hair in Augusta Bay. • Hg isotopes show mercury transfers from sediments to benthic and demersal fish. • MIF in fish appears to be driven by effect of photoreduction. • MIF in human hair is inherited by fish consumption. - The mercury (Hg) isotope composition of sediments, fish muscles and human hair has been investigated from the highly polluted Augusta Bay (SE Sicily, Italy)

  16. Estudio sobre la metrología de la ceca romana de Augusta Emerita

    Directory of Open Access Journals (Sweden)

    Cebrián Sánchez, Miguel Ángel

    2006-12-01

    Full Text Available Metrology analysis of the Roman currency in Augusta Emerita has allowed to distinguish two different metrological patterns. The former is a Roman imperial; the latter is a Hispanic one, this being used until the end of the Augustan reign. From B.C. 2 on, and throughout the Tiberian reign, coinage is only carried out following the imperial pattern. This happens at a time of high coinage production in Augusta Emerita, which might probably explain the city’s urban development and embellishment heyday.Se estudia la metrología en la ceca romana –imperial y provincial- de Augusta Emerita. Dividimos el trabajo metrológico en dos grandes apartados, el primero analiza los pesos de las doce emisiones de la Mérida romana y el segundo pretende hacer una comparación con las otras cecas hispanas que, por su emisiones, están más próximas a las emeritenses. A esos dos apartados se añade una pequeña sección dedicada a la metalografía. A través de todo ello se demuestra que hubo dos sistemas metrológicos conviviendo, el republicano y el augústeo, emitiendose en Emerita y que el periodo de mayor auge de las emisiones incluye la etapa final del reinado de Augusto, post 2 a.C., y todo el reinado de Tiberio, lo que podría muy bien señalar el momento de apogeo y embellecimiento de la ciudad.

  17. O desenvolvimento do comércio no Noroeste a partir da conquista. O caso de Bracara Augusta

    OpenAIRE

    Morais, Rui

    2016-01-01

    Neste estudo apresentam-se os dados atá à data conhecidos sobre a evolução económica e comercial da cidade romana de Bracara Augusta, nas suas primeiras décadas de vida. De modo a conhecermos melhor esses momentos procurámos contextualizar estratigraficamente alguns dos vestígios materiais recuperados em escavações realizadas no âmbito do projeto de «Salvamento de Bracara Augusta». Complementámos este estudo com recentes achados encontrados na orla costeira do conventus Bracaraugustanus, em E...

  18. In Memoriam doctora Augusta Noemí Ochoa López (1937-2015

    Directory of Open Access Journals (Sweden)

    Gabriela Rouillon

    2015-10-01

    Full Text Available La Doctora Augusta Noemí Ochoa López, nació un martes 4 de mayo de 1937 en Cañete, Lima. Empezó los estudios de la carrera de biología en la Universidad Nacional Mayor de San Marcos, en 1953, también llevo cursos de la carrera de Educación. Obtuvo su grado de Bachiller en Biología en el año 1966 con la Tesis “Observaciones sobre el Desove de la Anchoveta, Engraulis ringens J., en la zona del Callao”.

  19. Spatial pattern of groundwater arsenic occurrence and association with bedrock geology in greater augusta, maine

    Science.gov (United States)

    Yang, Q.; Jung, H.B.; Culbertson, C.W.; Marvinney, R.G.; Loiselle, M.C.; Locke, D.B.; Cheek, H.; Thibodeau, H.; Zheng, Yen

    2009-01-01

    In New England, groundwater arsenic occurrence has been linked to bedrock geology on regional scales. To ascertain and quantify this linkage at intermediate (100-101 km) scales, 790 groundwater samples from fractured bedrock aquifers in the greater Augusta, Maine area are analyzed, and 31% of the sampled wells have arsenic concentrations >10 ??g/L. The probability of [As] exceeding 10 ??g/L mapped by indicator kriging is highest in Silurian pelite-sandstone and pelite-limestone units (???40%). This probability differs significantly (p bedrock map. Thus, bedrock geology is associated with arsenic occurrence in fractured bedrock aquifers of the study area at intermediate scales relevant to water resources planning. The arsenic exceedance rate for each rock unit is considered robust because low, medium, and high arsenic occurrences in four cluster areas (3-20 km2) with a low sampling density of 1-6 wells per km2 are comparable to those with a greater density of 5-42 wells per km2. About 12,000 people (21% of the population) in the greater Augusta area (???1135 km2) are at risk of exposure to >10 ??g/L arsenic in groundwater. ?? 2009 American Chemical Society.

  20. Spatial Pattern of Groundwater Arsenic Occurrence and Association with Bedrock Geology in Greater Augusta, Maine, USA

    Science.gov (United States)

    Yang, Qiang; Jung, Hun Bok; Culbertson, Charles W.; Marvinney, Robert G.; Loiselle, Marc C.; Locke, Daniel B.; Cheek, Heidi; Thibodeau, Hilary; Zheng, Yan

    2009-01-01

    In New England, groundwater arsenic occurrence has been linked to bedrock geology on regional scales. To ascertain and quantify this linkage at intermediate (100-101 km) scales, 790 groundwater samples from fractured bedrock aquifers in the greater Augusta, Maine area are analyzed. 31% of the sampled wells have arsenic >10 μg/L. The probability of [As] exceeding 10 μg/L mapped by indicator kriging is highest in Silurian pelite-sandstone and pelite-limestone units (~40%). This probability differs significantly (pbedrock map. Thus, bedrock geology is associated with arsenic occurrence in fractured bedrock aquifers of the study area at intermediate scales relevant to water resources planning. The arsenic exceedance rate for each rock unit is considered robust because low, medium and high arsenic occurrences in 4 cluster areas (3-20 km2) with a low sampling density of 1-6 wells per km2 are comparable to those with a greater density of 5-42 wells per km2. About 12,000 people (21% of the population) in the greater Augusta area (~1135 km2) are at risk of exposure to >10 μg/L arsenic in groundwater. PMID:19475939

  1. Interpreting the cross-sectional flow field in a river bank based on a genetic-algorithm two-dimensional heat-transport method (GA-VS2DH)

    Science.gov (United States)

    Su, Xiaoru; Shu, Longcang; Chen, Xunhong; Lu, Chengpeng; Wen, Zhonghui

    2016-12-01

    Interactions between surface waters and groundwater are of great significance for evaluating water resources and protecting ecosystem health. Heat as a tracer method is widely used in determination of the interactive exchange with high precision, low cost and great convenience. The flow in a river-bank cross-section occurs in vertical and lateral directions. In order to depict the flow path and its spatial distribution in bank areas, a genetic algorithm (GA) two-dimensional (2-D) heat-transport nested-loop method for variably saturated sediments, GA-VS2DH, was developed based on Microsoft Visual Basic 6.0. VS2DH was applied to model a 2-D bank-water flow field and GA was used to calibrate the model automatically by minimizing the difference between observed and simulated temperatures in bank areas. A hypothetical model was developed to assess the reliability of GA-VS2DH in inverse modeling in a river-bank system. Some benchmark tests were conducted to recognize the capability of GA-VS2DH. The results indicated that the simulated seepage velocity and parameters associated with GA-VS2DH were acceptable and reliable. Then GA-VS2DH was applied to two field sites in China with different sedimentary materials, to verify the reliability of the method. GA-VS2DH could be applied in interpreting the cross-sectional 2-D water flow field. The estimates of horizontal hydraulic conductivity at the Dawen River and Qinhuai River sites are 1.317 and 0.015 m/day, which correspond to sand and clay sediment in the two sites, respectively.

  2. A landscape plan based on historical fire regimes for a managed forest ecosystem: the Augusta Creek study.

    Science.gov (United States)

    John H. Cissel; Frederick J. Swanson; Gordon E. Grant; Deanna H. Olson; Gregory V. Stanley; Steven L. Garman; Linda R. Ashkenas; Matthew G. Hunter; Jane A. Kertis; James H. Mayo; Michelle D. McSwain; Sam G. Swetland; Keith A. Swindle; David O. Wallin

    1998-01-01

    The Augusta Creek project was initiated to establish and integrate landscape and watershed objectives into a landscape plan to guide management activities within a 7600-hectare (19,000-acre) planning area in western Oregon. Primary objectives included the maintenance of native species, ecosystem processes and structures, and long-term ecosystem productivity in a...

  3. Assessment of mercury in the Savannah River Site environment

    International Nuclear Information System (INIS)

    Kvartek, E.J.; Carlton, W.H.; Denham, M.; Eldridge, L.; Newman, M.C.

    1994-09-01

    Mercury has been valued by humans for several millennia. Its principal ore, cinnabar, was mined for its distinctive reddish-gold color and high density. Mercury and its salts were used as medicines and aphrodisiacs. At SRS, mercury originated from one of the following: as a processing aid in aluminum dissolution and chloride precipitation; as part of the tritium facilities' gas handling system; from experimental, laboratory, or process support facilities; and as a waste from site operations. Mercury is also found in Par Pond and some SRS streams as the result of discharges from a mercury-cell-type chlor-alkali plant near the city of Augusta, GA. Reactor cooling water, drawn from the Savannah River, transported mercury onto the SRS. Approximately 80,000 kg of mercury is contained in the high level waste tanks and 10,000 kg is located in the SWDF. Additional quantities are located in the various seepage basins. In 1992, 617 wells were monitored for mercury contamination, with 47 indicating contamination in excess of the 0.002-ppm EPA Primary Drinking Water Standard. More than 20 Savannah River Ecology Laboratory (SREL) reports and publications pertinent to mercury (Hg) have been generated during the last two decades. They are divided into three groupings: SRS-specific studies, basic studies of bioaccumulation, and basic studies of effect. Many studies have taken place at Par Pond and Upper Three Runs Creek. Mercury has been detected in wells monitoring the groundwater beneath SRS, but not in water supply wells in excess of the Primary Drinking Water Limit of 0.002 ppm. There has been no significant release of mercury from SRS to the Savannah River. While releases to air are likely, based on process knowledge, modeling of the releases indicates concentrations that are well below the SCDHEC ambient standard

  4. Assessment of mercury in the Savannah River Site environment

    Energy Technology Data Exchange (ETDEWEB)

    Kvartek, E.J.; Carlton, W.H.; Denham, M.; Eldridge, L.; Newman, M.C.

    1994-09-01

    Mercury has been valued by humans for several millennia. Its principal ore, cinnabar, was mined for its distinctive reddish-gold color and high density. Mercury and its salts were used as medicines and aphrodisiacs. At SRS, mercury originated from one of the following: as a processing aid in aluminum dissolution and chloride precipitation; as part of the tritium facilities` gas handling system; from experimental, laboratory, or process support facilities; and as a waste from site operations. Mercury is also found in Par Pond and some SRS streams as the result of discharges from a mercury-cell-type chlor-alkali plant near the city of Augusta, GA. Reactor cooling water, drawn from the Savannah River, transported mercury onto the SRS. Approximately 80,000 kg of mercury is contained in the high level waste tanks and 10,000 kg is located in the SWDF. Additional quantities are located in the various seepage basins. In 1992, 617 wells were monitored for mercury contamination, with 47 indicating contamination in excess of the 0.002-ppm EPA Primary Drinking Water Standard. More than 20 Savannah River Ecology Laboratory (SREL) reports and publications pertinent to mercury (Hg) have been generated during the last two decades. They are divided into three groupings: SRS-specific studies, basic studies of bioaccumulation, and basic studies of effect. Many studies have taken place at Par Pond and Upper Three Runs Creek. Mercury has been detected in wells monitoring the groundwater beneath SRS, but not in water supply wells in excess of the Primary Drinking Water Limit of 0.002 ppm. There has been no significant release of mercury from SRS to the Savannah River. While releases to air are likely, based on process knowledge, modeling of the releases indicates concentrations that are well below the SCDHEC ambient standard.

  5. Vidrios romanos de Bracara Augusta (Portugal: Análisis Arqueométrico = Roman glass from Bracara Augusta (Portugal: Archaeometric analysys

    Directory of Open Access Journals (Sweden)

    Rosario García Giménez

    2015-11-01

    Full Text Available En este trabajo se han estudiado vidrios romanos de Bracara Augusta, actualmente Braga (Portugal, a través de su composición química, analizando los constituyentes mayoritarios, minoritarios y traza mediante espectrometría de plasma-masas (ICPMS. Los resultados obtenidos han sido tratados estadísticamente, por un lado realizando diversos análisis univariantes, y por otro llevando a cabo una clasificación de las muestras mediante análisis de clasificación jerárquica y varios análisis discriminantes. Se llega a la conclusión de que, si bien todas las muestras de vidrio presentan una composición parecida en cuanto a los elementos mayoritarios, existen algunas diferencias significativas tanto en éstos como en los elementos minoritarios estudiados que permiten su clasificación. Además, mediante el análisis discriminante se establecen grupos en función de la datación de los vidrios y se pueden incluir en ellos las muestras previamente no datadas en los grupos anteriores.In this work Roman glass from Bracara Augusta, nowadays Braga (Portugal, were studied through their chemical composition, analyzing the major, minor and trace constituents using plasma-mass spectrometry (ICP-MS. The obtained data were statistically analysed, with the following statistical methodologies: (i various  univariate analyses and (ii several multivariate analyses which gave rise to a sample classification using hierarchical classification and by multiple discriminant analyses. Results concluded that, while all the glass samples showed a similar composition in terms of major components, there were some significant differences in these and in the minor components that allowed their classification. Furthermore, discriminant analysis helped to establish groups based on the dating of the glass and include undated samples in the previous stated groups.

  6. Preliminary assessment report for Fort Custer Training Center, Installation 26035, Augusta, Michigan

    International Nuclear Information System (INIS)

    Flaim, S.; Krokosz, M.

    1993-08-01

    This report presents the results of the preliminary assessment (PA) conducted by Argonne National Laboratory at the Michigan Army National Guard property near Augusta, Michigan. Preliminary assessments of federal facilities are being conducted to compile the information necessary for completing preremedial activities and to provide a basis for establishing corrective actions in response to releases of hazardous substances. The principal objective of the PA is to characterize the site accurately and determine the need for further action by examining site activities, quantities of hazardous substances present, and potential pathways by which contamination could affect public health and the environment. This PA satisfies, for the Fort Custer Training Center, phase I of the Department of Defense Installation Restoration Program. The environmentally significant operations associated with the property are (1) storage of hazardous materials and hazardous waste, (2) storage and dispensing of fuel, (3) washing of vehicles and equipment, and (4) weapons training ranges that may have accumulated lead

  7. Portuguese nursing: history of the life and activism of Maria Augusta Sousa.

    Science.gov (United States)

    Almeida, Deybson Borba de; Silva, Gilberto Tadeu Reis da; Queirós, Paulo Joaquim Pina; Freitas, Genival Fernandes de; Laitano, Aline Di Carla; Almeida, Sirléia de Sousa; Santos, Victor Porfirio Ferreira Almeida

    2016-01-01

    To analyze the history of the life and activism of Portuguese nurse Maria Augusta Sousa. Sousa's life story was obtained by means of semi-structured interview swith Sousa as the oral source of data. NVivo qualitative research software was used for data analysis. Content analysis focused on thematic analysis based on the theoretical and philosophical ideas of Michel Foucault, in particular, power and techniques of the self. Alienation and political participation were revealed as pertinent issues. In techniques of production of activist subjects, the following were highlighted: the importance of the review of formal education; actions of involvement with the world, society and the profession; and finally, techniques of the self, techniques of constitution of activist subjects, professional identity and way of being. The constitution of the nurse Maria Augusta Sousa as an activist came about through questioning of how to be, education in the context of her family, and political engagement in Catholic Youth. This impacted her trajectory of contributions to Portuguese nursing, as expressed in the following achievements: the integration of nursing training into higher education; the creation of the Regulation of Nurses Professional Practice; and implementation of the Order of Nurses. Analisar a história de vida e militância da enfermeira Maria Augusta Sousa. História de vida, tendo como fonte oral a entrevista semiestruturada. Na análise de dados utilizou-se do software de pesquisa qualitativa Nvivo, e a análise de conteúdo com foco na análise temática e com base teórico-filosófica de Michel Foucault, em especial, o poder e as técnicas de si. Evidenciaram-se a alienação e a participação política comoquestões pertinentes. Nas técnicas de produção de sujeitos militantes destacam-se a importânciada revisão da educação formal, dos atos de implicação com o mundo, a sociedade e a profissão, e por fim, as técnicas de si, técnicas de constitui

  8. Ab urbe condita. Desde a fundaçao da cidade de Bracara Augusta

    Directory of Open Access Journals (Sweden)

    Rui Morais

    2005-01-01

    Full Text Available Neste estudo aborda-se a problemática da fundaçao da antiga cidade de Bracara Augusta, levando em consideraçao o registro arqueológico e sua problemática e significado. A parte da fundaçao ex novo da cidade ou da preexistência de populaçoes autóctones no local, apresentam-se fortes vestígios indicadores da importância do culto imperial e dinástico que pensamos fortemente associados ao acto simbólico da sua fundaçao ou "refundaçao" segundo uma cerimónia à da "Roma Quadrada" augústea.

  9. Abroma augusta Linn bark extract-mediated green synthesis of gold nanoparticles and its application in catalytic reduction

    Science.gov (United States)

    Das, Subhajit; Bag, Braja Gopal; Basu, Ranadhir

    2015-10-01

    The bark extract of Abroma augusta Linn is rich in medicinally important phytochemicals including antioxidants and polyphenols. First one step green synthesis of gold nanoparticles (AuNPs) has been described utilizing the bark extract of Abroma augusta L. and chloroauric acid under very mild reaction conditions. The phytochemicals present in the bark extract acted both as a reducing as well as a stabilizing agent, and no additional stabilizing and capping agents were needed. Detailed characterizations of the stabilized AuNPs were carried out by surface plasmon resonance spectroscopy, high resolution transmission electron microscopy, and X-ray diffraction studies. The catalytic activity of the freshly synthesized gold nanoparticles has been demonstrated for the sodium borohydride reduction of 4-nitrophenol to 4-aminophenol, and the kinetics of the reduction reaction have been studied spectrophotometrically.

  10. Remote Sensing for Risk Assessment of Via Iulia Augusta in Albenga

    Science.gov (United States)

    Van Meerbeek, Lore; Barazzetti, Luigi

    2017-04-01

    Today, the field of cultural heritage faces many challenges: cultural heritage is always at risk and heritage recording can be time-consuming and result in low accuracy. These challenges were visible during the risk assessment of Via Iulia Augusta in Albenga (Liguria, Italy). The traces of Via Iulia Augusta, a former Roman Road, connect several cultural heritage resources in Albenga's landscape. The cultural significance of these heritage sites is at risk. Threats and disturbances related to humans, development, site management, nature and climate were observed during the onsite visit. These impacts can be sudden or part of a very slow process, resulting in reduced values on cultural, social, economic and ecological level. Nature and climate (change) in Albenga impact the heritage sites the most. Water-related problems such as flooding and surface runoff have always been present in Albenga, but the amount seems to increase year by year due to global warming and is supposed to become even more critical in the future. The first step towards a risk management plan is recording and documenting these cultural heritage sites at risk. Heritage recording provides valuable documentation of the primary source, the cultural heritage itself. The produced ground plans, elevations, sections and details are the most important primary information source for every research. However, the size and complexity of the cultural heritage, the required accuracy and the time span could have a negative influence on heritage recording and documentation. This paper demonstrates the potential of remote sensing techniques for cultural heritage at risk. On site surveys with GPS, Unmanned Aerial Vehicle and photo camera gave reliable information of the heritage resources and its state of conservation. WorldView-2 Satellite images, extracted at different time periods, gave insight in the evolution of the cultural landscape in Albenga. This information resulted in several conclusions. First of all

  11. PEMURNIAN, IDENTIFIKASI DAN UJI AKTIVITAS ANTIDIABETES SENYAWA METABOLIT SEKUNDER EKSTRAK ETIL ASETAT DAUN KACA PIRING (Gardenia augusta, Merr

    Directory of Open Access Journals (Sweden)

    Chasani Mochamad

    2012-02-01

    Full Text Available Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Gardenia augusta, Merr is one of the family Rubiaceae species used as traditional medicine because it has medicinal properties, such as drug diabetes mellitus. These research have been done on this plant, among others, is the ability of the extract  and  the active fraction ethyl acetate extract of Gardenia augusta, Merr leaves to lowering blood sugar levels of rats.  The purpose of this research was to purification of the active fraction of the ethyl acetate extract and identify the secondary metabolites of Gardenia augusta, Merr leaves as well as test that can be used antidiabetic. Purification was done by column chromatography which was eluted with n-hexane: ethyl acetate (7:1 and obtained four groups of fractions.  The fractions of the TLC to obtain pure isolates F2 fraction with melting point 158-160 ° C. The antidiabetic activity of the isolate F2 fractions were tested into white rats by glucose tolerance methods. Isolate F2 fraction was identified by using UV and  IR spectrophotometer.  The results showed that isolate F2 fraction of ethyl acetate extract of Gardenia augusta, Merr leaves has a hypoglycemic effect of 21.05%. The secondary metabolites test showed a positive result for steroids. Analysis using UV

  12. «Colonia Augusta Emerita». Creación de una ciudad en tiempos de augusto

    Directory of Open Access Journals (Sweden)

    Trinidad NOGALES BASARRATE

    2015-03-01

    Full Text Available La fundación de la colonia Augusta Emerita en el año 25 a. C. se plasma en varios de los proyectos de estos primeros tiempos augusteos en la ciudad: su ordenación urbana, las obras d infraestructura, los edi?cios de espectáculos, teatro y an?teatro, así como sus primeros recintos religioso-administrativos, los foros. A los factores de carácter utilitario y de praxis constructiva se unen los aspectos ideológicos augusteos.

  13. Edificios con forjados postesados mediante tendones no adherentes. Edificio Mapfre-Vía Augusta, en Barcelona-España

    Directory of Open Access Journals (Sweden)

    Llombart Jaques, José Antonio

    1994-08-01

    Full Text Available The technique of unbonded tendons applied to post-tensioned flat-slabs of buildings of certain importance has not been very frequent in Spain to date; in fact, it was used on very few occasions. This article gives the basic characteristics of the post-tensioned floors comparing them with the conventional solutions of reinforced concrete floors. The second part of the article brings a description of the main aspects of the design and construction of the Mapfre-Vía Augusta building in Barcelona. This recently raised building has the floor construction with slabs post-tensioned by unbonded tendons.

    La técnica del postesado no adherente, aplicada a losas de forjado de edificios de cierta entidad, ha sido hasta el momento poco común en España, habiéndose utilizado solamente en contadas ocasiones. Se indican, en primer lugar, las características fundamentales de los forjados postesados y se establecen comparaciones con soluciones convencionales de forjados de hormigón armado. En la segunda parte del artículo se describen los principales aspectos de proyecto y construcción de la estructura del Edificio Mapfre-Vía Augusta, en Barcelona, de reciente construcción, cuyos forjados están constituidos por losas postesadas mediante tendones no adherentes.

  14. Control of spread of Augusta disease caused by tobacco necrosis virus in tulip by composting residual waste of small bulbs, tunics, roots and soil debris

    NARCIS (Netherlands)

    Asjes, C.J.; Barnhoorn, G.J.

    2002-01-01

    In this study the elimination of the infectious virus/fungus complex of tobacco necrosis virus (TNV; cause of Augusta disease in tulip) and Olpidium brassicae in different soil types and residual waste material of soil debris, small tulip bulbs, roots and tunics by temperature treatments of

  15. Programas de investigación en el Museo Nacional de Arte Romano: proyectos Foros de Augusta Emerita y Lusitania Romana

    Directory of Open Access Journals (Sweden)

    Nogales Basarrate, Trinidad

    2006-02-01

    Full Text Available This paper, taking as its starting point deficient position Museums find themselves in the course of their research activity, analyses two projects developed by the National Museum of Roman Art (MNAR. Both of these reflect two of the priority research avenues. First, the Foros de Augusta Emerita project is based on one of the Museum´s most important archaeological excavation and the corresponding exhibition discourse, and the results have aroused the interest of the international research community due to the evident link with Rome. Secondly, the Roman Lusitania programme aims to enlarge the scope from Augusta Emerita out in the colony´s sphere of influence.Este artículo, partiendo de la situación deficiente en que los Museos ejercitan su labor investigadora, analiza dos proyectos desarrollados desde el Museo Nacional de Arte Romano (MNAR. Ambos son reflejo de dos de sus líneas prioritarias de investigación. Por un lado, el proyecto Foros de Augusta Emerita se sustenta en uno de los trabajos de intervención arqueológica y discurso expositivo más importantes del MNAR, cuyos resultados han movido el interés de la comunidad científica internacional por sus evidentes conexiones con Roma. Por otra parte, el programa Lusitania Romana pretende ampliar las líneas científicas desde Augusta Emerita en relación con su territorio de influencia.

  16. Modeling, Analysis, and Preservation Techniques for Historic Reinforced Concrete Structures in Seismic Prone Regions Case Study: Augusta Airship Hangar, Sicily

    International Nuclear Information System (INIS)

    Cronin, Kelly; Whyte, Catherine; Reiner, Tom

    2008-01-01

    Throughout the world there are hundreds of historic monuments and structures considered to be invaluable and irreplaceable. They are symbols of cultural identity and a means of educating people about history. Preservation of historic monuments and structures is therefore an important part of safeguarding these cultural heritage sites so that they retain their value for future generations.This report discusses a procedure for the investigation of seismic hazards in existing buildings and possible steps that can be taken to avoid damage caused by these hazards. The Augusta Airship Hangar located in Sicily, will be used as a case study however the topics addressed in this paper can be applied to other structures of historic value around the world.First state-of-the-art scanning procedures were used to create scale digital models that were imported into a structural analysis program. Within this program dynamic analyses were performed on the model based on actual ground motions taken close to the site. This data was used to determine the period and mode shapes of the structure. Then a nonlinear analysis, including a static pushover analysis, was implemented on a two-dimensional model of the structural frame. From this analysis the failure mechanisms of the structure were revealed with relation to an allowable roof displacement. The structural integrity of the structure was evaluated based on pre-defined performance goals. Finally multiple suggestions were made how the Augusta Airship Hangar might be repaired and strengthened so that this structure will not be destroyed should an earthquake occur.The results of our study show that historic structures, despite their age, can still be strong and ductile. Also there are a multitude of effective preservation and retrofit techniques that can be used to strengthen these historic structures, should an earthquake occur. Through this study, the Augusta Airship Hangar has proven to be not only a historic symbol for Sicily but

  17. Aborto, abandono, y la muerte de Augusta García Platas en Ayacucho, Perú, 1946

    Directory of Open Access Journals (Sweden)

    Raúl Necochea López

    Full Text Available Resumen Augusta García Platas murió tras un aborto clandestino en Ayacucho en 1946. Este ensayo, basado en materiales del Archivo Histórico de Ayacucho, da cuenta del proceso criminal que se abrió para determinar los responsables de su muerte. A pesar de que sindicaron a ciertos individuos como culpables directos de provocar el aborto, las autoridades judiciales consideraban que la causa de fondo de la muerte de la joven había sido el abandono por parte de quienes debían velar por su salud física y moral. Este caso nos brinda la oportunidad de esclarecer las estrategias que los implicados usaban para defenderse de acusaciones criminales. Además, nos ayuda a entender las diversas deficiencias del Poder Judicial peruano de mediados del siglo XX.

  18. Un tesoro de tremises visigodos hallado en el llamado «Foro Provincial» de Augusta Emerita

    Directory of Open Access Journals (Sweden)

    Mateos Cruz, Pedro

    2005-12-01

    Full Text Available Since 1999 we are working on a research project about the so called «Provincial Forum of Augusta Emerita». The project deals with the realisation of archaeological interventions in the various lots where remains of public architecture linked with this monumental ensemble have been documented. One of these interventions has been realised in a lot where remains of the so called «Temple of the Holguin-Street» appeared some years ago. During the works on the same site has been brought to light a treasure of twenty gold coins from the time of Leovigild hidden under the walls of a room which in late Antiquity reused the southern side of the Roman temple podium. This article is a study of these pieces set in context with their hiding position and the historical moment in which they have been in use.Desde el año 1999 estamos desarrollando un proyecto de investigación en el llamado «foro Provincial de Augusta Emerita»; el proyecto contempla la realización de intervenciones arqueológicas en los distintos solares donde se han documentado restos de arquitectura pública vinculados a este conjunto monumental. Una de estas intervenciones se ha efectuado en el solar donde hace años aparecieron los restos del denominado «templo de la C/ Holguín», lugar en el que, durante el desarrollo de los trabajos, apareció un tesoro de veinte monedas de oro de época de Leovigildo, oculto bajo los muros de una estancia que reutilizo en época tardoantigua el alzado Sur del podio del templo romano. En este artículo se realiza un estudio de estas piezas contextualizándolas con el lugar de ocultamiento y el momento histórico en que estuvieron en uso.

  19. Huchas cerámicas de época romana. A propósito del hallazgo de una tumba en Augusta Emerita (Mérida, Badajoz

    Directory of Open Access Journals (Sweden)

    Ana María BEJARANO OSORIO

    2016-12-01

    Full Text Available En este trabajo analizamos un depósito funerario localizado en una tumba exhumada en Augusta Emerita (Mérida, Badajoz. Además del análisis contextual, realizamos una autopsia de una rara avis en el menaje cerámico hispano, las huchas. A propósito del hallazgo de una, se hace una reflexión tipológica y funcional de cihas piezas en el Imperio Romano.

  20. Accuracy of National Weather Service wind-direction forecasts at Macon and Augusta, Georgia

    Science.gov (United States)

    Leonidas G. Lavdas

    1997-01-01

    National Weather Service wind forecasts and observations over a nine-year period (1985 to 1993) were analyzed to determine the usefulness of these forecasts for forestry smoke management. Data from Macon, GA indicated that forecasts were accurate to within plus or minus 22.5E about 38 percent of the time. When a wider plus or minus 67.5E window was used, accuracy...

  1. Efeitos do CPPU e GA3 no cultivo de uva-'Itália' na região do submédio São Francisco, nordeste do Brasil Effect of CPPU and GA3 in grapes 'Itália' in Submedium São Francisco River Valley region, northeast Brazil

    Directory of Open Access Journals (Sweden)

    CARLOS AUGUSTO MENEZES FEITOSA

    2002-08-01

    Full Text Available Na região do submédio do São Francisco, a uva-'Itália' destaca-se com 63,2% da área total plantada. Atualmente, é a principal variedade para exportação. O objetivo principal deste trabalho foi avaliar o efeito das doses do CPPU (forchlorfenuron e GA3, no aumento do tamanho da baga, que foram aplicadas por meio de pulverização dirigida sobre os cachos durante a fase de pegamento dos frutos, quando as bagas haviam atingido, aproximadamente, 8 mm de diâmetro. Este experimento foi conduzido na Fazenda Cooperyama, no município de Juazeiro-BA. O delineamento experimental foi o inteiramente casualizado, com oito tratamentos e três repetições, avaliando-se 15 cachos por tratamento com as seguintes doses: 1- Testemunha absoluta; 2- GA3 20 mg/l;3- GA3 20 mg/l+ CPPU 3 mg/l; 4- GA3 20 mg/l + CPPU 5 mg/l; 5- GA3 20 mg/l + CPPU 10 mg/l; 6- CPPU 3 mg/l; 7- CPPU 5 mg/l; 8- CPPU 10 mg/l.O melhor resultado obtido no crescimento da baga deu-se com a aplicação do CPPU 10 mg/l. Este tratamento diferiu significativamente da testemunha e da aplicação convencional com GA3 20 mg/l, aumentando 8% e 4,6% o comprimento da baga, 13,6% e 7,3% sua largura, e o peso de baga em 32% e 16,3%, respectivamente. Nos tratamentos com CPPU aplicado isoladamente e/ou associado com GA3, a colheita foi retardada em oito dias. Não se verificou diferença significativa para os teores de sólidos solúveis; no entanto, foi constatado que a acidez titulável obteve valores mais elevados na testemunha e no tratamento com GA3, aplicando 20 mg/l. Com relação ao peso do engaço, não foi verificada diferença estatística entre os tratamentos.The Itália grape cultivar participates with 63,2% of the total growing area in Submedium São Francisco River Valley it's the main variety for exportation. The main objective in this work was to evaluate the effect of CPPU (forchlorfenuron and GA3 doses on the berry size increase. The products were applied by spraying them on the

  2. The sea-air exchange of mercury (Hg) in the marine boundary layer of the Augusta basin (southern Italy): concentrations and evasion flux.

    Science.gov (United States)

    Bagnato, E; Sproveri, M; Barra, M; Bitetto, M; Bonsignore, M; Calabrese, S; Di Stefano, V; Oliveri, E; Parello, F; Mazzola, S

    2013-11-01

    The first attempt to systematically investigate the atmospheric mercury (Hg) in the MBL of the Augusta basin (SE Sicily, Italy) has been undertaken. In the past the basin was the receptor for Hg from an intense industrial activity which contaminated the bottom sediments of the Bay, making this area a potential source of pollution for the surrounding Mediterranean. Three oceanographic cruises have been thus performed in the basin during the winter and summer 2011/2012, where we estimated averaged Hgatm concentrations of about 1.5±0.4 (range 0.9-3.1) and 2.1±0.98 (range 1.1-3.1) ng m(-3) for the two seasons, respectively. These data are somewhat higher than the background Hg atm value measured over the land (range 1.1±0.3 ng m(-3)) at downtown Augusta, while are similar to those detected in other polluted regions elsewhere. Hg evasion fluxes estimated at the sea/air interface over the Bay range from 3.6±0.3 (unpolluted site) to 72±0.1 (polluted site of the basin) ng m(-2) h(-1). By extending these measurements to the entire area of the Augusta basin (~23.5 km(2)), we calculated a total sea-air Hg evasion flux of about 9.7±0.1 g d(-1) (~0.004 tyr(-1)), accounting for ~0.0002% of the global Hg oceanic evasion (2000 tyr(-1)). The new proposed data set offers a unique and original study on the potential outflow of Hg from the sea-air interface at the basin, and it represents an important step for a better comprehension of the processes occurring in the marine biogeochemical cycle of this element. Copyright © 2013 Elsevier Ltd. All rights reserved.

  3. Marcadores da paisagem e intervenção cadastral no território próximo da cidade de Bracara Augusta (Hispania Citerior Tarraconensis

    Directory of Open Access Journals (Sweden)

    Carvalho, Helena Paula

    2012-12-01

    Full Text Available This paper focuses the organization of the rural landscape around the Roman town of Bracara Augusta and the identification of a Roman cadastre, perfectly adapted to the relief and to the main hydrographical network of the region. This cadastre is organized in modules of 20 by 20 actus with a predominant orientation of 16º NNW, what may be inferred by the clear intersection of some important axes. We have also detected two cippi with a cross engraved on their upper face, separated by 20 actus, probably connected with limits or termini.Este trabajo tiene como objetivo presentar algunos de los resultados del estudio sobre el poblamiento y la organizacion del paisaje rural en torno a la ciudad romana de Bracara Augusta. La existencia de un cadastro romano con una orientación dominante de 16º NNO y una modulación de 20x20 actus, se confirma gracias a la documentación de algunos elementos de delimitación, de los que podemos destacar dos cipos con una distancia entre sí de 20 actus. [pt] Este artigo propõe-se apresentar os resultados do estudo do povoamento e da organização da paisagem em torno da cidade romana de Bracara Augusta. Este objectivo orienta-se, mais especificamente, para os dados relativos à identificação de um cadastro romano perfeitamente adaptado às formas estruturantes do relevo e da rede hidrográfica. Este cadastro possui uma orientação de cerca de 16º NNO com uma modulação de 20x20 actus, e encontra-se confirmado por alguns elementos demarcatórios, nomeadamente dois cipos que possuem entre si 20 actus de distância.

  4. Transformações recentes na paisagem construída da cidade de São Paulo: o eixo da rua Augusta, do Centro à Marginal Pinheiros

    OpenAIRE

    Ana Carolina Ferreira Mendes

    2014-01-01

    A pesquisa tem por objetivo o levantamento, análise e crítica das transformações recentes na paisagem construída pelas quais São Paulo tem passado, especificamente em um eixo selecionado de seu quadrante sudoeste, historicamente dos mais valorizados da cidade. O eixo selecionado para estudo liga a região central à Marginal Pinheiros, iniciando-se na Rua Martins Fontes, continuando pela Rua Augusta, Rua Colômbia, Avenida Europa e finalmente culminando na Avenida Cidade Jardim...

  5. 77 FR 41668 - Standard Instrument Approach Procedures, and Takeoff Minimums and Obstacle Departure Procedures...

    Science.gov (United States)

    2012-07-16

    ... Obstacle DP, Amdt 2 Swainsboro, GA, Emanuel County, VOR/DME-A, Amdt 3, CANCELED Tifton, GA, Henry Tift... Minimums and Obstacle DP, Amdt 1 Pensacola, FL, Pensacola Gulf Coast Rgnl, VOR RWY 8, Amdt 4 Augusta, GA, Augusta Rgnl at Bush Field, ILS OR LOC RWY 17, Amdt 9 Augusta, GA, Augusta Rgnl at Bush Field, ILS OR LOC...

  6. Augusta Emérita. La investigación arqueológica en una ciudad de época romana

    Directory of Open Access Journals (Sweden)

    Mateos Cruz, Pedro

    2001-12-01

    Full Text Available This article is an ample summary of the recent archaeological results developed in the last years in the roman colony of Augusta Emerita (modern Mérida, Spain. Recent systematic research has change many old views and statements about the urbanistic development of the roman colony as a result of the new scientific proyects undetaken recently, that offer a new undestanding of the evolution of Mérida during the Roman period.En este artículo se plantea la evolución del conocimiento de la ciudad romana de Emerita Augusta a partir de las investigaciones desarrolladas por historiadores y arqueólogos en los últimos años. Con ellas se han puesto en duda argumentos cerrados secularmente, sugiriendo, al menos, una imagen ciudadana distinta a la supuesta hasta ahora, con una fisonomía urbana resultado de variados proyectos, y con procesos y ciclos que, aunque en ocasiones no acertamos a situar o valorar correctamente, ayudan a entender cómo se conformó el devenir y la evolución de Mérida en época antigua.

  7. Muchinako, GA

    African Journals Online (AJOL)

    Muchinako, GA. Vol 28, No 2 (2013) - Articles Children living and/or working on the streets in Harare: Issues and challenges. Abstract. ISSN: 1012-1080. AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's · More about AJOL · AJOL's Partners · Terms and Conditions of ...

  8. Hypoglycemic, hypolipidemic and antioxidant properties of combination ofCurcumin fromCurcuma longa, Linn, and partially purified product fromAbroma augusta, Linn. in streptozotocin induced diabetes.

    Science.gov (United States)

    Ali Hussain, Halim Eshrat M

    2002-07-01

    Dietary spice components ofCurcuma longa andAbroma augusta have been screened for their protective effect against reactive oxygen species induced lipid peroxidation. They have been found to be efficient antioxidant when administered in combination. The purpose of the study was to investigate the effect of oral administration (300mg/Kg) of the aqueous extract of turmeric whose active ingredient isCurcumin andAbromine powder as a hypoglycemic agent mixed with diet. The effect of this aqueous extract on blood glucose, lipid peroxidation (LPO) and the antioxidant defense system in rat tissues like liver, lung, kidney and brain was studied for 8 weeks in streptozotocin induced diabetic rats. The administration of an aqueous extract of turmeric and abromine powder resulted in a significant reduction in blood glucose and an increase in total haemoglobin. The aqueous extract also resulted in decreased free radical formation in the tissues studied.The decrease in thiobarbituric acid reactive substances (TBARS) and increase in reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) clearly showed the antioxidant property of the mixture. It is suggested that these changes initially counteract the oxidative stress in diabetes however, a gradual decrease in the antioxidative process may be one of the factors which results in chronic diabetes. These results indicate that the mixture of the two plants have shown antidiabetic activity and also reduced oxidative stress in diabetes. A combination ofAbroma augusta and Curcuma longa also restored the other general parameters in diabetic animals. The results were statistically analyzed and indicated that combination of herbal extracts showed better efficacy as compared to individual herbal plant extracts used.

  9. Using next-generation sequencing to analyse the diet of a highly endangered land snail (Powelliphanta augusta feeding on endemic earthworms.

    Directory of Open Access Journals (Sweden)

    Stéphane Boyer

    Full Text Available Predation is often difficult to observe or quantify for species that are rare, very small, aquatic or nocturnal. The assessment of such species' diet can be conducted using molecular methods that target prey DNA remaining in predators' guts and faeces. These techniques do not require high taxonomic expertise, are applicable to soft-bodied prey and allow for identification at the species level. However, for generalist predators, the presence of mixed prey DNA in guts and faeces can be a major impediment as it requires development of specific primers for each potential prey species for standard (Sanger sequencing. Therefore, next generation sequencing methods have recently been applied to such situations. In this study, we used 454-pyrosequencing to analyse the diet of Powelliphantaaugusta, a carnivorous landsnail endemic to New Zealand and critically endangered after most of its natural habitat has been lost to opencast mining. This species was suspected to feed mainly on earthworms. Although earthworm tissue was not detectable in snail faeces, earthworm DNA was still present in sufficient quantity to conduct molecular analyses. Based on faecal samples collected from 46 landsnails, our analysis provided a complete map of the earthworm-based diet of P. augusta. Predated species appear to be earthworms that live in the leaf litter or earthworms that come to the soil surface at night to feed on the leaf litter. This indicates that P. augusta may not be selective and probably predates any earthworm encountered in the leaf litter. These findings are crucial for selecting future translocation areas for this highly endangered species. The molecular diet analysis protocol used here is particularly appropriate to study the diet of generalist predators that feed on liquid or soft-bodied prey. Because it is non-harmful and non-disturbing for the studied animals, it is also applicable to any species of conservation interest.

  10. Using Next-Generation Sequencing to Analyse the Diet of a Highly Endangered Land Snail (Powelliphanta augusta) Feeding on Endemic Earthworms

    Science.gov (United States)

    Boyer, Stéphane; Wratten, Stephen D.; Holyoake, Andrew; Abdelkrim, Jawad; Cruickshank, Robert H.

    2013-01-01

    Predation is often difficult to observe or quantify for species that are rare, very small, aquatic or nocturnal. The assessment of such species’ diet can be conducted using molecular methods that target prey DNA remaining in predators’ guts and faeces. These techniques do not require high taxonomic expertise, are applicable to soft-bodied prey and allow for identification at the species level. However, for generalist predators, the presence of mixed prey DNA in guts and faeces can be a major impediment as it requires development of specific primers for each potential prey species for standard (Sanger) sequencing. Therefore, next generation sequencing methods have recently been applied to such situations. In this study, we used 454-pyrosequencing to analyse the diet of Powelliphantaaugusta , a carnivorous landsnail endemic to New Zealand and critically endangered after most of its natural habitat has been lost to opencast mining. This species was suspected to feed mainly on earthworms. Although earthworm tissue was not detectable in snail faeces, earthworm DNA was still present in sufficient quantity to conduct molecular analyses. Based on faecal samples collected from 46 landsnails, our analysis provided a complete map of the earthworm-based diet of P . augusta . Predated species appear to be earthworms that live in the leaf litter or earthworms that come to the soil surface at night to feed on the leaf litter. This indicates that P . augusta may not be selective and probably predates any earthworm encountered in the leaf litter. These findings are crucial for selecting future translocation areas for this highly endangered species. The molecular diet analysis protocol used here is particularly appropriate to study the diet of generalist predators that feed on liquid or soft-bodied prey. Because it is non-harmful and non-disturbing for the studied animals, it is also applicable to any species of conservation interest. PMID:24086671

  11. Effect of weir impoundments on methane dynamics in a river

    Czech Academy of Sciences Publication Activity Database

    Bednařík, A.; Blaser, M.; Matoušů, Anna; Hekera, P.; Rulík, M.

    2017-01-01

    Roč. 584, April (2017), s. 164-174 ISSN 0048-9697 R&D Projects: GA ČR(CZ) GA13-00243S Institutional support: RVO:60077344 Keywords : methane production * methane emission * methane ebullition * river impoundment * river sediment Subject RIV: DA - Hydrology ; Limnology OBOR OECD: Marine biology, freshwater biology, limnology Impact factor: 4.900, year: 2016

  12. Tsunami vulnerability and damage for buildings analyzed by means of two methods (PTVA-3 and SCHEMA) in the area of Augusta and Siracusa, eastern Sicily, Italy

    Science.gov (United States)

    Pagnoni, Gianluca; Tinti, Stefano

    2015-04-01

    The coast of the eastern Sicily is exposed to tsunamis that can be generated by local earthquakes (e.g. the 1169, 1693, 1908 events) and by earthquakes located in distant seismic zones (see the 365 AD tsunamigenic quake in Western Hellenic Arc). Tsunamis can also be generated by landslides possibly triggered by earthquakes. The Hyblean-Malta steep escarpment running offshore at a small angle with the coast is an ideal place for submarine mass failure occurrences with tsunamigenic effects. The entire eastern coast of Sicily from Messina in the north to Siracusa in the south is under the threat of tsunamis. In the frame of the FP7 European project ASTARTE (Assessment, Strategy And Risk Reduction for Tsunamis in Europe - FP7-ENV2013 6.4-3, Grant 603839), the segment of coast from Augusta to Siracusa was selected to undertake specific and detailed studies of tsunami hazard, vulnerability and damage to test existing methods and develop innovative approaches. The scope of the present work regards vulnerability and damage analyses. We chose to adopt two methods, known in the literature and briefly denoted as PTVA-3 and SCHEMA, that are based on two very different approaches, the former more qualitative and the latter more quantitative. The method PTVA-3 determines the vulnerability and damageability of a building by weighting and ranking a number of attributes covering the structural features of the edifice and the relevant characteristics of the surrounding environment such as the position with respect to the coast, the existence of defensive elements (e.g. walls, breakwaters, vegetation) and also the proximity to potential sources of floating objects that can feed damaging debris flows. On the other hand, the SCHEMA method uses a classification of building and a damage matrix that were derived from experimental fragility and damage curves first established after the Sumatra 2004 tsunami and later refined and adapted to the building stock of the Mediterranean region. The

  13. « Ni bas-bleu, ni pot-au-feu » : la conception de « la » femme selon Augusta Moll-Weiss (France, tournant des XIXe-XXe siècles

    Directory of Open Access Journals (Sweden)

    Sandrine Roll

    2009-12-01

    Full Text Available Cet article analyse les idées et l’œuvre de la directrice de l’École des mères, Augusta Moll-Weiss. Dans le contexte du tournant des XIXe-XXe siècles où l’éloge de la ménagère est un thème récurrent des discours moralisateurs émanant des ouvriers ou des bourgeois, Augusta Moll-Weiss met en place un projet de cours ménagers. Son œuvre offre une approche singulière de ce que des activités reconnues comme typiquement féminines peuvent offrir aux femmes. Loin de former uniquement des « fées du logis », les cours professés à l’École des mères donnent aussi aux élèves la possibilité de se préparer à une carrière professionnelle. Augusta Moll-Weiss imagine alors pléthore de débouchés qui placent les activités « du souci des autres » dans la sphère du travail social. Son engagement en faveur de l’enseignement ménager s’accompagne d’une réflexion sur de nouveaux modèles domestiques susceptibles d’accompagner l’entrée des femmes sur le marché du travail. La rationalisation et le partage sexué des tâches domestiques ainsi que la question du temps partiel sont au cœur de son projet. Aux marges de la philanthropie et du féminisme, Augusta Moll-Weiss s’engage donc dans une stratégie de reconnaissance du rôle des femmes dans l’espace civique. Après avoir présenté l’œuvre scolaire de cette femme, cet article s’intéresse à sa vision de la « Ménagère nouvelle » et à son approche du féminisme.This article explores the ideas and works of the Augusta Moll-Weiss, head of the École des mères. The latter started housewifery lessons at the turn of the 19th century at a moment when public discourse among both working and upper-class reformers sang the praises of the housewife. Her work offered a new approach to these typically feminine activities. Far from training only “angels of the home”, the lessons given at the Mothers’ School also offered students the possibility of

  14. Cs-137 and Co-60 concentrations in water from the Savannah River and water-treatment plants downstream of SRP

    International Nuclear Information System (INIS)

    1983-01-01

    In preparation for restart of L-Reactor, a comprehensive environmental sampling and analysis program was initiated in March 1983 to determine Cs-137 concentrations in off-site water downstream from Savannah River Plant (SRP). Concentrations of Co-60 also are determined in this sampling and analysis program. This report summarizes the first three months of results. Cesium-137 concentrations are reported for finished water from the Beaufort-Jasper, Port Wentworth and North Augusta water treatment plants for weekly continuous samples during April through June 1983. The very low concentrations of cesium-137 in finished water from downstream water treatment plants showed significant changes during this time. The changes in concentration occurred smoothly and correlate with changes in river flow. No changes in concentration during April through June can be attributed to L-Reactor's only cold water test which occurred June 8 and 9. No Co-60 was observed in any samples

  15. Vegetation succession on river sediments along the Nakdong River, South Korea

    Czech Academy of Sciences Publication Activity Database

    Prach, Karel; Petřík, Petr; Brož, Z.; Song, J. S.

    2014-01-01

    Roč. 49, č. 4 (2014), 507-519 ISSN 1211-9520 R&D Projects: GA ČR(CZ) GAP505/11/0256; GA AV ČR IAA600050802 Institutional support: RVO:67985939 Keywords : ordination * the Four River Project * species richness Subject RIV: EH - Ecology, Behaviour Impact factor: 1.778, year: 2014

  16. River engineering

    NARCIS (Netherlands)

    De Vries, M.

    1993-01-01

    One dimension models - basic eauations, analytical models, numberical models. One dimensional models -suspended load, roughness and resistance of river beds. Solving river problems - tools, flood mitigation, bank protection.

  17. Determinação de perdas de solo na bacia hidrográfica do córrego Ipiranga em Cidade Gaúcha, Estado do Paraná, com aplicação da Equação Universal de Perdas de Solo (EUPS = Estimates of soil losses in the Ipiranga river basin in Cidade Gaúcha, State of Paraná, with application of the Universal Soil Loss Equation (USLE

    Directory of Open Access Journals (Sweden)

    João Paulo Bueno do Prado

    2005-01-01

    Full Text Available Objetivando a predição das perdas de solo por erosão laminar na bacia do córrego Ipiranga no Município de Cidade Gaúcha, Estado do Paraná, foi empregada a Equação Universal de Perdas de Solo (EUPS com o auxílio de técnicas de geoprocessamento. O ambiente SIG permitiu a completa integração entre os dados, a obtenção dos parâmetros da EUPS e o cálculo das perdas de solo anuais e sazonais, considerando-se os diferentes tipos de solos e de usos e ocupação na área. Os resultadosobtidos associam as maiores perdas de solo às áreas cultivadas com cana-de-açúcar e mandioca (>20 ton.ha-1.no-1. A primavera é o período mais crítico para a erosão laminar enquanto que no outono são verificadas as taxas mais baixas de perdas de solo.The prediction of soil loss via laminar erosion at Ipiranga river basin, situated in Cidade Gaúcha county, State of Paraná, was carried out by applying both the Universal soil Loss Equation (USLE and the Geographic Information System (GIS. The GIS environment provided acomplete integration of the data, as well as helped the authors of this paper to obtain the USLE parameters and the calculus of the annual and seasonal soil losses, considering the different types of soil, their usage and the area cover-management. The results obtainedindicated a high soil loss in areas where sugar cane and manioc (>20 t.ha-1.no-1 are cultivated. Spring is the most critical period for laminar erosion, while autumn is the period which shows the smallest number of soil losses.

  18. Ga penetration into polymers

    Czech Academy of Sciences Publication Activity Database

    Hnatowicz, Vladimír; Švorčík, V.; Efimenko, K.; Rybka, V.

    1999-01-01

    Roč. 68, - (1999), s. 357-358 ISSN 0947-8396 R&D Projects: GA ČR GA202/96/0077; GA AV ČR KSK1048601 Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.753, year: 1999

  19. Earthquake-triggered landslides along the Hyblean-Malta Escarpment (off Augusta, eastern Sicily, Italy) - assessment of the related tsunamigenic potential

    Science.gov (United States)

    Ausilia Paparo, Maria; Armigliato, Alberto; Pagnoni, Gianluca; Zaniboni, Filippo; Tinti, Stefano

    2017-02-01

    Eastern Sicily is affected by earthquakes and tsunamis of local and remote origin, which is known through numerous historical chronicles. Recent studies have put emphasis on the role of submarine landslides as the direct cause of the main local tsunamis, envisaging that earthquakes (in 1693 and 1908) did produce a tsunami, but also that they triggered mass failures that were able to generate an even larger tsunami. The debate is still open, and though no general consensus has been found among scientists so far, this research had the merit to attract attention on possible generation of tsunamis by landslides off Sicily. In this paper we investigate the tsunami potential of mass failures along one sector of the Hyblean-Malta Escarpment (HME). facing Augusta. The HME is the main offshore geological structure of the region running almost parallel to the coast, off eastern Sicily. Here, bottom morphology and slope steepness favour soil failures. In our work we study slope stability under seismic load along a number of HME transects by using the Minimun Lithostatic Deviation (MLD) method, which is based on the limit-equilibrium theory. The main goal is to identify sectors of the HME that could be unstable under the effect of realistic earthquakes. We estimate the possible landslide volume and use it as input for numerical codes to simulate the landslide motion and the consequent tsunami. This is an important step for the assessment of the tsunami hazard in eastern Sicily and for local tsunami mitigation policies. It is also important in view of tsunami warning system since it can help to identify the minimum earthquake magnitude capable of triggering destructive tsunamis induced by landslides, and therefore to set up appropriate knowledge-based criteria to launch alert to the population.

  20. Dose Estimates from Irrigation with Tritiated Water at the Savannah River Site

    International Nuclear Information System (INIS)

    Lee, P.L.

    2000-01-01

    The Savannah River Site (SRS) is part of the U.S. Department of Energy (DOE) complex. It was constructed in the early 1950's to produce special nuclear materials (such as plutonium-239 and tritium) used in the production of nuclear weapons. The 310-square-mile site is located in South Carolina, about 15 miles southeast of Augusta, Georgia. The production of nuclear materials at SRS continued for more than 40 years. However, the end of the Cold War caused a downsizing of this original national defense mission. Current missions are focused on: (1) nuclear weapons stockpile stewardship which emphasizes science-based maintenance of the country's nuclear weapons stockpile; (2) nuclear materials stewardship for management of excess nuclear materials, including transportation, stabilization, storage, and safe and secure disposition; and (3) environmental stewardship involving management, treatment, and disposal of radioactive and nonradioactive wastes resulting from past, present, and future operations

  1. 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)

  2. Charles River

    Science.gov (United States)

    Information on the efforts of the US EPA, the Commonwealth of Massachusetts, the municipalities within the Charles River Watershed and nongovernmental organizations to improve the water quality of the Charles River.

  3. Movement of fish between a river and its backwater: diel activity and relation to environmental gradient

    Czech Academy of Sciences Publication Activity Database

    Hohausová, Eva; Copp, G.; Jankovský, P.

    2003-01-01

    Roč. 12, č. 2 (2003), s. 107-117 ISSN 0906-6691 R&D Projects: GA ČR GA206/93/0734; GA ČR GA206/97/0162; GA AV ČR IAA6087503; GA AV ČR KSK3046108; GA AV ČR KSK6005114 Institutional research plan: CEZ:AV0Z6017912 Keywords : river-backwater connection * behaviour * traps Subject RIV: EH - Ecology , Behaviour Impact factor: 0.949, year: 2003

  4. Aerial radiological survey of the Savannah River floodplain. Date of survey: July-October 1983

    International Nuclear Information System (INIS)

    Boyns, P.K.

    1984-12-01

    An aerial radiological survey of the Savannah River floodplain was conducted from late July through early October 1983 by EG and G Energy Measurements, Inc. for the United States Department of Energy, Office of Nuclear Safety, and E.I. Du Pont de Nemours and Company, Inc., Savannah River Plant. The survey consisted of airborne measurements of both natural and man-made gamma radiation emanating from the terrestrial surface. These measurements allowed an estimate of the distribution of isotopic concentrations in the floodplain area. Results are reported as isopleths superimposed on maps and aerial photographs of the area. Gamma ray energy spectra are also presented for the net man-made radionuclides. The survey was designed to cover all the Savannah River floodplain (over 8000 flight line miles) from Augusta to Savannah, Georgia. Several areas of man-made activity were detected in the vicinity of the Savannah River Plant (SRP). The presence of 60 Co was not detected below the Lower Three Runs Creek area. The 137 Cs activity decreased rapidly below Lower Three Runs Creek; at a distance of 15 kilometers (9 miles) the annual dose due to 137 Cs was less than 10 millirem (mrem). Typical backgrounds in the survey areas were between 65 and 125 mrem per year. 4 references, 51 figures, 8 tables

  5. Contributions of non-destructive testing for determining the provenance of the granites used in the Roman Amphitheatre from Emerita Augusta, Badajoz, Spain.

    Science.gov (United States)

    Mota, M. Isabel; Alvarez de Buergo, Monica; Fort, Rafael; Pizzo, Antonio

    2015-04-01

    The Archaeological Ensemble of Emérita Augusta (Mérida, Badajoz, Spain) was listed a World Heritage Site in 1993 by UNESCO. One of the monuments that belongs to this Archaeological Ensemble is the Roman amphitheatre, mainly built with granite from quarries located near the city. Every urban centre in the Roman Empire, in addition to many rural sites, had one or more local quarries from which they extracted the bulk of their stone. In Mérida, there are a group of documented quarries located near the ancient city. In this work the authors have been investigating five of these documented outcrops which, due the distance from the monument or the existence of ancient Roman routes of communication with the city, can be the possible original quarries. The provenance of these materials with which the monument is built is of significant interest in terms of the restoration and conservation and from a historical point of view of the monument. Nowadays, there are many examples of identification of the original quarries that use destructive procedures and techniques which are based on the physical, petrographical, geochemical, magnetic or mechanical properties that are a function of the mineralogical and textural characteristics of the rock. In this work, the combined use of two non-destructive and on-site techniques, ultrasonic velocity and surface hardness determined with a Schmidt hammer rebound tester, allows to determine first, the quality and degree of decay in the granites, usually affecting the material surface and consisting of a decline in surface cohesion, and second, it can discriminate possible provenance areas of the rock used in the building. These two techniques are very useful for this purpose for several reasons. Their combined use allows the selection of the most representative blocks and ashlars for sampling. This reduces sampling to a minimum showing representative results for the whole building, especially in the case of performing ageing tests in the

  6. Golden alga presence and abundance are inversely related to salinity in a high-salinity river ecosystem, Pecos River, USA

    Science.gov (United States)

    Israël, Natascha M.D.; VanLandeghem, Matthew M.; Denny, Shawn; Ingle, John; Patino, Reynaldo

    2014-01-01

    Prymnesium parvum (golden alga, GA) is a toxigenic harmful alga native to marine ecosystems that has also affected brackish inland waters. The first toxic bloom of GA in the western hemisphere occurred in the Pecos River, one of the saltiest rivers in North America. Environmental factors (water quality) associated with GA occurrence in this basin, however, have not been examined. Water quality and GA presence and abundance were determined at eight sites in the Pecos River basin with or without prior history of toxic blooms. Sampling was conducted monthly from January 2012 to July 2013. Specific conductance (salinity) varied spatiotemporally between 4408 and 73,786 mS/cm. Results of graphical, principal component (PCA), and zero-inflated Poisson (ZIP) regression analyses indicated that the incidence and abundance of GA are reduced as salinity increases spatiotemporally. LOWESS regression and correlation analyses of archived data for specific conductance and GA abundance at one of the study sites retrospectively confirmed the negative association between these variables. Results of PCA also suggested that at <15,000 mS/cm, GA was present at a relatively wide range of nutrient (nitrogen and phosphorus) concentrations whereas at higher salinity, GA was observed only at mid-to-high nutrient levels. Generally consistent with earlier studies, results of ZIP regression indicated that GA presence is positively associated with organic phosphorus and in samples where GA is present, GA abundance is positively associated with organic nitrogen and negatively associated with inorganic nitrogen. This is the first report of an inverse relation between salinity and GA presence and abundance in riverine waters and of interaction effects of salinity and nutrients in the field. These observations contribute to a more complete understanding of environmental conditions that influence GA distribution in inland waters.

  7. 67Ga lung scan

    International Nuclear Information System (INIS)

    Niden, A.H.; Mishkin, F.S.; Khurana, M.M.L.; Pick, R.

    1977-01-01

    Twenty-three patients with clinical signs of pulmonary embolic disease and lung infiltrates were studied to determine the value of gallium citrate 67 Ga lung scan in differentiating embolic from inflammatory lung disease. In 11 patients without angiographically proved embolism, only seven had corresponding ventilation-perfusion defects compatible with inflammatory disease. In seven of these 11 patients, the 67 Ga concentration indicated inflammatory disease. In the 12 patients with angiographically proved embolic disease, six had corresponding ventilation-perfusion defects compatible with inflammatory disease. None had an accumulation of 67 Ga in the area of pulmonary infiltrate. Thus, ventilation-perfusion lung scans are of limited value when lung infiltrates are present. In contrast, the accumulation of 67 Ga in the lung indicates an inflammatory process. Gallium imaging can help select those patients with lung infiltrates who need angiography

  8. Cesarzowa Bułgarów, augusta i bazylisa – Maria-Irena Lekapena i transfer bizantyńskiej idei kobiety-władczyni (imperial feminine w średniowiecznej Bułgarii

    Directory of Open Access Journals (Sweden)

    Zofia A. Brzozowska

    2017-10-01

    Full Text Available Empress of Bulgarians, augusta and basilissa – Maria-Irene Lekapene and the transfer of the idea of imperial feminine in the Medieval Bulgaria Maria Lekapene was a granddaughter of Byzantine Emperor Romanos I Lekapenos. In 927 she married Peter I of Bulgaria. Her marriage, ceremoniously entered into in Constantinople, aimed to strengthen the newly signed Byzantine-Bulgarian peace treaty. Historians attributed to the Empress a significant impact on the political moves of her husband. The Empress was also to introduce a lot of elements of the Byzantine theory of power in Bulgaria.   Cesarzowa Bułgarów, augusta i bazylisa – Maria-Irena Lekapena i transfer bizantyńskiej idei kobiety-władczyni (imperial feminine w średniowiecznej Bułgarii Maria Lekapena była wnuczką cesarza bizantyńskiego Romana I Lekapena. W 927 roku poślubiła władcę Bułgarii, Piotra. Jej małżeństwo, uroczyście zawarte w Konstantynopolu, miało za zadanie umocnić dopiero co podpisany pokój bizantyńsko-bułgarski. Historycy przypisywali carycy znaczny wpływ na polityczne posunięcia jej męża. Władczyni miała też zaszczepić na gruncie bułgarskim wiele elementów bizantyńskiej teorii władzy.

  9. Fish communities in the Poodří Protected Landscape Area (the Odra River basin)

    Czech Academy of Sciences Publication Activity Database

    Lojkásek, B.; Lusk, Stanislav; Halačka, Karel; Lusková, Věra

    2004-01-01

    Roč. 49, č. 3 (2004), s. 121-130 ISSN 1212-1819 R&D Projects: GA AV ČR IAA6093105; GA ČR GA206/00/0824; GA AV ČR KSK6005114 Institutional research plan: CEZ:AV0Z6093917 Keywords : fish communities * River Odra * floodplain Subject RIV: EH - Ecology, Behaviour Impact factor: 0.227, year: 2004 http://www.cazv.cz/attachments/5-Lojkásek.pdf

  10. Annual dynamics of the fish stock in a backwater of the River Dyje

    Czech Academy of Sciences Publication Activity Database

    Lusk, Stanislav; Halačka, Karel; Lusková, Věra; Horák, Václav

    2001-01-01

    Roč. 17, 4-5 (2001), s. 571-581 ISSN 0886-9375. [International Symposium on Regulated Streams /8./. Toulouse, 17.07.2000-21.07.2000] R&D Projects: GA ČR GA206/99/1519; GA ČR GA206/00/0668; GA AV ČR IBS6093007; GA AV ČR KSK6005114 Institutional research plan: CEZ:AV0Z6093917 Keywords : backwater * fish communities * River Dyje Subject RIV: EF - Botanics Impact factor: 1.169, year: 2001

  11. River nomads

    DEFF Research Database (Denmark)

    2016-01-01

    sail on the Niger River between Nigeria and Mali. Crossing villages, borders and cultures, they stop only to rest by setting up camp on riverbanks or host villages. In River Nomads, we join the nomadic Kebbawa fishermen on one of their yearly crossing, experiencing their relatively adventurous...

  12. River Piracy

    Indian Academy of Sciences (India)

    There was this highly venerated river Saraswati flowing through. Haryana, Marwar and Bahawalpur in Uttarapath and emptying itself in the Gulf ofKachchh, which has been described in glowing terms by the Rigveda. "Breaking through the mountain barrier", this "swift-flowing tempestuous river surpasses in majesty and.

  13. 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)

  14. 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

  15. River Mileages and Drainage Areas for Illinois Streams. Volume 2. Illinois River Basin.

    Science.gov (United States)

    1979-12-01

    52.2 WALNUT FORK L LIBERTY 53.1 WALKER BRANCH P LIBERTY 53.3 ROAn S06,TO?S,R05W LIBERTY 54.0 CURL CREEK L LIBERTY 54.4 ROAn S06,T02SR05W LIBERTY 34 QI...33TOI01N 5OW AUGUSTA T13.3 US HWY 24 AUGUSTA 14.4 TOPOGRAPHIC DIVIDE AUGUSTA WALKER BRANCH (MOUTH AT MCKEE CREEK MILE 53.1) ADAMS COUNTY 1.0 ROAD S07T2SRO5W...VERMILION R TRIR L LA SALLE 10.5 (ISGS GAGF 05555500 LOWELL 1278 411519 0A90044 LA SALLE 10.5 IL kT 178 LA SALLE 17.2 USGS GAGE 05555300 NEAR LEONORE

  16. 2015 Lowndes County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Lidar for Lowndes County, GA with the option to Collect Lidar in Cook and Tift Counties, GA Lidar Data Acquisition and Processing Production Task...

  17. Chemical composition analysis and product consistency tests to support Enhanced Hanford Waste Glass Models. Results for the Augusta and October 2014 LAW Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Fox, K. M. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Edwards, T. B. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Best, D. R. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2015-07-07

    In this report, the Savannah River National Laboratory provides chemical analyses and Product Consistency Test (PCT) results for several simulated low activity waste (LAW) glasses (designated as the August and October 2014 LAW glasses) fabricated by the Pacific Northwest National Laboratory. The results of these analyses will be used as part of efforts to revise or extend the validation regions of the current Hanford Waste Treatment and Immobilization Plant glass property models to cover a broader span of waste compositions.

  18. Annual review of cultural resource investigations by the Savannah River Archaeological Research Program. Fiscal year 1995

    Energy Technology Data Exchange (ETDEWEB)

    Brooks, M.J.; Brooks, R.D.; Sassaman, K.E.; Crass, D.C. [and others

    1995-10-01

    The Savannah River Archaeological Research Program (SRARP) continued through FY95 with the United States Department of Energy to fulfill a threefold mission of cultural resource management, research, and public education at the Savannah River Site. Over 2,300 acres of land on the SRS came under cultural resources review in FY95. This activity entailed 30 field surveys, resulting in the recording of 86 new sites. Twenty-two existing sites within survey tract boundaries were revisited to update site file records. Research conducted by SRARP was reported in 11 papers and monographs published during FY95. SRARP staff also presented research results in 18 papers at professional meetings. Field research included several testing programs, excavations, and remote sensing at area sites, as well as data collection abroad. Seven grants were acquired by SRARP staff to support off-site research. In the area of heritage education, the SRARP expanded its activities in FY95 with a full schedule of classroom education, public outreach, and on-site tours. Volunteer excavations at the Tinker Creek site were continued with the Augusta Archaeological Society and other avocational groups, and other off-site excavations provided a variety of opportunities for field experience. Some 80 presentations, displays and tours were provided for schools, historical societies, civic groups, and environmental and historical awareness day celebrations. Additionally, SRARP staff taught four anthropology courses at area colleges.

  19. 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.

  20. 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.

  1. 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

  2. Antecedent Rivers

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 1; Issue 8. Antecedent Rivers - Ganga Is Older Than Himalaya. K S Valdiya. General Article Volume 1 Issue 8 August 1996 pp 55-63. Fulltext. Click here to view fulltext PDF. Permanent link: https://www.ias.ac.in/article/fulltext/reso/001/08/0055-0063 ...

  3. RIVER STATE

    African Journals Online (AJOL)

    principals randomly selected from one hundred secondary schools in Cross River State. The data collected ... There was no siyriificant influerlce of gender on principals' leadership styles effectiveness. ... result of the cultural stereotyping of males and females by .... schools were single sex boys, another 10 were single sex ...

  4. A Review of Flood-Related Storage and Remobilization of Heavy Metal Pollutants in River Systems

    Czech Academy of Sciences Publication Activity Database

    Ciszewski, D.; Matys Grygar, Tomáš

    2016-01-01

    Roč. 227, č. 7 (2016), s. 227-239 ISSN 0049-6979 R&D Projects: GA ČR(CZ) GA15-00340S Institutional support: RVO:61388980 Keywords : River * Sediment * Heavy metals * Mobilization * Pollution Subject RIV: DD - Geochemistry Impact factor: 1.702, year: 2016

  5. Dolichospermum Uruguayense sp. nov., a planktic nostocacean cyanobacterium from the Lower Uruguay River, South America.

    Czech Academy of Sciences Publication Activity Database

    Kozlíková-Zapomělová, Eliška; Ferrari, G.; Del Carmen Pérez, M.

    2016-01-01

    Roč. 16, č. 2 (2016), s. 189-200 ISSN 1802-5439 R&D Projects: GA ČR GAP504/10/1501; GA ČR(CZ) GA14-18067S Institutional support: RVO:60077344 Keywords : 16s rRNA gene phylogeny * cyanobacteria * Dolichospermum * phytoplankton * polyphasic approach * taxonomy * Uruguay River Subject RIV: DA - Hydrology ; Limnology Impact factor: 1.350, year: 2016

  6. Ga-Bi-Te system

    International Nuclear Information System (INIS)

    Rustamov, P.G.; Seidova, N.A.; Shakhbazov, M.G.; AN Azerbajdzhanskoj SSR, Baku. Inst. Neorganicheskoj i Fizicheskoj Khimii)

    1976-01-01

    To elucidate the nature of interaction in the system Ga-Bi-Te, a study has been made of sections GaTe-Bi 2 Te 3 , Ga 2 Te 3 -Bi, GaTe-Bi and Bi 2 Te 3 -Ga. The alloys have been prepared by direct melting of the components or their alloys with subsequent homogenizin.o annealing at 400 deg C. The study has been made by the methods of differential thermal, microstructural analysis and by microhardness measurements. On the basis of literature data and data obtained a projection of the liquidus surface of the phase diagram for the system Ga-Bi-Te has been constructed. In the ternary system there are 17 curves of monovariant equilibrium dividing the liquidus into 10 fields of primary crystallization of phases, 9 points of non-variant equilibrium of which 4 points are triple eutectics and 5 points are triple peritectics

  7. 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)

  8. InGaN/GaN Nanowire LEDs and Lasers

    KAUST Repository

    Zhao, Chao; Ng, Tien Khee; Jahangir, Shafat; Frost, Thomas; Bhattacharya, Pallab; Ooi, Boon S.

    2016-01-01

    -droop issues. The phonon and carrier confinement in nanowires also led to junction heating, and reduced heat dissipation. In this paper, we will present our studies on effective surface states passivation in InGaN/GaN quantum-disks (Qdisks)-in-nanowire light

  9. Robust AlGaN/GaN MMIC Receiver Components

    NARCIS (Netherlands)

    Heijningen, M. van; Janssen, J.P.B.; Vliet, F.E. van

    2009-01-01

    Apart from delivering very high output powers, GaN can also be used to realize robust receiver components, such as Low Noise Amplifiersand Switches. This paper presents the designand measurement results of two GaN X-band switch and LNA MMICs, designed for integration in a radar front end. The switch

  10. Antecedent Rivers

    Indian Academy of Sciences (India)

    far north of the high NandaDevi (7,817 m) - Api Nampa. (7,132 m) range of the Himadri. The Sindhu flows northwestwards, the Satluj goes west, the Karnali takes the southerly course and the Tsangpo flows east. These rivers flow through their pristine channels, carved out at the very outset about 50 to 55 m.y (million years) ...

  11. 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

  12. 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.

  13. 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)

  14. 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.

  15. 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.

  16. 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.

  17. River Corridor Easements

    Data.gov (United States)

    Vermont Center for Geographic Information — A River Corridor Easement (RCE) is an area of conserved land adjacent to a river or stream that was conserved to permanently protect the lateral area the river needs...

  18. Electrical compensation by Ga vacancies in Ga2O3

    OpenAIRE

    Korhonen, Esa; Tuomisto, F.; Gogova, D.; Wagner, G.; Baldini, M.; Galazka, Z.; Schewski, R.; Albrecht, M.

    2015-01-01

    The authors have applied positron annihilation spectroscopy to study the vacancy defects in undoped and Si-doped Ga2O3 thin films. The results show that Ga vacancies are formed efficiently during metal-organic vapor phase epitaxy growth of Ga2O3 thin films. Their concentrations are high enough to fully account for the electrical compensation of Si doping. This is in clear contrast to another n-type transparent semiconducting oxide In2O3, where recent results show that n-type conductivity is n...

  19. 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.

  20. River Diversions and Shoaling

    National Research Council Canada - National Science Library

    Letter, Jr., Joseph V; Pinkard, Jr., C. F; Raphelt, Nolan K

    2008-01-01

    This Coastal and Hydraulics Engineering Technical Note describes the current knowledge of the potential impacts of river diversions on channel morphology, especially induced sedimentation in the river channel...

  1. 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)

  2. 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.

  3. 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.

  4. Assessment of Ga2O3 technology

    Science.gov (United States)

    2016-09-15

    this article has given the emerging technology of GaN a valuable push in term of encouragement to stay with it while the painful technology development...Ga2O3 α-Ga2O3 β-Ga2O3 β-Ga2O3 β-Ga2O3 poly - Ga2O3 β-Ga2O3 Epi-layer Growth Method MBE (ozone) MBE (ozone) MBE (ozone) Mist-CVD MBE (ozone... pains to treat the wafer surface with BCl3 RIE to create charges at the interface. The gate contact was also barely a Schottky contact evidenced by

  5. 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.

  6. GA microwave window development

    International Nuclear Information System (INIS)

    Moeller, C.P.; Kasugai, A.; Sakamoto, K.; Takahashi, K.

    1994-10-01

    The GA prototype distributed window was tested in a 32 mm diam. waveguide system at a power density suitable for a MW gyrotron, using the JAERI/Toshiba 110 GHz long pulse internal converter gyrotron in the JAERI test stand. The presence of the untilted distributed window had no adverse effect on the gyrotron operation. A pulse length of 10 times the calculated thermal equilibrium time (1/e time) of 30 msec was reached, and the window passed at least 750 pulses greater than 30 msec and 343 pulses greater than 60 msec. Beyond 100 msec, the window calorimetry reached steady state, allowing the window dissipation to be measured in a single pulse. The measured loss of 4.0% agrees both with the estimated loss, on which the stress calculations are based, and with the attenuation measured at low power in the HE 11 mode. After the end of the tests, the window was examined; no evidence of arcing air coating was found in the part of the window directly illuminated by the microwaves, although there was discoloration in a recess containing an optical diagnostic which outgassed, causing a local discharge to occur in that recess. Finally, there was no failure of the metal-sapphire joints during a total operating time of 50 seconds consisting of pulses longer than 30 msec

  7. /sup 67/Ga lung scan

    Energy Technology Data Exchange (ETDEWEB)

    Niden, A.H.; Mishkin, F.S.; Khurana, M.M.L.; Pick, R.

    1977-03-21

    Twenty-three patients with clinical signs of pulmonary embolic disease and lung infiltrates were studied to determine the value of gallium citrate /sup 67/Ga lung scan in differentiating embolic from inflammatory lung disease. In 11 patients without angiographically proved embolism, only seven had corresponding ventilation-perfusion defects compatible with inflammatory disease. In seven of these 11 patients, the /sup 67/Ga concentration indicated inflammatory disease. In the 12 patients with angiographically proved embolic disease, six had corresponding ventilation-perfusion defects compatible with inflammatory disease. None had an accumulation of /sup 67/Ga in the area of pulmonary infiltrate. Thus, ventilation-perfusion lung scans are of limited value when lung infiltrates are present. In contrast, the accumulation of /sup 67/Ga in the lung indicates an inflammatory process. Gallium imaging can help select those patients with lung infiltrates who need angiography.

  8. Linking vegetation pattern to hydrology and hydrochemistry in a montane river floodplain, the Šumava National Park, Central Europe

    Czech Academy of Sciences Publication Activity Database

    Bufková, I.; Prach, Karel

    2006-01-01

    Roč. 14, - (2006), s. 317-327 ISSN 0923-4861 R&D Projects: GA ČR GA526/00/1442 Institutional research plan: CEZ:AV0Z60050516 Keywords : diversity * river floodplain * vegetation Subject RIV: EF - Botanics

  9. Exploring the diversity of Diplostomum (Digenea: Diplostomidae) in fishes from the River Danube using mitochondrial DNA barcodes

    Czech Academy of Sciences Publication Activity Database

    Kudlai, Olena; Oros, M.; Kostadinova, Aneta; Georgieva, Simona

    2017-01-01

    Roč. 10, 2 December (2017), č. článku 592. ISSN 1756-3305 R&D Projects: GA ČR GA15-14198S; GA ČR(CZ) GBP505/12/G112 Institutional support: RVO:60077344 Keywords : Diplostomum * Diplostomidae * Metacercariae * Freshwater fishes * Barcodes * cox1 * nad3 * River Danube * Europe Subject RIV: EG - Zoology OBOR OECD: Zoology Impact factor: 3.080, year: 2016

  10. Savannah River bus project

    Energy Technology Data Exchange (ETDEWEB)

    Summers, W.A. [Westinghouse Savannah River Co., Aiken, SC (United States)

    1998-08-01

    The H2Fuel Bus is the world`s first hybrid hydrogen electric transit bus. It was developed through a public/private partnership involving several leading technology and industrial organizations in the Southeast, with primary funding and program management provided by the Department of Energy. The primary goals of the project are to gain valuable information on the technical readiness and economic viability of hydrogen buses and to enhance the public awareness and acceptance of emerging hydrogen technologies. The bus has been operated by the transit agency in Augusta, Georgia since April, 1997. It employs a hybrid IC engine/battery/electric drive system, with onboard hydrogen fuel storage based on the use of metal hydrides. Initial operating results have demonstrated an overall energy efficiency (miles per Btu) of twice that of a similar diesel-fueled bus and an operating range twice that of an all-battery powered electric bus. Tailpipe emissions are negligible, with NOx less than 0.2 ppm. Permitting, liability and insurance issues were addressed on the basis of extensive risk assessment and safety analyses, with the inherent safety characteristic of metal hydride storage playing a major role in minimizing these concerns. Future plans for the bus include continued transit operation and use as a national testbed, with potential modifications to demonstrate other hydrogen technologies, including fuel cells.

  11. 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

  12. 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

  13. 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

  14. 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)

  15. 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...

  16. 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.

  17. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Xing, Huili; Jena, Debdeep, E-mail: djena@cornell.edu [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)

    2015-10-19

    By the insertion of thin In{sub x}Ga{sub 1−x}N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors.

  18. Temperature coefficients for GaInP/GaAs/GaInNAsSb solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aho, Arto; Isoaho, Riku; Tukiainen, Antti; Polojärvi, Ville; Aho, Timo; Raappana, Marianna; Guina, Mircea [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere (Finland)

    2015-09-28

    We report the temperature coefficients for MBE-grown GaInP/GaAs/GaInNAsSb multijunction solar cells and the corresponding single junction sub-cells. Temperature-dependent current-voltage measurements were carried out using a solar simulator equipped with a 1000 W Xenon lamp and a three-band AM1.5D simulator. The triple-junction cell exhibited an efficiency of 31% at AM1.5G illumination and an efficiency of 37–39% at 70x real sun concentration. The external quantum efficiency was also measured at different temperatures. The temperature coefficients up to 80°C, for the open circuit voltage, the short circuit current density, and the conversion efficiency were determined to be −7.5 mV/°C, 0.040 mA/cm{sup 2}/°C, and −0.09%/°C, respectively.

  19. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    International Nuclear Information System (INIS)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick; Xing, Huili; Jena, Debdeep

    2015-01-01

    By the insertion of thin In x Ga 1−x N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors

  20. Allegheny County Major Rivers

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — This dataset contains locations of major rivers that flow through Allegheny County. These shapes have been taken from the Hydrology dataset. The Ohio River,...

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. Flowing with Rivers

    Science.gov (United States)

    Anderson, Heather

    2004-01-01

    This article describes a lesson in which students compare how artists have depicted rivers in paintings, using different styles, compositions, subject matter, colors, and techniques. They create a watercolor landscape that includes a river. Students can learn about rivers by studying them on site, through environmental study, and through works of…

  7. 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.

  8. Morava River floodplain development during the last millennium, Straznicke Pomoravi, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Kadlec, Jaroslav; Grygar, Tomáš; Světlík, Ivo; Ettler, V.; Mihaljevič, M.; Diehl, J. F.; Beske-Diehl, S.; Svitavská-Svobodová, Helena

    2009-01-01

    Roč. 19, č. 3 (2009), s. 499-509 ISSN 0959-6836 R&D Projects: GA AV ČR IAAX00130801; GA AV ČR IAA3013201 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z4032918; CEZ:AV0Z10480505; CEZ:AV0Z60050516 Keywords : floodplain deposits * river activity reconstruction * last millenium * Morava River (Czech Republic) * expandable clay minerals * Cu-trien analysis * mineral magnetic measurements * lead isotope analysis * Holocene fluvial records * land - use change * pollution sources * isotopic-ratios * clay minerals * soil- erosion Subject RIV: DO - Wilderness Conservation Impact factor: 2.481, year: 2009

  9. FLOODPLAIN, AUGUSTA COUNTY, USA AND INCORPORATED AREAS

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — The Floodplain Mapping/Redelineation study deliverables depict and quantify the flood risks for the study area. The primary risk classifications used are the...

  10. InGaN/GaN Nanowire LEDs and Lasers

    KAUST Repository

    Zhao, Chao

    2016-01-01

    The large specific surface, and the associated high density of surface states was found to limit the light output power and quantum efficiency of nanowire-array devices, despite their potential for addressing the “green-gap” and efficiency-droop issues. The phonon and carrier confinement in nanowires also led to junction heating, and reduced heat dissipation. In this paper, we will present our studies on effective surface states passivation in InGaN/GaN quantum-disks (Qdisks)-in-nanowire light-emitting diodes (LEDs) and lasers grown on silicon (Si), as well as our recent work on nanowires LEDs grown on bulk-metal, a non-conventional substrate.

  11. 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.

  12. 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

  13. 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

  14. River basin administration

    Science.gov (United States)

    Management of international rivers and their basins is the focus of the Centre for Comparative Studies on (International) River Basin Administration, recently established at Delft University of Technology in the Netherlands. Water pollution, sludge, and conflicting interests in the use of water in upstream and downstream parts of a river basin will be addressed by studying groundwater and consumption of water in the whole catchment area of a river.Important aspects of river management are administrative and policy aspects. The Centre will focus on policy, law, planning, and organization, including transboundary cooperation, posing standards, integrated environmental planning on regional scale and environmental impact assessments.

  15. 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

  16. 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

  17. Exploring the radiosynthesis and in vitro characteristics of [68Ga]Ga-DOTA-Siglec-9

    DEFF Research Database (Denmark)

    Jensen, Svend Borup; Käkelä, Meeri; Jødal, Lars

    2017-01-01

    (Siglec-9) "CARLSLSWRGLTLCPSK" bind to VAP-1 and hence makes the radioactive analogues of this compound ([68 Ga]Ga-DOTA-Siglec-9) interesting as a non-invasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [68 Ga]Ga-DOTA-Siglec-9 are presented and compared...

  18. 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 ...

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. The history of a continent from U-Pb ages of zircons from Orinoco River sand and Sm-Nd isotopes in Orinoco basin river sediments

    Science.gov (United States)

    Goldstein, S.L.; Arndt, N.T.; Stallard, R.F.

    1997-01-01

    We report SHRIMP U-Pb ages of 49 zircons from a sand sample from the lower Orinoco River, Venezuela, and Nd model ages of the fine sediment load from the main river and tributaries. The U-Pb ages reflect individual magmatic or metamorphic events, the Sm-Nd model ages reflect average crustal-residence ages of the sediment sources. Together they allow delineation of the crust-formation history of the basement precursors of the sediments. The U-Pb ages range from 2.83 to 0.15 Ga, and most are concordant or nearly so. Discrete age groupings occur at ??? 2.8, ??? 2.1, and ??? 1.1 Ga. The oldest group contains only three samples but is isolated from its closest neighbors by a ??? 600 Ma age gap. Larger age groupings at ??? 2.1 and ??? 1.1 Ga make up about a third and a quarter of the total number of analyses, respectively. The remaining analyses scatter along concordia, and most are younger than 1.6 Ga. The ??? 2.8 and ??? 2.1 Ga ages correspond to periods of crust formation of the Imataca and Trans-Amazonian provinces of the Guyana Shield, respectively, and record intervals of short but intensive continental growth. These ages coincide with ??? 2.9 and ??? 2.1 Ga Nd model ages of sediments from tributaries draining the Archean and Proterozoic provinces of the Guyana Shield, respectively, indicating that the U-Pb ages record the geological history of the crystalline basement of the Orinoco basin. Zircons with ages corresponding to the major orogenies of the North Atlantic continents (the Superior at ??? 2.7 Ga and Hudsonian at 1.7-1.9 Ga) were not found in the Orinoco sample. The age distribution may indicate that South and North America were separated throughout their history. Nd model ages of sediments from the lower Orinoco River and Andean tributaries are ??? 1.9 Ga, broadly within the range displayed by major rivers and dusts. This age does not coincide with known thermal events in the region and reflects mixing of sources with different crust-formation ages. The

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Morava River flood plain sediments deposited during the last millennium: Climatic and anthropogenic record

    Czech Academy of Sciences Publication Activity Database

    Kadlec, Jaroslav; Grygar, Tomáš; Světlík, Ivo; Ettler, V.; Mihaljevič, M.; Diehl, J.; Beske-Diehl, S.

    2008-01-01

    Roč. 34, 4/6 (2008), s. 1338314-1338314 ISSN 0161-6951. [International Geological Congress /33./. 06.08.2008-14.08.2008, Oslo ] R&D Projects: GA AV ČR IAA300130505; GA AV ČR IAA3013201; GA AV ČR IAAX00130801 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z40320502; CEZ:AV0Z10480505 Keywords : Morava River * flood * plain sediments * magnetic minerals Subject RIV: DB - Geology ; Mineralogy

  10. Buškové z Velhartic. Historie pánů z Velhartic ve 14. století ve světle kartoték Augusta Sedláčka

    Czech Academy of Sciences Publication Activity Database

    Doležalová, Eva

    2015-01-01

    Roč. 18, č. 2 (2015), s. 181-191 ISSN 0862-979X R&D Projects: GA MK(CZ) DF12P01OVV019 Keywords : lord of Velhartice * 14th century * Czech lands * Charles IV * Bušek of Velhartice Subject RIV: AB - History

  11. 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).

  12. 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

  13. 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.

  14. Operation of river systems. The Otra river

    International Nuclear Information System (INIS)

    Harby, A.; Vaskinn, K.A.; Wathne, M.; Heggenes, J.; Saltveit, S.J.

    1993-12-01

    The purpose of the project described in this report was to prepare an operative tool for making decisions about the operation of the power system on the river Otra (Norway) with regard to how this operation might affect the various users of the river system. Above all this affects fish, outdoor life and esthetic values. The connection between water quality and volume of discharge has been examined in a sub project. How suitable parts of the river are as habitats for trout has been simulated on a computer. From field investigation it is concluded that near the Steinfoss power station the physical conditions for trout depend on the operation of the river system. Outdoor life is not much affected downstream Vikeland. 11 refs., 22 figs., 2 tabs

  15. 76 FR 51887 - Safety Zone; Patuxent River, Patuxent River, MD

    Science.gov (United States)

    2011-08-19

    ...-AA00 Safety Zone; Patuxent River, Patuxent River, MD AGENCY: Coast Guard, DHS. ACTION: Temporary final rule. SUMMARY: The Coast Guard is establishing a temporary safety zone during the ``NAS Patuxent River... held over certain waters of the Patuxent River adjacent to Patuxent River, Maryland from September 1...

  16. Floodplain sediments of the 2002 catastrophic flood at the Vltava (Moldau) River and its tributaries: mineralogy, chemical composition, and post-sedimentary evolution

    Czech Academy of Sciences Publication Activity Database

    Navrátil, Tomáš; Rohovec, Jan; Žák, Karel

    2008-01-01

    Roč. 56, č. 2 (2008), s. 399-412 ISSN 0943-0105 R&D Projects: GA AV ČR IAA300130505 Institutional research plan: CEZ:AV0Z30130516 Keywords : Vltava (Moldau) River * Berounka River * floodplain sediments * 2002 catastrophic flood (Czech Republic) Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.026, year: 2008

  17. The response of benthic macroinvertebrate and fish assemblages to human impact along the lower stretch of the rivers Morava and Dyje (Danube basin, Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Adámek, Zdeněk; Zahrádková, S.; Jurajda, Pavel; Bernardová, I.; Jurajdová, Zdenka; Janáč, Michal; Němejcová, D.

    2013-01-01

    Roč. 71, č. 3 (2013), s. 93-115 ISSN 1330-061X R&D Projects: GA ČR GBP505/12/G112 Institutional support: RVO:68081766 Keywords : Macrozoobenthos * Fish * Diversity * River pollution * River regulation * Joint Danube Survey Subject RIV: EG - Zoology http://ribarstvo.agr.hr/volumes.php?lang=en&search=Article%3A656

  18. 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

  19. A Systematic Literature Review of the Average IQ of Sub-Saharan Africans

    Science.gov (United States)

    Wicherts, Jelte M.; Dolan, Conor V.; van der Maas, Han L. J.

    2010-01-01

    On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit Publishers.] concluded that the average IQ of the…

  20. A systematic literature review of the average IQ of sub-Saharan Africans

    NARCIS (Netherlands)

    Wicherts, J.M.; Dolan, C.V.; van der Maas, H.L.J.

    2010-01-01

    On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit

  1. Density Functional Theory Study on Defect Feature of AsGaGaAs in Gallium Arsenide

    Directory of Open Access Journals (Sweden)

    Deming Ma

    2015-01-01

    Full Text Available We investigate the defect feature of AsGaGaAs defect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT. Our calculations reveal that the lowest donor level of AsGaGaAs defect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of the AsGaGaAs defect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV. This suggests that AsGaGaAs defect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internal AsGaGaAs and surface AsGaGaAs defects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation of AsGaGaAs defect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.

  2. 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.

  3. 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.

  4. The vertebrate fauna of Ichauway, Baker County, GA

    Science.gov (United States)

    Smith, L.L.; Steen, D.A.; Stober, J.M.; Freeman, Mary C.; Golladay, S.W.; Conner, L.M.; Cochrane, J.

    2006-01-01

    Less than 4% of the once extensive Pinus palustris (longleaf pine) ecosystem remains today. Although longleaf pine habitats are recognized for their high species diversity, few published accounts document the vertebrate faunas of remaining tracts. Here we report on the vertebrate species richness of lchauway, an 11,300-ha property in Baker County, GA. The property includes ca. 7300 ha of longleaf pine with native ground cover, along with more than 30 seasonal wetlands and ca. 45 km of riparian habitat associated with Ichawaynochaway Creek, Big Cypress Creek, and the Flint River. The fauna includes 61 species of fish, 31 amphibians, 53 reptiles, 191 birds, and 41 mammals. Despite the relative isolation of the property from other natural ecosystems, the vertebrate fauna of lchauway is remarkably diverse and may offer an example of reference conditions to guide restoration of longleaf pine forests, associated seasonal wetlands, and riparian areas elsewhere in the southeastern U S.

  5. Down to the River

    DEFF Research Database (Denmark)

    Wessels, Josepha Ivanka

    2015-01-01

    Currently there is no coherent or sustainable water cooperation among the five states—Israel, Jordan, Lebanon, Palestinian territories and Syria—that share the Jordan River. Why do people not cooperate on sustainable river basin management, even if it seems the most rational course from the persp......Currently there is no coherent or sustainable water cooperation among the five states—Israel, Jordan, Lebanon, Palestinian territories and Syria—that share the Jordan River. Why do people not cooperate on sustainable river basin management, even if it seems the most rational course from...

  6. Investing in river health.

    Science.gov (United States)

    Bennett, J

    2002-01-01

    Rivers provide society with numerous returns. These relate to both the passive and extractive uses of the resources embodied in river environments. Some returns are manifest in the form of financial gains whilst others are non-monetary. For instance, rivers are a source of monetary income for those who harvest their fish. The water flowing in rivers is extracted for drinking and to water crops and livestock that in turn yield monetary profits. However, rivers are also the source of non-monetary values arising from biological diversity. People who use them for recreation (picnicking, swimming, boating) also receive non-monetary returns. The use of rivers to yield these returns has had negative consequences. With extraction for financial return has come diminished water quantity and quality. The result has been a diminished capacity of rivers to yield (non-extractive) environmental returns and to continue to provide extractive values. A river is like any other asset. With use, the value of an asset depreciates because its productivity declines. In order to maintain the productive capacity of their assets, managers put aside from their profits depreciation reserves that can be invested in the repair or replacement of those assets. Society now faces a situation in which its river assets have depreciated in terms of their capacity to provide monetary and non-monetary returns. An investment in river "repair" is required. But, investment means that society gives up something now in order to achieve some benefit in the future. Society thus has to grapple wih the choice between investing in river health and other investments--such as in hospitals, schools, defence etc. - as well as between investing in river health and current consumption--such as on clothes, food, cars etc. A commonly used aid for investment decision making in the public sector is benefit cost analysis. However, its usefulness in tackling the river investment problem is restricted because it requires all

  7. 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...

  8. 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.

  9. 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

  10. River Corridors (Jan 2, 2015)

    Data.gov (United States)

    Vermont Center for Geographic Information — River corridors are delineated to provide for the least erosive meandering and floodplain geometry toward which a river will evolve over time. River corridor maps...

  11. 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.)

  12. 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.

  13. 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.

  14. Structural Control and Human Impacts on the Opava River Fluvial System, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Hrádek, Mojmír; Loučková, B.

    -, č. 6 (2009), s. 23-30 ISSN 1897-5100 R&D Projects: GA AV ČR IAA300860903 Institutional research plan: CEZ:AV0Z30860518 Keywords : structural control * gold mining * alluvial placers * floods * wandering river Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  15. Magnetic properties of floodplain deposits along the banks of the Morava River (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Kadlec, Jaroslav; Diehl, J. F.

    2005-01-01

    Roč. 5, č. 3 (2005), s. 2-3 R&D Projects: GA AV ČR(CZ) IAA3013201 Institutional research plan: CEZ:AV0Z30130516 Keywords : rock magnetic properties * floodplain deposits * Morava River Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  16. Detecting dispersal of Nuphar lutea in river corridors using microsatellite markers

    Czech Academy of Sciences Publication Activity Database

    Fér, T.; Hroudová, Zdenka

    2008-01-01

    Roč. 53, č. 7 (2008), s. 1409-1422 ISSN 0046-5070 R&D Projects: GA AV ČR(CZ) KJB6111304 Institutional research plan: CEZ:AV0Z60050516 Keywords : Nuphar lutea * dispersal * river corridors Subject RIV: EF - Botanics Impact factor: 2.704, year: 2008

  17. Non-native Gobiid species in the lower River Rhine (Germany): recent range extensions and densities

    Czech Academy of Sciences Publication Activity Database

    Borcherding, J.; Staas, S.; Krüger, S.; Ondračková, Markéta; Šlapanský, Luděk; Jurajda, Pavel

    2011-01-01

    Roč. 27, č. 1 (2011), s. 153-155 ISSN 0175-8659 R&D Projects: GA MŠk LC522 Institutional research plan: CEZ:AV0Z60930519 Keywords : the lower River Rhine Subject RIV: EH - Ecology, Behaviour Impact factor: 0.869, year: 2011

  18. Terrestrial fishes: rivers are barriers to gene flow in annual fishes from the African savanna

    Czech Academy of Sciences Publication Activity Database

    Bartáková, Veronika; Reichard, Martin; Blažek, Radim; Polačik, Matej; Bryja, Josef

    2015-01-01

    Roč. 42, č. 10 (2015), s. 1832-1844 ISSN 0305-0270 R&D Projects: GA ČR(CZ) GAP506/11/0112 Institutional support: RVO:68081766 Keywords : genetic structure * geodispersal * Mozambique * Nothobranchius * phylogeography * population genetics * river morphology * vernal pool Subject RIV: EG - Zoology Impact factor: 3.997, year: 2015

  19. 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

  20. Lithium compensation of GaAs

    International Nuclear Information System (INIS)

    Alexiev, D.; Tavendale, A.J.

    1988-08-01

    Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments, the effect of Li diffusion on existing trap spectra, defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature, initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made

  1. Cation disorder in Ga1212.

    Science.gov (United States)

    Greenwood, K B; Ko, D; Vander Griend, D A; Sarjeant, G M; Milgram, J W; Garrity, E S; DeLoach, D I; Poeppelmeier, K R; Salvador, P A; Mason, T O

    2000-07-24

    Substitution of calcium for strontium in LnSr2-xCaxCu2GaO7 (Ln = La, Pr, Nd, Gd, Ho, Er, Tm, and Yb) materials at ambient pressure and 975 degrees C results in complete substitution of calcium for strontium in the lanthanum and praseodymium systems and partial substitution in the other lanthanide systems. The calcium saturation level depends on the size of the Ln cation, and in all cases, a decrease in the lattice parameters with calcium concentration was observed until a common, lower bound, average A-cation size is reached. Site occupancies from X-ray and neutron diffraction experiments for LnSr2-xCaxCu2GaO7 (x = 0 and x = 2) confirm that the A-cations distribute between the two blocking-layer sites and the active-layer site based on size. A quantitative link between cation distribution and relative site-specific cation enthalpy for calcium, strontium, and lanthanum within the gallate structure is derived. The cation distribution in other similar materials can potentially be modeled.

  2. GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions...

  3. Tunable High efficiency Resonant Tunneling GaN/AlGaN MQW UV Detectors

    National Research Council Canada - National Science Library

    Wang, W. B; Zhang, S. K; Alfano, R. R

    2005-01-01

    ...)-based UV photodetectors. During the grant period, more than twenty six GaN/AlGaN MQW phoptodetectors with different types of device structures and control samples have been fabricated and investigated to achieve the proposed...

  4. 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.

  5. Development of Passivation Technology for Improved GaN/AlGaN HEMT Performance and Reliability

    National Research Council Canada - National Science Library

    Abernathy, C. R; Hunter-Edwards, Angela

    2005-01-01

    .... As part of the recipe development we have studied fundamental characteristics of the native oxides on GaN and AlGaN surfaces using XPS and compared the results to oxides generated by exposure to UV...

  6. 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)

  7. Preserving the Dnipro River

    International Development Research Centre (IDRC) Digital Library (Canada)

    Humanity inherited the true sense of proportion, synergy, and harmony from the natural environment. ..... In Ukraine, the middle and lower sections of the Dnipro have a drainage ... The following large cities are located in the Dnipro basin: in Russia, .... In Kherson Oblast and in river basins of some small rivers it is as high as ...

  8. 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.

  9. 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.

  10. 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.”.

  11. 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

  12. Fabrication of InGaN/GaN nanopillar light-emitting diode arrays

    DEFF Research Database (Denmark)

    Ou, Yiyu; Fadil, Ahmed; Ou, Haiyan

    Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction.......Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction....

  13. 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

  14. Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure ...

    Indian Academy of Sciences (India)

    2017-03-08

    Mar 8, 2017 ... AlGaN/GaN high electron mobility transistor; breakdown voltage; output power density; short channel effect ... is an n-type heavily doped Al0.32Ga0.68N while the ..... [15] S E J Mahabadi, A A Orouji, P Keshavarzi and H A.

  15. 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,.

  16. A InGaN/GaN quantum dot green (λ=524 nm) laser

    KAUST Repository

    Zhang, Meng; Banerjee, Animesh; Lee, Chi-Sen; Hinckley, John M.; Bhattacharya, Pallab

    2011-01-01

    The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching

  17. 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)

  18. Characterization of a Ga-assisted GaAs nanowire array solar cell on si substrate

    DEFF Research Database (Denmark)

    Boulanger, J. P.; Chia, A. C. E.; Wood, B.

    2016-01-01

    A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet-...

  19. Exploring the radiosynthesis and in vitro characteristics of [68 Ga]Ga-DOTA-Siglec-9.

    Science.gov (United States)

    Jensen, Svend B; Käkelä, Meeri; Jødal, Lars; Moisio, Olli; Alstrup, Aage K O; Jalkanen, Sirpa; Roivainen, Anne

    2017-07-01

    Vascular adhesion protein 1 is a leukocyte homing-associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283-297 of sialic acid-binding IgG-like lectin 9 (Siglec-9) "CARLSLSWRGLTLCPSK" bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([ 68 Ga]Ga-DOTA-Siglec-9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [ 68 Ga]Ga-DOTA-Siglec-9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [ 68 Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non decay-corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [ 68 Ga]Ga-DOTA-Siglec-9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [ 68 Ga]Ga-DOTA-Siglec-9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [ 68 Ga]Ga-DOTA-Siglec-9 are suitable as a positron emission tomography tracer. Copyright © 2017 John Wiley & Sons, Ltd.

  20. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    Unknown

    of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the .... Considerable research is being carried out on GaN HEMTs at present. ... by InGaN/GaN multiquantum well in MOVPE was first.

  1. Numerical modelling of river processes: flow and river bed deformation

    NARCIS (Netherlands)

    Tassi, P.A.

    2007-01-01

    The morphology of alluvial river channels is a consequence of complex interaction among a number of constituent physical processes, such as flow, sediment transport and river bed deformation. This is, an alluvial river channel is formed from its own sediment. From time to time, alluvial river

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Geophysical research at the Obora lokality (NW from Brno) and its aplication to the knowledge of the Svratka River development between the Veverská Bítýška and Brno.

    Czech Academy of Sciences Publication Activity Database

    Peterková, L.; Kirchner, Karel; Hubatka, F.; Nehyba, S.

    -, č. 1 (2008), s. 55-62 ISSN 1337-6799 R&D Projects: GA ČR GA205/06/1024 Institutional research plan: CEZ:AV0Z30860518 Keywords : The Svratka River * ground penetrating radar * vertical electrical sounding Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  7. 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.

  8. AlGaAs and AlGaAs/GaAs/AlGaAs nanowires grown by molecular beam epitaxy on silicon substrates

    DEFF Research Database (Denmark)

    Cirlin, G E; Reznik, R R; Shtrom, I V

    2017-01-01

    The data on growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on different (1 1 1) substrates by Au-assisted molecular beam epitaxy are presented. The influence of nanowires growth conditions on structural and optical properties is studied in detail...

  9. Properties and Bibliography of GaSe

    Science.gov (United States)

    1994-02-01

    Musaev, A. E. Bakhyshev, N. M. Gasanly and L. G. Musaeva . (1975). "Anisotropy of the optical constants of GaS and GaSe near the absorption edge." Sov...Phys. Semiconductors. 9 94-95 Russian ref.: Fiz. Tekh. Poluprovodn. 9 142-145 (January 1975). Akhundov, G. A., L. G. Musaeva and M. D. Khomutova

  10. 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

  11. 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

  12. 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.

  13. Uranium in river water

    International Nuclear Information System (INIS)

    Palmer, M.R.; Edmond, J.M.

    1993-01-01

    The concentration of dissolved uranium has been determined in over 250 river waters from the Orinoco, Amazon, and Ganges basins. Uranium concentrations are largely determined by dissolution of limestones, although weathering of black shales represents an important additional source in some basins. In shield terrains the level of dissolved U is transport limited. Data from the Amazon indicate that floodplains do not represent a significant source of U in river waters. In addition, the authors have determined dissolved U levels in forty rivers from around the world and coupled these data with previous measurements to obtain an estimate for the global flux of dissolved U to the oceans. The average concentration of U in river waters is 1.3 nmol/kg, but this value is biased by very high levels observed in the Ganges-Brahmaputra and Yellow rivers. When these river systems are excluded from the budget, the global average falls to 0.78 nmol/kg. The global riverine U flux lies in the range of 3-6 x 10 7 mol/yr. The major uncertainty that restricts the accuracy of this estimate (and that of all other dissolved riverine fluxes) is the difficulty in obtaining representative samples from rivers which show large seasonal and annual variations in runoff and dissolved load

  14. Interface and transport properties of GaN/graphene junction in GaN-based LEDs

    International Nuclear Information System (INIS)

    Wang Liancheng; Zhang Yiyun; Liu Zhiqiang; Guo Enqing; Yi Xiaoyan; Wang Junxi; Wang Guohong; Li Xiao; Zhu Hongwei

    2012-01-01

    A normalized circular transmission line method pattern with uniform interface area was developed to obtain contact resistances of p-, u-, n-GaN/graphene contacts (p, u and n represent p-type doped, unintentionally doped and n-type doped, respectively) and N-polar u-, n-GaN/graphene contacts in GaN-based LEDs. The resistances of the graphene/GaN contacts were mainly determined by the work function gap and the carrier concentration in GaN. Annealing caused diffusion of metal atoms and significantly influenced the interface transport properties.

  15. Device Performance and Reliability Improvements of AlGaBN/GaN/Si MOSFET

    Science.gov (United States)

    2016-02-04

    AFRL-AFOSR-JP-TR-2016-0037 Device Performance and Reliablity Improvements of AlGaBN/GaN/Si MOSFET Robert Wallace UNIVERSITY OF TEXAS AT DALLAS Final...GaN/Si MOSFET 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-14-1-4069 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Robert Wallace 5d.  PROJECT...AOARD Grant FA2386-14-1-4069 Device Performance and Reliability Improvements of AlGaN/GaN/Si MOSFET US 12 month extension (2014 – 2015) for current

  16. Density of Ga2O3 Liquid

    OpenAIRE

    Dingwell, Donald B.

    1992-01-01

    The density of Ga2O3 liquid in equilibrium with air has been measured at 18000 to 19000C using an Ir double-bob Archimedean method. The data yield the following description of the density of Ga2O3 liquid: ρ= 4.8374(84)–0.00065(12)(T −18500C). This density-temperature relationship is compared with the partial molar volume of Ga2O3 in glasses in the systems CaO–Ga2O3–SiO2 and Na2O–Ga2O3–SiO2, corrected to the glass transition temperature using thermal expansivities. The comparison illustrates t...

  17. Study of 67Ga scan in sarcoidosis

    International Nuclear Information System (INIS)

    Han Lijun; Qu Wanyin; Liu Xiuqin

    1997-01-01

    Gallium scan and serum angiotensin-converting enzyme assay (SACE) were compared in patients with sarcoidosis. The examination of 67 Ga scan, SACE determination, pulmonary function test, chest CT and chest X-ray in 24 cases with sarcoidosis were studied. The results revealed that 4 of 24 cases had obviously high uptake of 67 Ga exceeding hepatic activity (3+) in clinical active stage, 3 patients had resembling the Greek letter lambda, symmetrically located in bilateral hilar lymph nodes, and among them two had an uptake of 67 Ga in the bilateral lacrimal and parotid gland simulating 'Panda Face'. 8 of 20 cases with inactive sarcoidosis had an abnormal 67 Ga scan (1+). In those patients with normal SACE level but increased uptake of 67 Ga, active stage of disease was demonstrated and steroid therapy was indicated. Gallium scan is a valuable method for the staging of its activity and evaluation of the therapeutic effect in the follow-up patients with sarcoidosis

  18. Savannah River Plant environment

    International Nuclear Information System (INIS)

    Dukes, E.K.

    1984-03-01

    On June 20, 1972, the Atomic Energy Commission designated 192,323 acres of land near Aiken, SC, as the nation's first National Environmental Research Park. The designated land surrounds the Department of Energy's Savannah River Plant production complex. The site, which borders the Savannah River for 17 miles, includes swampland, pine forests, abandoned town sites, a large man-made lake for cooling water impoundment, fields, streams, and watersheds. This report is a description of the geological, hydrological, meteorological, and biological characteristics of the Savannah River Plant site and is intended as a source of information for those interested in environmental research at the site. 165 references, 68 figures, 52 tables

  19. 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.

  20. 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.

  1. 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

  2. The influence of large-scale climatic patterns on precipitation, temperature, and discharge in Czech river basins

    Czech Academy of Sciences Publication Activity Database

    Šípek, Václav

    2013-01-01

    Roč. 61, č. 4 (2013), s. 278-285 ISSN 0042-790X R&D Projects: GA AV ČR IAA300600901 Institutional support: RVO:67985874 Keywords : macro-scale climatic patterns * cidlina river * Blanice river * hydrometeorology Subject RIV: DA - Hydrology ; Limnology Impact factor: 1.231, year: 2013 http://147.213.145.2/vc/vc1.asp

  3. 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%.

  4. 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)

  5. 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)

  6. Uncorrelated electron-hole transition energy in GaN|InGaN|GaN spherical QDQW nanoparticles

    International Nuclear Information System (INIS)

    Haddou El Ghazi; Anouar Jorio and Izeddine Zorkani

    2013-01-01

    The electron (hole) energy and uncorrelated 1S e - 1S h electron-hole transition in Core(GaN)|well(In x Ga 1-x N)|shell(GaN) spherical QDQW nanoparticles is investigated as a function of the inner and the outer radii. The calculations are performed within the framework of the effective-mass approximation and the finite parabolic potential confinement barrier in which two confined parameters are taking account. The Indium composition effect is also investigated. A critical value of the outer and the inner ratio is obtained which constitutes the turning point of two indium composition behaviors. (author)

  7. Double pulse doped InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor heterostructures

    International Nuclear Information System (INIS)

    Egorov, A. Yu.; Gladyshev, A. G.; Nikitina, E. V.; Denisov, D. V.; Polyakov, N. K.; Pirogov, E. V.; Gorbazevich, A. A.

    2010-01-01

    Double pulse doped (δ-doped) InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (HEMT) heterostructures were grown by molecular-beam epitaxy using a multiwafer technological system. The room-temperature electron mobility was determined by the Hall method as 6550 and 6000 cm 2 /(V s) at sheet electron densities of 3.00 x 10 12 and 3.36 x 10 12 cm -2 , respectively. HEMT heterostructures fabricated in a single process feature high uniformity of structural and electrical characteristics over the entire area of wafers 76.2 mm in diameter and high reproducibility of characteristics from process to process.

  8. Hunting camp. River Murray

    OpenAIRE

    ? Bayliss, Charles, 1850-1897, photographer

    2003-01-01

    200 x 149 mm. A good photograph showing a group of aborigines (in European clothes) with two hunting dogs, holding spears and standing in front of rough wooden cabins; with the river in the background. Photograph unknown, possible Charles Bayliss.

  9. Wild and Scenic Rivers

    Data.gov (United States)

    Earth Data Analysis Center, University of New Mexico — This map layer portrays the linear federally-owned land features (i.e., national parkways, wild and scenic rivers, etc.) of the United States, Puerto Rico, and the...

  10. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Science.gov (United States)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  11. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F. [University of Tsukuba, Institute of Applied Physics, Tsukuba, Ibaraki 305-8573 (Japan)

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerance of GaAs and that Ti can protected GaAs from erosion by NH{sub 3}. By depositing Ti on GaAs(111)A surface, a mirror-like GaN layer could be grown at 1000 C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. 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.

  13. 67Ga imaging in Hodgkin's disease

    International Nuclear Information System (INIS)

    Huys, J.; Schelstraete, K.; Simons, M.

    1982-01-01

    In order to answer the question if 67 Ga imaging has a practical utility for the management of the patient with Hodgkin's disease, 108 scans performed on 60 patients were reviewed. When used during the initial staging of the disease or during restaging because of recurrences, 67 Ga imaging-at least in our experience-gave many false negative results in the cervical, axillary and inguinal areas, whereas the majority of true positive scans was found at the mediastinal level (including the lower mediastinum), and also in the lung parenchyma and the upper epigastric regions. Because of its lack of sensitivity, 67 Ga imaging cannot replace other staging procedures, but nevertheless is a valuable adjunctive test, as it can identify tumor localization that may have remained undetected by other methods. Fifty-four scans were performed to monitor treatment with radiation therapy or chemotherapeutic agents. Disappearance or decreases of 67 Ga uptake after treatment usually corresponded to a disappearance or regression of the tumor as ascertained by other methods. When the treatment was shown to be ineffective, 67 Ga uptake persisted or even became more prominent. When during follow-up, a new concentration of 67 Ga appeared at the original location or elsewhere, a relapse was extremely likely. However, one must be aware of false positive images. In our material, no correlation was found between the intensity of the 67 Ga uptake and the histological subtypes of Hodgkin's disease. Neither did we observe any relation to the blood sedimentation rate or serum iron levels

  14. 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

  15. GaN-based blue laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Miyajima, Takao; Yanashima, Katsunori; Funato, Kenji; Asatsuma, Tsunenori; Kobayashi, Toshimasa [CT Development Centre, CNC, Sony Corporation, Atsugi, Kanagawa (Japan); Tojyo, Tsuyoshi; Asano, Takeharu; Kijima, Satoru; Hino, Tomonori; Takeya, Motonobu; Uchida, Shiro; Ikeda, Masao [Sony Shiroishi Semiconductor Inc., Shiroishi, Miyagi (Japan); Tomiya, Shigetaka [Environment and Analyhsis Technology Department, Sony Corporation, Hodogaya, Yokohama (Japan)

    2001-08-13

    We report our recent progress on GaN-based high-power laser diodes (LDs), which will be applied as a light source in high-density optical storage systems. We have developed raised-pressure metal-organic chemical vapour deposition (RP-MOCVD), which can reduce the threading-dislocation density in the GaN layer to several times 10{sup 8} cm{sup -2}, and demonstrated continuous-wave (cw) operation of GaN-based LD grown by RP-MOCVD. Furthermore, we found that the epitaxial lateral overgrowth (ELO) technique is useful for further reducing threading-dislocation density to 10{sup 6} cm{sup -2} and reducing the roughness of the cleaved facet. By using this growth technique and optimizing device parameters, the lifetime of LDs was improved to more than 1000 hours under 30 mW cw operation at 60 deg. C. Our results proved that reducing both threading-dislocation density and consumption power is a valid approach to realizing a practical GaN-based LD. On the other hand, the practical GaN-based LD was obtained when threading-dislocation density in ELO-GaN was only reduced to 10{sup 6} cm{sup -2}, which is a relatively small reduction as compared with threading-dislocation density in GaAs- and InP-based LDs. We believe that the multiplication of non-radiative centres is very slow in GaN-based LDs, possibly due to the innate character of the GaN-based semiconductor itself. (author)

  16. Growth and properties of the MOVPE GaAs/InAs/GaAsSb quantum dot structures

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Oswald, Jiří; Pangrác, Jiří; Kuldová, Karla; Zíková, Markéta; Vyskočil, Jan; Hulicius, Eduard

    2016-01-01

    Roč. 480, Jan (2016), 14-22 ISSN 0921-4526 R&D Projects: GA ČR GA13-15286S; GA ČR(CZ) GP14-21285P; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dot * band alignment * InAs/GaAs * GaAsSb * MOVPE * luminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2016

  17. GaAs/AlAs/InGaP heterostructure: a versatile material basis for cantilever designs

    International Nuclear Information System (INIS)

    Gregušová, Dagmar; Kúdela, Róbert; Eliáš, Peter; Šoltýs, Ján; Cambel, Vladimír; Kostič, Ivan

    2010-01-01

    We report on the design, fabrication and initial mechanical testing of cantilevers with tips based on a GaAs/In 0.485 Ga 0.515 P/AlAs heterostructure grown by metal organic chemical vapor deposition. They were produced using a dedicated technological process based on (1) the formation of integrated tips through an AlAs-assisted surface sacrificial wet-etching process and (2) the GaAs cantilever release fully protected between two InGaP etch-stop layers. 2 µm thick InGaP/GaAs/InGaP cantilevers had integrated pyramidal tips with the sides at ∼45° to (1 0 0). Metallic elements were processed close to the tip apexes using non-standard optical lithography. The cantilever release was accomplished using photolithography, Ar ion milling of InGaP and wet chemical etching of GaAs via resist layers deposited by a draping technique. A tip–cantilever prototype with length, width and thickness of 150, 35 and 2 µm, respectively, exhibited a resonance frequency of 66.2 kHz, which correlated well with a theoretical value of 57 kHz for a GaAs cantilever of identical dimensions. (technical note)

  18. 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...

  19. An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Cao Meng-Yi; Lu Yang; Chen Yong-He; Zheng Jia-Xin; Ma Xiao-Hua; Hao Yue; Wei Jia-Xing; Li Wei-Jun

    2014-01-01

    In this paper, a new current expression based on both the direct currect (DC) characteristics of the AlGaN/GaN high election mobility transistor (HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I–V, S-parameter, and radio frequency (RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide (Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT (10 × 125 μm)). The improved large signal model simulates the I–V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  20. 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.

  1. 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.

  2. Comparison of damage introduced into GaN/AlGaN/GaN heterostructures using selective dry etch recipes

    International Nuclear Information System (INIS)

    Green, R T; Luxmoore, I J; Houston, P A; Ranalli, F; Wang, T; Parbrook, P J; Uren, M J; Wallis, D J; Martin, T

    2009-01-01

    A SiCl 4 /SF 6 dry etch plasma recipe is presented giving a selectivity of 14:1 between GaN and AlGaN. Using a leakage test structure, which enables bulk and surface leakage components to be identified independently, the optimized recipe is compared to an un-etched sample and devices recessed using a Cl 2 /Ar/O 2 -based plasma chemistry. Devices etched using the SiCl 4 /SF 6 recipe demonstrated reduced bulk and surface leakage currents when operated over a wide range of temperatures. Consequently the SiCl 4 /SF 6 recipe is identified as most suitable for the fabrication of gate recessed AlGaN/GaN HEMTs

  3. Phonon replica dynamics in high quality GaN epilayers and AlGaN/GaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Alderighi, D.; Vinattieri, A.; Colocci, M. [Ist. Nazionale Fisica della Materia, Firenze (Italy); Dipt. di Fisica and LENS, Firenze (Italy); Bogani, F. [Ist. Nazionale Fisica della Materia, Firenze (Italy); Dipt. di Energetica, Firenze (Italy); Gottardo, S. [Dipt. di Fisica and LENS, Firenze (Italy); Grandjean, N.; Massies, J. [Centre de Recherche sur l' Hetero-Epitaxie et ses Applications, CNRS, Valbonne (France)

    2001-01-01

    We present an experimental study of the exciton and phonon replica dynamics in high quality GaN epilayers and AlGaN/GaN quantum wells (QW) by means of picosecond time-resolved photoluminescence (PL) measurements. A non-exponential decay is observed both at the zero phonon line (ZPL) and at the n = 1 LO replica. Time-resolved spectra unambiguously assign the replica to the free exciton A recombination. Optical migration effects are detected both in the epilayer and the QWs samples and disappear as the temperature increases up to 60-90 K. Even though the sample quality is comparable to state-of-the-art samples, localization effects dominate the exciton dynamics at low temperature in the studied GaN based structures. (orig.)

  4. Role of electronic correlations in Ga

    KAUST Repository

    Zhu, Zhiyong

    2011-06-13

    An extended around mean field (AMF) functional for less localized pelectrons is developed to quantify the influence of electronic correlations in α-Ga. Both the local density approximation (LDA) and generalized gradient approximation are known to mispredict the Ga positional parameters. The extended AMF functional together with an onsite Coulomb interaction of Ueff=1.1 eV, as obtained from constraint LDA calculations, reduces the deviations by about 20%. The symmetry lowering coming along with the electronic correlations turns out to be in line with the Ga phase diagram.

  5. Gallium adsorption on (0001) GaN surfaces

    International Nuclear Information System (INIS)

    Adelmann, Christoph; Brault, Julien; Mula, Guido; Daudin, Bruno; Lymperakis, Liverios; Neugebauer, Joerg

    2003-01-01

    We study the adsorption behavior of Ga on (0001) GaN surfaces combining experimental specular reflection high-energy electron diffraction with theoretical investigations in the framework of a kinetic model for adsorption and ab initio calculations of energy parameters. Based on the experimental results we find that for substrate temperatures and Ga fluxes typically used in molecular-beam epitaxy of GaN, finite equilibrium Ga surface coverages can be obtained. The measurement of a Ga/GaN adsorption isotherm allows the quantification of the equilibrium Ga surface coverage as a function of the impinging Ga flux. In particular, we show that a large range of Ga fluxes exists, where 2.5±0.2 monolayers (in terms of the GaN surface site density) of Ga are adsorbed on the GaN surface. We further demonstrate that the structure of this adsorbed Ga film is in good agreement with the laterally contracted Ga bilayer model predicted to be most stable for strongly Ga-rich surfaces [Northrup et al., Phys. Rev. B 61, 9932 (2000)]. For lower Ga fluxes, a discontinuous transition to Ga monolayer equilibrium coverage is found, followed by a continuous decrease towards zero coverage; for higher Ga fluxes, Ga droplet formation is found, similar to what has been observed during Ga-rich GaN growth. The boundary fluxes limiting the region of 2.5 monolayers equilibrium Ga adsorption have been measured as a function of the GaN substrate temperature giving rise to a Ga/GaN adsorption phase diagram. The temperature dependence is discussed within an ab initio based growth model for adsorption taking into account the nucleation of Ga clusters. This model consistently explains recent contradictory results of the activation energy describing the critical Ga flux for the onset of Ga droplet formation during Ga-rich GaN growth [Heying et al., J. Appl. Phys. 88, 1855 (2000); Adelmann et al., J. Appl. Phys. 91, 9638 (2002).

  6. 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.

  7. Improved interface quality and luminescence capability of InGaN/GaN quantum wells with Mg pretreatment

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Zhengyuan; Shen, Xiyang; Xiong, Huan; Li, Qingfei; Kang, Junyong; Fang, Zhilai [Xiamen University, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen (China); Lin, Feng; Yang, Bilan; Lin, Shilin [San' an Optoelectronics Co., Ltd, Xiamen (China); Shen, Wenzhong [Shanghai Jiao Tong University, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai (China); Zhang, Tong-Yi [Shanghai University, Shanghai University Materials Genome Institute and Shanghai Materials Genome Institute, Shanghai (China)

    2016-02-15

    Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface. The indium in the Mg-pretreated InGaN layer was homogeneously distributed, making the interfaces abrupt. The improved interface quality greatly enhanced light emission capacity. The cathodoluminescence intensity of the Mg-pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment. (orig.)

  8. 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.

  9. Theoretical study of electronic structures and spectroscopic properties of Ga 3Sn, GaSn 3, and their ions

    Science.gov (United States)

    Zhu, Xiaolei

    2007-01-01

    Ground and excited states of mixed gallium stannide tetramers (Ga 3Sn, Ga 3Sn +, Ga 3Sn -, GaSn 3, GaSn 3+, and GaSn 3-) are investigated employing the complete active space self-consistent-field (CASSCF), density function theory (DFT), and the coupled-cluster single and double substitution (including triple excitations) (CCSD(T)) methods. The ground states of Ga 3Sn, Ga 3Sn +, and Ga 3Sn - are found to be the 2A 1, 3B 1, and 1A 1 states in C2v symmetry with a planar quadrilateral geometry, respectively. The ground states of GaSn 3 and GaSn 3- is predicted to be the 2A 1 and 1A 1 states in C2v point group with a planar quadrilateral structure, respectively, while the ground state of GaSn 3+ is the 1A 1 state with ideal triangular pyramid C3v geometry. Equilibrium geometries, vibrational frequencies, binding energies, electron affinities, ionization energies, and other properties of Ga 3Sn and GaSn 3 are computed and discussed. The anion photoelectron spectra of Ga 3Sn - and GaSn 3- are also predicted. It is interesting to find that the amount of charge transfer between Ga and Sn 2 atoms in the 1A 1 state of GaSn 3+ greatly increases upon electron ionization from the 2A 1 state of GaSn 3, which may be caused by large geometry change. On the other hand, the results of the low-lying states of Ga 3Sn and GaSn 3 are compared with those of Ga 3Si and GaSi 3.

  10. [Health assessment of river ecosystem in Haihe River Basin, China].

    Science.gov (United States)

    Hao, Li-Xia; Sun, Ran-Hao; Chen, Li-Ding

    2014-10-01

    With the development of economy, the health of river ecosystem is severely threatened because of the increasing effects of human activities on river ecosystem. In this paper, the authors assessed the river ecosystem health in aspects of chemical integrity and biological integrity, using the criterion in water quality, nutrient, and benthic macroinvertebrates of 73 samples in Haihe River Basin. The research showed that the health condition of river ecosystem in Haihe River Basin was bad overall since the health situation of 72. 6% of the samples was "extremely bad". At the same time, the health situation in Haihe River Basin exhibited obvious regional gathering effect. We also found that the river water quality was closely related to human activities, and the eutrophication trend of water body was evident in Haihe River Basin. The biodiversity of the benthic animal was low and lack of clean species in the basin. The indicators such as ammonia nitrogen, total nitrogen and total phosphorus were the key factors that affected the river ecosystem health in Haihe River Basin, so the government should start to curb the deterioration of river ecosystem health by controlling these nutrients indicators. For river ecosystem health assessment, the multi-factors comprehensive evaluation method was superior to single-factor method.

  11. Elimination of trench defects and V-pits from InGaN/GaN structures

    International Nuclear Information System (INIS)

    Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert; Schiavon, Dario; Leszczyński, Mike

    2015-01-01

    The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defects were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits

  12. Modeling and simulation of InGaN/GaN quantum dots solar cell

    International Nuclear Information System (INIS)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-01-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In 0.25 Ga 0.75 N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In 0.25 Ga 0.75 N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  13. Modeling and simulation of InGaN/GaN quantum dots solar cell

    Science.gov (United States)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-07-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In0.25Ga0.75N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In0.25Ga0.75N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  14. 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.

  15. 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

  16. MOVPE growth of violet GaN LEDs on β-Ga2O3 substrates

    Science.gov (United States)

    Li, Ding; Hoffmann, Veit; Richter, Eberhard; Tessaro, Thomas; Galazka, Zbigniew; Weyers, Markus; Tränkle, Günther

    2017-11-01

    We report that a H2-free atmosphere is essential for the initial stage of metalorganic vapour phase epitaxy (MOVPE) growth of GaN on β-Ga2O3 to prevent the surface from damage. A simple growth method is proposed that can easily transfer established GaN growth recipes from sapphire to β-Ga2O3 with both (-2 0 1) and (1 0 0) orientations. This method features a thin AlN nucleation layer grown below 900 °C in N2 atmosphere to protect the surface of β-Ga2O3 from deterioration during further growth under the H2 atmosphere. Based on this, we demonstrate working violet vertical light emitting diodes (VLEDs) on n-conductive β-Ga2O3 substrates.

  17. 60Co gamma radiation effect on AlGaN//AlN/GaN HEMT devices

    International Nuclear Information System (INIS)

    Wang Yanping; Luo Yinhong; Wang Wei; Zhang Keying; Guo Hongxia; Guo Xiaoqiang; Wang Yuanming

    2013-01-01

    The testing techniques and experimental methods of the 60 Co gamma irradiation effect on AlGaN/AlN/GaN high electron mobility transistors (HEMTs) are established. The degradation of the electrical properties of the device under the actual radiation environment are analyzed theoretically, and studies of the total dose effects of gamma radiation on AlGaN/AlN/GaN HEMTs at three different radiation bias conditions are carried out. The degradation patterns of the main parameters of the AlGaN/AlN/GaN HEMTs at different doses are then investigated, and the device parameters that were sensitive to the gamma radiation induced damage and the total dose level induced device damage are obtained. (authors)

  18. Strong correlation and ferromagnetism in (Ga,Mn)As and (Ga,Mn)N

    International Nuclear Information System (INIS)

    Filippetti, A.; Spaldin, N.A.; Sanvito, S.

    2005-01-01

    The band energies of the ferromagnetic diluted magnetic semiconductors (Ga,Mn)As and (Ga,Mn)N are calculated using a self-interaction-free approach which describes covalent and strongly correlated electrons without adjustable parameters. Both materials are half-metallic, although the contribution of Mn-derived d states to the bands around the Fermi energy is very different in the two cases. In (Ga,Mn)As the bands are strongly p-d hybridized, with a dominance of As p states. In contrast in (Ga,Mn)N the Fermi energy lies within three flat bands of mainly d character that are occupied by two electrons. Thus the Mn ion in (Ga,Mn)N behaves as a deep trap acceptor, with the hole at 1.39 eV above the GaN valence band top, and is in excellent agreement with the experimental data

  19. 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.

  20. Amphoteric arsenic in GaN

    CERN Document Server

    Wahl, U; Araújo, J P; Rita, E; Soares, JC

    2007-01-01

    We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\\scriptstyle_{Ga}\\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\\scriptstyle_{1-x}$N$\\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.

  1. 2015 Cook & Tift County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Tift and Cook Counties GA Lidar Data Acquisition and Processing Production Task NOAA Contract No. EA133C-11-CQ-0010 Woolpert Order No. 75271...

  2. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p-n diodes and InGaN LEDs

    Science.gov (United States)

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-12-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal-organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p-n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm-3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10-3-3.4 × 10-3 Ω·cm2, and the turn-on voltages of the diodes.

  3. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.

    2017-11-27

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  4. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-01-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  5. Photoconductive GaN UV Detectors

    National Research Council Canada - National Science Library

    Baranowski, Jacek

    1999-01-01

    This report results from a contract tasking University of Warsaw as follows: The contractor will investigate the growth of GaN material using atmospheric pressure metalorganic chemical vapor deposition method (MOCVD...

  6. Data processing system of GA and PPPL

    International Nuclear Information System (INIS)

    Oshima, Takayuki

    2001-11-01

    Results of research in 1997 to General Atomics (GA) and Princeton Plasma Physics Laboratory (PPPL) are reported. The author visited the computer system of fusion group in GA. He joined the tokamak experiment in DIII-D, especially on the demonstration of the remote experiment inside U.S., and investigated the data processing system of DIII-D and the computer network, etc. After the visit to GA, He visited PPPL and exchanged the information about the equipment of remote experiment between JAERI and PPPL based on the US-Japan fusion energy research cooperation. He also investigated the data processing system of TFTR tokamak, the computer network and so on. Results of research of the second visit to GA in 2000 are also reported, which describes a rapid progress of each data processing equipment by the advance on the computer technology in just three years. (author)

  7. Atomic ordering in GaAsP

    Science.gov (United States)

    Chen, G. S.; Jaw, D. H.; Stringfellow, G. B.

    1991-04-01

    CuPt type ordering, which consists of a monolayer compositional modulation along one of the 4 directions in the lattice, was studied using transmission electron microscopy for GaAs1-xPx with values of x extending from 0.25 to 0.85. The samples were grown by organometallic vapor phase epitaxy on nominal (001) GaAs substrates that were misoriented by varying amounts in three directions. No CuPt type ordering was observed for GaAs1-xPx with x ≤0.35, while ordering was found to occur for 0.4≤x≤0.85. The direction of substrate misorientation has a major effect on the determination of which of the four possible CuPt variants are formed for 0.4≤x≤0.85. Two variants, with ordering on the (1¯11) and (11¯1) planes, appear for epilayers grown on substrates oriented exactly on the (001) plane and for substrates misoriented by 6° towards the [110] direction. Only one variant, with ordering on the (1¯11) plane, appears for epilayers grown on substrates misoriented by 6° towards [1¯10]. These ordering-induced spots observed in transmission electron diffraction (TED) patterns for GaAsP occur only for the [110] cross section. From TED studies of GaInP grown on similar substrates, we conclude that the CuPt variants in GaAsP are exactly the same as for GaInP. Further evidence supporting this conclusion was obtained by growing first a layer of GaInP followed by a layer of GaAsP. High-resolution dark field electron micrographs show domains of the same variants in both layers. A mechanism describing the formation of the specific ordered variant for both GaAsP and GaInP is proposed. From studies of ordering in a strain-layer superlattice, the strain due to lattice mismatch was found to play no significant role in the propagation of ordered domains. Microtwins, also generated due to lattice mismatch, can act as domain boundaries and prevent the propagation of the ordered domains.

  8. Modeling and Simulation of Monolithic AlGaAs/InGaAs Tandem Solar Cell

    Directory of Open Access Journals (Sweden)

    Samia SLIMANI

    2015-06-01

    Full Text Available Employing conventional III-V junctions we report a classical calculation of conduction and valence band edge and the electron and hole densities. It is shown that the optimum performance can be achieved by employing AlGaAs /AlGaAs/InGaAs monolithic cascade solar cells, we have established these calculations by solving the Poisson equation within the framework of the Nextnano.

  9. Development of the GA-4 and GA-9 legal weight truck spent fuel casks

    International Nuclear Information System (INIS)

    Grenier, R.M.; Meyer, R.J.; Mings, W.J.

    1993-01-01

    General Atomics (GA) has designed two new truck casks under contract to the U.S. Department of Energy as part of the Office of Civilian Radioactive Waste Management (OCRWM) Cask System Development Program. The GA-4 and GA-9 Casks, when licensed by the U.S. Nuclear Regulatory Commission, will transport intact spent fuel assemblies from commercial nuclear reactor sites to a monitored retrievable storage facility or permanent repository. (J.P.N.)

  10. Crystal Structures of GaN Nanodots by Nitrogen Plasma Treatment on Ga Metal Droplets

    Directory of Open Access Journals (Sweden)

    Yang-Zhe Su

    2018-06-01

    Full Text Available Gallium nitride (GaN is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111 by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiNx layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.

  11. Investigation of localization effect in GaN-rich InGaN alloys and ...

    Indian Academy of Sciences (India)

    Abstract. The temperature-dependent PL properties of GaN-rich InxGa1−xN alloys is investigated and S-shaped temperature dependence is observed in all InGaN samples. It is found that the origin of localization effect in samples. A and B are different from that in sample C. For samples A and B, In content fluctuations ...

  12. Simplified 2DEG carrier concentration model for composite barrier AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Das, Palash; Biswas, Dhrubes

    2014-01-01

    The self consistent solution of Schrodinger and Poisson equations is used along with the total charge depletion model and applied with a novel approach of composite AlGaN barrier based HEMT heterostructure. The solution leaded to a completely new analytical model for Fermi energy level vs. 2DEG carrier concentration. This was eventually used to demonstrate a new analytical model for the temperature dependent 2DEG carrier concentration in AlGaN/GaN HEMT

  13. Site-controlled InGaN/GaN single-photon-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lei; Deng, Hui, E-mail: dengh@umich.edu [Department of Physics, University of Michigan, 450 Church St., Ann Arbor, Michigan 48109 (United States); Teng, Chu-Hsiang; Ku, Pei-Cheng, E-mail: peicheng@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)

    2016-04-11

    We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots. The device is fabricated from a planar light-emitting diode structure containing a single InGaN quantum well, using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

  14. Core level photoelectron spectroscopy of LiGaS2 and Ga-S bonding in complex sulfides

    International Nuclear Information System (INIS)

    Atuchin, V.V.; Isaenko, L.I.; Kesler, V.G.; Lobanov, S.I.

    2010-01-01

    The electronic parameters of the lithium thiogallate LiGaS 2 have been evaluated by X-ray photoelectron spectroscopy (XPS). Spectral features of all constituent element core levels and Auger lines have been considered. The Ga-S bonding effects in Ga-bearing sulfide crystals have been discussed using binding energy difference Δ 2p (S-Ga) = BE(S 2p) - BE(Ga 3d) as a representative parameter to quantify the valence electron shift from gallium to sulfur atoms. The value Δ 2p (S-Ga) = 141.9 eV found for LiGaS 2 is very close to that evaluated for AgGaS 2 . This relation is an indicator of closely coincident ionicity of Ga-S bonds in LiGaS 2 and AgGaS 2 .

  15. Core level photoelectron spectroscopy of LiGaS{sub 2} and Ga-S bonding in complex sulfides

    Energy Technology Data Exchange (ETDEWEB)

    Atuchin, V.V., E-mail: atuchin@thermo.isp.nsc.r [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, 13, Lavrentieva Ave., Novosibirsk 90, 630090 (Russian Federation); Isaenko, L.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Kesler, V.G. [Laboratory of Physical Bases of Integrated Microelectronics, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Lobanov, S.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 90, 630090 (Russian Federation)

    2010-05-14

    The electronic parameters of the lithium thiogallate LiGaS{sub 2} have been evaluated by X-ray photoelectron spectroscopy (XPS). Spectral features of all constituent element core levels and Auger lines have been considered. The Ga-S bonding effects in Ga-bearing sulfide crystals have been discussed using binding energy difference {Delta}{sub 2p}(S-Ga) = BE(S 2p) - BE(Ga 3d) as a representative parameter to quantify the valence electron shift from gallium to sulfur atoms. The value {Delta}{sub 2p}(S-Ga) = 141.9 eV found for LiGaS{sub 2} is very close to that evaluated for AgGaS{sub 2}. This relation is an indicator of closely coincident ionicity of Ga-S bonds in LiGaS{sub 2} and AgGaS{sub 2}.

  16. 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)

  17. 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

  18. 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.

  19. Enhanced optical output power of InGaN/GaN light-emitting diodes grown on a silicon (111) substrate with a nanoporous GaN layer.

    Science.gov (United States)

    Lee, Kwang Jae; Chun, Jaeyi; Kim, Sang-Jo; Oh, Semi; Ha, Chang-Soo; Park, Jung-Won; Lee, Seung-Jae; Song, Jae-Chul; Baek, Jong Hyeob; Park, Seong-Ju

    2016-03-07

    We report the growth of InGaN/GaN multiple quantum wells blue light-emitting diodes (LEDs) on a silicon (111) substrate with an embedded nanoporous (NP) GaN layer. The NP GaN layer is fabricated by electrochemical etching of n-type GaN on the silicon substrate. The crystalline quality of crack-free GaN grown on the NP GaN layer is remarkably improved and the residual tensile stress is also decreased. The optical output power is increased by 120% at an injection current of 20 mA compared with that of conventional LEDs without a NP GaN layer. The large enhancement of optical output power is attributed to the reduction of threading dislocation, effective scattering of light in the LED, and the suppression of light propagation into the silicon substrate by the NP GaN layer.

  20. 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.

  1. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    International Nuclear Information System (INIS)

    Li Yanbo; Zhang Yang; Zhang Yuwei; Wang Baoqiang; Zhu Zhanping; Zeng Yiping

    2012-01-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (Ga Sb ) defect.

  2. Current transport in graphene/AlGaN/GaN vertical heterostructures probed at nanoscale.

    Science.gov (United States)

    Fisichella, Gabriele; Greco, Giuseppe; Roccaforte, Fabrizio; Giannazzo, Filippo

    2014-08-07

    Vertical heterostructures combining two or more graphene (Gr) layers separated by ultra-thin insulating or semiconductor barriers represent very promising systems for next generation electronics devices, due to the combination of high speed operation with wide-range current modulation by a gate bias. They are based on the specific mechanisms of current transport between two-dimensional-electron-gases (2DEGs) in close proximity. In this context, vertical devices formed by Gr and semiconductor heterostructures hosting an "ordinary" 2DEG can be also very interesting. In this work, we investigated the vertical current transport in Gr/Al(0.25)Ga(0.75)N/GaN heterostructures, where Gr is separated from a high density 2DEG by a ∼ 24 nm thick AlGaN barrier layer. The current transport from Gr to the buried 2DEG was characterized at nanoscale using conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM). From these analyses, performed both on Gr/AlGaN/GaN and on AlGaN/GaN reference samples using AFM tips with different metal coatings, the Gr/AlGaN Schottky barrier height ΦB and its lateral uniformity were evaluated, as well as the variation of the carrier densities of graphene (ngr) and AlGaN/GaN 2DEG (ns) as a function of the applied bias. A low Schottky barrier (∼ 0.40 eV) with excellent spatial uniformity was found at the Gr/AlGaN interface, i.e., lower compared to the measured values for metal/AlGaN contacts, which range from ∼ 0.6 to ∼ 1.1 eV depending on the metal workfunction. The electrical behavior of the Gr/AlGaN contact has been explained by Gr interaction with AlGaN donor-like surface states located in close proximity, which are also responsible of high n-type Gr doping (∼ 1.3 × 10(13) cm(-2)). An effective modulation of ns by the Gr Schottky contact was demonstrated by capacitance analysis under reverse bias. From this basic understanding of transport properties in Gr/AlGaN/GaN heterostructures, novel vertical field effect

  3. Behavior of misfit dislocations in semipolar InGaN/GaN grown by MOVPE

    Energy Technology Data Exchange (ETDEWEB)

    Kuwahara, Takaaki [Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Kuwano, Noriyuki [Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Kurisu, Akihiko; Okada, Narihito; Tadatomo, Kazuyuki [Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611 (Japan)

    2012-03-15

    A microstructure in an InGaN/GaN layer grown at the semipolar direction was observed in detail by means of transmission electron microscopy (TEM) in order to analyze the behaviour of dislocations. A (11 anti 22) GaN layer was first deposited on a maskless r (1 anti 102)-plane patterned-substrate, and then an In{sub x} Ga{sub 1-x}N (x =0.10, 0.24) was overgrown to be about 1 {mu}m in thickness. Dislocations near the interface of InGaN/GaN are classified into several types: 1 Threading dislocations lying on (0001). 2. Misfit dislocations lying on the interface of InGaN/GaN. 3. Dislocations along [1 anti 100] at a certain distance from the interface. 4. Dislocations newly formed at the interface and developing along [11 anti 20] on (0001). 5. Partial dislocations accompanied with a stacking fault on (0001). It was found that the misfit dislocations are arrayed in pairs at the direction along [1 anti 100] on the interface of (11 anti 22). Burgers vector of the misfit dislocations was found to be B = <2 anti 1 anti 13>/3. In case of B = [ anti 1 anti 123]/3, they are edge dislocations. The densities of dislocations and stacking faults increase with the In-content in InGaN. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Binding of biexcitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, Vygantas; Birkedal, Dan; Langbein, Wolfgang Werner

    1997-01-01

    Properties of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices are studied using linear and nonlinear optical techniques. In superlattices with miniband halfwidths less than the exciton binding energy, the biexciton binding energy is found to be the same as in the noninte......Properties of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices are studied using linear and nonlinear optical techniques. In superlattices with miniband halfwidths less than the exciton binding energy, the biexciton binding energy is found to be the same...

  5. 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.

  6. Growth mechanism of InGaN nanodots on three-dimensional GaN structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Donghwy; Min, Daehong; Nam, Okhyun [Department of Nano-Optical Engineering, Convergence Center for Advanced Nano-Semiconductor (CANS), Korea Polytechnic University (KPU), Siheung-si, Gyeonggi-do (Korea, Republic of)

    2017-07-15

    In this study, we investigated the growth mechanism of indium gallium nitride (InGaN) nanodots (NDs) and an InGaN layer, which were simultaneously formed on a three-dimensional (3D) gallium nitride (GaN) structure, having (0001) polar, (11-22) semi-polar, and (11-20) nonpolar facets. We observed the difference in the morphological and compositional properties of the InGaN structures. From the high resolution transmission electron microscopy (HR-TEM) images, it can be seen that the InGaN NDs were formed only on the polar and nonpolar facets, whereas an InGaN layer was formed on the semi-polar facet. The indium composition variation in all the InGaN structures was observed using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray spectroscopy (EDS). The different growth mechanism can be explained by two reasons: (i) The difference in the diffusivities of indium and gallium adatoms at each facet of 3D GaN structure; and (ii) the difference in the kinetic Wulff plots of polar, semi-polar, and nonpolar GaN planes. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. GA-4/GA-9 honeycomb impact limiter tests and analytical model

    International Nuclear Information System (INIS)

    Koploy, M.A.; Taylor, C.S.

    1991-01-01

    General Atomics (GA) has a test program underway to obtain data on the behavior of a honeycomb impact limiter. The program includes testing of small samples to obtain basic information, as well as testing of complete 1/4-scale impact limiters to obtain load-versus-deflection curves for different crush orientations. GA has used the test results to aid in the development of an analytical model to predict the impact limiter loads. The results also helped optimize the design of the impact limiters for the GA-4 and GA-9 Casks

  8. 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)

  9. The Effects of Climate Change on Variability of the Growing Seasons in the Elbe River Lowland, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Potopová, V.; Zahradníček, Pavel; Türkot, L.; Štěpánek, Petr; Soukup, J.

    2015-01-01

    Roč. 2015, č. 546920 (2015), s. 546920 ISSN 1687-9309 R&D Projects: GA MŠk(CZ) EE2.3.20.0248 Institutional support: RVO:67179843 Keywords : Central Europe * extremes * climate change * growing seasons * Elbe River Lowland Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.107, year: 2015

  10. Occurrence of the Kessler’s gudgeon Romanogobio kesslerii (Dybowski, 1862) (Cyprinidae) in the Upper Vistula River (Poland)

    Czech Academy of Sciences Publication Activity Database

    Nowak, M.; Klaczak, A.; Szczerbik, P.; Mendel, Jan; Popek, W.

    2014-01-01

    Roč. 30, č. 5 (2014), s. 1062-1064 ISSN 0175-8659 R&D Projects: GA ČR GP206/09/P608 Institutional support: RVO:68081766 Keywords : Kessler's gudgeon * Upper Vistula River Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 0.867, year: 2014

  11. The recent distribution and abundance of non-native Neogobius fishes in the Slovak section of the River Danube

    Czech Academy of Sciences Publication Activity Database

    Jurajda, Pavel; Černý, J.; Polačik, Matej; Valová, Zdenka; Janáč, Michal; Blažek, R.; Ondračková, Markéta

    2005-01-01

    Roč. 21, č. 4 (2005), s. 319-323 ISSN 0175-8659 R&D Projects: GA ČR GP524/05/P291 Institutional research plan: CEZ:AV0Z60930519 Keywords : fish * River Danube Subject RIV: EG - Zoology Impact factor: 0.563, year: 2005

  12. Determination of 68Ga production parameters by different reactions ...

    Indian Academy of Sciences (India)

    Gallium-68 (1/2 = 68 min, + = 89%) is an important positron-emitting radionuclide for positron emission tomography and used in nuclear medicine for diagnosing tumours. This study gives a suitable reaction to produce 68Ga. Gallium-68 excitation function via 68Zn(, ) 68Ga, 68Zn(, 2) 68Ga, 70Zn(, 3) 68Ga and ...

  13. 78 FR 31988 - Atomic Safety and Licensing Board; In the Matter of Charlissa C. Smith (Denial of Senior Reactor...

    Science.gov (United States)

    2013-05-28

    ... hearing will be held in Room A of the Augusta Public Library, 823 Telfair Street, Augusta, GA 30901. It... Regulatory Commission's Agencywide Documents Access and Management System (ADAMS), which can be accessed through http://www.nrc.gov/reading-rm/adams.html#web-based-adams . General information regarding...

  14. Endogenous gibberellins in Arabidopsis thaliana and possible steps blocked in the biosynthetic pathways of the semidwarf ga4 and ga5 mutants

    International Nuclear Information System (INIS)

    Talon, M.; Zeevaart, J.A.D.; Koornneef, M.

    1990-01-01

    Twenty gibberellins (GAs) have been identified in extracts from shoots of the Landsberg erecta line of Arabidopsis thaliana by full-scan gas chromatography-mass spectrometry and Kovats retention indices. Eight of them are members of the early-13-hydroxylation pathway (GA 53 , GA 44 , GA 19 , GA 17 , GA 20 , GA 1 , GA 29 , and GA 8 ), six are members of the early-3-hydroxylation pathway (GA 37 , GA 27 , GA 36 , GA 13 , GA 4 , and GA 34 ), and the remaining six are members of the non-3,13-hydroxylation pathway (GA 12 , GA 15 , GA 24 , GA 25 , GA 9 , and GFA 51 ). Seven of these GAs were quantified in the Landsberg erecta line of Arabidopsis and in the semidwarf ga4 and ga5 mutants by gas chromatography-selected ion monitoring (SIM) using internal standards. The relative levels of the remaining 13 GAs were compared by the use of ion intensities only. The growth-response data, as well as the accumulation of GA 9 in the ga4 mutant, indicate that GA 9 is not active in Arabidopsis, but it must be 3β-hydroxytlated to GA 4 to become bioactive. It is concluded that the reduced levels of the 3β-hydroxy-GAs, GA 1 and GA 4 , are the cause of the semidwarf growth habit of both mutants

  15. 33 CFR 117.734 - Navesink River (Swimming River).

    Science.gov (United States)

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Navesink River (Swimming River). 117.734 Section 117.734 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY... (Swimming River). The Oceanic Bridge, mile 4.5, shall open on signal; except that, from December 1 through...

  16. Skjern River Restoration Counterfactual

    DEFF Research Database (Denmark)

    Clemmensen, Thomas Juel

    2014-01-01

    In 2003 the Skjern River Restoration Project in Denmark was awarded the prestigious Europa Nostra Prize for ‘conserving the European cultural heritage’ (Danish Nature Agency 2005). In this case, however, it seems that the conservation of one cultural heritage came at the expense of another cultural...... this massive reconstruction work, which involved moving more than 2,7 million cubic meters of earth, cause a lot of ‘dissonance’ among the local population, the resulting ‘nature’ and its dynamic processes are also constantly compromising the preferred image of the restored landscape (Clemmensen 2014......). The presentation offers insight into an on-going research and development project - Skjern River Restoration Counterfactual, which question existing trends and logics within nature restoration. The project explores how the Skjern River Delta could have been ‘restored’ with a greater sensibility for its cultural...

  17. Missouri River 1943 Compact Line

    Data.gov (United States)

    Iowa State University GIS Support and Research Facility — Flood Control, Bank Stabilization and development of a navigational channel on the Missouri River had a great impact on the river and adjacent lands. The new...

  18. Haw River PFCs Data Set

    Data.gov (United States)

    U.S. Environmental Protection Agency — PFAS concentrations in river and drinking water in and around the Haw River in North Carolina. This dataset is associated with the following publication: Sun, M., E....

  19. 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.)

  20. Growth and characterization of GaAs-GaSb III-V pseudo-binary nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Schamp, C.T. [Cerium Laboratories, Austin, TX 78741 (United States); Jesser, W.A. [Department of Materials Science and Engineering, 116 Engineer' s Way, University of Virginia, Charlottesville, VA 22904 (United States)

    2008-07-01

    The GaAs-GaSb pseudo-binary materials system presents an interesting challenge for growth because of 1) the existence of a miscibility gap in the solid-solid portion of the equilibrium phase diagram, and 2) the large differences in vapor pressure between the column III element, Ga, and the column V elements, As and Sb. To overcome these challenges in the growth of GaAs, GaSb, and Ga{sub 50}As{sub x}Sb{sub 50-x} alloy nanoparticles, single- and dual-target pulsed laser deposition (PLD) techniques were implemented using an Nd:YAG laser operated with a harmonic generator to utilize the second harmonic wavelength (532 nm) and a combination of the fundamental and the second harmonic wavelengths (1064 nm+532 nm). The nanoparticles were collected on amorphous carbon films for subsequent characterization by transmission electron microscopy. The analysis shows that single phase GaAs-rich Ga{sub 50}As{sub x}Sb{sub 50-x} (28>x>50) nanoparticles and nanocrystalline films have been formed through dual-target, single-wavelength (532 nm) pulsed laser ablation. Interestingly, through the ablation of the single component targets, two-phase particles were also found to form. These two phase particles resemble ''nano-ice cream cones'' with solid cones of either GaAs or GaSb with a spherical ''ice cream'' ball of Ga located at the wide portion of the cone, which is either an amorphous phase or liquid phase. Through an analysis by STEM-EDX spectroscopy, these particles are found to be consistant with this model. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

    Energy Technology Data Exchange (ETDEWEB)

    Kalygina, V. M., E-mail: Kalygina@ngs.ru; Vishnikina, V. V.; Petrova, Yu. S.; Prudaev, I. A.; Yaskevich, T. M. [National Research Tomsk State University (Russian Federation)

    2015-03-15

    We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga{sub 2}O{sub 3}-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga{sub 2}O{sub 3} crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga{sub 2}O{sub 3} crystallites and become transparent. Under illumination of the Ga{sub 2}O{sub 3}-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga{sub 2}O{sub 3} film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga{sub 2}O{sub 3}-GaAs interface and in the Ga{sub 2}O{sub 3} film.

  2. 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.

  3. A new wire fabrication processing using high Ga content Cu-Ga compound in V3Ga compound superconducting wire

    International Nuclear Information System (INIS)

    Hishinuma, Yoshimitsu; Nishimura, Arata; Kikuchi, Akihiro; Iijima, Yasuo; Takeuchi, Takao

    2007-01-01

    A superconducting magnet system is also one of the important components in an advanced magnetic confinement fusion reactor. Then it is required to have a higher magnetic field property to confine and maintain steady-sate burning deuterium (D)-tritium (T) fusion plasma in the large interspace during the long term operation. Burning plasma is sure to generate 14 MeV fusion neutrons during deuterium-tritium reaction, and fusion neutrons will be streamed and penetrated to superconducting magnet through large ports with damping neutron energy. Therefore, it is necessary to consider carefully not only superconducting property but also neutron irradiation property in superconducting materials for use in a future fusion reactor, and a 'low activation and high field superconducting magnet' will be required to realize the fusion power plant beyond International Thermonuclear Experimental Reactor (ITER). V-based superconducting material has a much shorter decay time of induced radioactivity compared with the Nb-based materials. We thought that the V 3 Ga compound was one of the most promising materials for the 'low activation and higher field superconductors' for an advanced fusion reactor. However, the present critical current density (J c ) property of V 3 Ga compound wire is insufficient for apply to fusion magnet applications. We investigated a new route PIT process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V 3 Ga compound wire. (author)

  4. 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

  5. 68Ga-triacetylfusarinine C and 68Ga-ferrioxamine E for Aspergillus infection imaging: uptake specificity in various microorganisms

    NARCIS (Netherlands)

    Petrik, M.; Haas, H. de; Laverman, P.; Schrettl, M.; Franssen, G.M.; Blatzer, M.; Decristoforo, C.

    2014-01-01

    (68)Ga-triacetylfusarinine C ((68)Ga-TAFC) and (68)Ga-ferrioxamine E ((68)Ga-FOXE) showed excellent targeting properties in Aspergillus fumigatus rat infection model. Here, we report on the comparison of specificity towards different microorganisms and human lung cancer cells (H1299).The in vitro

  6. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

  7. Red to near-infrared emission from InGaN/GaN quantum-disks-in-nanowires LED

    KAUST Repository

    Ng, Tien Khee; Zhao, Chao; Shen, Chao; Jahangir, Shafat; Janjua, Bilal; Ben Slimane, Ahmed; Kang, Chun Hong; Syed, Ahad A.; Li, Jingqi; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Bhattacharya, Pallab K.; Ooi, Boon S.

    2014-01-01

    The InGaN/GaN quantum-disks-in-nanowire light-emitting diode (LED) with emission centered at ~830nm, the longest emission wavelength ever reported in the InGaN/GaN system, and spectral linewidth of 290nm, has been fabricated with p-side-down on a Cu substrate.

  8. 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.

  9. Stochastic Modelling of River Geometry

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Schaarup-Jensen, K.

    1996-01-01

    Numerical hydrodynamic river models are used in a large number of applications to estimate critical events for rivers. These estimates are subject to a number of uncertainties. In this paper, the problem to evaluate these estimates using probabilistic methods is considered. Stochastic models for ...... for river geometries are formulated and a coupling between hydraulic computational methods and numerical reliability methods is presented....

  10. The Gediz River fluvial archive

    NARCIS (Netherlands)

    Maddy, D.; Veldkamp, A.; Demir, T.; Gorp, van W.; Wijbrans, J.R.; Hinsbergen, van D.J.J.; Dekkers, M.J.; Schreve, D.; Schoorl, J.M.; Scaife, R.

    2017-01-01

    The Gediz River, one of the principal rivers of Western Anatolia, has an extensive Pleistocene fluvial archive that potentially offers a unique window into fluvial system behaviour on the western margins of Asia during the Quaternary. In this paper we review our work on the Quaternary Gediz River

  11. Electronic passivation of n- and p-type GaAs using chemical vapor deposited GaS

    Science.gov (United States)

    Tabib-Azar, Massood; Kang, Soon; Macinnes, Andrew N.; Power, Michael B.; Barron, Andrew R.; Jenkins, Phillip P.; Hepp, Aloysius F.

    1993-01-01

    We report on the electronic passivation of n- and p-type GaAs using CVD cubic GaS. Au/GaS/GaAs-fabricated metal-insulator-semiconductor (MIS) structures exhibit classical high-frequency capacitor vs voltage (C-V) behavior with well-defined accumulation and inversion regions. Using high- and low-frequency C-V, the interface trap densities of about 10 exp 11/eV per sq cm on both n- and p-type GaAs are determined. The electronic condition of GaS/GaAs interface did not show any deterioration after a six week time period.

  12. Raman Scattering analysis of InGaAs and AlGaAs superlattices grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Oeztuerk, N.; Bahceli, S.

    2010-01-01

    InGaAs/GaAs and AlGaAs/GaAs multiple quantum well structures were grown by molecular beam epitaxy and investigated by X-ray diffraction and micro Raman spectroscopy. Phonon modes are investigated in backscattering from (001) surface. In the measured micro Raman spectrum for both structure, phonon peaks can be resolved for GaAs. These are longitudinal optical (LO) mode at 293 cm - 1 and 294 cm - 1 for InGaAs and AlGaAs, respectively.

  13. Concentration changeability of phosphorus, calcium and magnesium in selected partial drainage basins of the River Drwęca

    Directory of Open Access Journals (Sweden)

    Pius Bożena

    2015-12-01

    Full Text Available The paper presents the results of the research conducted between November 2008 and October 2009. The research included seasonal dynamics of the flow and runoff of phosphorus compounds (TP and P-PO43-, as well as Ca2+ and Mg2+ from 13 partial drainage basins of the River Drwęca. Water levels were registered automatically every day by recorders, and measurements of the flow were conducted once a month. Major differences were found in the water abundance as indicated by specific discharges in individual, partial drainage basins: from 1.87 dm3 s-1 km-2 (Lubianka - a lower part of the River Drwęca drainage basin to 8.22 dm3 s-1 km-2 (Gizela - an upper part of the River Drwęca drainage basin. The studied rivers were characterised by very diverse average content of total phosphorus compounds: from 0.047 mg dm-3 (Iłga to 0.816 mg dm-3 (Sandela; calcium: from 47.18 mg dm-3 (Iłga to 131.65 mg dm-3 (Trynka; and magnesium: from 9.71 mg dm-3 (Wel to 36.76 mg dm-3 (Struga Rychnowska. Analysis of variance carried out on hydrochemical properties of the studied rivers divides the rivers into two separate groups: rivers with much higher content of phosphorus, calcium and magnesium compounds (Struga Rychnowska, Trynka, Ruziec, Lubianka, Kujawka, Sandela and Gizela, and a group of rivers with low content of these compounds (Brynica, Brodniczanka, Skarlanka, Wel, Iłga.

  14. The effect of river water circulation on the distribution and functioning of reservoir microbial communities as determined by a relative distance approach

    Czech Academy of Sciences Publication Activity Database

    Šimek, Karel; Comerma, M.; García, J. C.; Nedoma, Jiří; Marcé, R.; Armengol, J.

    2011-01-01

    Roč. 14, č. 1 (2011), s. 1-14 ISSN 1432-9840 R&D Projects: GA ČR(CZ) GA206/08/0015 Institutional research plan: CEZ:AV0Z60170517 Keywords : canyon-shaped reservoir * ongitudinal gradients * relative distance model * river-reservoir ecosystem * water circulation patterns * plankton succession * microbial dynamics Subject RIV: EE - Microbiology, Virology Impact factor: 3.495, year: 2011

  15. Significant performance enhancement in AlGaN/GaN high electron mobility transistor by high-κ organic dielectric

    International Nuclear Information System (INIS)

    Ze-Gao, Wang; Yuan-Fu, Chen; Cao, Chen; Ben-Lang, Tian; Fu-Tong, Chu; Xing-Zhao, Liu; Yan-Rong, Li

    2010-01-01

    The electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with and without high-κ organic dielectrics are investigated. The maximum drain current I D max and the maximum transconductance g m max of the organic dielectric/AlGaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare AlGaN/GaN HEMT, respectively. Both the threshold voltage V T and g m max of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the AlGaN/GaN HEMT by introducing the high-κ organic dielectric. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  16. Misfit dislocation reduction in InGaAs epilayers grown on porous GaAs substrates

    Czech Academy of Sciences Publication Activity Database

    Dimitrakopulos, G.P.; Bazioti, C.; Grym, Jan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Pacherová, Oliva; Komninou, Ph.

    2014-01-01

    Roč. 306, Jul (2014), s. 89-93 ISSN 0169-4332 R&D Projects: GA MŠk 7AMB12GR034 Institutional support: RVO:68378271 ; RVO:67985882 Keywords : compound semiconductors * InGaAs * porous substrate * misfit dislocations * strain Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.711, year: 2014

  17. Integrated photonic platform based on semipolar InGaN/GaN multiple section laser diodes

    KAUST Repository

    Shen, Chao

    2017-11-30

    The challenges to realizing III-nitride photonic integrated circuit (PIC) are discussed. Utilizing InGaN-based multi-section laser diode (LD) on semipolar GaN substrate, the seamless on-chip integration of III-nitride waveguide photodetector (WPD) in the visible regime has been demonstrated.

  18. Robust X-band LNAs in AlGaN/GaN technology

    NARCIS (Netherlands)

    Janssen, J.P.B.; Heijningen, M. van; Visser, G.C.; Rodenburg, M.; Johnson, H.K.; Uren, M.J.; Morvan, E.; Vliet, F.E. van

    2009-01-01

    Gallium-Nitride technology is known for its high power density and power amplifier designs, but is also very well suited to realise robust receiver components. This paper presents the design, realisation and measurement of two robust AlGaN/GaN low noise amplifiers. The two versions have been

  19. Robust X-band LNAs in AlGaN/GaN technology

    NARCIS (Netherlands)

    Janssen, J.P.B.; van Heiningen, M.; Visser, G.C.; Rodenburg, M.; Johnson, H.K.; Uren, M.J.; Morvan, E.; van Vliet, Frank Edward

    2009-01-01

    Abstract Gallium-Nitride technology is known for its high power density and power amplifier designs, but is also very well suited to realise robust receiver components. This paper presents the design, realisation and measurement of two robust AlGaN/GaN low noise amplifiers. The two versions have

  20. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2014-01-01

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact

  1. Characterization of recessed Ohmic contacts to AlGaN/GaN

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2015-01-01

    In this work the choice of appropriate test structures and characterization methods for recessed Ohmic contacts to AlGaN/GaN is discussed. It is shown that, in the worst-case scenario, the prevailing assumption of identical sheet resistance between and under the contacts can lead to errors of up to

  2. Integrated photonic platform based on semipolar InGaN/GaN multiple section laser diodes

    KAUST Repository

    Shen, Chao; Lee, Changmin; Ng, Tien Khee; Speck, James S.; Nakamura, Shuji; DenBaars, Steven P.; Ooi, Boon S.

    2017-01-01

    The challenges to realizing III-nitride photonic integrated circuit (PIC) are discussed. Utilizing InGaN-based multi-section laser diode (LD) on semipolar GaN substrate, the seamless on-chip integration of III-nitride waveguide photodetector (WPD) in the visible regime has been demonstrated.

  3. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  4. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light...

  5. Coherent dynamics of interwell excitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, V.; Birkedal, Dan; Langbein, Wolfgang Werner

    1997-01-01

    Coherent exciton dynamics in a GaAs/AlxGa1-xAs narrow-miniband superlattice is studied by spectrally resolved transient four-wave mixing. Coherent optical properties of the investigated structure are found to be strongly affected by the existence of two different heavy-hole excitonic states. One...

  6. Stability of AlGaN/GaN heterostructures after hydrogen plasma treatment

    Energy Technology Data Exchange (ETDEWEB)

    Babchenko, O., E-mail: oleg.babchenko@savba.sk [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Dzuba, J.; Lalinský, T. [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Vojs, M. [Institute of Electronics and Photonics STU, Ilkovičova 3, 812 19 Bratislava (Slovakia); Vincze, A. [International Laser Centre, Ilkovičova 3, 841 04 Bratislava (Slovakia); Ižák, T. [Institute of Physics AS CR, v.v.i., Cukrovarnicka 10, 162 53 Prague (Czech Republic); Vanko, G. [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia)

    2017-02-15

    Highlights: • AlGaN/GaNheterostructures with electric contacts were treated by hydrogen plasma. • No surface degradation after treatment was detected by SEM. • Hydrogen plasma caused increasing of sheet resistance up to 3.5 times after 60 min. • Incorporation of hydrogen in AlGaN sub-surface region was observed by SIMS. • Electrical measurements indicate hydrogen induced Schottky barrier lowering. - Abstract: We report on the investigation of low temperature (300 °C) hydrogen plasma treatment influence on the AlGaN/GaN heterostructures. This issue was raised in the frame of study on processes related to hybrid integration of diamond with GaN-based devices. At the same time, the capabilities of thin SiN{sub x} covering were investigated. The samples were exposed to low pressure hydrogen plasma ignited in the linear plasma system at low temperature. We analyze the surface morphology of samples by scanning electron microscopy while microstructural changes down to AlGaN/GaN interface were studied using secondary ion mass spectrometry. The sheet resistance, monitored using circular transmission line measurements, increases more than 3.5 times after 60 min treatment. The basic transport properties of the fabricated circular high electron mobility transistors after H{sub 2} plasma treatment were analyzed. The sheet resistance increasing was attributed to the decrease of effective mobility. Whilst, the observed Schottky barrier lowering indicates necessity of gate contact protection.

  7. Spin injection from Co2MnGa into an InGaAs quantum well

    DEFF Research Database (Denmark)

    Hickey, M. C.; Damsgaard, Christian Danvad; Holmes, S. N.

    2008-01-01

    We have demonstrated spin injection from a full Heusler alloy Co2MnGa thin film into a (100) InGaAs quantum well in a semiconductor light-emitting diode structure at a temperature of 5 K. The detection is performed in the oblique Hanle geometry, allowing quantification of the effective spin lifet...

  8. 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

  9. Micro-photoluminescence of GaAs/AlGaAs triple concentric quantum rings.

    Science.gov (United States)

    Abbarchi, Marco; Cavigli, Lucia; Somaschini, Claudio; Bietti, Sergio; Gurioli, Massimo; Vinattieri, Anna; Sanguinetti, Stefano

    2011-10-31

    A systematic optical study, including micro, ensemble and time resolved photoluminescence of GaAs/AlGaAs triple concentric quantum rings, self-assembled via droplet epitaxy, is presented. Clear emission from localized states belonging to the ring structures is reported. The triple rings show a fast decay dynamics, around 40 ps, which is expected to be useful for ultrafast optical switching applications.

  10. Photoluminescence studies of individual and few GaSb/GaAs quantum rings

    NARCIS (Netherlands)

    Young, M.P.; Woodhead, C.S.; Roberts, J.; Noori, Y.J.; Noble, M.T.; Krier, A.; Smakman, E.P.; Koenraad, P.M.; Hayne, M.; Young, R.J.

    2014-01-01

    We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at

  11. Carrier dynamics in submonolayer InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Zhang, Yating; Hvam, Jørn Märcher

    2006-01-01

    Carrier dynamics of submonolayer InGaAs/GaAs quantum dots (QDs) were studied by microphotoluminecence (MPL), selectively excited photoluminescence (SEPL), and time-resolved photoluminescence (TRPL). MPL and SEPL show the coexistence of localized and delocalized states, and different local phonon...

  12. 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.

  13. InAlGaAs/AlGaAs quantum wells: line widths, transition energies and segregation

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    2000-01-01

    We investigate the optical properties of InAlCaAs/AlGaAs quantum wells pseudomorphically grown on GaAs using molecular beam epitaxy (MBE). The transition energies, measured with photoluminescence (PL), are modelled solving the Schrodinger equation, and taking into account segregation in the group...

  14. A localized orbital description of ideal vacancies in GaP and GaSb

    International Nuclear Information System (INIS)

    Erbarut, E.; Tomak, M.

    1986-10-01

    Gaussian orbitals of s and p symmetry and an empirical pseudopotential Hamiltonian is employed for the study of electronic structures of ideal vacancies in GaP and GaSb. A reasonably accurate description of band structures and densities of states are attained. (author)

  15. Achieving Room Temperature Orange Lasing Using InGaP/InAlGaP Diode Laser

    KAUST Repository

    Al-Jabr, Ahmad

    2015-09-28

    We demonstrated the first orange laser diode at room temperature with a decent total output power of ∼46mW and lasing wavelength of 608nm, using a novel strain-induced quantum well intermixing in InGaP/InAlGaP red laser structure.

  16. Ka-Band AlGaN/GaN HEMT high power and driver amplifier MMICs

    NARCIS (Netherlands)

    Heijningen, M. van; Vliet, F.E. van; Quay, R.; Raay, F. van; Kiefer, R.; Mueller, S.; Krausse, D.; Seelmann-Eggebert, M.; Mikulla, M.; Schlechtweg, M.

    2005-01-01

    In this paper the MMIC technology, design and characterization of a high power amplifier and driver amplifier MMIC at 30 GHz in AlGaN/GaN HEMT technology are presented. The MMICs are designed using CPW technology on a 390 μm thick SiC substrate. The measured small-signal gain of the driver is 14 dB

  17. Exciton dynamics in GaAs/AlxGa1-xAs quantum wells

    DEFF Research Database (Denmark)

    Litvinenko, K.; Birkedal, Dan; Lyssenko, V. G.

    1999-01-01

    The changes induced in the optical absorption spectrum of a GaAs/AlxGa1-xAs multiple quantum well due to a photoexcited carrier distribution are reexamined. We use a femtosecond pump-probe technique to excite excitons and free electron-hole pairs. We find that for densities up to 10(11) cm(-2...

  18. GaAsP solar cells on GaP/Si with low threading dislocation density

    International Nuclear Information System (INIS)

    Yaung, Kevin Nay; Vaisman, Michelle; Lang, Jordan; Lee, Minjoo Larry

    2016-01-01

    GaAsP on Si tandem cells represent a promising path towards achieving high efficiency while leveraging the Si solar knowledge base and low-cost infrastructure. However, dislocation densities exceeding 10"8 cm"−"2 in GaAsP cells on Si have historically hampered the efficiency of such approaches. Here, we report the achievement of low threading dislocation density values of 4.0–4.6 × 10"6 cm"−"2 in GaAsP solar cells on GaP/Si, comparable with more established metamorphic solar cells on GaAs. Our GaAsP solar cells on GaP/Si exhibit high open-circuit voltage and quantum efficiency, allowing them to significantly surpass the power conversion efficiency of previous devices. The results in this work show a realistic path towards dual-junction GaAsP on Si cells with efficiencies exceeding 30%.

  19. AlGaN/InGaN Nitride Based Modulation Doped Field Effect Transistor

    National Research Council Canada - National Science Library

    Blair, S

    2003-01-01

    The goal of the proposed work is to investigate the potential advantages of the InGaN channel as a host of the 2DEG and to address the material related problems facing this ternary alloy in the AlGaN...

  20. Magnetic field-dependent of binding energy in GaN/InGaN/GaN spherical QDQW nanoparticles

    International Nuclear Information System (INIS)

    El Ghazi, Haddou; Jorio, Anouar; Zorkani, Izeddine

    2013-01-01

    Simultaneous study of magnetic field and impurity's position effects on the ground-state shallow-donor binding energy in GaN|InGaN|GaN (core|well|shell) spherical quantum dot–quantum well (SQDQW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated within the framework of the effective-mass approximation and an infinite deep potential describing the quantum confinement effect. A Ritz variational approach is used taking into account of the electron-impurity correlation and the magnetic field effect in the trial wave-function. It appears that the binding energy depends strongly on the external magnetic field, the impurity's position and the structure radius. It has been found that: (i) the magnetic field effect is more marked in large layer than in thin layer and (ii) it is more pronounced in the spherical layer center than in its extremities

  1. 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.

  2. GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates

    Science.gov (United States)

    Gutiérrez, M.; Lloret, F.; Jurczak, P.; Wu, J.; Liu, H. Y.; Araújo, D.

    2018-05-01

    The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

  3. N-polar GaN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor formed on sapphire substrate with minimal step bunching

    Science.gov (United States)

    Prasertsuk, Kiattiwut; Tanikawa, Tomoyuki; Kimura, Takeshi; Kuboya, Shigeyuki; Suemitsu, Tetsuya; Matsuoka, Takashi

    2018-01-01

    The metal-insulator-semiconductor (MIS) gate N-polar GaN/AlGaN/GaN high-electron-mobility transistor (HEMT) on a (0001) sapphire substrate, which can be expected to operate with lower on-resistance and more easily work on the pinch-off operation than an N-polar AlGaN/GaN HEMT, was fabricated. For suppressing the step bunching and hillocks peculiar in the N-polar growth, a sapphire substrate with an off-cut angle as small as 0.8° was introduced and an N-polar GaN/AlGaN/GaN HEMT without the step bunching was firstly obtained by optimizing the growth conditions. The previously reported anisotropy of transconductance related to the step was eliminated. The pinch-off operation was also realized. These results indicate that this device is promising.

  4. 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

  5. Near-field microscopy of waveguide architectures of InGaN/GaN diode lasers

    Science.gov (United States)

    Friede, Sebastian; Tomm, Jens W.; Kühn, Sergei; Hoffmann, Veit; Wenzel, Hans; Weyers, Markus

    2016-11-01

    Waveguide (WG) architectures of 420 nm emitting InGaN/GaN diode lasers are analyzed by photoluminescence and photocurrent spectroscopy using a nearfield scanning optical microscope that scans along their front facets. The components of the ‘optical active cavity’, quantum wells, WGs, and cladding layers are individually inspected with a spatial resolution of ∼100 nm. Separate analysis of the p- and n-sections of the WG was achieved, and reveals defect levels in the p-part. Moreover, it is demonstrated that the homogeneity of the n-WG section directly affects the quantum wells that are grown on top of this layer. Substantially increased carrier capture efficiencies into InGaN/GaN-WGs compared to GaN-WGs are demonstrated.

  6. A hole accelerator for InGaN/GaN light-emitting diodes

    Science.gov (United States)

    Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

    2014-10-01

    The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

  7. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    International Nuclear Information System (INIS)

    Bietti, Sergio; Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano; Fedorov, Alexey

    2014-01-01

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E A =1.31±0.15 eV, a diffusivity prefactor of D 0  = 0.53(×2.1±1) cm 2 s −1 that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  8. Optimization of the GaAs et GaAs/Si annealing using halogen lamp flashes

    International Nuclear Information System (INIS)

    Blanck, H.

    1989-01-01

    The aim of the work is to check whether the flash annealing of GaAs and GaAs/Si, using halogen lamps, allows an improvement in the results obtained by usual methods. The electrical activation, defects behavior and results uniformity are studied. The results on the activation and diffusion of implanted impurities are shown to be equivalent to those obtained with classical annealing methods. However, residual impurities (or defects) diffusion phenomena are restrained by the flash annealing technique. The Hall effect cartographic measurements showed an improvement of the uniformity of the implanted coating surface resistance. Flash annealing is a suitable method for the Si activation in GaAs. It allows an improvement of the GaAs results obtained with standard techniques, as well as the formation, by means of ion implantation, of active zones in the GaAs/Si layers [fr

  9. Strain-dependent magnetic anisotropy in GaMnAs on InGaAs templates

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim; Glunk, Michael; Schwaiger, Stephan; Dreher, Lukas; Schoch, Wladimir; Sauer, Rolf; Limmer, Wolfgang [Institut fuer Halbleiterphysik, Universitaet Ulm, 89069 Ulm (Germany)

    2008-07-01

    We have systematically studied the influence of strain on the magnetic anisotropy of GaMnAs by means of HRXRD reciprocal space mapping and angle-dependent magnetotransport. For this purpose, a series of GaMnAs layers with Mn contents of {proportional_to}5% was grown by low-temperature MBE on relaxed InGaAs/GaAs templates with different In concentrations, enabling us to vary the strain in the GaMnAs layers continuously from tensile to compressive, including the unstrained state. Considering both, as-grown and annealed samples, the anisotropy parameter describing the uniaxial out-of-plane magnetic anisotropy has been found to vary linearly with hole density and strain. As a consequence, the out-of-plane direction gradually undergoes a transition from a magnetic hard axis to a magnetic easy axis from compressive to tensile strain.

  10. GaMnAs on patterned GaAs(001) substrates: Growth and magnetotransport

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim; Glunk, Michael; Hummel, Thomas; Schoch, Wladimir; Limmer, Wolfgang; Sauer, Rolf [Institut fuer Halbleiterphysik, Universitaet Ulm, 89069 Ulm (Germany)

    2007-07-01

    A new type of GaMnAs microstructures with laterally confined electronic and magnetic properties has been realized in a bottom-up procedure by growing GaMnAs films on [1 anti 10]-oriented ridge structures with (113)A sidewalls and (001) top layers prepared on GaAs(001) substrates. Previous studies on planar GaMnAs samples have revealed different incorporation of Mn and excess As in (001) and (113)A layers. Accordingly, temperature- and field-dependent magnetotransport measurements on the overgrown ridge structures clearly demonstrate the coexistence of electronic and magnetic properties specific for (001) and (113)A GaMnAs in one single sample. This introduces an additional degree of freedom in the development of new functional structures.

  11. Angular dependent XPS study of surface band bending on Ga-polar n-GaN

    Science.gov (United States)

    Huang, Rong; Liu, Tong; Zhao, Yanfei; Zhu, Yafeng; Huang, Zengli; Li, Fangsen; Liu, Jianping; Zhang, Liqun; Zhang, Shuming; Dingsun, An; Yang, Hui

    2018-05-01

    Surface band bending and composition of Ga-polar n-GaN with different surface treatments were characterized by using angular dependent X-ray photoelectron spectroscopy. Upward surface band bending of varying degree was observed distinctly upon to the treatment methods. Besides the nitrogen vacancies, we found that surface states of oxygen-containing absorbates (O-H component) also contribute to the surface band bending, which lead the Fermi level pined at a level further closer to the conduction band edge on n-GaN surface. The n-GaN surface with lower surface band bending exhibits better linear electrical properties for Ti/GaN Ohmic contacts. Moreover, the density of positively charged surface states could be derived from the values of surface band bending.

  12. Noise performance in AlGaN/GaN HEMTs under high drain bias

    International Nuclear Information System (INIS)

    Pang Lei; Pu Yan; Lin Xinyu; Wang Liang; Liu Jian

    2009-01-01

    The advent of fully integrated GaN PA-LNA circuits makes it meaningful to investigate the noise performance under high drain bias. However, noise performance of AlGaN/GaN HEMTs under high bias has not received worldwide attention in theoretical studies due to its complicated mechanisms. The noise value is moderately higher and its rate of increase is fast with increasing high voltage. In this paper, several possible mechanisms are proposed to be responsible for it. Impact ionization under high electric field incurs great fluctuation of carrier density, which increases the drain diffusion noise. Besides, higher gate leakage current related shot noise and a more severe self-heating effect are also contributors to the noise increase at high bias. Analysis from macroscopic and microscopic perspectives can help us to design new device structures to improve noise performance of AlGaN/GaN HEMTs under high bias. (semiconductor devices)

  13. Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors.

    Science.gov (United States)

    Fontserè, A; Pérez-Tomás, A; Placidi, M; Llobet, J; Baron, N; Chenot, S; Cordier, Y; Moreno, J C; Jennings, M R; Gammon, P M; Fisher, C A; Iglesias, V; Porti, M; Bayerl, A; Lanza, M; Nafría, M

    2012-10-05

    AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

  14. Does GaH5 exist?

    Science.gov (United States)

    Speakman, Lucas D.; Turney, Justin M.; Schaefer, Henry F.

    2005-11-01

    The existence or nonexistence of GaH5 has been widely discussed [N. M. Mitzel, Angew. Chem. Int. Ed. 42, 3856 (2003)]. Seven possible structures for gallium pentahydride have been systematically investigated using ab initio electronic structure theory. Structures and vibrational frequencies have been determined employing self-consistent field, coupled cluster including all single and double excitations (CCSD), and CCSD with perturbative triples levels of theory, with at least three correlation-consistent polarized-valence-(cc-pVXZ and aug-cc-pVXZ) type basis sets. The X˜A'1 state for GaH5 is predicted to be weakly bound complex 1 between gallane and molecular hydrogen, with Cs symmetry. The dissociation energy corresponding to GaH5→GaH3+H2 is predicted to be De=2.05kcalmol-1. The H-H stretching fundamental is predicted to be v =4060cm-1, compared to the tentatively assigned experimental feature of Wang and Andrews [J. Phys. Chem. A 107, 11371 (2003)] at 4087cm-1. A second Cs structure 2 with nearly equal energy is predicted to be a transition state, corresponding to a 90° rotation of the H2 bond. Thus the rotation of the hydrogen molecule is essentially free. However, hydrogen scrambling through the C2v structure 3 seems unlikely, as the activation barrier for scrambling is at least 30kcalmol-1 higher in energy than that for the dissociation of GaH5 to GaH3 and H2. Two additional structures consisting of GaH3 with a dihydrogen bond perpendicular to gallane (C3v structure 4) and an in-plane dihydrogen bond [Cs(III) structure 5] were also examined. A C3v symmetry second-order saddle point has nearly the same energy as the GaH3+H2 dissociation limit, while the Cs(III) structure 5 is a transition structure to the C3v structure. The C4v structure 6 and the D3h structure 7 are much higher in energy than GaH3+H2 by 88 and 103kcalmol-1, respectively.

  15. Geomorphic classification of rivers

    Science.gov (United States)

    J. M. Buffington; D. R. Montgomery

    2013-01-01

    Over the last several decades, environmental legislation and a growing awareness of historical human disturbance to rivers worldwide (Schumm, 1977; Collins et al., 2003; Surian and Rinaldi, 2003; Nilsson et al., 2005; Chin, 2006; Walter and Merritts, 2008) have fostered unprecedented collaboration among scientists, land managers, and stakeholders to better understand,...

  16. Savannah River Technology Center

    International Nuclear Information System (INIS)

    1993-01-01

    This is a monthly progress report from the Savannah River Laboratory for the month of January 1993. It has sections with work in the areas of reactor safety, tritium processes and absorption, separations programs and wastes, environmental concerns and responses, waste management practices, and general concerns

  17. Alligator Rivers Region

    International Nuclear Information System (INIS)

    1992-01-01

    An introduction to the Alligator Rivers Region is presented. It contains general information regarding the physiography, climate, hydrology and mining of the region. The Alligator Rivers Region is within an ancient basin, the Pine Creek Geosyncline, which has an area of approximately 66000 km 2 . The Geosyncline has a history of mineral exploitation dating back to 1865, during which time 16 metals have been extracted (silver, arsenic, gold, bismuth, cadmium, cobalt, copper, iron, manganese, molybdenum, lead, tin, tantalum, uranium, tungsten, zinc). Uranium exploration in the Pine Creek Geosyncline was stimulated by the discovery in 1949 of secondary uranium mineralisation near Rum June, 70 km south-east of Darwin. This was followed by a decade of intense exploration activity resulting in the discoveries of economic uranium ore bodies at Rum Jungle and in the upper reaches of the South Alligator River Valley. All the known major uranium deposits of the East Alligator River uranium field have been discovered since 1969. The present known resources of the Geosyncline are approximately 360 000 tonnes of contained U 3 O 8 . 2 refs., 2 figs., 1 tab

  18. Discover the Nile River

    Science.gov (United States)

    Project WET Foundation, 2009

    2009-01-01

    Bordering on the Fantastic. As the longest river on earth, the Nile passes through 10 countries. Presented through a wide range of activities and a winning array of games, it's also unsurpassed at taking young minds into exploring the world of water, as well as natural and man made wonders.

  19. Two Pontic rivers

    DEFF Research Database (Denmark)

    Bekker-Nielsen, Tønnes; Jensen, Marit

    2015-01-01

    The accounts of the landscape around the Iris (Yeşilirmak) and the Thermodon (Terme) given by ancient authors are diverse and often contradictory. The Periegesis of the World by Dionysius of Alexandria, a didactic poem written in the early IInd c. A.D., established an image of the two rivers that...

  20. Indications for scintigraphy with 67Ga

    International Nuclear Information System (INIS)

    Plechl, S.C.; Berges, G.; Blut, J.; Bohle, H.; Gessat, C.; Hethey, B.; Linneborn, G.; Ostermann, W.; Prack, G.; Scheitza, B.

    1976-01-01

    The validity and exactness of 67 Ga scintigraphy was tested in more than 70 patients by a comparison with clinical, radiological and histological findings as well as with scintigraphs obtained with other nuclides. It was found that 67 Ga scintigraphy is a good and often even a vital supplementation to the other methods. Its main field of application, according to the authors' obervations, is the differential diagnosis of three-dimensional changes in the thorax region, in particular the diagnosis of malignant tumours of the lungs in combination with X-ray examinations. Furthermore, 67 Ga may be of use in localization diagnoses of non-malignant changes, e.g. abscesses. 67 Ga scintigraphy, which is non-hazardous and does not involve discomfort to the patients, appears to be particularly useful for course control after surgical treatment of breast cancer and for early diagnoses of metastases, provided that examination starts early enough and is repeated at regular intervals, not only in the soft parts but also in the skeleton. The question whether 67 Ga scintigraphy may be a substitute for scintigraphy with other nuclides in these fields still remains to be solved. (orig.) [de

  1. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  2. Implantation doping of GaN

    International Nuclear Information System (INIS)

    Zolper, J.C.

    1996-01-01

    Ion implantation has played an enabling role in the realization of many high performance photonic and electronic devices in mature semiconductor materials systems such as Si and GaAs. This can also be expected to be the case in III-Nitride based devices as the material quality continues to improve. This paper reviews the progress in ion implantation processing of the III-Nitride materials, namely, GaN, AlN, InN and their alloys. Details are presented of the successful demonstrations of implant isolation as well as n- and p-type implantation doping of GaN. Implant doping has required activation annealing at temperatures in excess of 1,000 C. The nature of the implantation induced damage and its response to annealing is addressed using Rutherford Backscattering. Finally, results are given for the first demonstration of a GaN device fabricated using ion implantation doping, a GaN junction field effect transistor (JFET)

  3. The Effect of the number of InGaN/GaN pairs on the photoelectrochemical properties of InGaN/GaN multi quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Hyojung; Park, Jun-Beom [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Fujii, Katsushi [Institute of Environmental Science and Technology, The University of Kitakyushu, Kitakyushu, Fukuoka (Japan); Lee, Hyo-Jong [Materials Science and Engineering, Dong-A University, Busan 49315 (Korea, Republic of); Lee, Sang-Hyun [Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Joellabuk-do 55324 (Korea, Republic of); Ryu, Sang-Wan; Lee, June Key [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Ha, Jun-Seok, E-mail: jsha@jnu.ac.kr [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of)

    2017-04-15

    Highlights: • The 1–5 period InGaN/GaN quantum well (QW) structures were grown on sapphire. • The photoelectrochemical properties of these structures were investigated. • The saturated photocurrent density increased with increasing number of QW pairs. • But, it was different in the stability of the photoanode. • We reported the reason for this difference. - Abstract: In this study, the effects of the number of quantum well (QW) pairs on the photoelectrochemical (PEC) properties of InGaN/GaN multi-QW structures (MQWs) were investigated. MQW samples were grown using metal-organic chemical vapor deposition, and their structural characteristics were confirmed by X-ray diffraction measurements. The photoluminescence measurements revealed that the optical properties of MQWs may be related to the PEC properties. The cyclic voltammetry data revealed that the saturated photocurrent density increased with increasing number of QW pairs; the photocurrent density of MQW5 was twice that of an nGaN reference. However, in the chronoamperometry measurement of the photoanode stability, MQWs with 3 QWs displayed the highest photocurrent stability, although the saturated photocurrent density was highest for MQW5. This was also confirmed by field-emission scanning electron microscopy of the surface morphology after PEC measurements. The stability and photocurrent density may be attributed to the quality of crystallinity of the MQWs.

  4. Ga-67 imaging in pediatric oncology

    International Nuclear Information System (INIS)

    Edeling, C.J.

    1983-01-01

    One hundred sixty-nine children suspected of having malignant disease were examined by Ga-67 scintigraphy. In 99 children with untreated diseases at the time of examination, abnormal accumulation of Ga-67 was found in 51 patients, including 40 with malignant tumor. Forty-three negative results were obtained in children with benign disorders. Five false-negative results were obtained in patients with neuroblastoma of the adrenal gland. In 70 children with malignant diseases treated before the examination, abnormal accumulation of Ga-67 was seen in 40 patients, including 38 with malignant disease and two with no clinical evidence of recurrence. Normal results were obtained in 30 patients, including 11 still suffering from malignant disease. The results of Ga-67 scintigraphy in all of the children were evaluated qualitatively. For the final diagnosis of malignant disease, diagnostic specificity was 86% and diagnostic sensitivity 79%. The prevalence of malignant disease was 56%. It is concluded that Ga-67 scintigraphy should be used for primary visualization and control of malignant tumors in children

  5. Indications for scintigraphy with /sup 67/Ga

    Energy Technology Data Exchange (ETDEWEB)

    Plechl, S C; Berges, G; Blut, J; Bohle, H; Gessat, C; Hethey, B; Linneborn, G; Ostermann, W; Prack, G; Scheitza, B [Berufsgenossenschaftliche Krankenanstalten Bergmannsheil, Bochum (Germany, F.R.)

    1976-06-01

    The validity and exactness of /sup 67/Ga scintigraphy was tested in more than 70 patients by a comparison with clinical, radiological and histological findings as well as with scintigraphs obtained with other nuclides. It was found that /sup 67/Ga scintigraphy is a good and often even a vital supplementation to the other methods. Its main field of application, according to the authors' obervations, is the differential diagnosis of three-dimensional changes in the thorax region, in particular the diagnosis of malignant tumours of the lungs in combination with X-ray examinations. Furthermore, /sup 67/Ga may be of use in localization diagnoses of non-malignant changes, e.g. abscesses. /sup 67/Ga scintigraphy, which is non-hazardous and does not involve discomfort to the patients, appears to be particularly useful for course control after surgical treatment of breast cancer and for early diagnoses of metastases, provided that examination starts early enough and is repeated at regular intervals, not only in the soft parts but also in the skeleton. The question whether /sup 67/Ga scintigraphy may be a substitute for scintigraphy with other nuclides in these fields still remains to be solved.

  6. Two-dimensional electron and hole gases in GaN/AlGaN heterostructures; Zweidimensionale Elektronen- und Loechergase in GaN/AlGaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Link, A.

    2004-12-01

    The aim of this PhD thesis is to investigate the electronic properties of electron and hole gases in GaN/AlGaN heterostructures. Particularly, a deeper and broadened understanding of scattering mechanisms and transport properties is in the focus of this work. The main experimental techniques used for this purpose are the study of Shubnikov-de Haas (SdH) effect and Hall measurements at low temperatures. By means of these magnetotransport measurements, a series of GaN/AlGaN heterostructures with different Al content of the AlGaN barrier were investigated. Since the sheet carrier density of the 2DEG in these semiconductor structures is strongly dependent on the Al content (n{sub s}=2 x 10{sup 12}-10{sup 13} cm{sup -2}), the variation of transport parameters was determined as a function of sheet carrier concentration. First, from the temperature dependence of the SdH oscillations the effective transport mass was calculated. A Hall bar structure with an additional gate contact was used as an alternative to tune the carrier density of a 2DEG system independent of varying structural parametes such as Al content. Thus, the scattering mechanisms were investigated in the carrier density region between 3 x 10{sup 12} and 9.5 x 10{sup 12} cm{sup -2}. The transport properties of subband electrons were studied for a 2DEG system with two occupied subbands. (orig.)

  7. 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.

  8. Two-dimensional simulation of GaAsSb/GaAs quantum dot solar cells

    Science.gov (United States)

    Kunrugsa, Maetee

    2018-06-01

    Two-dimensional (2D) simulation of GaAsSb/GaAs quantum dot (QD) solar cells is presented. The effects of As mole fraction in GaAsSb QDs on the performance of the solar cell are investigated. The solar cell is designed as a p-i-n GaAs structure where a single layer of GaAsSb QDs is introduced into the intrinsic region. The current density–voltage characteristics of QD solar cells are derived from Poisson’s equation, continuity equations, and the drift-diffusion transport equations, which are numerically solved by a finite element method. Furthermore, the transition energy of a single GaAsSb QD and its corresponding wavelength for each As mole fraction are calculated by a six-band k · p model to validate the position of the absorption edge in the external quantum efficiency curve. A GaAsSb/GaAs QD solar cell with an As mole fraction of 0.4 provides the best power conversion efficiency. The overlap between electron and hole wave functions becomes larger as the As mole fraction increases, leading to a higher optical absorption probability which is confirmed by the enhanced photogeneration rates within and around the QDs. However, further increasing the As mole fraction results in a reduction in the efficiency because the absorption edge moves towards shorter wavelengths, lowering the short-circuit current density. The influences of the QD size and density on the efficiency are also examined. For the GaAsSb/GaAs QD solar cell with an As mole fraction of 0.4, the efficiency can be improved to 26.2% by utilizing the optimum QD size and density. A decrease in the efficiency is observed at high QD densities, which is attributed to the increased carrier recombination and strain-modified band structures affecting the absorption edges.

  9. Adsorption of tetrabutylammonium cations on negatively charged surfaces of the Hg, Ga, In-Ga, Tl-Ga electrodes

    International Nuclear Information System (INIS)

    Damaskin, B.B.; Baturina, O.A.; Vykhodtseva, L.N.; Emets, V.V.; Kazarinov, V.E.

    1999-01-01

    The differential capacitance curves in the 0.05M Na 2 SO 4 + [(C 4 H 9 ) 4 N]BF 4 aqueous solutions on the electrodes of mercury gallium and also of the In-Ga and Tl-Ga alloys are obtained. The adsorption parameters of the tetrabutylammonium cations on each of the electrodes within the frames of two parallel condensers model, supplemented by the Frumkin isotherm are calculated. The conclusion is made that different adsorption behaviour of the (C 4 H 9 ) 4 N + cations on the gallium subgroup metals by the electrodes high negative charges is related to nonuniform electrochemical work of the output electrons [ru

  10. River water pollution condition in upper part of Brantas River and Bengawan Solo River

    Science.gov (United States)

    Roosmini, D.; Septiono, M. A.; Putri, N. E.; Shabrina, H. M.; Salami, I. R. S.; Ariesyady, H. D.

    2018-01-01

    Wastewater and solid waste from both domestic and industry have been known to give burden on river water quality. Most of river water quality problem in Indonesia has start in the upper part of river due to anthropogenic activities, due to inappropriate land use management including the poor wastewater infrastructure. Base on Upper Citarum River Water pollution problem, it is interesting to study the other main river in Java Island. Bengawan Solo River and Brantas River were chosen as the sample in this study. Parameters assessed in this study are as follows: TSS, TDS, pH, DO, and hexavalent chromium. The status of river water quality are assess using STORET method. Based on (five) parameters, STORET value showed that in Brantas River, Pagerluyung monitoring point had the worst quality relatively compared to other monitoring point in Brantas River with exceeding copper, lead and tin compared to the stream standard in East Java Provincial Regulation No. 2 in 2008. Brantas River was categorized as lightly polluted river based on monitoring period 2011-2015 in 5 monitoring points, namely Pendem, Sengguruh, Kademangan, Meritjan and Kertosono.

  11. Lateral epitaxial overgrowth of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Wang, Yongjin; Hu, Fangren; Hane, Kazuhiro

    2011-01-01

    We report here the lateral epitaxial overgrowth (LEO) of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy (MBE) growth with radio frequency nitrogen plasma as a gas source. Two kinds of GaN nanostructures are defined by electron beam lithography and realized on a GaN substrate by fast atom beam etching. The epitaxial growth of GaN by MBE is performed on the prepared GaN template, and the selective growth of GaN takes place with the assistance of GaN nanostructures. The LEO of GaN produces novel GaN epitaxial structures which are dependent on the shape and the size of the processed GaN nanostructures. Periodic GaN hexagonal pyramids are generated inside the air holes, and GaN epitaxial strips with triangular section are formed in the grating region. This work provides a promising way for producing novel GaN-based devices by the LEO of GaN using the MBE technique

  12. Prediction and optimization of runoff via ANFIS and GA

    Directory of Open Access Journals (Sweden)

    D.K. Ghose

    2013-06-01

    Full Text Available In planning of water resource projects, the estimation of the availability of water plays an important role. The first step in the water availability estimation is the computation of runoff resulting from the precipitation on river catchments. The length of the runoff measured in a stream may be of short period or long period depending upon the catchment characteristics. Keeping this in mind the present work is focused on two different model generation. In the first phase of this study, runoff rating curves are developed considering present day water level (H(t as input and present day runoff (Q(t as the model output. In the second phase of the study runoff prediction models are developed considering 1 day lag water level (H(t − 1, 2 day lag water level (H(t − 2 and 1 day lag runoff (Q(t − 1 as inputs and 1 day ahead runoff (Q(t + 1 as the output of the model. Models developed and used for prediction of runoff are Non-Linear Multiple Regression (NLMR and Adaptive Neuro-Fuzzy Inference System (ANFIS. Both the models were trained and tested to predict the performance of models. Genetic Algorithm (GA is then coupled with NLMR model to obtain the condition of hydrological parameter for which the runoff is maximum.

  13. 71Ga Chemical Shielding and Quadrupole Coupling Tensors of the Garnet Y(3)Ga(5)O(12) from Single-Crystal (71)Ga NMR

    DEFF Research Database (Denmark)

    Vosegaard, Thomas; Massiot, Dominique; Gautier, Nathalie

    1997-01-01

    A single-crystal (71)Ga NMR study of the garnet Y(3)Ga(5)O(12) (YGG) has resulted in the determination of the first chemical shielding tensors reported for the (71)Ga quadrupole. The single-crystal spectra are analyzed in terms of the combined effect of quadrupole coupling and chemical shielding ...

  14. 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.

  15. 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.

  16. Spin injection into GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Endres, Bernhard

    2013-11-01

    In this work spin injection into GaAs from Fe and (Ga,Mn)As was investigated. For the realization of any spintronic device the detailed knowledge about the spin lifetime, the spatial distribution of spin-polarized carriers and the influence of electric fields is essential. In the present work all these aspects have been analyzed by optical measurements of the polar magneto-optic Kerr effect (pMOKE) at the cleaved edge of the samples. Besides the attempt to observe spin pumping and thermal spin injection into n-GaAs the spin solar cell effect is demonstrated, a novel mechanism for the optical generation of spins in semiconductors with potential for future spintronic applications. Also important for spin-based devices as transistors is the presented realization of electrical spin injection into a two-dimensional electron gas.

  17. The gamma ray spectrometer GA.SP

    Energy Technology Data Exchange (ETDEWEB)

    Bazzacco, D [Instituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova (Italy)

    1992-08-01

    GA.SP is a general purpose 4{pi} detector array for advanced {gamma}-spectroscopy and, in the same time, a suitable system for reaction mechanism studies. The detector is sited at the LNL Tandem+Linac accelerator and has been built as a joint project of INFN Padova, LNL, Milano and Firenze. The array consists of 40 Compton suppressed HPGe detectors and of a 4{pi} calorimeter composed of 80 BGO crystals. The detector houses a reaction chamber of 34 cm diameter where a charged particles multiplicity filter composed of 40 Si detectors is going to be installed. Evaporation residues produced in the centre of GA.SP can be injected into the recoil mass spectrometer (RMS, named CAMEL) in use at LNL, without the need to remove any of the gamma detectors. The coupled operation of GA.SP, RMS and Si ball will give a unique instrument for identification and study of weak reaction channels. (author). 6 figs.

  18. The gamma ray spectrometer GA.SP

    International Nuclear Information System (INIS)

    Bazzacco, D.

    1992-01-01

    GA.SP is a general purpose 4π detector array for advanced γ-spectroscopy and, in the same time, a suitable system for reaction mechanism studies. The detector is sited at the LNL Tandem+Linac accelerator and has been built as a joint project of INFN Padova, LNL, Milano and Firenze. The array consists of 40 Compton suppressed HPGe detectors and of a 4π calorimeter composed of 80 BGO crystals. The detector houses a reaction chamber of 34 cm diameter where a charged particles multiplicity filter composed of 40 Si detectors is going to be installed. Evaporation residues produced in the centre of GA.SP can be injected into the recoil mass spectrometer (RMS, named CAMEL) in use at LNL, without the need to remove any of the gamma detectors. The coupled operation of GA.SP, RMS and Si ball will give a unique instrument for identification and study of weak reaction channels. (author). 6 figs

  19. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2 \\xAF 01 )

    Science.gov (United States)

    Kollmannsberger, Sebastian L.; Walenta, Constantin A.; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N.; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

    2017-09-01

    In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α -H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2 ¯ 01 ) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

  20. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01).

    Science.gov (United States)

    Kollmannsberger, Sebastian L; Walenta, Constantin A; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

    2017-09-28

    In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga 2 O 3 (2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

  1. Determination of Ga-67 disintegration rate

    International Nuclear Information System (INIS)

    Fonseca, Katia A.; Koskinas, Maria F.; Dias, Mauro S.

    1996-01-01

    One of the consequences of the production by IPEN of new radioisotopes used in nuclear medicine, as the case of Ga-67, is the need of new standard sources of the radionuclide obtained in a fast and simple way. The Laboratorio de Metrologia de Radionuclideos at IPEN has a well-type ionization chamber system, the most suitable for this purpose. In order to calibrate this system it was necessary to standardize Ga-67 solutions by an absolute system. The present work gives details on the Ga-67 disintegration rate determination by an 4 π β-γ coincidence system, gamma spectrometry using an HPGe detector and measurements using a 1383A - type ionization chamber, in order to check the consistency in the adopted methodology. (author)

  2. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in ``avalanche`` mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into ``avalanche`` mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  3. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  4. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1990-01-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential of GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into an avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large are (1 sq cm) and small area (<1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs., 11 figs.

  5. Subnanosecond photoconductive switching in GaAs

    Science.gov (United States)

    Druce, R. L.; Pocha, M. D.; Griffin, K. L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in 'avalanche' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into 'avalanche' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (less than 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300-1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on, and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation.

  6. River-corridor habitat dynamics, Lower Missouri River

    Science.gov (United States)

    Jacobson, Robert B.

    2010-01-01

    Intensive management of the Missouri River for navigation, flood control, and power generation has resulted in substantial physical changes to the river corridor. Historically, the Missouri River was characterized by a shifting, multithread channel and abundant unvegetated sandbars. The shifting channel provided a wide variety of hydraulic environments and large areas of connected and unconnected off-channel water bodies.Beginning in the early 1800s and continuing to the present, the channel of the Lower Missouri River (downstream from Sioux City, Iowa) has been trained into a fast, deep, single-thread channel to stabilize banks and maintain commercial navigation. Wing dikes now concentrate the flow, and revetments and levees keep the channel in place and disconnect it from the flood plain. In addition, reservoir regulation of the Missouri River upstream of Yankton, South Dakota, has substantially changed the annual hydrograph, sediment loads, temperature regime, and nutrient budgets.While changes to the Missouri River have resulted in broad social and economic benefits, they have also been associated with loss of river-corridor habitats and diminished populations of native fish and wildlife species. Today, Missouri River stakeholders are seeking ways to restore some natural ecosystem benefits of the Lower Missouri River without compromising traditional economic uses of the river and flood plain.

  7. Dielectric function and electro-optical properties of (Al,Ga)N/GaN-heterostructures; Dielektrische Funktion und elektrooptische Eigenschaften von (Al,Ga)N/GaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Buchheim, Carsten

    2010-04-23

    In this work extensive investigations on nitride semiconductors by optical spectroscopy are presented. The ordinary and the extraordinary component of the dielectric function of GaN in the spectral range from 1.2 to 9.8 eV is shown for the first time. It is demonstrated, that the transparent spectral range is clearly influenced by higher energetic critical points of the band structure. The optical selection rules for GaN and AlN are verified considering the actual strain state. The change of the valence band ordering of AlN in comparison to GaN is proven and the crystal field splitting is estimated for AlN. The ordinary dielectric function of AlGaN is determined for different Al contents. The data are used for developing an analytical model, which includes excitonic effects and bowings. It allows the calculation of the dielectric function for arbitrary alloy compositions. (GaN/)AlGaN/GaN heterostructures are investigated by spectroscopic ellipsometry as well as by photoreflectance and electroreflectance. The optical data yields the electric field strengths of the individual layers to determine the density of the two-dimensional carrier gases at the heterointerfaces with high accuracy. The surface potential is calculated from the combination of experiments and Schroedinger-Poisson calculations. Its dependency on the Al content is quantified. For the special case of thick cap layers the coexistence of electron and hole gases in one sample is experimentally proven for the first time. Several interband transitions between quantized states in AlN/GaN superlattices are observed by electroreflectance. The comparison to quantum mechanical calculations demonstrates the influence of strain and electrical fields (quantum confined Stark effect). For both the ratio of the thicknesses of quantum wells and barriers is crucial. From the dielectric function of the superlattices it becomes obvious, that quantum size effects are not only important for the vicinity of the bandgap, but

  8. Origin of magnetostriction in Fe-Ga

    DEFF Research Database (Denmark)

    Mudivarthi, Chaitanya; Laver, Mark; Cullen, James

    2010-01-01

    This paper investigates the origin of large magnetostriction in Fe-Ga alloys using small-angle neutron scattering (SANS) and Kerr microscopy. The SANS data for a single-crystal, electron irradiated, and quenched Fe81Ga19 sample under externally applied magnetic and elastic fields revealed...... the existence of magnetostrictive nanoclusters spaced at similar to 15 nm apart that have a different magnetization than the A2 matrix. Combining the SANS results and the magnetization orientation obtained from the magnetic domain images using a Kerr microscope, it appears that the nanoclusters contribute...

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. Picosecond electron bunches from GaAs/GaAsP strained superlattice photocathode

    International Nuclear Information System (INIS)

    Jin, Xiuguang; Matsuba, Shunya; Honda, Yosuke; Miyajima, Tsukasa; Yamamoto, Masahiro; Utiyama, Takashi; Takeda, Yoshikazu

    2013-01-01

    GaAs/GaAsP strained superlattices are excellent candidates for use as spin-polarized electron sources. In the present study, picosecond electron bunches were successfully generated from such a superlattice photocathode. However, electron transport in the superlattice was much slower than in bulk GaAs. Transmission electron microscopy observations revealed that a small amount of variations in the uniformity of the layers was present in the superlattice. These variations lead to fluctuations in the superlattice mini-band structure and can affect electron transport. Thus, it is expected that if the periodicity of the superlattice can be improved, much faster electron bunches can be produced. - Highlights: • GaAs/GaAsP strained superlattices are excellent candidates for spin-polarized electron beam. • Pulse spin-polarized electron beam is required for investigating the magnetic domain change. • Picosecond electron bunches were achieved from GaAs/GaAsP superlattice photocathode. • TEM observation revealed a small disorder of superlattice layers. • Improvement of superlattice periodicity can achieve much faster electron bunches

  14. Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

    Energy Technology Data Exchange (ETDEWEB)

    Gerlach, J. W.; Ivanov, T.; Neumann, L.; Hoeche, Th.; Hirsch, D.; Rauschenbach, B. [Leibniz-Institut fuer Oberflaechenmodifizierung (IOM), D-04318 Leipzig (Germany)

    2012-06-01

    Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630 Degree-Sign C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained.

  15. 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

  16. A gate current 1/f noise model for GaN/AlGaN HEMTs

    International Nuclear Information System (INIS)

    Liu Yu'an; Zhuang Yiqi

    2014-01-01

    This work presents a theoretical and experimental study on the gate current 1/f noise in AlGaN/GaN HEMTs. Based on the carrier number fluctuation in the two-dimensional electron gas channel of AlGaN/GaN HEMTs, a gate current 1/f noise model containing a trap-assisted tunneling current and a space charge limited current is built. The simulation results are in good agreement with the experiment. Experiments show that, if V g < V x (critical gate voltage of dielectric relaxation), gate current 1/f noise comes from the superimposition of trap-assisted tunneling RTS (random telegraph noise), while V g > V x , gate current 1/f noise comes from not only the trap-assisted tunneling RTS, but also the space charge limited current RTS. This indicates that the gate current 1/f noise of the GaN-based HEMTs device is sensitive to the interaction of defects and the piezoelectric relaxation. It provides a useful characterization tool for deeper information about the defects and their evolution in AlGaN/GaN HEMTs. (semiconductor devices)

  17. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

    Science.gov (United States)

    Pérez-Tomás, A; Catalàn, G; Fontserè, A; Iglesias, V; Chen, H; Gammon, P M; Jennings, M R; Thomas, M; Fisher, C A; Sharma, Y K; Placidi, M; Chmielowska, M; Chenot, S; Porti, M; Nafría, M; Cordier, Y

    2015-03-20

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  18. Optical properties of GaS:Ho3+ and GaS:Tm3+ single crystals

    International Nuclear Information System (INIS)

    Jin, Moon-Seog; Kim, Chang-Dae; Kim, Wha-Tek

    2004-01-01

    GaS:Ho 3+ and GaS:Tm 3+ single crystals were grown by using the chemical transport reaction method. We measured the optical absorption, the infra-red absorption, and the photoluminescence spectra of the single crystals. The direct and the indirect energy band gaps of the single crystals at 13 K were identified. Infra-red absorption peaks at 6 K appeared in the single crystals. Broad emission bands at 6 K were observed at 464 nm and 580 nm for GaS:Ho 3+ and 462 nm and 581 nm for GaS:Tm 3+ . These broad emission bands were identified as originating from donor-acceptor pair recombinations. Sharp emission peak groups were observed near 435 nm, 495 nm, and 660 nm for GaS:Ho 3+ and near 672 nm for GaS:Tm 3+ . These sharp emission peak groups were identified as being due to the electron transitions between the energy levels of Ho 3+ and Tm 3+ . Especially, white photoluminescence was obtained in the GaS:Ho 3+ single crystal.

  19. Hydrogenation of GaAs covered by GaAlAs and subgrain boundary passivation

    Science.gov (United States)

    Djemel, A.; Castaing, J.; Chevallier, J.; Henoc, P.

    1992-12-01

    Cathodoluminescence (CL) has been performed to study the influence of hydrogen on electronic properties of GaAs with and without a GaAlAs layer. Recombination at sub-boundaries has been examined. These extended defects have been introduced by high temperature plastic deformation. The results show that they are passivated by hydrogen. The penetration of hydrogen is slowed down by the GaAlAs layer. La cathodoluminescence (CL) a été utilisée pour étudier l'influence de l'hydrogène sur les propriétés électroniques de GaAs nu et recouvert d'une couche de GaAlAs. Le caractère recombinant des sous-joints de grains a été examiné. Ces défauts étendus ont été introduits par déformation plastique à chaud. Les résultats montrent que l'hydrogène passive ces défauts. La pénétration de l'hydrogène à l'intérieur de GaAs est retardée par la présence de la couche de GaAlAs.

  20. Selected Ga-68-siderophores versus Ga-68-colloid and Ga-68-citrate: biodistribution and small animal imaging in mice

    Czech Academy of Sciences Publication Activity Database

    Petřík, M.; Vlčková, A.; Nový, Z.; Urbánek, Lubor; Haas, H.; Decristoforo, C.

    2015-01-01

    Roč. 159, č. 1 (2015), s. 60-66 ISSN 1213-8118 R&D Projects: GA MŠk(CZ) LO1304 Institutional support: RVO:61389030 Keywords : gallium-68 * siderophores * colloid Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 0.924, year: 2015

  1. Donors, Acceptors, and Traps in AlGaN and AlGaN/GaN Epitaxial Layers

    National Research Council Canada - National Science Library

    Look, David C

    2006-01-01

    .... The present grant, F49620-03-1-0197, has covered the period 1 May 03 - 30 Apr 06. The overall goal has been to understand defects and impurities in GaN, and determine how to reduce them, if possible...

  2. Field isolation for GaN MOSFETs on AlGaN/GaN heterostructure with boron ion implantation

    International Nuclear Information System (INIS)

    Jiang, Y; Wang, Q P; Wang, D J; Tamai, K; Li, L A; Ao, J-P; Ohno, Y; Shinkai, S; Miyashita, T; Motoyama, S-I

    2014-01-01

    We report the investigation of boron ion implantation as a device field isolation process for GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure. In the mesa isolation region of a bar-type MOSFET, a parasitic MOS-channel existed and widened the designed channel width, which would result in an overestimated mobility compared with a ring-type MOSFET. After boron ions implantation in the isolation region, the overestimation of field-effect mobility of bar-type MOSFETs was eliminated. The sub-threshold characteristics and on-state drain current of the bar-type MOSFETs coincide with the ring-type devices. Long-channel ring-type MOSFETs, with and without ion implantation, were fabricated on the recess region to evaluate the sub-threshold characteristics. The MOSFETs with boron ions implanted into the recess region showed a low drain current up to the gate bias of 10V. The result indicated that boron ion implantation prevented the formation of parasitic MOS-channel in the isolation region and achieved field isolation. The current–voltage characteristics of MOSFETs with the normal recess condition demonstrated no degradation of device performance after boron ions implanted into the isolation region. Boron ion implantation by further optimization can be a field isolation method for GaN MOSFETs. (paper)

  3. Metazoan parasites of Neogobius fishes in the Slovak section of the River Danube

    Czech Academy of Sciences Publication Activity Database

    Ondračková, Markéta; Dávidová, M.; Pečínková, M.; Blažek, R.; Gelnar, M.; Valová, Zdenka; Černý, J.; Jurajda, Pavel

    2005-01-01

    Roč. 21, č. 4 (2005), s. 345-349 ISSN 0175-8659. [European Congress of Ichthyology /11./. Tallinn, 06.09.2004-10.09.2004] R&D Projects: GA ČR(CZ) GP524/05/P291 Institutional research plan: CEZ:AV0Z60930519 Keywords : Nematoda * River Danube Subject RIV: GL - Fishing Impact factor: 0.563, year: 2005

  4. InGaN/GaNおよびInGaN/InN気相成長における気相-固相関係 : 結晶成長理論シンポジウム

    OpenAIRE

    寒川, 義裕; 伊藤, 智徳; 熊谷, 義直; 纐纈, 明伯; KANGAWA, Yoshihiro; ITO, Tomonori; KUMAGAI, Yoshinao; KOUKITU, Akinori

    2002-01-01

    Thermodynamic analyses were carried out to understand compositional instability of InGaN/GaN and InGaN/InN in the MBE growth. In the thermodynamic analysis, contribution of lattice constraint from bottom layer was incorporated using enthalpy of mixing of InGaN/GaN and InGaN/InN, ΔH_m^ and ΔH_m^, which can be obtained by empirical interatomic potential calculations. The results suggest that compositional unstable region for InGaN/InN shifted toward Ga-rich side compared with that for InGaN/GaN...

  5. Anisotropic magnetoresistance components in (Ga,Mn)As

    Czech Academy of Sciences Publication Activity Database

    Rushforth, A.W.; Výborný, Karel; King, C.S.; Edmonds, K. W.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.; Irvine, A.C.; Vašek, Petr; Novák, Vít; Olejník, Kamil; Sinova, J.; Jungwirth, Tomáš; Gallagher, B. L.

    2007-01-01

    Roč. 99, č. 14 (2007), 147207/1-147207/4 ISSN 0031-9007 R&D Projects: GA ČR GA202/05/0575; GA ČR GA202/04/1519; GA ČR GEFON/06/E002; GA MŠk LC510 Grant - others:UK(GB) GR/S81407/01 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * anisotropic magnetoresistence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.944, year: 2007

  6. Electronic properties of GaV 4 S 8

    Indian Academy of Sciences (India)

    ... different in GaV4S8-1 and GaV4S8-2. This statement is strongly supported by the calculated bandwidth per cluster in GaV4S8 (∼0.342 eV in GaV4S8-1 and ∼0.374 eV in GaV4S8-2). A negative magnetoresistance (MR) is also found around 43 K in GaV4S8-2 at 6.0 T magnetic field associated with structural transition.

  7. Huge tunnelling anisotropic magnetoresistance in (Ga,Mn)As nanoconstrictions

    Czech Academy of Sciences Publication Activity Database

    Giddings, A.D.; Makarovsky, O. N.; Khalid, M.N.; Yasin, S.; Edmonds, K. W.; Campion, R. P.; Wunderlich, J.; Jungwirth, Tomáš; Williams, D.A.; Gallagher, B. L.; Foxon, C. T.

    2008-01-01

    Roč. 10, č. 8 (2008), 085004/1-085004/9 ISSN 1367-2630 R&D Projects: GA ČR GEFON/06/E002; GA MŠk LC510; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductor * nanoconstriction * tunneling anisotropic magnetoresistance , Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.440, year: 2008

  8. Domain walls in (Ga,Mn)As diluted magnetic semiconductor

    Czech Academy of Sciences Publication Activity Database

    Sugawara, A.; Kasai, H.; Tonomura, A.; Brown, P.D.; Campion, R. P.; Edmonds, K. W.; Gallagher, B. L.; Zemen, Jan; Jungwirth, Tomáš

    2008-01-01

    Roč. 100, č. 4 (2008), 047202/1-047202/4 ISSN 0031-9007 R&D Projects: GA MŠk LC510; GA ČR GEFON/06/E002; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : dilute ferromagnetic semiconductor * Néel domain walls * electron holography * Landau-Lifshitz-Gilbert simulation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.180, year: 2008

  9. Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

    International Nuclear Information System (INIS)

    De-Gang, Zhao; Shuang, Zhang; Wen-Bao, Liu; De-Sheng, Jiang; Jian-Jun, Zhu; Zong-Shun, Liu; Hui, Wang; Shu-Ming, Zhang; Hui, Yang; Xiao-Peng, Hao; Long, Wei

    2010-01-01

    The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  10. Influence of AlGaN Buffer Growth Temperature on GaN Epilayer based on Si(lll) Substrate

    International Nuclear Information System (INIS)

    Wei Meng; Wang Xiaoliang; Pan Xu; Xiao Hongling; Wang Cuimei; Zhang Minglan; Wang Zhanguo

    2011-01-01

    This paper investigated the influence of AlGaN buffer growth temperature on strain status and crystal quality of the GaN film on Si(111) sbustrates by metal organic chemical vapor deposition. It was demonstrated by the optical microscopy that AlGaN buffer gorwth temperature had a remarkable effect on compensating tensil stress in top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed crystal quality and surface morphology of the GaN epilayer could be improved through increasing AlGaN buffer growth temperature. 1μm crack-free GaN epilayer on Si (111) substrates was obtained with graded AlGaN buffer layer at optimized temperature of 1050 deg. C. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer.

  11. First Pb-Pb dating results from carbonado diamonds from Chapada Diamantina (BA) and Jequitinhonha River (MG), Espinhaco Range

    International Nuclear Information System (INIS)

    Chaves, Mario Luiz de Sa Carneiro; Sano, Yuji; Chambel, Luis

    2005-01-01

    Most carbonados found in Brazil occur along the Espinhaco Range, associated to conglomeratic rocks of the Espinhaco Supergroup. This paper presents Pb-Pb radiometric ages on mineral inclusions (quartz, rutile and clay) and matrix of carbonados from the Andarai and Jequitinhonha River areas. Even with a large experimental error, the results obtained of 3,8±1,8Ga and 3,3±0,7 Ga respectively, are of regional geologic interest. The minimum carbonado formation age (ca.2,5 Ga) is older than the Espinhaco Supergroup deposition age (≅ 1,7 Ga). Other evidences suggest that this minimum age corresponds to the seed aggregation phase; the crustal inclusions being aggregated in an environment rich in high-energy radioactive particles. (author)

  12. The effect of the In concentration on the surface morphology of InGaAs-GaAs heterostructures grown by MBE on GaAs substrate

    International Nuclear Information System (INIS)

    Gómez-Barojas, E; Serrano-Rojas, R M; Rodríguez-Moreno, M A; Santamaría-Juárez, G; Silva-González, R; a. Sección, San Luis Potosí, S. L. P., 78100 (Mexico))" data-affiliation=" (Instituto de Investigación en Comunicación Óptica. Universidad Autónoma de San Luis Potosí, Av. Karakorum 1470, Col. Lomas Altas 4a. Sección, San Luis Potosí, S. L. P., 78100 (Mexico))" >Vidal-Borbolla, M A

    2014-01-01

    A set of 3 heterostructures were formed by 10 periods of InGaAs-GaAs epitaxially grown on GaAs substrate by means of a molecular beam epitaxial system. Scanning electron microscopy (SEM) cross section images at high magnification show that the heterostructures present good periodicity. SEM micrographs of the surface morphology chemically etched show the coalescence effect of In due to an unequal etching rate of In and GaAs. Auger electron spectroscopy (AES) depth profiles show that the first GaAs layers in the 3 samples are off-stoichiometric and that the alloy layers present In square and triangular depth profiles

  13. 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)

  14. 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.

  15. Electrical properties of Ga ion beam implanted GaAs epilayer

    International Nuclear Information System (INIS)

    Hirayama, Yoshiro; Okamoto, Hiroshi

    1985-01-01

    Resistivity enhancement by 5 orders or more was realized by Ga focused ion beam implantation into n + and p + GaAs epilayers. For originally n + epilayers, this resistivity enhancement is maintained after annealing as high as 800 deg C. However this enhancement disappears after annealing at above 650 deg C for p + epilayer. This property makes GaAs high resistive only in a limited area whose minimum dimension is 0.1 μm or less, and is attractive for a device fabrication process to electrically isolate integrated elements. (author)

  16. Defect Structure of High-Temperature-Grown GaMnSb/GaSb

    International Nuclear Information System (INIS)

    Romanowski, P.; Bak-Misiuk, J.; Dynowska, E.; Domagala, J.Z.; Wojciechowski, T.; Jakiela, R.; Sadowski, J.; Barcz, A.; Caliebe, W.

    2010-01-01

    GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga1-xMnxSb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique. (authors)

  17. High resolution study of proton resonances in 65Ga and 67Ga

    International Nuclear Information System (INIS)

    Sales, K.B.

    1980-01-01

    Differential cross sections were measured for 64 Zn(p,p) from 2.50 to 3.24 MeV and for 66 Zn(p,p) from 2.60 to 3.26 MeV at laboratory angles of 90 0 , 105 0 , 135 0 , and 160 0 . These experiments were performed with the Triangle Universities Nuclear Laboratory 3 MV Van de Graaff accelerator and associated electrostatic analyzer-homogenizer system. The total overall energy resolution was 420 to 525 eV for 64 Zn(p,p) and 360 to 405 eV for 66 Zn(p,p). Resonances observed in the excitation functions were analyzed with a multilevel R-Matrix formalism. Resonance energies, spins, parities, and elastic widths were extracted for 39 resonances in 65 Ga and 148 resonances in 67 Ga. The l = 0 proton strength functions were calculated for 64 Zn and 66 Zn. The s-wave strength function shows an increase for A=66, which is consistent with earlier results from (p,n) cross section studies. Statistical properties of the 1/2 + resonances in 65 Ga and 67 Ga were examined. The spacing and reduced width distributions were compared with the Wigner and Porter-Thomas distributions, respectively. This comparison indicates that 50% of the 1/2 + resonances were missed in 65 Ga and that 70% of the 1/2 + resonances were missed in 67 Ga. The observed s-wave level densities in 65 Ga and 67 Ga are compared with predictions from conventional level density models. The analogs of the 0.867 MeV, the 0.910 MeV, and the 1.370 MeV states of 65 Zn are observed in 65 Ga; the analogs of the 0.093 MeV and the 0.394 MeV states of 67 Zn are observed in 67 Ga. The analog states in 65 Ga were fragmented into only two or three resonances, while the two analog states in 67 Ga were highly fragmented. Fits to the fine structure distributions of these two analogs were obtained and the resulting parameters compared with the Robson model. Coulomb energies were extracted for these five analogs

  18. Unconventional superconductivity in PuRhGa5: Ga NMR/NQR study

    International Nuclear Information System (INIS)

    Sakai, H.; Tokunaga, Y.; Fujimoto, T.; Kambe, S.; Walstedt, R.E.; Yasuoka, H.; Aoki, D.; Homma, Y.; Yamamoto, E.; Nakamura, A.; Shiokawa, Y.; Nakajima, K.; Arai, Y.; Matsuda, T.D.; Haga, Y.; Onuki, Y.

    2006-01-01

    69,71 Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa 5 with T c ∼9K. The spin-lattice relaxation rate 1/T 1 reveals that PuRhGa 5 is an unconventional superconductor having an anisotropic superconducting gap. Moreover, Korringa behavior (1/T 1 T=const.) is observed in the normal state below ∼30K. This result suggests that the superconductivity sets in after the formation of a Fermi liquid state in this compound

  19. A new theoretical approach to adsorption desorption behavior of Ga on GaAs surfaces

    Science.gov (United States)

    Kangawa, Y.; Ito, T.; Taguchi, A.; Shiraishi, K.; Ohachi, T.

    2001-11-01

    We propose a new theoretical approach for studying adsorption-desorption behavior of atoms on semiconductor surfaces. The new theoretical approach based on the ab initio calculations incorporates the free energy of gas phase; therefore we can calculate how adsorption and desorption depends on growth temperature and beam equivalent pressure (BEP). The versatility of the new theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on the GaAs(0 0 1)-(4×2)β2 Ga-rich surface. This new approach is feasible to predict how adsorption and desorption depend on the growth conditions.

  20. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O. [Université Européenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes, 35708 Rennes (France); Nestoklon, M. O. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pereira da Silva, K. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Departamento de Física, Universidade Federal do Ceará, P.O. Box 6030, Fortaleza–CE, 60455-970 (Brazil); Alonso, M. I. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Goñi, A. R. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); ICREA, Passeig Lluís Companys 23, 08010 Barcelona (Spain); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France)

    2014-01-06

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  1. Nucleation and Growth of GaN on GaAs (001) Substrates

    International Nuclear Information System (INIS)

    Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei; Sullivan, John P.

    1999-01-01

    The nucleation of GaN thin films on GaAs is investigated for growth at 620 ''C. An rf plasma cell is used to generate chemically active nitrogen from N 2 . An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio

  2. Sapucai River Project

    International Nuclear Information System (INIS)

    Duarte, A.L.; Rosa, M.J.

    1988-01-01

    The Sapucai River Project is a gold, ilmenite, monazite and zircon alluvial deposit. It is located on Sapucai River valley in the south of Minas Gerais State. The reserves are 28.000.000 m 3 of pay bed. The production will be 1.400.000 m 3 /year and the mine's life 20 years. A cutterhead suction dredge will do the overburden removal. The pay bed will be mined with an underwater bucket-wheel dredge. The ROM will be concentrated in a washing plant. The gold will be recovered by leaching method. The other heavy minerals will be recovered by electrostatic, magnetic and gravitic methods. SAMITRI believes that it's possible to implant and operate the Project without ecological damage. (author) [pt

  3. Geomorphology and River Management

    Directory of Open Access Journals (Sweden)

    GARY BRIERLEY

    2008-01-01

    Full Text Available Engineering-dominated practices, visible in a "command and control" outlook on natural systems, have induced enormous damage to the environment. Biodiversity losses and declining provision of ecosystem services are testimony to the non-sustainable outcomes brought about by such practices. More environmentally friendly approaches that promote a harmonious relationship between human activities and nature are required. Moves towards an "ecosystem approach" to environmental management require coherent (integrative scientific guidance. Geomorphology, the study of the form of the earth, provides a landscape template with which to ground this process. This way of thinking respects the inherent diversity and complexity of natural systems. Examples of the transition toward such views in environmental practice are demonstrated by the use of science to guide river management, emphasising applications of the River Styles framework.

  4. Heat dispersion in rivers

    International Nuclear Information System (INIS)

    Shaw, T.L.

    1974-01-01

    One of the tasks of the Sonderforschungsbereich 80 is to study the dispersion of heat discharged into rivers and other bodies of water and to develop methods which permit prediction of detrimental effects caused by the heated discharges. In order to help the SFB 80 to specify this task, Dr. Shaw, lecturer of Civil Engineering at the Bristol University, conducted a literature survey on heat-dispersion studies during the two months which he spent as a visiting research fellow with the SFB 80 at the University of Karlsruhe in the summer of 1973. The following report is the outcome of this survey. It gives Dr. Shaw's assessment of the present state of knowledge - based almost exclusively on literature in the English language - and compares this with the knowledge required by river planners. The apparent discrepancy leads to suggestions for future research. Selected references as well as a representative bibliography can be found at the end of the report. (orig.) [de

  5. 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)

  6. 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.

  7. 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.

  8. 50 CFR 226.205 - Critical habitat for Snake River sockeye salmon, Snake River fall chinook salmon, and Snake River...

    Science.gov (United States)

    2010-10-01

    ... salmon, Snake River fall chinook salmon, and Snake River spring/summer chinook salmon. 226.205 Section... Snake River sockeye salmon, Snake River fall chinook salmon, and Snake River spring/summer chinook salmon. The following areas consisting of the water, waterway bottom, and adjacent riparian zone of...

  9. 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.

  10. Degradation of AlGaN/GaN High Electron Mobility Transistors with Different AlGaN Layer Thicknesses under Strong Electric Field

    International Nuclear Information System (INIS)

    Ling, Yang; Yue, Hao; Xiao-Hua, Ma; Jing-Jing, Ma; Cheng, Zhu

    2010-01-01

    The degradation of AlGaN/GaN high electron mobility transistors (HEMTs) has a close relationship with a model of traps in AlGaN barriers as a result of high electric field. We mainly discuss the impacts of strong electrical field on the AlGaN barrier thickness of AlGaN/GaN HEMTs. It is found that the device with a thin AlGaN barrier layer is more easily degraded. We study the degradation of four parameters, i.e. the gate series resistance R Gate , channel resistance R channel , gate current I G,off at V GS = −5 and V DS = 0.1 V, and drain current I D,max at V GS = 2 and V DS = 5 V. In addition, the degradation mechanisms of the device electrical parameters are also investigated in detail. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  11. 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)

  12. Gate length scaling effect on high-electron mobility transistors devices using AlGaN/GaN and AlInN/AlN/GaN heterostructures.

    Science.gov (United States)

    Liao, S Y; Lu, C C; Chang, T; Huang, C F; Cheng, C H; Chang, L B

    2014-08-01

    Compared to AlGaN/GaN HEMT with 0.15 μm T-gate length, the AlInN/AlN/GaN one exhibits much higher current density and transconductance of 1558 mA/mm at Vd = 2 V and 330 mS/mm, respectively. The high extrinsic ft and fmax of 82 GHz and 70 GHz are extracted from AlInN/AlN/GaN HEMT. Besides, we find that the transconductance roll-off is significant in AlGaN/GaN, but largely improved in AlInN/AlN/GaN HEMT, suggesting that the high carrier density and lattice-matched epitaxial heterostructure is important to reach both large RF output power and high operation frequency, especially for an aggressively gate length scaling.

  13. Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN (0001) substrates

    International Nuclear Information System (INIS)

    Oikawa, Takeshi; Ishikawa, Fumitaro; Sato, Taketomo; Hashizume, Tamotsu; Hasegawa, Hideki

    2005-01-01

    This paper attempts to form AlGaN/GaN quantum wire (QWR) network structures on patterned GaN (0001) substrates by selective molecular beam epitaxy (MBE) growth. Substrate patterns were prepared along - and -directions by electron cyclotron resonance assisted reactive-ion beam etching (ECR-RIBE) process. Selective growth was possible for both directions in the case of GaN growth, but only in the -direction in the case of AlGaN growth. A hexagonal QWR network was successfully grown on a hexagonal mesa pattern by combining the -direction and two other equivalent directions. AFM observation confirmed excellent surface morphology of the grown network. A clear cathodoluminescence (CL) peak coming from the embedded AlGaN/GaN QWR structure was clearly identified

  14. Thermal etching rate of GaN during MOCVD growth interruption in hydrogen and ammonia ambient determined by AlGaN/GaN superlattice structures

    Science.gov (United States)

    Zhang, Feng; Ikeda, Masao; Zhang, Shuming; Liu, Jianping; Tian, Aiqin; Wen, Pengyan; Cheng, Yang; Yang, Hui

    2017-10-01

    Thermal etching effect of GaN during growth interruption in the metalorganic chemical vapor deposition reactor was investigated in this paper. The thermal etching rate was determined by growing a series of AlGaN/GaN superlattice structures with fixed GaN growth temperature at 735 °C and various AlGaN growth temperature changing from 900 °C to 1007 °C. It was observed that the GaN layer was etched off during the growth interruption when the growth temperature ramped up to AlGaN growth temperature. The etching thickness was determined by high resolution X-ray diffractometer and the etching rate was deduced accordingly. An activation energy of 2.53 eV was obtained for the thermal etching process.

  15. Onilahy River, Madagascar

    Science.gov (United States)

    1982-01-01

    Near the southern tip of Madagascar, the Onilahy River (23.5S, 44E) drains a near barren landscape, the result of rapid deforestation for quick profits from the lumber industry with no regard to the environmental impact. At the turn of the century, the island was a lush tropical paradise with about 90 percent of the surface forested. Now, at the close of the century, only about 10 percent of the forests remain in inaccessible rugged terrain.

  16. Charles River Crossing

    Science.gov (United States)

    2012-04-06

    duration, deck sections will be prefabricated off-site and delivered just-in-time for assembly and installation. The schedule assumes that the parts of...on one side (the side which abuts the existing bridges) there will be the appearance that the new bridges cantilever off the existing bridges. (See...many events that takes place on the Charles River such as crew racings and the “Head of the Charles”. Prefabricated off 19  ANCHORAGE GROUP, LTD

  17. AHP 45: Review: River

    Directory of Open Access Journals (Sweden)

    Phun tshogs dbang rgyal ཕུན་ཚོགས་དབང་རྒྱལ།

    2017-03-01

    Full Text Available Zon thar rgyal says that inspiration for River came with the arrival of his second child (a son, which made his daughter very uncomfortable. "At first, I just wanted to make a simple movie for children as a gift for my daughter,"6 he said during an interview in Lha sa. Later, however, the film became more elaborate with the addition of a grandfather, creating a story that embraces three generations.

  18. Columbia River pathway report

    International Nuclear Information System (INIS)

    1991-07-01

    This report summarizes the river-pathway portion of the first phase of the Hanford Environmental Dose Reconstruction (HEDR) Project. The HEDR Project is estimating radiation doses that could have been received by the public from the Department of Energy's Hanford Site, in southeastern Washington State. Phase 1 of the river-pathway dose reconstruction effort sought to determine whether dose estimates could be calculated for populations in the area from above the Hanford Site at Priest Rapids Dam to below the site at McNary Dam from January 1964 to December 1966. Of the potential sources of radionuclides from the river, fish consumption was the most important. Doses from drinking water were lower at Pasco than at Richland and lower at Kennewick than at Pasco. The median values of preliminary dose estimates calculated by HEDR are similar to independent, previously published estimates of average doses to Richland residents. Later phases of the HEDR Project will address dose estimates for periods other than 1964--1966 and for populations downstream of McNary Dam. 17 refs., 19 figs., 1 tab

  19. The river ecosystem

    International Nuclear Information System (INIS)

    Descy, J.P.; Lambinon, J.

    1984-01-01

    From the standpoint of the ecologist, a river is an ecosystem characterized by its biocoenosis, in dynamic equilibrium with the abiotic environment. This ecosystem can be envisaged at the structural level by examining its physical, chemical and biological properties, together with the relationships existing between these compartments. The biocoenotic structure of a river is relatively complex: it manifests, among other specific features, the presence of plankton communities which show marked space-time variations. The function of the river ecosystem can be approximated by a study of the relationships between the biotic and abiotic components: primary production, secondary production, recycling of organic matter, etc. Lotic environments are subject to frequent disturbance from various forms of man-made pollution: organic pollution, eutrophization, thermal pollution, mineral pollution, contamination by organic and mineral micropollutants, as well as by radionuclides, mechanical pollution and physical degradation. The biocoenotic effects of these forms of pollution may be evaluated, in particular, using biological indicators (bioindicators): these are either able to show the overall impact of the pollution on the biocoenosis or else they permit the detection and evaluation of certain pollutant forms. (author)

  20. Electroluminescence from GaN-polymer heterojunction

    International Nuclear Information System (INIS)

    Chitara, Basant; Lal, Nidhi; Krupanidhi, S.B.; Rao, C.N.R.

    2011-01-01

    Inorganic and organic semiconductor devices are generally viewed as distinct and separate technologies. Herein we report a hybrid inorganic-organic light-emitting device employing the use of an air stable polymer, Poly (9,9-dioctylfluorene-alt-benzothiadiazole) as a p-type layer to create a heterojunction, avoiding the use of p-type GaN, which is difficult to grow, being prone to the complex and expensive fabrication techniques that characterises it. I-V characteristics of the GaN-polymer heterojunction fabricated by us exhibits excellent rectification. The luminescence onset voltage is typically about 8-10 V. The device emits yellowish white electroluminescence with CIE coordinates (0.42, 0.44). - Highlights: → We use a polymer Poly (9,9-dioctylfluorene-alt-benzothiadiazole) as a p-type layer to create a heterojunction. → I-V characteristics of the device fabricated by us exhibits excellent rectification. → The p-type polymer also emits yellow light, which when combined in proper composition with GaN, give rise to white light. → Device can be readily fabricated by just spin coating the polymer over GaN reducing the cost of the device.

  1. Doping assessment in GaAs nanowires

    DEFF Research Database (Denmark)

    Goktas, N. Isik; Fiordaliso, Elisabetta Maria; LaPierre, R. R.

    2018-01-01

    Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs...

  2. Role of electronic correlations in Ga

    KAUST Repository

    Zhu, Zhiyong; Schwingenschlö gl, Udo; Wang, Xuhui

    2011-01-01

    to mispredict the Ga positional parameters. The extended AMF functional together with an onsite Coulomb interaction of Ueff=1.1 eV, as obtained from constraint LDA calculations, reduces the deviations by about 20%. The symmetry lowering coming along

  3. GaAs optoelectronic neuron arrays

    Science.gov (United States)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  4. Myositis ossificans with Ga-67 citrate positivity

    International Nuclear Information System (INIS)

    Moreno, A.J.; Yedinak, M.A.; Spicer, M.J.; Turnbull, G.L.; Byrd, B.F.; Brown, T.J.

    1985-01-01

    A 16 year-old boy presented with a firm mass within the left thigh. Ga-67 citrate and bone scintigraphy revealed soft tissue radiotracer accumulation within the mass lesion. Radiographs and xerography of the left thigh revealed calcification within the soft tissue mass typical of myositis ossificans. The patient's clinical course was uneventful

  5. Ti on GaAs(110)

    International Nuclear Information System (INIS)

    McCants, C.E.; Kendelewicz, T.; Williams, M.D.; List, R.S.; Lindau, I.; Spicer, W.E.

    1985-01-01

    The chemical and electronic properties of the Ti:GaAs interface have been studied using soft x-ray and ultraviolet photoemission spectroscopies. The Fermi level pinning position is observed to be 0.7 eV for n-type, consistent with both the Unified Defect Model and the charge transfer effects observed by Williams et. al. The interface is quite disrupted, as evidenced by shifts in both the Ga and As 3d core levels and marked changes in their lineshapes. The Ga core level moves to higher kinetic energy and shifts to a metallic-like state with increasing Ti coverages. The As core level also shifts to higher KE; in addition, as appears to diffuse through the Ti overlayer for thin (<10 monolayers) coverage. This, in addition to a change in the intensity ratio between the As 3d/sub 5/2/ and 3d/sub 3/2/ peaks suggests the formation of a Ti-arsenide, which is predicted by bulk thermodynamics. The room temperature data imply a laminar coverage, although annealing studies suggest the possibility of cluster formation with increasing temperature (0<10 monolayers). These results are also consistent with those obtained by Waldrop et. al. for Ti:GaAs(100) interfaces

  6. Ga-67 uptake post cesarean section

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, O.L.; Maisano, E.R.

    1984-02-01

    Gallium-67 distribution in normal patients is well known; it is also known that the concentration in some tissues may vary according to an individual physiologic stimulus. In this report, the case of a young woman is presented who was studied 15 days after a cesarean section and showed physiologic and pathologic Ga-67 accumulation.

  7. Ga-67 uptake post cesarean section

    International Nuclear Information System (INIS)

    Lopez, O.L.; Maisano, E.R.

    1984-01-01

    Gallium-67 distribution in normal patients is well known; it is also known that the concentration in some tissues may vary according to an individual physiologic stimulus. In this report, the case of a young woman is presented who was studied 15 days after a cesarean section and showed physiologic and pathologic Ga-67 accumulation

  8. GaN membrane MSM ultraviolet photodetectors

    Science.gov (United States)

    Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

    2006-12-01

    GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

  9. InGaAs/GaAs quantum-dot-quantum-well heterostructure formed by submonolayer deposition

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Leosson, K.; Birkedal, Dan

    2003-01-01

    -dot-quantum-well (QDQW) structure, by using high power PL and selective PL with excitation energies below the band gap of the GaAs barriers and temperature dependent PL. As the temperature is increased from 10 to 300 K, a narrowing of the full width at half-maximum at intermediate temperatures and a sigmoidal behaviour......Discrete emission lines from self-assembled InGaAs quantum dots (QDs) grown in the submonolayer (SML) deposition mode have been observed in micro-photoluminescence (PL) spectra at 10 K. For the first time, the SML-grown InGaAs/GaAs QD heterostructure is verified to be a quantum...

  10. Linearly polarized photoluminescence of InGaN quantum disks embedded in GaN nanorods.

    Science.gov (United States)

    Park, Youngsin; Chan, Christopher C S; Nuttall, Luke; Puchtler, Tim J; Taylor, Robert A; Kim, Nammee; Jo, Yongcheol; Im, Hyunsik

    2018-05-25

    We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn't show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures. In order to characterize a single nanostructure, the quantum disks were dispersed on a SiO 2 substrate patterned with a metal reference grid. By rotating the excitation polarization angle from parallel to perpendicular relative to the nanorods, the variation of overall PL for the 3.21 eV peak was recorded and it clearly showed the degree of linear polarization (DLP) of 51.5%.

  11. Raman Scattering and Surface Photovoltage Spectroscopy Studies of InGaAs/GaAs Radial Superlattices

    Science.gov (United States)

    Angelova, T.; Cros, A.; Ivanov, Ts.; Donchev, V.; Cantarero, A.; Shtinkov, N.; Deneke, Ch.; Schmidt, O. G.

    2011-12-01

    In this work we get insight into the multilayer structure of rolled-up microtube radial superlattices (RSLs) by the study of the optical and folded acoustic phonon modes of individual microtubes. Raman results show shifts of the InGaAs and GaAs related longitudinal optical modes that can be related to the strain state of the tubes. The folding of the acoustic modes has been related with the periodicity of the artificial superlattice formed by the multiple turns of the heterostructures. Information on the electronic structure and optical transitions of RSLs has been obtained by surface photovoltage spectroscopy. Room temperature spectra reveal several electronic transitions with energies below 1.3 eV. These transitions have been identified as originating from defect levels at the interfaces, as well as from the RSLs and the In0.215Ga0.785As/GaAs quantum well in the unfolded regions of the sample.

  12. Electronic structures of GaAs/AlxGa1-xAs quantum double rings

    Directory of Open Access Journals (Sweden)

    Li Shu-Shen

    2006-01-01

    Full Text Available AbstractIn the framework of effective mass envelope function theory, the electronic structures of GaAs/AlxGa1-xAs quantum double rings (QDRs are studied. Our model can be used to calculate the electronic structures of quantum wells, wires, dots, and the single ring. In calculations, the effects due to the different effective masses of electrons and holes in GaAs and AlxGa1-xAs and the valence band mixing are considered. The energy levels of electrons and holes are calculated for different shapes of QDRs. The calculated results are useful in designing and fabricating the interrelated photoelectric devices. The single electron states presented here are useful for the study of the electron correlations and the effects of magnetic fields in QDRs.

  13. Four-junction AlGaAs/GaAs laser power converter

    Science.gov (United States)

    Huang, Jie; Sun, Yurun; Zhao, Yongming; Yu, Shuzhen; Dong, Jianrong; Xue, Jiping; Xue, Chi; Wang, Jin; Lu, Yunqing; Ding, Yanwen

    2018-04-01

    Four-junction AlGaAs/GaAs laser power converters (LPCs) with n+-GaAs/p+-Al0.37Ga0.63As heterostructure tunnel junctions (TJs) have been designed and grown by metal-organic chemical vapor deposition (MOCVD) for converting the power of 808 nm lasers. A maximum conversion efficiency η c of 56.9% ± 4% is obtained for cells with an aperture of 3.14 mm2 at an input laser power of 0.2 W, while dropping to 43.3% at 1.5 W. Measured current–voltage (I–V) characteristics indicate that the performance of the LPC can be further improved by increasing the tunneling current density of TJs and optimizing the thicknesses of sub-cells to achieve current matching in LPC. Project financially supported by the National Natural Science Foundation of China (No. 61376065) and Zhongtian Technology Group Co. Ltd.

  14. Interfacial recombination at /AlGa/As/GaAs heterojunction structures

    Science.gov (United States)

    Ettenberg, M.; Kressel, H.

    1976-01-01

    Experiments were conducted to determine the interfacial recombination velocity at Al0.25Ga0.75As/GaAs and Al0.5Ga0.5As/GaAs heterojunctions. The recombination velocity was derived from a study of the injected minority-carrier lifetime as a function of the junction spacing. It is found that for heterojunction spacings in excess of about 1 micron, the interfacial recombination can be characterized by a surface recombination velocity of 4,000 and 8,000 cm/sec for the two types of heterojunctions, respectively. For double-heterojunction spacings below 1 micron, the constancy of the minority-carrier lifetime suggests that the interfacial recombination velocity decreases effectively. This effect is technologically very important since it makes it possible to construct very low-threshold injection lasers. No such effect is observed in single-heterojunction diodes.

  15. Short circuit current changes in electron irradiated GaAlAs/GaAs solar cells

    Science.gov (United States)

    Walker, G. H.; Conway, E. J.

    1978-01-01

    Heteroface p-GaAlAs/p-GaAs/n-GaAs solar cells with junction depths of 0.8, 1.5, and 4 microns were irradiated with 1 MeV electrons. The short-circuit current for the 4 micron junction depth cells is significantly reduced by the electron irradiation. Reduction of the junction depth to 1.5 microns improves the electron radiation resistance of the cells while further reduction of the junction depth to 0.8 microns improves the stability of the cells even more. Primary degradation is in the blue region of the spectrum. Considerable recovery of lost response is obtained by annealing the cells at 200 C. Computer modeling shows that the degradation is caused primarily by a reduction in the minority carrier diffusion length in the p-GaAs.

  16. Electric field driven plasmon dispersion in AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Tan Ren-Bing; Qin Hua; Zhang Xiao-Yu; Xu Wen

    2013-01-01

    We present a theoretical study on the electric field driven plasmon dispersion of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMTs). By introducing a drifted Fermi—Dirac distribution, we calculate the transport properties of the 2DEG in the AlGaN/GaN interface by employing the balance-equation approach based on the Boltzmann equation. Then, the nonequilibrium Fermi—Dirac function is obtained by applying the calculated electron drift velocity and electron temperature. Under random phase approximation (RPA), the electric field driven plasmon dispersion is investigated. The calculated results indicate that the plasmon frequency is dominated by both the electric field E and the angle between wavevector q and electric field E. Importantly, the plasmon frequency could be tuned by the applied source—drain bias voltage besides the gate voltage (change of the electron density)

  17. Effect of Passivation on Microwave Power Performances of AlGaN/GaN/Si HEMTs

    Directory of Open Access Journals (Sweden)

    H. MOSBAHI

    2014-05-01

    Full Text Available This paper reports on the use of plasma assisted molecular beam epitaxy of AlGaN/GaN high electron mobility transistors (HEMTs grown on silicon substrate. Surface passivation effects on AlGaN/GaN HEMTs were studied using SiO2/SiN dielectric layers grown by plasma enhanced chemical vapor deposition. The direct current measurement, pulsed characteristics and microwave small-signal characteristics were studied before and after passivation. An improvement of drain-source current density and the extrinsic transconductance was observed on the passivated HEMTs when compared with the unpassivated HEMTs. An enhancement of cut-off frequency (ft and maximum power gain (fmax was also observed for the devices with full SiO2/SiN passivation. A good correlation is found between pulsed and power measurements.

  18. Fabrication of MnGa/GaAs contacts for optoelectronics and spintronics applications

    Energy Technology Data Exchange (ETDEWEB)

    Dorokhin, M. V., E-mail: dorokhin@nifti.unn.ru [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Pavlov, D. A.; Bobrov, A. I. [Lobachevsky State University, Physical Department (Russian Federation); Danilov, Yu. A.; Lesnikov, V. P.; Zvonkov, B. N.; Zdoroveyshchev, A. V. [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Kudrin, A. V. [Lobachevsky State University, Physical Department (Russian Federation); Demina, P. B. [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Usov, Yu. V.; Nikolichev, D. E.; Kryukov, R. N.; Zubkov, S. Yu. [Lobachevsky State University, Physical Department (Russian Federation)

    2016-11-15

    The crystal structure, composition, and magnetic, and electric-transport properties of Mn{sub x}Ga{sub y} layers deposited onto a GaAs surface by pulsed laser deposition in a hydrogen atmosphere, pulsed laser deposition in vacuum, and electron-beam evaporation in vacuum are investigated. It is shown that the features of each technique affect the composition and crystal structure of the formed layers, and the degree of abruptness and crystalline quality of the heterointerface. Apparently, the composition and crystal structure are responsible for modification of the ferromagnetic properties. The defects in the heterointerface affect the properties of the Mn{sub x}Ga{sub y}/GaAs diode structure, in particular, the height of the Schottky diode potential barrier.

  19. Open circuit potential monitored digital photocorrosion of GaAs/AlGaAs quantum well microstructures

    Science.gov (United States)

    Aithal, Srivatsa; Dubowski, Jan J.

    2018-04-01

    Nanostructuring of semiconductor wafers with an atomic level depth resolution is a challenging task, primarily due to the limited availability of instruments for in situ monitoring of such processes. Conventional digital etching relies on calibration procedures and cumbersome diagnostics applied between or at the end of etching cycles. We have developed a photoluminescence (PL) based process for monitoring in situ digital photocorrosion (DPC) of GaAs/AlGaAs microstructures at rates below 0.2 nm per cycle. In this communication, we demonstrate that DPC of GaAs/AlGaAs microstructures could be monitored with open circuit potential (OCP) measured between the photocorroding surface of a microstructure and an Ag/AgCl reference electrode installed in the sample chamber. The excellent correlation between the position of both PL and OCP maxima indicates that the DPC process could be monitored in situ for materials that do not necessarily exhibit measurable PL emission.

  20. Raman scattering from In0.2Ga0.8N/GaN superlattices

    International Nuclear Information System (INIS)

    Kisoda, Kenji; Hirakura, Kohji; Harima, Hiroshi

    2006-01-01

    We have performed Raman scattering experiments on high quality In 0.2 Ga 0.8 N/GaN superlattices(SLs). The A 1 LO phonon mode from the In 0.2 Ga 0.8 N layer was observed in the Mg doped SL. This was attributable to manifestation of a resonance enhancement via acceptor levels formed by magnesium doping. The peak frequency of the A 1 LO mode shifted to high frequency side with the excitation energy. The frequency shift suggested that the composition of indium was fluctuated along the growth direction in the InGaN layer. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. 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.

  2. Development of methods for the purification of 67Ga and 68Ga for biomolecules labeling

    International Nuclear Information System (INIS)

    Costa, Renata Ferreira

    2012-01-01

    For more than fifty years, the long-lived 68 Ge/ 68 Ga generators have been in development, obtaining 68 Ga without the need of having in house cyclotron, which is a considerable convenience for PET centers that have no nearby cyclotrons. 68 Ga decays 89% by positron emission and low photon emission (1077 keV) and the physical half life of 67.7 minutes is compatible with the pharmacokinetics of low biomolecular weight substances like peptides and antibody fragments. Moreover, its established metallic chemistry allows it to be stably bound to the carrier peptide sequence via a suitable bifunctional chelator, such as DOTA. All these reasons together with the technology of PET/CT allowed advances in molecular imaging, in particular in the diagnosis of neuroendocrine diseases. However, the eluate from the commercial 68 Ge/ 68 Ga generators still contains high levels of long lived 68 Ge, besides other metallic impurities, which competes with 68 Ga with a consequent reduction of the labeling yield of biomolecules, such as Fe 3+ and Zn 2+ . Thus, the lower the amount of impurities in the eluate, the competition between the radiolabeled and unlabeled peptide by the receptor will be smaller and the quality of imaging will be better, a subsequent purification step is needed after the generator elution. The aim of this work is to evaluate different purifications methods of 68 Ga to label biomolecules, with emphasis on the study of the chemical impurities contained in the eluate and to develop a new purification method. Several purification methods were studied. Many cationic resin were tested simulating the commercial process. 68 Ga is adsorbed in cationic resin, which is not commercial available and eluted in acid/acetone solution. The use of minor particles of cationic resin AG50W-X4 (200-400 mesh) showed the best results. An innovate method was the extraction chromatography, which is based on the absorption of diisopropyl ether in XAD 16 and 68 Ga recovery in deionized

  3. Schottky barrier diode embedded AlGaN/GaN switching transistor

    International Nuclear Information System (INIS)

    Park, Bong-Ryeol; Lee, Jung-Yeon; Lee, Jae-Gil; Lee, Dong-Myung; Cha, Ho-Young; Kim, Moon-Kyung

    2013-01-01

    We developed a Schottky barrier diode (SBD) embedded AlGaN/GaN switching transistor to allow negative current flow during off-state condition. An SBD was embedded in a recessed normally-off AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET). The fabricated device exhibited normally-off characteristics with a gate threshold voltage of 2.8 V, a diode turn-on voltage of 1.2 V, and a breakdown voltage of 849 V for the anode-to-drain distance of 8 µm. An on-resistance of 2.66 mΩcm 2 was achieved at a gate voltage of 16 V in the forward transistor mode. Eliminating the need for an external diode, the SBD embedded switching transistor has advantages of significant reduction in parasitic inductance and chip area. (paper)

  4. The Formation and Characterization of GaN Hexagonal Pyramids

    Science.gov (United States)

    Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

    2013-05-01

    GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

  5. A Frontal Attack on Limiting Defects in GaN

    National Research Council Canada - National Science Library

    Morkoc, Hadis

    2002-01-01

    GaN community, particularly under the leadership of Drs. Wood, Win, and Litton, recognized that it is imperative that the extended, and point defects in GaN and related materials, and the mechanisms for their formation are understood...

  6. GaN Nanowires Synthesized by Electroless Etching Method

    KAUST Repository

    Najar, Adel; Anjum, Dalaver H.; Ng, Tien Khee; Ooi, Boon S.; Ben Slimane, Ahmed

    2012-01-01

    Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

  7. Synthetic Strategies and Applications of GaN Nanowires

    Directory of Open Access Journals (Sweden)

    Guoquan Suo

    2014-01-01

    Full Text Available GaN is an important III-V semiconductor material with a direct band gap of 3.4 eV at 300 K. The wide direct band gap makes GaN an attractive material for various applications. GaN nanowires have demonstrated significant potential as fundamental building blocks for nanoelectronic and nanophotonic devices and also offer substantial promise for integrated nanosystems. In this paper, we provide a comprehensive review on the general synthetic strategies, characterizations, and applications of GaN nanowires. We first summarize several growth techniques of GaN nanowires. Subsequently, we discuss mechanisms involved to generate GaN nanowires from different synthetic schemes and conditions. Then we review some characterization methods of GaN nanowires. Finally, several kinds of main applications of GaN nanowires are discussed.

  8. 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.

  9. The effect of Ga vacancies on the defect and magnetic properties of Mn-doped GaN

    International Nuclear Information System (INIS)

    Kang, Joongoo; Chang, K. J.

    2007-01-01

    We perform first-principles theoretical calculations to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (V Ga ) is introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurs from the Mn d band to the acceptor levels of V Ga , and strong Mn-N bonds are formed between the Mn ion and the N atoms in the neighborhood of V Ga . The charge transfer and chemical bonding effects significantly affect the defect and magnetic properties of Mn-doped GaN. In a Mn-V Ga complex, which consists of a Ga vacancy and one Mn ion, the dangling bond orbital of the N atom involved in the Mn-N bond is electrically deactivated, and the remaining dangling bond orbitals of V Ga lead to the shallowness of the defect level. When a Ga vacancy forms a complex with two Mn ions located at a distance of about 6 A, which corresponds to the percolation length in determining the Curie temperature in diluted Mn-doped GaN, the Mn d band is broadened and the density of states at the Fermi level is reduced due to two strong Mn-N bonds. Although the broadening and depopulation of the Mn d band weaken the ferromagnetic stability between the Mn ions, the ferromagnetism is still maintained because of the lack of antiferromagnetic superexchange interactions at the percolation length

  10. 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

  11. Gallium isotope fractionation during Ga adsorption on calcite and goethite

    Science.gov (United States)

    Yuan, Wei; Saldi, Giuseppe D.; Chen, JiuBin; Vetuschi Zuccolini, Marino; Birck, Jean-Louis; Liu, Yujie; Schott, Jacques

    2018-02-01

    Gallium (Ga) isotopic fractionation during its adsorption on calcite and goethite was investigated at 20 °C as a function of the solution pH, Ga aqueous concentration and speciation, and the solid to solution ratio. In all experiments Ga was found to be enriched in light isotopes at the solid surface with isotope fractionation △71Gasolid-solution up to -1.27‰ and -0.89‰ for calcite and goethite, respectively. Comparison of Ga isotopic data of this study with predictions for 'closed system' equilibrium and 'Rayleigh fractionation' models indicates that the experimental data are consistent with a 'closed system' equilibrium exchange between the fluid and the solid. The results of this study can be interpreted based on Ga aqueous speciation and the structure of Ga complexes formed at the solid surfaces. For calcite, Ga isotope fractionation is mainly triggered by increased Ga coordination and Ga-O bond length, which vary respectively from 4 and 1.84 Å in Ga(OH)4- to 6 and 1.94 Å in the >Ca-O-GaOH(OH2)4+ surface complex. For goethite, despite the formation of Ga hexa-coordinated >FeOGa(OH)20 surface complexes (Ga-O distances of 1.96-1.98 Å) both at acid and alkaline pH, a similar extent of isotope fractionation was found at acid and alkaline pH, suggesting that Ga(OH)4- is preferentially adsorbed on goethite for all investigated pH conditions. In addition, the observed decrease of Ga isotope fractionation magnitude observed with increasing Ga surface coverage for both calcite and goethite is likely related to the formation of Ga surface polymers and/or hydroxides with reduced Ga-O distances. This first study of Ga isotope fractionation during solid-fluid interactions suggests that the adsorption of Ga by oxides, carbonates or clay minerals could yield significant Ga isotope fractionation between secondary minerals and surficial fluids including seawater. Ga isotopes thus should help to better characterize the surficial biogeochemical cycles of gallium and its

  12. Optically detected cyclotron resonance in a single GaAs/AlGaAs heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Bartsch, Gregor

    2011-09-23

    Optically detected far-infrared cyclotron resonance (FIR-ODCR) in GaAs/AlGaAs HJs is interpreted in the frame of an exciton-dissociation mechanism. It is possible to explain the ODR mechanism by an exciton drag, mediated by ballistically propagating phonons. Furthermore, very narrow resonances are presented and realistic electron mobility values can be calculated. The exceptionally narrow ODCRs allow to measure conduction-band nonparabolicity effects and resolve satellite resonances, close to the main cyclotron resonance line.

  13. Absorption from Neutral Acceptors in GaAs and GaP

    DEFF Research Database (Denmark)

    Christensen, Ove

    1973-01-01

    We present a new calculation of the absorption due to transitions of holes between neutral acceptors and the various valence-band sublevels in GaAs and GaP. The acceptor wave function was approximated by a previously suggested expression for ground-state wave functions appropriate to complicated...... band extrema. Numerical calculations of the absorption from intervalence-band transitions of free holes and neutral acceptors have been performed. Good agreement with experimental results is obtained....

  14. InGaN/GaN light-emitting diode microwires of submillimeter length

    Energy Technology Data Exchange (ETDEWEB)

    Lundin, W. V., E-mail: lundin.vpegroup@mail.ioffe.ru; Rodin, S. N.; Sakharov, A. V.; Lundina, E. Yu. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Usov, S. O. [Russian Academy of Sciences, Research and Engineering Center of Submicron Heterostructures for Microelectronics (Russian Federation); Zadiranov, Yu. M.; Troshkov, S. I. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Tsatsulnikov, A. F. [Russian Academy of Sciences, Research and Engineering Center of Submicron Heterostructures for Microelectronics (Russian Federation)

    2017-01-15

    Microcrystalline wire-like InGaN/GaN light-emitting diodes designed as core–shell structures 400–600 μm in length are grown by metal–organic vapor-phase epitaxy on sapphire and silicon substrates. The technology of the titanium-nanolayer-induced ultrafast growth of nanowire and microwire crystals is used. As a current is passed through the microcrystals, an electroluminescence signal is observed in the blue–green spectral region.

  15. Preparation and properties of thick not intentionally doped GaInP(As)/GaAs layers

    CERN Document Server

    Nohavica, D; Zdansky, K

    1999-01-01

    We report on liquid-phase epitaxial growth of thick layers of GaInP(As), lattice matched to GaAs. Layers with thicknesses up to 10 mu m were prepared in a multi-melt bin, step-cooling, one-phase configuration. Unintentionally doped layers, grown from moderate purity starting materials, show a significant decrease in the residual impurity level when erbium is added to the melt. Fundamental electrical and optical properties of the layers were investigated. (author)

  16. Inverse temperature dependence of reverse gate leakage current in AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Kaushik, J K; Balakrishnan, V R; Muralidharan, R; Panwar, B S

    2013-01-01

    The experimentally observed inverse temperature dependence of the reverse gate leakage current in AlGaN/GaN HEMT is explained using a virtual gate trap-assisted tunneling model. The virtual gate is formed due to the capture of electrons by surface states in the vicinity of actual gate. The increase and decrease in the length of the virtual gate with temperature due to trap kinetics are used to explain this unusual effect. The simulation results have been validated experimentally. (paper)

  17. Barrier Height Variation in Ni-Based AlGaN/GaN Schottky Diodes

    NARCIS (Netherlands)

    Hajlasz, Marcin; Donkers, Johan J.T.M.; Pandey, Saurabh; Hurkx, Fred; Hueting, Raymond J.E.; Gravesteijn, Dirk J.

    2017-01-01

    In this paper, we have investigated Ni-based AlGaN/GaN Schottky diodes comprising capping layers with silicon-Technology-compatible metals such as TiN, TiW, TiWN, and combinations thereof. The observed change in Schottky barrier height of a Ni and Ni/TiW/TiWN/TiW contact can be explained by stress

  18. 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.

  19. 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.

  20. Auger recombination suppression and band alignment in GaAsBi/GaAs heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hild, K.; Batool, Z.; Jin, S. R.; Hossain, N.; Marko, I. P.; Sweeney, S. J. [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); Hosea, T. JC. [1 Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, GU2 7XH, UK and also, Ibnu Sina Institute, Universiti Teknologi Malaysia, Johor Bahru, 81310 (Malaysia); Lu, X. [Department of Electrical and Computer Engineering, University of Victoria, Victoria BC, V8W 3P6, Canada and now VarianSemiconductor Equipment Associates, Gloucester, MA 01930 (United States); Tiedje, T. [Department of Electrical and Computer Engineering, University of Victoria, Victoria BC, V8W 3P6 (Canada)

    2013-12-04

    Using a combination of experimental and theoretical techniques we present the dependence of the bandgap E{sub g} and the spin orbit splitting energy Δ{sub so}, with Bi concentration in GaAsBi/GaAs samples. We find that the concentration at which Δ{sub so},> E{sub g} occurs at 9%. Both spectroscopic as well as first device results indicate a type I alignment.

  1. Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor

    DEFF Research Database (Denmark)

    MacLeod, S. J.; See, A. M.; Keane, Z. K.

    2014-01-01

    Radio frequency reflectometry is demonstrated in a sub-micron undoped AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive candidates to study single electron phenomena, due to their charge stability and robust electronic properties after thermal cycling. However......, these devices require a large top-gate, which is unsuitable for the fast and sensitive radio frequency reflectometry technique. Here, we demonstrate that rf reflectometry is possible in an undoped SET....

  2. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    Energy Technology Data Exchange (ETDEWEB)

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021 (Russian Federation); Luque, Antonio [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021, Russia and Instituto de Energia Solar, Universidad Politecnica de Madrid, Madrid (Spain)

    2014-09-26

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (λ = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  3. Graded GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Zíková, Markéta; Pangrác, Jiří; Oswald, Jiří; Kuldová, Karla; Vyskočil, Jan; Hulicius, Eduard

    2013-01-01

    Roč. 370, MAY (2013), s. 303-306 ISSN 0022-0248 R&D Projects: GA ČR GAP102/10/1201 Institutional research plan: CEZ:AV0Z10100521 Keywords : band alignment * photoluminescence * strain reducing layer * quantum dot * MOVPE * InAs/GaAs Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.693, year: 2013

  4. Temperature-dependent stress in diamond-coated AlGaN/GaN heterostructures

    Czech Academy of Sciences Publication Activity Database

    Ižák, Tibor; Jirásek, Vít; Vanko, G.; Dzuba, J.; Kromka, Alexander

    2016-01-01

    Roč. 106, Sep (2016), s. 305-312 ISSN 0264-1275 R&D Projects: GA ČR(CZ) GP14-16549P Grant - others:AV ČR(CZ) SAV-16-02 Program:Bilaterální spolupráce Institutional support: RVO:68378271 Keywords : thermally induced stress * Raman spectroscopy * polycrystalline diamond film * GaN Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.364, year: 2016

  5. Selective area deposition of diamond films on AlGaN/GaN heterostructures

    Czech Academy of Sciences Publication Activity Database

    Ižák, Tibor; Babchenko, Oleg; Jirásek, Vít; Vanko, G.; Vallo, M.; Vojs, M.; Kromka, Alexander

    2014-01-01

    Roč. 250, č. 12 (2014), 2574-2580 ISSN 0370-1972 R&D Projects: GA ČR(CZ) GP14-16549P Institutional support: RVO:68378271 Keywords : circular high electron mobility transistors * diamond films * GaN substrates * microwave chemical vapor deposition * selective area deposition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.489, year: 2014

  6. Evaluation of resonant tunneling transmission coefficient from multilayer structures GaAlAs/GaAs

    Directory of Open Access Journals (Sweden)

    L. Moghaddasi

    2003-12-01

    Full Text Available   A theoretical study of resonant tunneling in multilayered GaAlAs/GaAs structures are presented. The spectrum of resonant energies and its dependence on the barrier structure are analyzed from calculated profiles of barrier transparency versus energy, and from current voltage characteristics computed at selected temperatures and Fermi levels. The present formalism is based on the effective mass approximation and results are via direct numerical evaluations.

  7. Optical displacement measurement with GaAs/AlGaAs-based monolithically integrated Michelson interferometers

    OpenAIRE

    Hofstetter, Daniel; Zappe, H. P.; Dändliker, René

    2008-01-01

    Two monolithically integrated optical displacement sensors fabricated in the GaAs/AlGaAs material system are reported. These single-chip microsystems are configured as Michelson interferometers and comprise a distributed Bragg reflector (DBR) laser, photodetectors, phase shifters, and waveguide couplers. While the use of a single Michelson interferometer allows measurement of displacement magnitude only, a double Michelson interferometer with two interferometer signals in phase quadrature als...

  8. Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires

    OpenAIRE

    Butschkow, Christian H.; Reiger, Elisabeth; Geißler, Stefan; Rudolph, Andreas; Soda, Marcello; Schuh, Dieter; Woltersdorf, Georg; Wegscheider, Werner; Weiss, Dieter

    2011-01-01

    We investigate, angle dependent, the magnetoresistance (MR) of individual self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic temperatures. The shape of the MR traces and the observed strong anisotropies in transport can be ascribed to the interplay of the negative magnetoresistance effect and a strong uniaxial anisotropy with the magnetic easy direction pointing along the wire axis. The magnetoresistance can be well described by a quantitative analysis based on the ...

  9. Light-hole conduction in InGaAs/GaAs strained-layer superlattices

    International Nuclear Information System (INIS)

    Schirber, J.E.; Fritz, I.J.; Dawson, L.R.

    1985-01-01

    We report the first observation of light-hole band carriers in In/sub 0.2/Ga/sub 0.8/As/GaAs strained-layer superlattices by direct measurements of their effective mass (m*m/sub o/ = 0.14) using oscillatory magnetoresistance data. Preferential population of light-hole states, due to splitting of the degenerate bulk valence bands by built-in strain, allows this direct observation

  10. On-sun concentrator performance of GaInP/GaAs tandem cells

    Energy Technology Data Exchange (ETDEWEB)

    Friedman, D.J.; Kurtz, S.R.; Sinha, K.; McMahon, W.E.; Olson, J.M. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The GaInP/GaAs concentrator device has been adapted for and tested in a prototype {open_quotes}real-world{close_quotes} concentrator power system. The device achieved an on-sun efficiency of 28% {+-} 1% in the range of approximately 200-260 suns with device operating temperatures of 38{degrees}C to 42{degrees}C. The authors discuss ways of further improving this performance for future devices.

  11. 78 FR 28492 - Special Local Regulation; Low Country Splash, Wando River, Cooper River, and Charleston Harbor...

    Science.gov (United States)

    2013-05-15

    ...-AA08 Special Local Regulation; Low Country Splash, Wando River, Cooper River, and Charleston Harbor... establishing a special local regulation on the waters of the Wando River, Cooper River, and Charleston Harbor... rulemaking (NPRM) entitled, ``Special Local Regulation; Low Country Splash, Wando River, Cooper River, and...

  12. 78 FR 18277 - Special Local Regulation; Low Country Splash, Wando River, Cooper River, and Charleston Harbor...

    Science.gov (United States)

    2013-03-26

    ...-AA08 Special Local Regulation; Low Country Splash, Wando River, Cooper River, and Charleston Harbor... proposes to issue a special local regulation on the waters of the Wando River, Cooper River, and Charleston... Country Splash is scheduled to take place on the waters of the Wando River, Cooper River, and Charleston...

  13. Dislocation mechanism of twinning in Ni-Mn-Ga

    Czech Academy of Sciences Publication Activity Database

    Zárubová, Niva; Ge, Y.; Gemperlová, Juliana; Gemperle, Antonín; Hannula, S.-P.

    2012-01-01

    Roč. 5, č. 1 (2012), "1250006-1"-"1250006-4" ISSN 1793-6047 R&D Projects: GA ČR GAP107/10/0824; GA ČR(CZ) GAP107/11/0391; GA AV ČR IAA100100920 Institutional research plan: CEZ:AV0Z10100520 Keywords : Ni-Mn-Ga shape memory alloy * martensitic transformation * in situ TEM straining Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.270, year: 2012

  14. Evaluation of Edge Assembly Crossover for Hybrid GA

    OpenAIRE

    Yoshihara, Ikuo; Sato, Masakazu; Nguyen, Hung Dinh; Yamanori, Kunihito

    2004-01-01

    Abstract ###Traveling Salesman Problem (TSP) is one of the representative combinatorial optimization prob-###lems. The promising approach to solve TSP is Genetic Algorithm (GA). GA has global search ability, ###and heuristic is used in order to compensate local search ability, because GA is lack of local search abil-###ity. Hybrid (GA (HGA) combined with heuristics can be expected to obtain high quality solutions.We ###employ Lin-Kernighan heuristics which is very effective in TSP. Because cr...

  15. Interlayer exchange coupling in (Ga,Mn)As based multilayers

    Czech Academy of Sciences Publication Activity Database

    Giddings, A.D.; Jungwirth, Tomáš; Gallagher, B. L.

    2006-01-01

    Roč. 3, č. 12 (2006), s. 4070-4073 ISSN 1610-1634 R&D Projects: GA ČR GA202/05/0575; GA AV ČR(CZ) IAA100100530; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * standing-wave fluorescence * x-ray diffraction Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. 68Ga-DOTA-TOC Uptake in Pleomorphic Adenoma.

    Science.gov (United States)

    Laurens, S Tom; Netea-Maier, Romana T; Aarntzen, Erik J H G

    2018-07-01

    A 56-year-old man who was recently diagnosed with a carcinoid tumor of the os petrosum was referred for a Ga-DOTA-TOC PET/CT scan. Besides the moderately increased Ga-DOTA-TOC accumulation in the carcinoid tumor, the scan showed strongly increased and focal Ga-DOTA-TOC uptake in an additional lesion in the right parotid gland. The markedly different Ga-DOTA-TOC avidity suggested a different etiology, and histological examination demonstrated a pleomorphic adenoma.

  17. 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

  18. 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.

  19. Mn doped GaN thin films and nanoparticles

    Czech Academy of Sciences Publication Activity Database

    Šofer, Z.; Sedmidubský, D.; Huber, Š.; Hejtmánek, Jiří; Macková, Anna; Fiala, R.

    2012-01-01

    Roč. 9, 8-9 (2012), s. 809-824 ISSN 1475-7435 R&D Projects: GA ČR GA104/09/0621 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10480505 Keywords : GaN nanoparticles * GaN thin films * manganese * transition metals * MOVPE * ion implantations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.087, year: 2012

  20. 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.