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Sample records for technology atlanta ga

  1. 78 FR 76810 - Information Collection; Environmental Justice and the Urban Forest in Atlanta, GA

    Science.gov (United States)

    2013-12-19

    ... of, city trees in Atlanta. This dimension of environmental justice will be combined with data on..., electronic, mechanical, or other technological collection techniques or other forms of information technology...

  2. 75 FR 76953 - Reorganization of Foreign-Trade Zone 26 Under Alternative Site Framework, Atlanta, GA

    Science.gov (United States)

    2010-12-10

    ... DEPARTMENT OF COMMERCE Foreign-Trade Zones Board [Order No. 1725] Reorganization of Foreign-Trade Zone 26 Under Alternative Site Framework, Atlanta, GA Pursuant to its authority under the Foreign-Trade... reorganization of general-purpose zones; Whereas, the Georgia Foreign-Trade Zone, Inc., grantee of Foreign- Trade...

  3. Photochemistry of ozone formation in Atlanta, GA-Models and measurements

    Science.gov (United States)

    Sillman, Sanford; Al-Wali, Khalid I.; Marsik, Frank J.; Nowacki, Peter; Samson, Perry J.; Rodgers, Michael O.; Garland, Leslie J.; Martinez, Jose E.; Stoneking, Chris; Imhoff, Robert; Lee, Jai Hoon; Newman, Leonard; Weinstein-Lloyd, Judith; Aneja, Viney P.

    Chemical measurements made during an air pollution event in Atlanta, GA have been compared with results from several photochemical simulations. Measurements included O 3, primary reactive organic gases (ROG), aldehydes, PAN, total reactive nitrogen (NO y) and H 2O 2, with vertical profiles for primary ROG. Photochemical models using two different chemical representations and a range of assumptions about winds, vertical mixing and emissions were used to simulate the event. Results show that assumptions about vertical mixing can cause a variation in simulated surface concentrations of primary hydrocarbons of a factor of two or more. A tendency to underestimate isoprene was found in comparison with measured vertical profiles. The models tend to overestimate concentrations of HCHO, H202 and PAN in comparison with measurements. Peak O 3 and concurrent NO y from helicopter measurements was used as a basis for evaluating individual model scenarios. Scenarios were developed with different O3 NOx- ROG sensitivity, but only the NO x- sensitive scenarios are consistent with measured O 3, NO y and isoprene.

  4. Characterization of CCN and IN activity of bacterial isolates collected in Atlanta, GA

    Science.gov (United States)

    Purdue, Sara; Waters, Samantha; Karthikeyan, Smruthi; Konstantinidis, Kostas; Nenes, Athanasios

    2016-04-01

    Characterization of CCN activity of bacteria, other than a few select types such as Pseudomonas syringae, is limited, especially when looked at in conjunction with corresponding IN activity. The link between these two points is especially important for bacteria as those that have high CCN activity are likely to form an aqueous phase required for immersion freezing. Given the high ice nucleation temperature of bacterial cells, especially in immersion mode, it is important to characterize the CCN and IN activity of many different bacterial strains. To this effect, we developed a droplet freezing assay (DFA) which consists of an aluminum cold plate, cooled by a continuous flow of an ethylene glycol-water mixture, in order to observe immersion freezing of the collected bacteria. Here, we present the initial results on the CCN and IN activities of bacterial samples we have collected in Atlanta, GA. Bacterial strains were collected and isolated from rainwater samples taken from different storms throughout the year. We then characterized the CCN activity of each strain using a DMT Continuous Flow Streamwise Thermal Gradient CCN Counter by exposing the aerosolized bacteria to supersaturations ranging from 0.05% to 0.6%. Additionally, using our new DFA, we characterized the IN activity of each bacterial strain at temperatures ranging from -20oC to 0oC. The combined CCN and IN activity gives us valuable information on how some uncharacterized bacteria contribute to warm and mixed-phase cloud formation in the atmosphere.

  5. 77 FR 5429 - Proposed Modification of the Atlanta Class B Airspace Area; GA

    Science.gov (United States)

    2012-02-03

    ... due to traffic volume. On hot summer days, heavy aircraft on departure are sometimes unable to climb... airspace. Due to heavy traffic volume and procedures necessary to manage the flow of traffic, it has not... 1, 2010, in Chamblee, GA; and on March 4, 2010, at Peachtree City Falcon Field, Peachtree City, GA...

  6. GaAs TECHNOLOGY

    Directory of Open Access Journals (Sweden)

    Mustafa TEMİZ

    1995-02-01

    Full Text Available The object of this work is to review the important for the future and the characteristic properties of gallium - arsenide. On this work, a realistic statement of current status of gallium-arsenide technology will provide and for future this will help to realise the enormous possibilities which we believe lie ahead. Gallium-arsenide integrated circuit technology has historically been portrayed as the technology of future. Now although it has not attained the wide complete applicability, it has gradually becoming an accepted and commercially available source of high-speed integrated circuits. High-speed logic circuits fabricated in gallium arsenide have shown promise for applications such as computing and signal processing. The past fifteen-twenty years have seen the emergence of gallium-arsenide technology from laboratuary to the market place. This innovations have been accompanied by dramatic increases in complexity from early single devices to the integrated circuits of considerable complexity for both digital and analogue applications. The aims to lay down sound principles of forthcoming developments in which both the speed and level of the complexity of gallium-arsenide circuits will increase dramatically meeting needs in such as areas as ultra fast computers, personnel communications and new broadcasting technology.

  7. GLOBECOM '84 - Global Telecommunications Conference, Atlanta, GA, November 26-29, 1984, Conference Record. Volume 3

    Science.gov (United States)

    Attention is given to aspects of quality assurance methodologies in development life cycles, optical intercity transmission systems, multiaccess protocols, system and technology aspects in the case of regional/domestic satellites, advances in SSB-AM radio transmission over terrestrial and satellite network, and development environments for telecommunications systems. Other subjects studied are concerned with business communication networks for voice and data, VLSI in local network and communication protocol, product evaluation and support, an update regarding Videotex, topics in communication theory, topics in radio propagation, a status report regarding societal effects of technology in the workplace, digital image processing, and adaptive signal processing for communications. The management of the reliability function in the development process is considered along with Giga-bit technologies for long distance large capacity optical transmission equipment. The application of gallium arsenide analog and digital integrated circuits for high-speed fiber optical communications, and a simple algorithm for image data coding.

  8. GLOBECOM '84 - Global Telecommunications Conference, Atlanta, GA, November 26-29, 1984, Conference Record. Volume 1

    Science.gov (United States)

    The subjects discussed are related to LSI/VLSI based subscriber transmission and customer access for the Integrated Services Digital Network (ISDN), special applications of fiber optics, ISDN and competitive telecommunication services, technical preparations for the Geostationary-Satellite Orbit Conference, high-capacity statistical switching fabrics, networking and distributed systems software, adaptive arrays and cancelers, synchronization and tracking, speech processing, advances in communication terminals, full-color videotex, and a performance analysis of protocols. Advances in data communications are considered along with transmission network plans and progress, direct broadcast satellite systems, packet radio system aspects, radio-new and developing technologies and applications, the management of software quality, and Open Systems Interconnection (OSI) aspects of telematic services. Attention is given to personal computers and OSI, the role of software reliability measurement in information systems, and an active array antenna for the next-generation direct broadcast satellite.

  9. Advancing Residential Retrofits in Atlanta

    Energy Technology Data Exchange (ETDEWEB)

    Jackson, Roderick K [ORNL; Kim, Eyu-Jin [Southface Energy Institute; Roberts, Sydney [Southface Energy Institute; Stephenson, Robert [Southface Energy Institute

    2012-07-01

    This report will summarize the home energy improvements performed in the Atlanta, GA area. In total, nine homes were retrofitted with eight of the homes having predicted source energy savings of approximately 30% or greater based on simulated energy consumption.

  10. Epidemiology of Methicillin-Resistant Staphylococcus aureus Bloodstream Coinfection Among Adults With Candidemia in Atlanta, GA, 2008-2012.

    Science.gov (United States)

    Reno, Jessica; Doshi, Saumil; Tunali, Amy K; Stein, Betsy; Farley, Monica M; Ray, Susan M; Jacob, Jesse T

    2015-11-01

    Patients with candidemia are at risk for other invasive infections, such as methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI). To identify the risk factors for, and outcomes of, BSI in adults with Candida spp. and MRSA at the same time or nearly the same time. Population-based cohort study. Metropolitan Atlanta, March 1, 2008, through November 30, 2012. All residents with Candida spp. or MRSA isolated from blood. The Georgia Emerging Infections Program conducts active, population-based surveillance for candidemia and invasive MRSA. Medical records for patients with incident candidemia were reviewed to identify cases of MRSA coinfection, defined as incident MRSA BSI 30 days before or after candidemia. Multivariate logistic regression was performed to identify factors associated with coinfection in patients with candidemia. Among 2,070 adult candidemia cases, 110 (5.3%) had coinfection within 30 days. Among these 110 coinfections, MRSA BSI usually preceded candidemia (60.9%; n=67) or occurred on the same day (20.0%; n=22). The incidence of coinfection per 100,000 population decreased from 1.12 to 0.53 between 2009 and 2012, paralleling the decreased incidence of all MRSA BSIs and candidemia. Thirty-day mortality was similarly high between coinfection cases and candidemia alone (45.2% vs 36.0%, P=.10). Only nursing home residence (odds ratio, 1.72 [95% CI, 1.03-2.86]) predicted coinfection. A small but important proportion of patients with candidemia have MRSA coinfection, suggesting that heightened awareness is warranted after 1 major BSI pathogen is identified. Nursing home residents should be targeted in BSI prevention efforts.

  11. Sending a Dear John Letter: Public Information Campaigns and the Movement to “End Demand” for Prostitution in Atlanta, GA

    Directory of Open Access Journals (Sweden)

    Samantha Majic

    2017-11-01

    Full Text Available This paper examines “Dear John”, a public information campaign that ran from 2006–2008 in Atlanta, GA, to ask what narrative it conveys about commercial sex and those who engage in it, in order to understand the gendered (and other discursive constructions it produces, reflects, and complicates about these activities and subjects. Drawing from both policy and sex work/trafficking scholarship, this paper argues that Dear John used symbolic images and direct and consequential text to convey a “male demand” narrative, which holds that men’s demand for sexual services harms girls and young women and will not be tolerated. Yet, in so doing, Dear John also reinforced particularly gendered characterizations of individuals who trade sex, while de-emphasizing other factors that increase young peoples’ vulnerabilities to and within sex work. The paper concludes by discussing Dear John’s outcomes and significance for scholars concerned with sex work, policy, and social change.

  12. HIV sexual transmission risks in the context of clinical care: a prospective study of behavioural correlates of HIV suppression in a community sample, Atlanta, GA, USA.

    Science.gov (United States)

    Kalichman, Seth C; Cherry, Chauncey; Kalichman, Moira O; Washington, Christopher; Grebler, Tamar; Merely, Cindy; Welles, Brandi; Pellowski, Jennifer; Kegler, Christopher

    2015-01-01

    Antiretroviral therapy (ART) improves the health of people living with HIV and has the potential to reduce HIV infectiousness, thereby preventing HIV transmission. However, the success of ART for HIV prevention hinges on sustained ART adherence and avoiding sexually transmitted infections (STI). To determine the sexual behaviours and HIV transmission risks of individuals with suppressed and unsuppressed HIV replication (i.e., viral load). Assessed HIV sexual transmission risks among individuals with clinically determined suppressed and unsuppressed HIV. Participants were 760 men and 280 women living with HIV in Atlanta, GA, USA, who completed behavioural assessments, 28-daily prospective sexual behaviour diaries, one-month prospective unannounced pill counts for ART adherence, urine screening for illicit drug use and medical record chart abstraction for HIV viral load. Individuals with unsuppressed HIV demonstrated a constellation of behavioural risks for transmitting HIV to uninfected sex partners that included symptoms of STI and substance use. In addition, 15% of participants with suppressed HIV had recent STI symptoms/diagnoses, indicating significant risks for sexual infectiousness despite their HIV suppression in blood plasma. Overall, 38% of participants were at risk for elevated sexual infectiousness and just as many engaged in unprotected sexual intercourse with non-HIV-infected partners. Implementation strategies for using HIV treatments as HIV prevention requires enhanced behavioural interventions that extend beyond ART to address substance use and sexual health that will otherwise undermine the potential preventive impact of early ART.

  13. Disparities in herpes simplex virus type 2 infection between black and white men who have sex with men in Atlanta, GA.

    Science.gov (United States)

    Okafor, Netochukwu; Rosenberg, Eli S; Luisi, Nicole; Sanchez, Travis; del Rio, Carlos; Sullivan, Patrick S; Kelley, Colleen F

    2015-09-01

    HIV disproportionately affects black men who have sex with men, and herpes simplex virus type 2 is known to increase acquisition of HIV. However, data on racial disparities in herpes simplex virus type 2 prevalence and risk factors are limited among men who have sex with men in the United States. InvolveMENt was a cohort study of black and white HIV-negative men who have sex with men in Atlanta, GA. Univariate and multivariate cross-sectional associations with herpes simplex virus type 2 seroprevalence were assessed among 455 HIV-negative men who have sex with men for demographic, behavioural and social determinant risk factors using logistic regression. Seroprevalence of herpes simplex virus type 2 was 23% (48/211) for black and 16% (38/244) for white men who have sex with men (p = 0.05). Education, poverty, drug/alcohol use, incarceration, circumcision, unprotected anal intercourse, and condom use were not associated with herpes simplex virus type 2. In multivariate analyses, black race for those ≤25 years, but not >25 years, and number of sexual partners were significantly associated. Young black men who have sex with men are disproportionately affected by herpes simplex virus type 2, which may contribute to disparities in HIV acquisition. An extensive assessment of risk factors did not explain this disparity in herpes simplex virus type 2 infection suggesting differences in susceptibility or partner characteristics. © The Author(s) 2014.

  14. 77 FR 46685 - In the Matter of: Steven Neal Greenoe, Currently Incarcerated at: Inmate #54450-056, USP Atlanta...

    Science.gov (United States)

    2012-08-06

    ... DEPARTMENT OF COMMERCE Bureau of Industry and Security In the Matter of: Steven Neal Greenoe, Currently Incarcerated at: Inmate 54450-056, USP Atlanta, U.S. Penitentiary, P.O. Box 1150160, Atlanta, GA...: Currently incarcerated at: Inmate 54450-056, USP Atlanta, U.S. Penitentiary, P.O. Box 1150160, Atlanta, GA...

  15. Assessment of Ga2O3 technology

    Science.gov (United States)

    2016-09-15

    electronics application is the only driver for the technology at present. This type of electronics have a large commercial market , but there are...vol. 43, p. 7133, 2004. [119] A. J. Freeman, K. R. Poeppelmeier, T. O. Mason, R. P. H. Chang, and T. J. Marks, "Chemical and Thin-Film Strategies for...doped β-Ga2O3 single crystals," Applied Physics Letters, vol. 92, p. 201914, 2008. [138] R. A. Laudise, J. B. Mullin , B. Mutaftschiev, and K. Nassau

  16. Modeling the Effect of Onsite Wastewater Treatment Systems on Nitrate Load Using SWAT in an Urban Watershed of Metropolitan Atlanta, GA

    Science.gov (United States)

    Onsite Wastewater Treatment Systems (OWTSs) can be a source of nitrate (NO3-) contamination in both surface and ground waters as a result of failing or high density systems. In metropolitan Atlanta, more than 26% of homes are on OWTS and this percentage is expected to increase wi...

  17. High efficiency low cost GaAs/Ge cell technology

    Science.gov (United States)

    Ho, Frank

    1990-01-01

    Viewgraphs on high efficiency low cost GaAs/Ge cell technology are presented. Topics covered include: high efficiency, low cost GaAs/Ge solar cells; advantages of Ge; comparison of typical production cells for space applications; panel level comparisons; and solar cell technology trends.

  18. The use of sustainable and scalable health care technologies in developing countries

    OpenAIRE

    Gari D. Clifford, Gari

    2016-01-01

    Gari D Clifford1–3 1Department of Biomedical Informatics, Emory University, Atlanta, GA, USA; 2Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA; 3Centre for Affordable Health Care Technology, Kellogg College, University of Oxford, Oxford, UK Abstract: Although health care technology is progressing, in important ways access is dropping for many communities across the globe. Contributing factors include increasing awareness and options for diagn...

  19. Selected papers from the 12th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2012) (Atlanta, GA, USA, 2-5 December 2012)

    Science.gov (United States)

    Allen, Mark G.; Lang, Jeffrey

    2013-11-01

    Welcome to this special section of the Journal of Micromechanics and Microengineering (JMM). This section, co-edited by myself and by Professor Jeffrey Lang of the Massachusetts Institute of Technology, contains expanded versions of selected papers presented at the Power MEMS meeting held in Atlanta, GA, USA, in December of 2012. Professor Lang and I had the privilege of co-chairing Power MEMS 2012, the 12th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications. The scope of the PowerMEMS series of workshops ranges from basic principles, to materials and fabrication, to devices and systems, to applications. The many applications of power MEMS (microelectromehcanical systems) range from MEMS-enabled energy harvesting, storage, conversion and conditioning, to integrated systems that manage these processes. Why is the power MEMS field growing in importance? Smaller-scale power and power supplies (microwatts to tens of watts) are gaining in prominence due to many factors, including the ubiquity of low power portable electronic equipment and the proliferation of wireless sensor nodes that require extraction of energy from their embedding environment in order to function. MEMS manufacturing methods can be utilized to improve the performance of traditional power supply elements, such as allowing batteries to charge faster or shrinking the physical size of passive elements in small-scale power supplies. MEMS technologies can be used to fabricate energy harvesters that extract energy from an embedding environment to power wireless sensor nodes, in-body medical implants and other devices, in which the harvesters are on the small scales that are appropriately matched to the overall size of these microsystems. MEMS can enable the manufacturing of energy storage elements from nontraditional materials by bringing appropriate structure and surface morphology to these materials as well as fabricating the electrical interfaces

  20. Effect of photocatalytic oxidation technology on GaN CMP

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jie, E-mail: jie-wang11@mails.tsinghua.edu.cn; Wang, Tongqing, E-mail: wtq@mail.tsinghua.edu.cn; Pan, Guoshun, E-mail: pangs@mail.tsinghua.edu.cn; Lu, Xinchun, E-mail: xclu@mail.tsinghua.edu.cn

    2016-01-15

    Graphical abstract: - Highlights: • Photocatalytic oxidation technology was introduced to GaN CMP for the first time and proves to be more efficient than before. • XPS analysis reveals the planarization process by different N-type semiconductor particles. • Analyzing the effect of pH on photocatalytic oxidation in GaN CMP. • Proposing the photocatalytic oxidation model to reveal the removal mechanism. - Abstract: GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO{sub 2}, SnO{sub 2}, and Fe{sub 2}O{sub 3}) are used as catalysts and added to the H{sub 2}O{sub 2}–SiO{sub 2}-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH{sup −} and H{sub 2}O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H{sub 2}O{sub 2}–SiO{sub 2}-based polishing system combined with catalysts are improved significantly, especially when using TiO{sub 2}, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO{sub 2} is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  1. Advances in AlGaInN laser diode technology

    Science.gov (United States)

    Najda, S. P.; Perlin, P.; Suski, T.; Marona, L.; Bockowski, Mike; Leszczyński, M.; Wisniewski, P.; Czernecki, R.; Kucharski, R.; Targowski, G.; Watson, S.; Kelly, A. E.

    2014-03-01

    The latest developments in AlGaInN laser diode technology are reviewed. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of >100mW in the 400-420nm wavelength range that are suitable for telecom applications. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is demonstrated with a single chip, AlGaInN laser diode `mini-array' with a common p-contact configuration at powers up to 2.5W cw at 410nm. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. GaN laser bars of up to 5mm with 20 emitters, mounted in a CS mount package, give optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.

  2. Long term impacts of combined sewer overflow remediation on water quality and population dynamics of Culex quinquefasciatus, the main urban West Nile virus vector in Atlanta, GA.

    Science.gov (United States)

    Lund, Andrea; McMillan, Joseph; Kelly, Rosmarie; Jabbarzadeh, Shirin; Mead, Daniel G; Burkot, Thomas R; Kitron, Uriel; Vazquez-Prokopec, Gonzalo M

    2014-02-01

    Combined sewers are a significant source of urban water pollution due to periodic discharges into natural streams. Such events (called combined sewer overflows, or CSOs) contribute to the impairment of natural waterways and are associated with increased mosquito productivity and elevated risk of West Nile virus transmission. We investigated the impact of CSOs on water quality and immature mosquito productivity in the city of Atlanta, Georgia, one year before and four years after CSO facility remediation. Water quality (ammonia, phosphate, nitrate and dissolved oxygen concentrations), immature mosquitoes (larvae and pupae), water temperature and rainfall were quantified biweekly between June-October at two urban creeks during 2008-2012. A before-after control-intervention design tested the impact of remediation on mosquito productivity and water quality, whereas generalized linear mixed-effect models quantified the factors explaining the long term impacts of remediation on mosquito productivity. Ammonia and phosphate concentrations and late immature (fourth-instar and pupae) mosquito populations were significantly higher in CSO than in non-CSO creeks, while dissolved oxygen concentrations were lower. Remediation significantly improved water quality estimates (particularly ammonia and dissolved oxygen) and reduced the number of overflows, mosquito productivity and the overall contribution of CSO-affected streams as sources of vectors of West Nile virus. The quality of water in CSOs provided a suitable habitat for immature mosquitoes. Remediation of the CSO facility through the construction of a deep storage tunnel improved water quality indices and reduced the productivity of mosquito species that can serve as vectors of West Nile virus. Copyright © 2013 Elsevier Inc. All rights reserved.

  3. GaN Technology for Power Electronic Applications: A Review

    Science.gov (United States)

    Flack, Tyler J.; Pushpakaran, Bejoy N.; Bayne, Stephen B.

    2016-06-01

    Power semiconductor devices based on silicon (Si) are quickly approaching their limits, set by fundamental material properties. In order to address these limitations, new materials for use in devices must be investigated. Wide bandgap materials, such as silicon carbide (SiC) and gallium nitride (GaN) have suitable properties for power electronic applications; however, fabrication of practical devices from these materials may be challenging. SiC technology has matured to point of commercialized devices, whereas GaN requires further research to realize full material potential. This review covers fundamental material properties of GaN as they relate to Si and SiC. This is followed by a discussion of the contemporary issues involved with bulk GaN substrates and their fabrication and a brief overview of how devices are fabricated, both on native GaN substrate material and non-native substrate material. An overview of current device structures, which are being analyzed for use in power switching applications, is then provided; both vertical and lateral device structures are considered. Finally, a brief discussion of prototypes currently employing GaN devices is given.

  4. A Very Robust AlGaN/GaN HEMT Technology to High Forward Gate Bias and Current

    Directory of Open Access Journals (Sweden)

    Bradley D. Christiansen

    2012-01-01

    Full Text Available Reports to date of GaN HEMTs subjected to forward gate bias stress include varied extents of degradation. We report an extremely robust GaN HEMT technology that survived—contrary to conventional wisdom—high forward gate bias (+6 V and current (>1.8 A/mm for >17.5 hours exhibiting only a slight change in gate diode characteristic, little decrease in maximum drain current, with only a 0.1 V positive threshold voltage shift, and, remarkably, a persisting breakdown voltage exceeding 200 V.

  5. Quaternary InGaAsSb Thermophotovoltaic Diode Technology

    International Nuclear Information System (INIS)

    M Dashiell; J Beausang; H Ehsani; G Nichols; D DePoy; L Danielson; P Talamo; K Rahner; E Brown; S Burger; P Fourspring; W Topper; P Baldasaro; C Wang; R Huang; M Connors; G Turner; Z Shellenbarger; G Taylor; Jizhong Li; R Martinelli; D Donetski; S Anikeev; G Belenky; S Luryl

    2005-01-01

    Thermophotovoltaic (TPV) diodes fabricated from InGaAsSb alloys lattice-matched to GaSb substrates are grown by Metal Organic Vapor Phase Epitaxy (MOVPE). 0.53eV InGaAsSb TPV diodes utilizing front-surface spectral control filters have been tested in a vacuum cavity and a TPV thermal-to-electric conversion efficiency (η TPV ) and a power density (PD) of η TPV = 19% and PD=0.58 W/cm 2 were measured for T radiator = 950 C and T diode = 27 C. Recombination coefficients deduced from minority carrier measurements and the theory reviewed in this article predict a practical limit to the maximum achievable conversion efficiency and power density for 0.53eV InGaAsSb TPV. The limits for the above operating temperatures are projected to be η TPV = 26% and PD = 0.75 W/cm 2 . These limits are extended to η TPV = 30% and PD = 0.85W/cm 2 if the diode active region is bounded by a reflective back surface to enable photon recycling and a two-pass optical path length. The internal quantum efficiency of the InGaAsSb TPV diode is close to the theoretically predicted limits, with the exception of short wavelength absorption in GaSb contact layers. Experiments show that the open circuit voltage of the 0.53eV InGaAsSb TPV diodes is not strongly dependent on the device architectures studied in this work where both N/P and P/N double heterostructure diodes have been grown with various acceptor and donor doping levels, having GaSb and AlGaAsSb confinement, and also partial back surface reflectors. Lattice matched InGaAsSb TPV diodes were fabricated with bandgaps ranging from 0.6 to 0.5eV without significant degradation of the open circuit voltage factor, quantum efficiency, or fill factor as the composition approached the miscibility gap. The key diode performance parameter which is limiting efficiency and power density below the theoretical limits in InGaAsSb TPV devices is the open circuit voltage. The open circuit voltages of state-of-the-art 0.53eV InGaAsSb TPV diode are ∼10

  6. GaN MODFET microwave power technology for future generation radar and communications systems

    Science.gov (United States)

    Grider, D. E.; Nguyen, N. X.; Nguyen, C.

    1999-08-01

    In order to gain a better understanding of the role that GaN MODFET technology will play in future generation radar and communications systems, a comparison of the state-of-the-art performance of alternative microwave power technologies will be reviewed. The relative advantages and limitations of each technology will be discussed in relation to system needs. Device results from recent MBE-grown GaN MODFETs will also be presented. In particular, 0.25 μm gate GaN MODFETs grown by MBE have been shown to exhibit less than 5% variation in maximum drain current density ( Idmax) from the center to the edge of a 2 inch wafer. This level of uniformity is a substantially higher than that normally found in MOCVD-grown GaN devices (˜28% variation). In addition, evidence is also presented to demonstrate the excellent reproducibility of MBE-grown GaN MODFETs.

  7. Quaternary InGaAsSb Thermophotovoltaic Diode Technology

    Energy Technology Data Exchange (ETDEWEB)

    M Dashiell; J Beausang; H Ehsani; G Nichols; D DePoy; L Danielson; P Talamo; K Rahner; E Brown; S Burger; P Fourspring; W Topper; P Baldasaro; C Wang; R Huang; M Connors; G Turner; Z Shellenbarger; G Taylor; Jizhong Li; R Martinelli; D Donetski; S Anikeev; G Belenky; S Luryl

    2005-01-26

    Thermophotovoltaic (TPV) diodes fabricated from InGaAsSb alloys lattice-matched to GaSb substrates are grown by Metal Organic Vapor Phase Epitaxy (MOVPE). 0.53eV InGaAsSb TPV diodes utilizing front-surface spectral control filters have been tested in a vacuum cavity and a TPV thermal-to-electric conversion efficiency ({eta}{sub TPV}) and a power density (PD) of {eta}{sub TPV} = 19% and PD=0.58 W/cm{sup 2} were measured for T{sub radiator} = 950 C and T{sub diode} = 27 C. Recombination coefficients deduced from minority carrier measurements and the theory reviewed in this article predict a practical limit to the maximum achievable conversion efficiency and power density for 0.53eV InGaAsSb TPV. The limits for the above operating temperatures are projected to be {eta}{sub TPV} = 26% and PD = 0.75 W/cm{sup 2}. These limits are extended to {eta}{sub TPV} = 30% and PD = 0.85W/cm{sup 2} if the diode active region is bounded by a reflective back surface to enable photon recycling and a two-pass optical path length. The internal quantum efficiency of the InGaAsSb TPV diode is close to the theoretically predicted limits, with the exception of short wavelength absorption in GaSb contact layers. Experiments show that the open circuit voltage of the 0.53eV InGaAsSb TPV diodes is not strongly dependent on the device architectures studied in this work where both N/P and P/N double heterostructure diodes have been grown with various acceptor and donor doping levels, having GaSb and AlGaAsSb confinement, and also partial back surface reflectors. Lattice matched InGaAsSb TPV diodes were fabricated with bandgaps ranging from 0.6 to 0.5eV without significant degradation of the open circuit voltage factor, quantum efficiency, or fill factor as the composition approached the miscibility gap. The key diode performance parameter which is limiting efficiency and power density below the theoretical limits in InGaAsSb TPV devices is the open circuit voltage. The open circuit voltages of

  8. AlGaInN laser diode technology and systems for defence and security applications

    Science.gov (United States)

    Najda, Stephen P.; Perlin, Piotr; Suski, Tadek; Marona, Lujca; Boćkowski, Mike; Leszczyński, Mike; Wisniewski, Przemek; Czernecki, Robert; Kucharski, Robert; Targowski, Grzegorz; Watson, Scott; Kelly, Antony E.

    2015-10-01

    AlGaInN laser diodes is an emerging technology for defence and security applications such as underwater communications and sensing, atomic clocks and quantum information. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Thus AlGaInN laser diode technology is a key enabler for the development of new disruptive system level applications in displays, telecom, defence and other industries. Ridge waveguide laser diodes are fabricated to achieve single mode operation with optical powers up to 100mW with the 400-440nm wavelength range with high reliability. Visible free-space and underwater communication at frequencies up to 2.5GHz is reported using a directly modulated 422nm GaN laser diode. Low defectivity and highly uniform GaN substrates allow arrays and bars to be fabricated. High power operation operation of AlGaInN laser bars with up to 20 emitters have been demonstrated at optical powers up to 4W in a CS package with common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space or optical fibre system integration with a very small form-factor.

  9. Examination of thermophotovoltaic GaSb cell technology in low and medium temperatures waste heat

    Science.gov (United States)

    Utlu, Z.; Önal, B. S.

    2018-02-01

    In this study, waste heat was evaluated and examined by means of thermophotovoltaic systems with the application of energy production potential GaSb cells. The aim of our study is to examine GaSb cell technology at low and medium temperature waste heat. The evaluation of the waste heat to be used in the system is designed to be used in the electricity, industry and iron and steel industry. Our work is research. Graphic analysis is done with Matlab program. The low and medium temperature waste heat graphs applied on the GaSb cell are in the results section. Our study aims to provide a source for future studies.

  10. Performance evaluation of thermophotovoltaic GaSb cell technology in high temperature waste heat

    Science.gov (United States)

    Utlu, Z.; Önal, B. S.

    2018-02-01

    In this study, waste heat was evaluated and examined by means of thermophotovoltaic systems with the application of energy production potential GaSb cells. The aim of our study is to examine GaSb cell technology at high temperature waste heat. The evaluation of the waste heat to be used in the system is designed to be used in the electricity, industry and iron and steel industry. Our work is research. Graphic analysis is done with Matlab program. The high temperature waste heat graphs applied on the GaSb cell are in the results section. Our study aims to provide a source for future studies.

  11. AlGaInN laser diode technology for defence, security and sensing applications

    Science.gov (United States)

    Najda, Stephen P.; Perlin, Piotr; Suski, Tadek; Marona, Lucja; Boćkowski, Mike; Leszczyński, Mike; Wisniewski, Przemek; Czernecki, Robert; Kucharski, Robert; Targowski, Grzegorz; Watson, Scott; Kelly, Antony E.

    2014-10-01

    The latest developments in AlGaInN laser diode technology are reviewed for defence, security and sensing applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW in the 400-420nm wavelength range that are suitable for telecom applications. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Gallium-nitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is demonstrated with a single chip, AlGaInN laser diode `mini-array' with a common p-contact configuration at powers up to 2.5W cw at 410nm. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. GaN laser bars of up to 5mm with 20 emitters, mounted in a CS mount package, give optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.or.

  12. Latest developments in AlGaInN laser diode technology for defence applications

    Science.gov (United States)

    Najda, S. P.; Perlin, P.; Suski, T.; Marona, L.; Boćkowski, M.; Leszczyński, M.; Wisniewski, P.; Czernecki, R.; Kucharski, R.; Targowski, G.

    2012-09-01

    The latest developments in AlGaInN laser diode technology is reviewed for defence applications such as underwater telecommunications, sensor systems etc. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW in the 400-420nm wavelength range with high reliability. High power operation of AlGaInN laser diodes is also reviewed. We demonstrate the operation of a single chip, high power AlGaInN laser diode 'mini-array' consisting of a 3 stripe common p-contact configuration at powers up to 2.5W cw in the 408-412 nm wavelength range. Low defectivity and highly uniform TopGaN GaN substrates allow arrays and bars of nitride lasers to be fabricated. Packaging of nitride laser diodes is substantially different compared to GaAs laser technology and new processes and techniques are required to optimize the optical power from a nitride laser bar. Laser bars of up to 5mm with 20 emitters have shown optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor. TopGaN are developing a new range of high power laser array technology over the u.v.- visible spectrum together with new packaging solutions for optical integration.

  13. Wideband Monolithic Microwave Integrated Circuit Frequency Converters with GaAs mHEMT Technology

    DEFF Research Database (Denmark)

    Krozer, Viktor; Johansen, Tom Keinicke; Djurhuus, Torsten

    2005-01-01

    We present monolithic microwave integrated circuit (MMIC) frequency converter, which can be used for up and down conversion, due to the large RF and IF port bandwidth. The MMIC converters are based on commercially available GaAs mHEMT technology and are comprised of a Gilbert mixer cell core...

  14. Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology

    Directory of Open Access Journals (Sweden)

    Ying-Chang Li

    2017-04-01

    Full Text Available Monolithic phosphor-free two-color gallium nitride (GaN-based white light emitting diodes (LED have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN/GaN quantum dot and reported LED’s color rendering index (CRI are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL and electroluminescence (EL spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications.

  15. Characterization and technology of AlGaAs/GaAs phototransistor with double delta-doped base

    International Nuclear Information System (INIS)

    Radziewicz, D.; Sciana, B.; Pucicki, D.; Zborowska-Lindert, I.; Kovac, J.; Skriniarova, J.; Vincze, A.

    2011-01-01

    This work describes the fabrication and measurements of n-p-n AlGaAs/GaAs heterojunction phototransistor with double Zn-delta-doped 50 nm - thick GaAs base region. Parameters of the particular transistor epilayers were optimized by computer simulations using Silvaco Atlas program. (authors)

  16. Limited spillover to humans from West Nile Virus viremic birds in Atlanta, Georgia.

    Science.gov (United States)

    Levine, Rebecca S; Mead, Daniel G; Kitron, Uriel D

    2013-11-01

    West Nile Virus (WNV) is a mosquito-borne pathogen that impacts the health of its passerine bird hosts as well as incidentally infected humans in the United States. Intensive enzootic activity among the hosts and vectors does not always lead to human outbreaks, as is the situation throughout much of the southeastern United States. In Georgia, substantial yearly evidence of WNV in the mosquito vectors and avian hosts since 2001 has only led to 324 human cases. Although virus has been consistently isolated from mosquitoes trapped in Atlanta, GA, little is known about viral activity among the passerine hosts. A possible reason for the suppression of WNV spillover to humans is that viremic birds are absent from high human-use areas of the city. To test this hypothesis, multiseason, multihabitat, longitudinal WNV surveillance for active WNV viremia was conducted within the avian host community of urban Atlanta by collection of blood samples from wild passerine birds in five urban microhabitats. WNV was isolated from the serum of six blood samples collected from 630 (0.95%) wild passerine birds in Atlanta during 2010-2012, a proportion similar to that found in the Chicago, IL, area in 2005, when over 200 human cases were reported. Most of the viremic birds were Northern Cardinals, suggesting they may be of particular importance to the WNV transmission cycle in Georgia. Results indicated active WNV transmission in all microhabitats of urban Atlanta, except in the old-growth forest patches. The number of viremic birds was highest in Zoo Atlanta, where 3.5% of samples were viremic. Although not significant, these observations may suggest a possible transmission reduction effect of urban old-growth forests and a potential role in WNV amplification for Zoo Atlanta. Overall, spillover to humans remains a rare occurrence in urban Atlanta settings despite active WNV transmission in the avian population.

  17. High-performance N-polar GaN enhancement-mode device technology

    International Nuclear Information System (INIS)

    Singisetti, Uttam; Wong, Man Hoi; Mishra, Umesh K

    2013-01-01

    In this paper, we report the recent progress in the high-frequency performance of enhancement-mode devices in the novel N-polar GaN technology and provide a pathway for further scaling. The intrinsic advantages of electron confinement, polarization doping of the back-barrier and the absence of a source barrier in N-polar GaN technology were leveraged with polarization engineering with a top barrier for enhancement mode operation and advanced self-aligned source/drain technology for low parasitic access resistances. The scalability of the device structures are explored in terms of short-channel effects and high-frequency performance. Low-field electron mobility in vertically scaled channel was also investigated providing insights on the scattering mechanism. (invited review)

  18. High mobility AlGaN/GaN heterostructures grown on Si substrates using a large lattice-mismatch induced stress control technology

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Jianpeng; Yang, Xuelin, E-mail: xlyang@pku.edu.cn; Sang, Ling; Guo, Lei; Hu, Anqi; Xu, Fujun; Tang, Ning [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wang, Xinqiang; Shen, Bo, E-mail: bshen@pku.edu.cn [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)

    2015-04-06

    A large lattice-mismatch induced stress control technology with a low Al content AlGaN layer has been used to grow high quality GaN layers on 4-in. Si substrates. The use of this technology allows for high mobility AlGaN/GaN heterostructures with electron mobility of 2040 cm{sup 2}/(V·s) at sheet charge density of 8.4 × 10{sup 12 }cm{sup −2}. Strain relaxation and dislocation evolution mechanisms have been investigated. It is demonstrated that the large lattice mismatch between the low Al content AlGaN layer and AlN buffer layer could effectively promote the edge dislocation inclination with relatively large bend angles and therefore significantly reduce the dislocation density in the GaN epilayer. Our results show a great potential for fabrication of low-cost and high performance GaN-on-Si power devices.

  19. Advanced digital modulation: Communication techniques and monolithic GaAs technology

    Science.gov (United States)

    Wilson, S. G.; Oliver, J. D., Jr.; Kot, R. C.; Richards, C. R.

    1983-01-01

    Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case.

  20. A Hybrid Readout Solution for GaN-Based Detectors Using CMOS Technology

    Directory of Open Access Journals (Sweden)

    Preethi Padmanabhan

    2018-02-01

    Full Text Available Gallium nitride (GaN and its alloys are becoming preferred materials for ultraviolet (UV detectors due to their wide bandgap and tailorable out-of-band cutoff from 3.4 eV to 6.2 eV. GaN based avalanche photodiodes (APDs are particularly suitable for their high photon sensitivity and quantum efficiency in the UV region and for their inherent insensitivity to visible wavelengths. Challenges exist however for practical utilization. With growing interests in such photodetectors, hybrid readout solutions are becoming prevalent with CMOS technology being adopted for its maturity, scalability, and reliability. In this paper, we describe our approach to combine GaN APDs with a CMOS readout circuit, comprising of a linear array of 1 × 8 capacitive transimpedance amplifiers (CTIAs, implemented in a 0.35 µm high voltage CMOS technology. Further, we present a simple, yet sustainable circuit technique to allow operation of APDs under high reverse biases, up to ≈80 V with verified measurement results. The readout offers a conversion gain of 0.43 µV/e−, obtaining avalanche gains up to 103. Several parameters of the CTIA are discussed followed by a perspective on possible hybridization, exploiting the advantages of a 3D-stacked technology.

  1. A Hybrid Readout Solution for GaN-Based Detectors Using CMOS Technology

    Science.gov (United States)

    Hancock, Bruce; Nikzad, Shouleh; Bell, L. Douglas; Kroep, Kees; Charbon, Edoardo

    2018-01-01

    Gallium nitride (GaN) and its alloys are becoming preferred materials for ultraviolet (UV) detectors due to their wide bandgap and tailorable out-of-band cutoff from 3.4 eV to 6.2 eV. GaN based avalanche photodiodes (APDs) are particularly suitable for their high photon sensitivity and quantum efficiency in the UV region and for their inherent insensitivity to visible wavelengths. Challenges exist however for practical utilization. With growing interests in such photodetectors, hybrid readout solutions are becoming prevalent with CMOS technology being adopted for its maturity, scalability, and reliability. In this paper, we describe our approach to combine GaN APDs with a CMOS readout circuit, comprising of a linear array of 1 × 8 capacitive transimpedance amplifiers (CTIAs), implemented in a 0.35 µm high voltage CMOS technology. Further, we present a simple, yet sustainable circuit technique to allow operation of APDs under high reverse biases, up to ≈80 V with verified measurement results. The readout offers a conversion gain of 0.43 µV/e−, obtaining avalanche gains up to 103. Several parameters of the CTIA are discussed followed by a perspective on possible hybridization, exploiting the advantages of a 3D-stacked technology. PMID:29401655

  2. Proceedings of the seminar on optimization technology of the use of G.A. Siwabessy Research Reactor

    International Nuclear Information System (INIS)

    1999-01-01

    Seminar on optimization technology of the use of G.A. Siwabessy research reactor was held on March 16, 1999 at the Multipurpose Reactor Center, Serpong, Indonesia. During the seminar, have presented 14 papers about activities or researches on reactor operation technology, use of G.A. Siwabessy research reactor, engineering and nuclear installation development, maintenance and quality assurances. The seminar was held as a tool for developing non-researcher functional workers

  3. Risk Factors for HIV Transmission and Barriers to HIV Disclosure: Metropolitan Atlanta Youth Perspectives

    OpenAIRE

    Camacho-Gonzalez, Andres F.; Wallins, Amy; Toledo, Lauren; Murray, Ashley; Gaul, Zaneta; Sutton, Madeline Y.; Gillespie, Scott; Leong, Traci; Graves, Chanda; Chakraborty, Rana

    2016-01-01

    Youth carry the highest incidence of HIV infection in the United States. Understanding adolescent and young adult (AYA) perspectives on HIV transmission risk is important for targeted HIV prevention. We conducted a mixed methods study with HIV-infected and uninfected youth, ages 18–24 years, from Atlanta, GA. We provided self-administered surveys to HIV-infected and HIV-uninfected AYAs to identify risk factors for HIV acquisition. By means of computer-assisted thematic analyses, we examined t...

  4. Improved High-Energy Response of AlGaAs/GaAs Solar Cells Using a Low-Cost Technology

    Science.gov (United States)

    Noorzad, Camron D.; Zhao, Xin; Harotoonian, Vache; Woodall, Jerry M.

    2016-12-01

    We report on an AlGaAs/GaAs solar cell with a significantly increased high-energy response that was produced via a modified liquid phase epitaxy (LPE) technique. This technique uses a one-step process in which the solid-liquid equilibrium Al-Ga-As:Zn melt in contact with an n-type vendor GaAs substrate simultaneously getters impurities in the substrate that shorten minority carrier lifetimes, diffuses Zn into the substrate to create a p- n junction, and forms a thin p-AlGaAs window layer that enables more high-energy light to be efficiently absorbed. Unlike conventional LPE, this process is performed isothermally. In our "double Al" method, the ratio of Al in the melt ("Al melt ratio") that was used in our process was two times more than what was previously reported in the record 1977 International Business Machines (IBM) solar cell. Photoluminescence (PL) results showed our double Al sample yielded a response to 405 nm light ("blue light"), which was more than twice as intense as the response from our replicated IBM cell. The original 1977 cell had a low-intensity spectral response to photon wavelengths under 443 nm (Woodall and Hovel in Sol Energy Mater Sol Cells 29:176, 1990). Secondary ion mass spectrometry results confirmed the increased blue light response was due to a large reduction in AlGaAs window layer thickness. These results proved increasing the Al melt ratio broadens the spectrum of light that can be transmitted through the window layer into the active GaAs region for absorption, increasing the overall solar cell efficiency. Our enhanced double Al method can pave the way for large-scale manufacturing of low-cost, high-efficiency solar cells.

  5. Photonic Mach-Zehnder modulators driven by surface acoustic waves in AlGaAs technology

    Science.gov (United States)

    Crespo-Poveda, A.; Gargallo, B.; Artundo, I.; Doménech, J. D.; Muñoz, P.; Hey, R.; Biermann, K.; Tahraoui, A.; Santos, P. V.; Cantarero, A.; de Lima, M. M.

    2014-03-01

    In this paper, photonic devices driven by surface acoustic waves and operating in the GHz frequency range are presented. The devices were designed and fabricated in (Al,Ga)As technology. In contrast to previously realized modulators, where part of the light transmission is lost due to destructive interference, in the present devices light only switches paths, avoiding losses. One of the devices presents two output channels with 180°-dephasing synchronization. Odd multiples of the fundamental driving frequency are enabled by adjusting the applied acoustic power. A second and more complex photonic integrated device, based on the acoustic modulation of tunable Arrayed Waveguide Gratings, is also proposed.

  6. Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology

    Energy Technology Data Exchange (ETDEWEB)

    Limbach, Friederich

    2012-06-22

    This work is concerned with the realization and investigation of a light emitting diode (LED) structure within single GaN nanowires (NWs) and its integration with Si technology. To this end first a general understanding of the GaN NW growth is given. This is followed by investigations of the influence which doping species, such as Mg and Si, have on the growth of the NWs. The experience gathered in these studies set the basis for the synthesis of nominal p-i-n and n-i-p junctions in GaN NWs. Investigations of these structures resulted in the technologically important insight, that p-type doping with Mg is achieved best if it is done in the later NW growth stage. This implies that it is beneficial for a NW LED to place the p-type segment on the NW top. Another important component of an LED is the active zone where electron-hole recombination takes place. In the case of planar GaN LEDs, this is usually achieved by alloying Ga and In to form InGaN. In order to be able to control the growth under a variety of conditions, we investigate the growth of InGaN in the form of extended segments on top of GaN NWs, as well as multi quantum wells (MQWs) in GaN NWs. All the knowledge gained during these preliminary studies is harnessed to reach the overall goal: The realization of a GaN NW LED. Such structures are fabricated, investigated and processed into working LEDs. Finally, a report on the efforts of integrating III-nitride NW LEDs and Si based metaloxide-semiconductor field effect transistor (MOSFET) technology is given. This demonstrates the feasibility of the monolithic integration of both devices on the same wafer at the same time.

  7. Solar Heating and Cooling Experiment for a School in Atlanta. Performance Report.

    Science.gov (United States)

    Westinghouse Electric Corp., Falls Church, VA.

    This report documents the performance and conclusions of a 13-month period of monitoring the performance of the experimental solar heating and cooling system installed in the George A. Towns Elementary School, Atlanta, Georgia. The objectives of the project were to (1) make a significant contribution to solar design, technology, and acceptability;…

  8. 77 FR 24399 - Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year...

    Science.gov (United States)

    2012-04-24

    ... Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year Emissions Inventory AGENCY... approve the ozone 2002 base year emissions inventory, portion of the state implementation plan (SIP... technology (RACT), contingency measures, a 2002 base- year emissions inventory and other planning SIP...

  9. 78 FR 1742 - Amendment to Class B Airspace; Atlanta, GA

    Science.gov (United States)

    2013-01-09

    ... airspace. The FAA finds that the new 6,000-floor still provides sufficient space for safe operations in... rarely uses the published MAP, and instead controllers offer vectors or alternate instructions; the... that serves general aviation satellite airport departures and arrivals at 5,000 and 6,000 feet. One...

  10. Test results from the GA Technologies engineering-scale off-gas treatment system

    International Nuclear Information System (INIS)

    Jensen, D.D.; Olguin, L.J.; Wilbourn, R.G.

    1985-01-01

    Test results are available from the GA Technologies (GA) off-gas treatment facilities using gas streams from both the graphite fuel element burner system and from the spent fuel dissolver. The off-gas system is part of a pilot plant for development of processes for treating spent fuel from high temperature gas-cooled reactors (HTGRs). One method for reducing the volume of HTGR fuel prior to reprocessing or spent fuel storage is to crush and burn the graphite fuel elements. The burner off-gas (BOG) contains radioactive components, principally H-3, C-14, Kr-85, I-129, and Rn-220, as well as chemical forms such as CO 2 , CO, O 2 , and SO 2 . The BOG system employs components designed to remove these constituents. Test results are reported for the iodine and SO 2 adsorbers and the CO/HT oxidizer. Integrated testing of major BOG system components confirmed the performance of units evaluated in individual tests. Design decontamination and conversion factors were maintained for up to 72 h. In a reprocessing flowsheet, the solid product from the burners is dissolved in nitric or Thorex acid. The dissolver off-gas (DOG) contains radioactive components H-3, Kr-85, I-129, Rn-220 plus chemical forms such as nitrogen oxides (NO/sub x/). In the pilot-scale system iodine is removed from the DOG by adsorption. Tests of iodine removal have been conducted using either silver-exchanged mordenite (AgZ) or AgNO 3 -impregnated silica gel (AC-6120). Although each sorbent performed well in the presence of NO/sub x/, the silica gel adsorbent proved more efficient in silver utilization and, thus, more cost effective

  11. Progress in GaAs Metamorphic HEMT Technology for Microwave Applications. High Efficiency Ka-Band MHEMT Power MMICs

    Science.gov (United States)

    Smith, P. M.; Dugas, D.; Chu, K.; Nichols, K.; Duh, K. H.; Fisher, J.; MtPleasant, L.; Xu, D.; Gunter, L.; Vera, A.

    2003-01-01

    This paper reviews recent progress in the development of GaAs metamorphic HEMT (MHEMT) technology for microwave applications. Commercialization has begun, while efforts to further improve performance, manufacturability and reliability continue. We also report the first multi-watt MHEMT MMIC power amplifiers, demonstrating up to 3.2W output power and record power-added efficiency (PAE) at Ka-band.

  12. Demonstration of an RF front-end based on GaN HEMT technology

    Science.gov (United States)

    Ture, Erdin; Musser, Markus; Hülsmann, Axel; Quay, Rüdiger; Ambacher, Oliver

    2017-05-01

    The effectiveness of the developed front-end on blocking the communication link of a commercial drone vehicle has been demonstrated in this work. A jamming approach has been taken in a broadband fashion by using GaN HEMT technology. Equipped with a modulated-signal generator, a broadband power amplifier, and an omni-directional antenna, the proposed system is capable of producing jamming signals in a very wide frequency range between 0.1 - 3 GHz. The maximum RF output power of the amplifier module has been software-limited to 27 dBm (500 mW), complying to the legal spectral regulations of the 2.4 GHz ISM band. In order to test the proof of concept, a real-world scenario has been prepared in which a commercially-available quadcopter UAV is flown in a controlled environment while the jammer system has been placed in a distance of about 10 m from the drone. It has been proven that the drone of interest can be neutralized as soon as it falls within the range of coverage (˜3 m) which endorses the promising potential of the broadband jamming approach.

  13. Complejo Omni - Atlanta – (EE. UU.

    Directory of Open Access Journals (Sweden)

    Housworth, Marvin

    1976-12-01

    Full Text Available This complex of buildings, situated in the centre of Atlanta City, forms a dynamic nucleus for various social activities, such as recreational, commercial and business activities. These buildings are constructed above railway nets, due to special property rights for this lot, which constituted one of the main determinants for the characteristics of the property. The unit is made up by a luxurious hotel, two restaurants, office buildings and shopping arcades, arranged around a spacious inner yard. This patio is covered by means of an exceedingly big glass roof, supported by beams and steel framework and is provided with walls of big glazed surfaces. Thus, an intimate and friendly atmosphere is created, free from the contamination and noise of the big city whereby the square displays the typical characteristics of open squares in smaller towns.Este conjunto de edificios, emplazado en el centro de la ciudad de Atlanta, conforma un núcleo dinámico en donde se encuentran diversas actividades de tipo social: recreativas, comerciales y empresariales. Se ha construido sobre ruedas ferroviarias, en virtud de derechos especiales de propiedad que conservaba la parcela, lo que constituyó uno de los principales condicionamientos de fas características del proyecto. El complejo dispone de un hotel de lujo, dos restaurantes, edificios de oficinas y galerías comerciales, dispuestos en torno a un amplio espacio interior, cerrado por una enorme cubierta acristalada, apoyada en vigas y entramados metálicos, y por grandes ventanales corridos entre bloques. Conforma así un ambiente íntimo y acogedor, liberado del ruido y de la atmósfera turbulenta de la gran ciudad, con características propias de las pequeñas plazas populares.

  14. GaAs Industry in Europe-Technologies, Trends and New Developments

    Science.gov (United States)

    Jung, Helmut; Blanck, Hervé; Bösch, Wolfgang; Mayock, Jim

    The GaAs industry has been growing immensely during recent years. This is mainly driven by the tremendous growth of the wireless communication market, which is still continuously growing. Additionally, an emerging mmW market with applications in automotive, defense and optoelectronics is further driving the demand for GaAs components. The two largest European GaAs fabrication companies, UMS and Filtronic are very well positioned to address the complete frequency range from 1GHz up to 100GHz for commercial, high volume low cost markets, as well as individual niche applications. An overview of the companies' structures, their processes and design capabilities and also their new product developments will be presented in this paper.

  15. Semi-polar GaN materials technology for high IQE green LEDs.

    Energy Technology Data Exchange (ETDEWEB)

    Koleske, Daniel; Lee, Stephen Roger; Crawford, Mary H; Coltrin, Michael Elliott; Fini, Paul

    2013-06-01

    The goal of this NETL funded program was to improve the IQE in green (and longer wavelength) nitride- based LEDs structures by using semi-polar GaN planar orientations for InGaN multiple quantum well (MQW) growth. These semi-polar orientations have the advantage of significantly reducing the piezoelectric fields that distort the QW band structure and decrease electron-hole overlap. In addition, semipolar surfaces potentially provide a more open surface bonding environment for indium incorporation, thus enabling higher indium concentrations in the InGaN MQW. The goal of the proposed work was to select the optimal semi-polar orientation and explore wafer miscuts around this orientation that produced the highest quantum efficiency LEDs. At the end of this program we had hoped to have MQWs active regions at 540 nm with an IQE of 50% and an EQE of 40%, which would be approximately twice the estimated current state-of-the-art.

  16. Semipolar AlN and GaN on Si(100): HVPE technology and layer properties

    Science.gov (United States)

    Bessolov, V.; Kalmykov, A.; Konenkova, E.; Kukushkin, S.; Myasoedov, A.; Poletaev, N.; Rodin, S.

    2017-01-01

    Hydride vapor phase epitaxy (HVPE) growth of semipolar AlN and GaN layers on planar Si(100) substrates with SiC nanolayer is investigated. It is shown experimentally that the solid-phase epitaxial formation of a specially oriented SiC nucleation layer followed by epitaxy of AlN layer by HVPE at low rates enables growth of aluminum and gallium nitrides in the semipolar direction. For the best GaN(20-23) layers obtained, the full width at half maximum (FWHM) value for the x-ray diffraction rocking curve is 24 arcmin. The photoluminescence spectrum of the semipolar GaN measured at 4 K exhibits bands related to basal-plane and prismatic stacking faults (BSF and PSF).

  17. A Decade-Bandwidth Distributed Power Amplifier MMIC Using 0.25 μm GaN HEMT Technology

    Directory of Open Access Journals (Sweden)

    Dong-Hwan Shin

    2017-10-01

    Full Text Available This study presents a 2–20 GHz monolithic distributed power amplifier (DPA using a 0.25 μm AlGaN/GaN on SiC high electron mobility transistor (HEMT technology. The gate width of the HEMT was selected after considering the input capacitance of the unit cell that guarantees decade bandwidth. To achieve high output power using small transistors, a 12-stage DPA was designed with a nonuniform drain line impedance to provide optimal output power matching. The maximum operating frequency of the proposed DPA is above 20 GHz, which is higher than those of other DPAs manufactured with the same gate-length process. The measured output power and power-added efficiency of the DPA monolithic microwave integrated circuit (MMIC are 35.3–38.6 dBm and 11.4%–31%, respectively, for 2–20 GHz.

  18. Atlanta congestion reduction demonstration. National evaluation : content analysis test plan.

    Science.gov (United States)

    2011-08-01

    This report presents the test plan for collecting and analyzing information on outreach activities, media : coverage, and establishment of the partnership for the projects comprising the Atlanta Congestion : Reduction Demonstration (CRD) under the Un...

  19. 1996 Atlanta Centennial Olympic Games and Paralympic Games, event study

    Science.gov (United States)

    1997-01-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation : Systems (ITS) deployments in the United States. This deployment included several individual projects-a : Central Transportation Management Cent...

  20. The Official Report of the Centennial Olympic Games: Atlanta 1996

    OpenAIRE

    2014-01-01

    “The Official Report of the Centennial Olympic Games: Atlanta 1996” marked a return to a more sober and traditional form. There were French and English box sets, published in 1997. The work consisted of three volumes (Planning and organizing; The centennial Olympic Games; The competition results). Volume 3 was bilingual. Vol.1 Part I: Prologue the Bid ; Management and organization ; Accomodations ; Accreditation ; Atlanta Olympic broadcasting ; Centennial Olympic park ; Communications.- Vol.1...

  1. Power cycling test of a 650 V discrete GaN-on-Si power device with a laminated packaging embedding technology

    DEFF Research Database (Denmark)

    Song, Sungyoung; Munk-Nielsen, Stig; Uhrenfeldt, Christian

    2017-01-01

    A GaN-on-Si power device is a strong candidate to replace power components based on silicon in high-end market for low-voltage applications, thanks to its electrical characteristics. To maximize opportunities of the GaN device in field applications, a package technology plays an important role...... cycling test of a discrete GaN power device employing a laminated embedded packaging technology subjected to 125 degrees Celsius junction temperature swing. Failure modes are described with collected electrical characteristics and measured temperature data under the test. In conclusion, physical...

  2. Plaza Central Peachtree Atlanta-(EE.UU.

    Directory of Open Access Journals (Sweden)

    Portman, John

    1976-10-01

    Full Text Available This 70-storey hotel has been constructed to meet the requirements of the city of Atlanta which needed a building with a sufficient room capacity and adequate premises for Conventions. On a structure of reinforced concrete which serves as a base and in which the common areas are situated rises a big cylindric tower, covered with coloured glass and which contains the 1.100 rooms. 230 m above ground level, the construction is crowned with a roof top cocktail lounge and a revolving restaurant with a splendid view of the city. Among the most noteworthy characteristics of this hotel is the elegantly decorated entrance hall —atrium shaped and 7 storeys high— with a pond in the centre. Further premises worth mentioning in view of their design and dimensions are the great ball room, coffee-shops and luxurious restaurants, one of which is planned in different levels and in which the most impressive feature is a 30 m high waterfall.Este edificio de setenta plantas se construyó para responder a las necesidades hoteleras de la ciudad de Atlanta, que precisaba de una instalación con suficiente capacidad de habitaciones y preparación para albergar Convenciones. Sobre una estructura de hormigón armado, que sirve de base y en la que se sitúan las zonas comunes, se eleva una gran torre cilíndrica, recubierta de vidrio coloreado reflectante, destinada a distribuir las 1.100 habitaciones con las que cuenta el edificio. La construcción se corona, a 230 m de la cimentación, con una sala para cócteles y un restaurante giratorio desde el que se domina una espléndida vista del contorno. El edificio dispone de importantes servicios comunes, entre los que cabe destacar el hall de entrada —a modo de atrio y con una altura equivalente a siete plantas—, que está dotado de un gran estanque y variados elementos de gran efecto decorativo. Otros servicios notables por su diseño y dimensiones son la gran sala de baile, y las cafeterías, comedores y

  3. Vertical thinking in blue light emitting diodes: GaN-on-graphene technology

    Science.gov (United States)

    Bayram, C.; Kim, J.; Cheng, C.-W.; Ott, J.; Reuter, K. B.; Bedell, S. W.; Sadana, D. K.; Park, H.; Dimitrakopoulos, C.

    2014-03-01

    In this work, we show that a 2D cleave layer (such as epitaxial graphene on SiC) can be used for precise release of GaNbased light emitting diodes (LEDs) from the LED-substrate interface. We demonstrate the thinnest GaN-based blue LED and report on the initial electrical and optical characteristics. Our LED device employs vertical architecture: promising excellent current spreading, improved heat dissipation, and high light extraction with respect to the lateral one. Compared to conventional LED layer release techniques used for forming vertical LEDs (such as laser-liftoff and chemical lift-off techniques), our process distinguishes itself with being wafer-scalable (large area devices are possible) and substrate reuse opportunity.

  4. Technology computer aided design for Si, SiGe and GaAs integrated circuits

    CERN Document Server

    Armstrong, GA

    2007-01-01

    The first book to deal with a broad spectrum of process and device design, and modelling issues related to semiconductor devices, bridging the gap between device modelling and process design using TCAD. Examples for types of Si-, SiGe-, GaAs- and InP-based heterostructure MOS and bipolar transistors are compared with experimental data from state-of-the-art devices. With various aspects of silicon heterostructures, this book presents a comprehensive perspective of emerging fields and covers topics ranging from materials to fabrication, devices, modelling and applications. Aimed at research-and-

  5. Advanced technology steps in the fabrication of GaAs microstrip detectors

    Energy Technology Data Exchange (ETDEWEB)

    Albertz, D.; Braunschweig, W.; Karpinski, W.; Krais, R.; Kubicki, T.; Luebelsmeyer, K.; Rente, C.; Syben, O.; Tenbusch, F.; Toporowski, M.; Wittmer, B.; Xiao, W.J. [Technische Hochschule Aachen (Germany). 1. Physikalisches Inst.

    1998-02-01

    We report on the fabrication of GaAs microstrip detectors with integrated coupling capacitors and biasing resistors. The characteristics of the dielectrica SiO{sub 2} and Si{sub 3}N{sub 4} are compared. The SiO{sub 2} layers were fabricated by evaporation. The Si{sub 3}N{sub 4} layers were grown by plasma enhanced vapour deposition. The IV-properties and the yield of the devices is investigated. First results of ion implanted back side contacts without an annealing step are presented. (orig.). 4 refs.

  6. Increasing Walking in the Hartsfield-Jackson Atlanta International Airport: The Walk to Fly Study.

    Science.gov (United States)

    Fulton, Janet E; Frederick, Ginny M; Paul, Prabasaj; Omura, John D; Carlson, Susan A; Dorn, Joan M

    2017-07-01

    To test the effectiveness of a point-of-decision intervention to prompt walking, versus motorized transport, in a large metropolitan airport. We installed point-of-decision prompt signage at 4 locations in the airport transportation mall at Hartsfield-Jackson Atlanta International Airport (Atlanta, GA) at the connecting corridor between airport concourses. Six ceiling-mounted infrared sensors counted travelers entering and exiting the study location. We collected traveler counts from June 2013 to May 2016 when construction was present and absent (preintervention period: June 2013-September 2014; postintervention period: September 2014-May 2016). We used a model that incorporated weekly walking variation to estimate the intervention effect on walking. There was an 11.0% to 16.7% relative increase in walking in the absence of airport construction where 580 to 810 more travelers per day chose to walk. Through May 2016, travelers completed 390 000 additional walking trips. The Walk to Fly study demonstrated a significant and sustained increase in the number of airport travelers choosing to walk. Providing signage about options to walk in busy locations where reasonable walking options are available may improve population levels of physical activity and therefore improve public health.

  7. Atlanta NAVIGATOR case study. Final report, May 1996--Jun 1997

    Energy Technology Data Exchange (ETDEWEB)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCC), one Transit Information Center (TIC), the Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on line in time for the Olympic Games. This report presents the findings of the NAVIGATOR Case Study and documents the lessons learned from the Atlanta ITS deployment experience in order to improve other ITS deployments in the future. The Case Study focuses on the institutional, programmatic, and technical issues and opportunities from planning and implementing the ITS deployment in Atlanta. The Case Study collected data and information from interviews, observations, focus groups, and documentation reviews. It presents a series of lessons learned and recommendations for enabling successful ITS deployments nationwide.

  8. Evolution of Monolithic Technology for Wireless Communications: GaN MMIC Power Amplifiers For Microwave Radios

    Directory of Open Access Journals (Sweden)

    Vittorio Camarchia

    2014-09-01

    Full Text Available This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research foundry, while thesecond and the third are a 7 GHz Doherty and a 7–15 GHz dual-band combined poweramplifiers, both based on a commercial foundry process. The employed architectures, themain design steps and the pros and cons of using gallium nitride technology are highlighted.The measured performance demonstrates the potentialities of the employed technology, andthe progress in the accuracy, reliability and performance of the process.

  9. Cryptosporidium and Giardia in Swimming Pools, Atlanta, Georgia

    Centers for Disease Control (CDC) Podcasts

    2008-05-29

    In this podcast, Dan Rutz speaks with Dr. Joan Shields, a guest researcher with the Healthy Swimming Program at CDC, about an article in June 2008 issue of Emerging Infectious Diseases reporting on the results of a test of swimming pools in the greater Atlanta, Georgia area. Dr. Shields tested 160 pools in metro Atlanta last year for Cryptosporidium and Giardia. These germs cause most recreational water associated outbreaks.  Created: 5/29/2008 by Emerging Infectious Diseases.   Date Released: 5/29/2008.

  10. A 6-bit 3-Gsps ADC implemented in 1 μm GaAs HBT technology

    International Nuclear Information System (INIS)

    Zhang Jincan; Zhang Yuming; Lü Hongliang; Zhang Yimen; Xiao Guangxing; Ye Guiping

    2014-01-01

    The design and test results of a 6-bit 3-Gsps analog-to-digital converter (ADC) using 1 μm GaAs heterojunction bipolar transistor (HBT) technology are presented. The monolithic folding-interpolating ADC makes use of a track-and-hold amplifier (THA) with a highly linear input buffer to maintain a highly effective number of bits (ENOB). The ADC occupies an area of 4.32 × 3.66 mm 2 and achieves 5.53 ENOB with an effective resolution bandwidth of 1.1 GHz at a sampling rate of 3 Gsps. The maximum DNL and INL are 0.36 LSB and 0.48 LSB, respectively. (semiconductor integrated circuits)

  11. Developing chiral-technologies. Chiral technology that Alice in the mirror land gave a birth to; Hattensuru kiraru technology. Kagami no kuni no Alice ga unda kiraru technology

    Energy Technology Data Exchange (ETDEWEB)

    Ohashi, T. [Kanegafuchi Chemical Industry Co. Ltd., Osaka (Japan)

    1998-05-01

    Since the theory for optical isomers has been advocated by Van`t Hoff et al, studies were developed on correlation between structures and functions of optically active bodies through separation of 1-tartaric acid by Pasteur. Technologies to create freely the optically active bodies has contributed to advancement of chemistry. This paper describes improvement in the method of manufacturing D-amino acid by using biomass. Kaneka Co., Ltd. uses an enzyme method to produce D-parahydroxyphenylglycin (D-HPG) which is an important chiral block in manufacturing amoxicillin, a constituent substance. Its prescription is represented by a method to covert hydantoin compound of racemic modification into D-amino acid through hydrolysis by utilizing two kinds of enzymes. Heat resistance was imparted to elevate stability of the parent decarbamylase. The decarbamylase genes originated from the 712 bacteria were introduced into a phage, which were randomly mutated by using a mutant. These mutated genes were introduced into colibacilli to select bacteria having decarbamylase whose heat resistance was increased by using recombined colibacilli. 2 refs., 2 figs., 3 tabs.

  12. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    Science.gov (United States)

    Dinetta, L. C.; Hannon, M. H.

    1995-10-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual

  13. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    Science.gov (United States)

    Dinetta, L. C.; Hannon, M. H.

    1995-01-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual

  14. Predictive maintenance technology development at G.A. Siwabessy multipurpose reactor

    International Nuclear Information System (INIS)

    Jupiter Sitorus Pane; Imron, M.; Sapto Hartoko; Sentot Alibasya Harahap

    1999-01-01

    Safe operation of reactor is certainly influenced by condition of system and component equipped to the reactor's system. In order to maintain the condition of that systems and components, RSG-GAS has arranged maintenance program with time-basis. All 6 (six) groups of reactor systems are maintained within interval of weekly, monthly, three monthly, six-monthly, yearly, five-yearly appropriately. The experience showed that event though the maintenance was performed persistently, the condition of system and component are still not able to determine exactly. The possibility of accidental failure is open since the failure factor are varied and complicated. In order to limit an uncertainty of the component condition a based maintenance shall be introduced. An infrared investigation and manual vibration analysis had been used to diagnose the condition of some RSG-GAS' components. In addition, other alternative technology for predictive maintenance was developed. It is started by computerizing the database maintenance and doing historical review for its aging management, and developing data acquisition and processing equipment using Lab View computer program for collecting and processing signal data from dynamics system. This paper describes briefly the status of those development results. (author)

  15. Project ATLANTA (ATlanta Land-use ANalysis: Temperature and Air quality): A Study of how the Urban Landscape Affects Meteorology and Air Quality Through Time

    Science.gov (United States)

    Quattrochi, Dale A.; Luvall, Jeffrey C.; Estes, Maurice G.; Lo, C. P.; Kidder, Stanley Q.; Hafner, Jan; Taha, Haider; Bornstein, Robert D.; Gillies, Robert R.; Gallo, Kevin P.

    1998-01-01

    It is our intent through this investigation to help facilitate measures that can be Project ATLANTA (ATlanta Land-use ANalysis: applied to mitigate climatological or air quality Temperature and Air-quality) is a NASA Earth degradation, or to design alternate measures to sustain Observing System (EOS) Interdisciplinary Science or improve the overall urban environment in the future. investigation that seeks to observe, measure, model, and analyze how the rapid growth of the Atlanta. The primary objectives for this research effort are: 1) To In the last half of the 20th century, Atlanta, investigate and model the relationship between Atlanta Georgia has risen as the premier commercial, urban growth, land cover change, and the development industrial, and transportation urban area of the of the urban heat island phenomenon through time at southeastern United States. The rapid growth of the nested spatial scales from local to regional; 2) To Atlanta area, particularly within the last 25 years, has investigate and model the relationship between Atlanta made Atlanta one of the fastest growing metropolitan urban growth and land cover change on air quality areas in the United States. The population of the through time at nested spatial scales from local to Atlanta metropolitan area increased 27% between 1970 regional; and 3) To model the overall effects of urban and 1980, and 33% between 1980-1990 (Research development on surface energy budget characteristics Atlanta, Inc., 1993). Concomitant with this high rate of across the Atlanta urban landscape through time at population growth, has been an explosive growth in nested spatial scales from local to regional. Our key retail, industrial, commercial, and transportation goal is to derive a better scientific understanding of how services within the Atlanta region. This has resulted in land cover changes associated with urbanization in the tremendous land cover change dynamics within the Atlanta area, principally in transforming

  16. Guidance, Navigation and Control Digital Emulation Technology Laboratory. Volume 1. Part 2. Task 1: Digital Emulation Technology Laboratory

    Science.gov (United States)

    1991-09-27

    Engineering Research Laboratory " Autnor: Stephen R. Wachtel extern int level; I extern char "list( vic. ca.. staterent ( identifier, opion...ENGINEERING RESEARCH LABORATORY Georgia Institute of Technology Atlanta, Georgia 30332 - 0540 Contract Data Requirements List Item A005 Period Covered: FY 91...COMPUTER ENGINEERING RESEARCH LABORATORY Georgia Institute of Technology Atlanta, Georgia 30332 - 0540 Eugene L. Sanders Cecil 0. Alford USASDC Georgia

  17. Climate change adaptation through urban heat management in Atlanta, Georgia.

    Science.gov (United States)

    Stone, Brian; Vargo, Jason; Liu, Peng; Hu, Yongtao; Russell, Armistead

    2013-07-16

    This study explores the potential effectiveness of metropolitan land cover change as a climate change adaptation strategy for managing rising temperatures in a large and rapidly warming metropolitan region of the United States. Through the integration of a mesoscale meteorological model with estimated land cover data for the Atlanta, Georgia region in 2010, this study quantifies the influence of extensive land cover change at the periphery of a large metropolitan region on temperature within the city center. The first study to directly model a metropolitan scale heat transfer mechanism, we find both enhanced tree canopy and impervious cover in the suburban zones of the Atlanta region to produce statistically significant cooling and warming effects in the urban core. Based on these findings, we conclude that urban heat island management both within and beyond the central developed core of large cities may provide an effective climate change adaptation strategy for large metropolitan regions.

  18. NEOPLASIA IN SNAKES AT ZOO ATLANTA DURING 1992-2012.

    Science.gov (United States)

    Page-Karjian, Annie; Hahne, Megan; Leach, Kate; Murphy, Hayley; Lock, Brad; Rivera, Samuel

    2017-06-01

    A retrospective study was conducted to review neoplasia of captive snakes in the Zoo Atlanta collection from 1992 to 2012. Of 255 snakes that underwent necropsy and histopathologic examination at Zoo Atlanta during the study period, 37 were observed with neoplasia at necropsy. In those 37 snakes, 42 neoplastic lesions of 18 primary cell types were diagnosed. Thirty-five of those neoplasms (83.3%) were malignant, and of those, 19 were of mesenchymal origin, whereas 14 were of epithelial origin. The median annual rate of neoplasia at necropsy was 12.5% (interquartile range = 2.8-19.5%) over the 21-yr study period. The mean estimated age at death for snakes with neoplasia was 13.2 yr (range, 1-24 yr). Investigating the incidence and clinical significance of neoplasia in captive snakes is vital for developing effective preventative and treatment regimes.

  19. Atlanta, revised Atlanta, and Determinant-based classification--application in a cohort of Portuguese patients with acute pancreatitis.

    Science.gov (United States)

    Fernandes, Samuel R; Carvalho, Joana; Santos, Patrícia; Moura, Carlos M; Antunes, Teresa; Velosa, José

    2016-01-01

    Acute pancreatitis (AP) represents a complex and potentially fatal disease with a highly variable clinical course. Three classification systems for assessing the severity in AP have been validated for clinical use. The aim of the present study was to evaluate the performance of the Atlanta and Determinant-based classifications in predicting severe clinical outcomes in patients with AP. In this retrospective study we reviewed the treatment and follow-up records of 525 patients with AP admitted to our unit between the years of 2003 and 2014. Outcomes included mortality, admission to the ICU, need for interventional procedures or nutritional support, and duration of hospital and ICU stay. The prevalence of organ failure and persistent organ failure in our cohort was 23.0 and 10.7%, respectively, and the mortality rate was 5.9%. Higher grades of severity were associated with worse outcomes in all classification systems. The revised Atlanta and Determinant-based classifications performed similarly in predicting outcomes, and both proved to be superior to the former classic Atlanta classification. Recent classifications proved to be more accurate in predicting important clinical outcomes in patients with AP.

  20. Acute pancreatitis: reflections through the history of the Atlanta Consensus

    OpenAIRE

    Torres López, Ana María; Hoyos Duque, Sergio Iván

    2014-01-01

    Acute pancreatitis is an inflammatory process with systemic and local repercussions. Most cases are mild with low mortality rate, but 20% of the patients have severe pancreatitis with a mortality rate up to 30%. Through the years the medical community has tried to reach consensus about this disease in order to better understand, classify and treat it. The most important of these has been known as the Atlanta Consensus 1992, in use for many years. However, it has been recently the subject of v...

  1. Acute pancreatitis: reflections through the history of the Atlanta Consensus

    Directory of Open Access Journals (Sweden)

    Torres López, Ana María

    2014-10-01

    Full Text Available Acute pancreatitis is an inflammatory process with systemic and local repercussions. Most cases are mild with low mortality rate, but 20% of the patients have severe pancreatitis with a mortality rate up to 30%. Through the years the medical community has tried to reach consensus about this disease in order to better understand, classify and treat it. The most important of these has been known as the Atlanta Consensus 1992, in use for many years. However, it has been recently the subject of various proposals for changes and updates, which are discussed in this review article.

  2. Falsification, Annual Targets, and Errant Leadership: Media Portrayal of the Atlanta Test-Cheating Scandal

    Science.gov (United States)

    Freeman, Eric

    2015-01-01

    This analysis of the Atlanta test-cheating scandal differs markedly from the version reported in the press. Using discourse analysis, I examined over 50 articles published in the "Atlanta Journal-Constitution" ("AJC"), the hometown newspaper at the center of the investigation. Because newspapers are a primary source of…

  3. Why, Where, and How to Infuse the Atlanta Sociological Laboratory into the Sociology Curriculum

    Science.gov (United States)

    Wright, Earl, II

    2012-01-01

    The Atlanta Sociological Laboratory is the moniker bestowed on scholars engaged in sociological research at Atlanta University between 1895 and 1924. Under the leadership of W. E. B. Du Bois, 1897-1914, this school made substantive yet marginalized contributions to the discipline. Its accomplishments include, but are not limited to, its…

  4. 40 CFR 81.45 - Metropolitan Atlanta Intrastate Air Quality Control Region.

    Science.gov (United States)

    2010-07-01

    ... Quality Control Region. 81.45 Section 81.45 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Air Quality Control Regions § 81.45 Metropolitan Atlanta Intrastate Air Quality Control Region. The Metropolitan Atlanta Intrastate Air Quality Control Region (Georgia) has been revised to consist of the...

  5. 78 FR 65877 - Approval and Promulgation of Implementation Plans; Atlanta, Georgia 1997 8-Hour Ozone...

    Science.gov (United States)

    2013-11-04

    ... Subjects in 40 CFR Part 52 Environmental protection, Air pollution control, Incorporation by reference.... County-Sigman at I-20 and Metropolitan Area. Douglas County-Chapel Hill at I- 20. MARTA Express Bus routes (15 Atlanta 6/17/96 4/26/99. buses). Metropolitan Area. Signal preemption for MARTA Atlanta 6/17...

  6. Fabrication of a novel RF switch device with high performance using In0.4Ga0.6As MOSFET technology

    Science.gov (United States)

    Jiahui, Zhou; Hudong, Chang; Xufang, Zhang; Jingzhi, Yang; Guiming, Liu; Haiou, Li; Honggang, Liu

    2016-02-01

    A novel radio frequency (RF) switch device has been successfully fabricated using InGaAs metal-oxide-semiconductor field-effect transistor (MOSFET) technology. The device showed drain saturation currents of 250 mA/mm, a maximum transconductance of 370 mS/mm, a turn-on resistance of 0.72 mω·mm2 and a drain current on-off (Ion/Ioff) ratio of 1 × 106. The maximum handling power of on-state of 533 mW/mm and off-state of 3667 mW/mm is obtained. The proposed In0.4Ga0.6 As MOSFET RF switch showed an insertion loss of less than 1.8 dB and an isolation of better than 20 dB in the frequency range from 0.1 to 7.5 GHz. The lowest insertion loss and the highest isolation can reach 0.27 dB and more than 68 dB respectively. This study demonstrates that the InGaAs MOSFET technology has a great potential for RF switch application. Project supported by the National Natural Science Foundation of China (Nos. 61274077, 61474031), the Guangxi Natural Science Foundation (No. 2013GXNSFGA019003), the Guangxi Department of Education Project (No. 201202ZD041), the Guilin City Technology Bureau (Nos. 20120104-8, 20130107-4), the China Postdoctoral Science Foundation Funded Project (Nos. 2012M521127, 2013T60566), the National Basic Research Program of China (Nos. 2011CBA00605, 2010CB327501), the Innovation Project of GUET Graduate Education (Nos. GDYCSZ201448, GDYCSZ201449), the State key Laboratory of Electronic Thin Films and Integrated Devices, UESTC (No. KFJJ201205), and the Guilin City Science and Technology Development Project (Nos. 20130107-4, 20120104-8).

  7. 1987 IEEE International Symposium on Electromagnetic Compatibility, Atlanta, GA, Aug. 25-27, 1987, Symposium Record

    Science.gov (United States)

    Various papers on the state of the art in electromagnetic compatibility (EMC) are presented. The general topics addressed include: EMC analysis; simulators, facilities, and instrumentation; shield performance assessments; open area test sites; electromagnetic pulse; EMI suppression; and EMC measurements. Also considered are: cable coupling/crosstalk; radiated emission measurement concerns; electrostatic discharge; lightning/EMP; antenna-related EMC; statistical approach to EMC; and electromagnetic environment/system level EMC.

  8. DOE ZERH Case Study: Heirloom Design Build, Euclid Avenue, Atlanta, GA

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2015-09-01

    Case study of a DOE 2015 Housing Innovation Award winning custom home in the mixed-humid climate that got a HERS 50 without PV, with 2x6 16” on center walls with R-19 ocsf; basement with R-28 ccsf, R-5 rigid foam under slab; sealed attic with R-28 ocsf under roof deck; 22.8 SEER; 12.5 HSPF heat pump.

  9. Social network composition and sexual risk-taking among gay and bisexual men in Atlanta, GA.

    Science.gov (United States)

    Finneran, Catherine; Stephenson, Rob

    2014-01-01

    Social network composition is known to effect patterns of reported sexual risk-taking among men who have sex with men (MSM); however, consensus as to the directionality and size of these effects is lacking. We examined the relationships between novel aspects of social network composition and sexual risk-taking using a cross-sectional survey of 870 MSM. Social network composition was found to have mixed effects on reported sexual risk-taking: reporting proportionally more lesbian, gay, or bisexual (LGB)-identified friends and reporting friends who were on average significantly older than the respondent were both associated with reporting increased sexual risk, while reporting proportionally more LGB-identified friends in relationships and reporting a social network proportionally more aware of the respondent's homosexuality/bisexuality were both associated with reporting decreased sexual risk. The support structures created by differing social network compositions-and particularly the presence of LGB couples-may be a potential area for targeting sexual risk-reduction interventions for MSM.

  10. 78 FR 70895 - Proposed Establishment and Modification of Area Navigation (RNAV) Routes; Atlanta, GA

    Science.gov (United States)

    2013-11-27

    ... Charlotte, NC (CLT) Metroplex areas. DATES: Comments must be received on or before January 13, 2014... from the CLT area and overflying ATL. The route would parallel J-37 between COLZI and CHOPZ thereby.... The route would facilitate CLT departures traveling northwest-bound and overflying the Cincinnati, OH...

  11. 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)

  12. SEMICONDUCTOR DEVICES: Structural and electrical characteristics of lanthanum oxide gate dielectric film on GaAs pHEMT technology

    Science.gov (United States)

    Chia-Song, Wu; Hsing-Chung, Liu

    2009-11-01

    This paper investigates the feasibility of using a lanthanum oxide thin film (La2O3) with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain breakdown voltage relative to the conventional GaAs pHEMT. An E/D mode pHEMT in a single chip was realized by selecting the appropriate La2O3 thickness. The thin La2O3 film was characterized: its chemical composition and crystalline structure were determined by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. La2O3 exhibited good thermal stability after post-deposition annealing at 200, 400 and 600 °C because of its high binding-energy (835.6 eV). Experimental results clearly demonstrated that the La2O3 thin film was thermally stable. The DC and RF characteristics of Pt/La2O3/Ti/Au gate and conventional Pt/Ti/Au gate pHEMTs were examined. The measurements indicated that the transistor with the Pt/La2O3/Ti/Au gate had a higher breakdown voltage and lower gate leakage current. Accordingly, the La2O3 thin film is a potential high-k material for use as a gate dielectric to improve electrical performance and the thermal effect in high-power applications.

  13. NASA Low Visibility Landing and Surface Operations (LVLASO) Atlanta Demonstration: Surveillance Systems Performance Analysis

    Science.gov (United States)

    Cassell, Rick; Evers, Carl; Hicok, Dan; Lee, Derrick

    1999-01-01

    NASA conducted a series of flight experiments at Hartsfield Atlanta International Airport as part of the Low Visibility Landing and Surface Operations (LVLASO) Program. LVLASO is one of the subelements of the NASA Terminal Area Productivity (TAP) Program, which is focused on providing technology and operating procedures for achieving clear-weather airport capacity in instrument-weather conditions, while also improving safety. LVLASO is investigating various technologies to be applied to airport surface operations, including advanced flight deck displays and surveillance systems. The purpose of this report is to document the performance of the surveillance systems tested as part of the LVLASO flight experiment. There were three surveillance sensors tested: primary radar using Airport Surface Detection Equipment (ASDE-3) and the Airport Movement Area Safety System (AMASS), Multilateration using the Airport Surface Target Identification System (ATIDS), and Automatic Dependent Surveillance - Broadcast (ADS-B) operating at 1090 MHz. The performance was compared to the draft requirements of the ICAO Advanced Surface Movement Guidance and Control System (A-SMGCS). Performance parameters evaluated included coverage, position accuracy, and update rate. Each of the sensors was evaluated as a stand alone surveillance system.

  14. Atlanta congestion reduction demonstration. National evaluation : surveys and interviews test plan.

    Science.gov (United States)

    2011-08-01

    This report presents the test plan for collecting and analyzing data survey and interview data for the : Atlanta Congestion Reduction Demonstration (CRD) under the United States Department of : Transportation (U.S. DOT) Urban Partnership Agreement (U...

  15. Office development, parking management, and travel behavior : the case of midtown Atlanta

    Science.gov (United States)

    1999-05-01

    The effects of special parking provision in zoning ordinances are assessed based on a case study of midtown Atlanta. The study results indicate that it is somewhat easier to promote increased office development around rail transit stations than it is...

  16. Atlanta congestion reduction demonstration. National evaluation : travel demand management (TDM) data test plan.

    Science.gov (United States)

    2011-08-01

    This report presents the test plan for collecting and analyzing data dealing with travel demand : management (TDM) activities for the Atlanta Congestion Reduction Demonstration (CRD) under the : United States Department of Transportation (U.S. DOT) U...

  17. Counseling Spanish-speaking patients: Atlanta pharmacists' cultural sensitivity, use of language-assistance services, and attitudes.

    Science.gov (United States)

    Muzyk, Andrew J; Muzyk, Tara L; Barnett, Candace W

    2004-01-01

    To document the types of language-assistance services available in pharmacies and the perceptions of pharmacists regarding the effectiveness of these services, and to measure the attitudes toward counseling Spanish-speaking patients and cultural sensitivity of pharmacists. Cross-sectional assessment. Metropolitan Atlanta, Ga. Registered Georgia pharmacists residing in metropolitan Atlanta. Mailed survey, with repeat mailing 2 weeks later. 38 survey items measuring demographic and practice-site characteristics, types of language-assistance services available with an assessment of the effectiveness of each measured on a nominal scale, and attitudinal items concerning counseling of Spanish-speaking patients and pharmacists' cultural sensitivity using a 5-point Likert-type response scale. Of 1,975 questionnaires mailed, 608 were returned, a 30.8% response rate. Nearly two thirds of the pharmacists had recently counseled a Spanish-speaking patient, but only one fourth of those respondents considered their interactions effective. Nearly all pharmacists, 88.0%, worked in pharmacies with language-assistance services. Of seven types of these services, a mean of 2.19 were available in pharmacies, and the majority of pharmacists (84.4% or more) identifying a service considered it to be effective. The pharmacists were neutral about counseling Spanish-speaking patients (mean = 2.94) and indifferent toward other cultures (mean = 3.28); however, they agreed they had a responsibility to counsel Spanish-speaking patients, and they believed that use of language-assistance services would constitute a reasonable effort to counsel these patients. Pharmacists have an opportunity to address barriers to communication with the Spanish-speaking population through use of language-assistance services and educational measures within the profession.

  18. Modeling the Effects of Onsite Wastewater Treatment Systems on Nitrate Loads Using SWAT in an Urban Watershed of Metropolitan Atlanta.

    Science.gov (United States)

    Hoghooghi, Nahal; Radcliffe, David E; Habteselassie, Mussie Y; Jeong, Jaehak

    2017-05-01

    Onsite wastewater treatment systems (OWTSs) can be a source of nitrogen (N) pollution in both surface and ground waters. In metropolitan Atlanta, GA, >26% of homes are on OWTSs. In a previous article, we used the Soil Water Assessment Tool to model the effect of OWTSs on stream flow in the Big Haynes Creek Watershed in metropolitan Atlanta. The objective of this study was to estimate the effect of OWTSs, including failing systems, on nitrate as N (NO-N) load in the same watershed. Big Haynes Creek has a drainage area of 44 km with mainly urban land use (67%), and most of the homes use OWTSs. A USGS gauge station where stream flow was measured daily and NO-N concentrations were measured monthly was used as the outlet. The model was simulated for 12 yr. Overall, the model showed satisfactory daily stream flow and NO-N loads with Nash-Sutcliffe coefficients of 0.62 and 0.58 for the calibration period and 0.67 and 0.33 for the validation period at the outlet of the Big Haynes Watershed. Onsite wastewater treatment systems caused an average increase in NO-N load of 23% at the watershed scale and 29% at the outlet of a subbasin with the highest density of OWTSs. Failing OWTSs were estimated to be 1% of the total systems and did not have a large impact on stream flow or NO-N load. The NO-N load was 74% of the total N load in the watershed, indicating the important effect of OWTSs on stream loads in this urban watershed. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  19. High-Efficiency, Ka-band Solid-State Power Amplifier Utilizing GaN Technology, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — QuinStar Technology proposes to develop an efficient, solid-state power amplifier (SSPA), operating at Ka-band frequencies, for high data rate, long range space...

  20. High-Efficiency, Ka-Band Solid-State Power Amplifier Utilizing GaN Technology, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — QuinStar Technology proposes to develop a high-efficiency, solid-state power amplifier (SSPA), operating at Ka-band frequencies, for high data rate, long range space...

  1. Risk Factors for HIV Transmission and Barriers to HIV Disclosure: Metropolitan Atlanta Youth Perspectives.

    Science.gov (United States)

    Camacho-Gonzalez, Andres F; Wallins, Amy; Toledo, Lauren; Murray, Ashley; Gaul, Zaneta; Sutton, Madeline Y; Gillespie, Scott; Leong, Traci; Graves, Chanda; Chakraborty, Rana

    2016-01-01

    Youth carry the highest incidence of HIV infection in the United States. Understanding adolescent and young adult (AYA) perspectives on HIV transmission risk is important for targeted HIV prevention. We conducted a mixed methods study with HIV-infected and uninfected youth, ages 18-24 years, from Atlanta, GA. We provided self-administered surveys to HIV-infected and HIV-uninfected AYAs to identify risk factors for HIV acquisition. By means of computer-assisted thematic analyses, we examined transcribed focus group responses on HIV education, contributors to HIV transmission, and pre-sex HIV status disclosure. The 68 participants had the following characteristics: mean age 21.5 years (standard deviation: 1.8 years), 85% male, 90% black, 68% HIV-infected. HIV risk behaviors included the perception of condomless sex (Likert scale mean: 8.0) and transactional sex (88% of participants); no differences were noted by HIV status. Qualitative analyses revealed two main themes: (1) HIV risk factors among AYAs, and (2) barriers to discussing HIV status before sex. Participants felt the use of social media, need for immediate gratification, and lack of concern about HIV disease were risk factors for AYAs. Discussing HIV status with sex partners was uncommon. Key reasons included: fear of rejection, lack of confidentiality, discussion was unnecessary in temporary relationships, and disclosure negatively affecting the mood. HIV prevention strategies for AYAs should include improving condom use frequency and HIV disclosure skills, responsible utilization of social media, and education addressing HIV prevention including the risks of transactional sex.

  2. Outcomes among Asylum Seekers in Atlanta, Georgia, 2003--2012.

    Science.gov (United States)

    Evans, Dabney P; Donato, Caitlin E; Malewezi, Bridget A; Li, Anyie J; Corea, Mario J; Mitchell, Andrew B

    2015-10-01

    INTRODUCTION Asylum seekers face a wide array of challenges, including the need for a fair and just adjudication process. In the state of Georgia, the Atlanta Asylum Network addresses the needs of such individuals by providing them physical, psychological and gynecological assessments, the results of which are presented to the courts in the asylum appeal process. OBJECTIVE As a component of the Network's program evaluation, assess outcomes among asylum seekers using its services, as well as relation of outcomes to type of service provided, the individual's geographic origin and English language proficiency. METHODS A retrospective examination was conducted of program data gathered by the Network between 2003 and 2012. Subjects included asylum seekers who received assessments by the Network during this period. The primary variable of interest was the final case outcome, defined as determination of asylum status: granted, withholding of removal, administrative closure and prosecutorial discretion, denied or voluntary departure. Outcomes were subsequently collapsed into a single positive or negative outcome variable. Positive outcomes included asylum granted, removal withheld, administrative closure and prosecutorial discretion. Negative outcomes included asylum denied and voluntary departure. We conducted bivariate and multivariate analyses, relating final case outcomes to Network services, geographic origin and English language proficiency, among the key variables. RESULTS A total of 69 of 120 asylum seekers in the study had a known final case outcome, and of those, 63.8% (44) had a positive outcome; or 37% of the total number of asylum seekers (n = 120). Among the 20 who received 2 of the 3 types of assessment (physical, psychological, gynecological), 16 (80%) received a positive case outcome. Most persons with a known final outcome came from Africa (41), where 78% (32) of cases resulted positive. Asylum seekers not proficient in English were 2.4 times more likely

  3. Effects of instrument precision and spatial variability on the assessment of the temporal variation of ambient air pollution in Atlanta, Georgia

    Energy Technology Data Exchange (ETDEWEB)

    Katherine S. Wade; James A. Mulholland; Amit Marmur; Armistead G. Russell; Ben Hartsell; Eric Edgerton; Mitch Klein; Lance Waller; Jennifer L. Peel; Paige E. Tolbert [Georgia Institute of Technology, Atlanta, GA (United States). School of Civil and Environmental Engineering

    2006-06-15

    Data from the U.S. Environmental Protection Agency Air Quality System, the Southeastern Aerosol Research and Characterization database, and the Assessment of Spatial Aerosol Composition in Atlanta database for 1999 through 2002 have been used to characterize error associated with instrument precision and spatial variability on the assessment of the temporal variation of ambient air pollution in Atlanta, GA. These data are being used in time series epidemiologic studies in which associations of acute respiratory and cardiovascular health outcomes and daily ambient air pollutant levels are assessed. Modified semivariograms are used to quantify the effects of instrument precision and spatial variability on the assessment of daily metrics of ambient gaseous pollutants (SO{sub 2}, CO, NOx, and O{sub 3}) and fine particulate matter (PM2.5) (PM2.5 mass, sulfate, nitrate, ammonium, elemental carbon (EC), and organic carbon (OC)). Variation because of instrument imprecision represented 7-40% of the temporal variation in the daily pollutant measures and was largest for the PM2.5 EC and OC. Spatial variability was greatest for primary pollutants (SO{sub 2}, CO, NOx, and EC). Population-weighted variation in daily ambient air pollutant levels because of both instrument imprecision and spatial variability ranged from 20% of the temporal variation for O{sub 3} to 70% of the temporal variation for SO{sub 2} and EC. Wind rose plots, corrected for diurnal and seasonal pattern effects, are used to demonstrate the impacts of local sources on monitoring station data. The results presented are being used to quantify the impacts of instrument precision and spatial variability on the assessment of health effects of ambient air pollution in Atlanta and are relevant to the interpretation of results from time series health studies that use data from fixed monitors. 38 refs., 8 figs., 4 tabs.

  4. Project ATLANTA (Atlanta Land use Analysis: Temperature and Air Quality): Use of Remote Sensing and Modeling to Analyze How Urban Land Use Change Affects Meteorology and Air Quality Through Time

    Science.gov (United States)

    Quattrochi, Dale A.; Luvall, Jeffrey C.; Estes, Maurice G., Jr.

    1999-01-01

    This paper presents an overview of Project ATLANTA (ATlanta Land use ANalysis: Temperature and Air-quality) which is an investigation that seeks to observe, measure, model, and analyze how the rapid growth of the Atlanta, Georgia metropolitan area since the early 1970's has impacted the region's climate and air quality. The primary objectives for this research effort are: (1) To investigate and model the relationships between land cover change in the Atlanta metropolitan, and the development of the urban heat island phenomenon through time; (2) To investigate and model the temporal relationships between Atlanta urban growth and land cover change on air quality; and (3) To model the overall effects of urban development on surface energy budget characteristics across the Atlanta urban landscape through time. Our key goal is to derive a better scientific understanding of how land cover changes associated with urbanization in the Atlanta area, principally in transforming forest lands to urban land covers through time, has, and will, effect local and regional climate, surface energy flux, and air quality characteristics. Allied with this goal is the prospect that the results from this research can be applied by urban planners, environmental managers and other decision-makers, for determining how urbanization has impacted the climate and overall environment of the Atlanta area. Multiscaled remote sensing data, particularly high resolution thermal infrared data, are integral to this study for the analysis of thermal energy fluxes across the Atlanta urban landscape.

  5. Water crisis: the metropolitan Atlanta, Georgia, regional water supply conflict

    KAUST Repository

    Missimer, Thomas M.

    2014-07-01

    Many large population centres are currently facing considerable difficulties with planning issues to secure future water supplies, as a result of water allocation and environmental issues, litigation, and political dogma. A classic case occurs in the metropolitan Atlanta area, which is a rapidly growing, large population centre that relies solely on surface water for supply. Lake Lanier currently supplies about 70% of the water demand and has been involved in a protracted legal dispute for more than two decades. Drought and environmental management of the reservoir combined to create a water shortage which nearly caused a disaster to the region in 2007 (only about 35 days of water supply was in reserve). While the region has made progress in controlling water demand by implementing a conservation plan, per capita use projections are still very high (at 511 L/day in 2035). Both non-potable reuse and indirect reuse of treated wastewater are contained in the most current water supply plan with up to 380,000 m3/day of wastewater treated using advanced wastewater treatment (nutrient removal) to be discharged into Lake Lanier. The water supply plan, however, includes no additional or new supply sources and has deleted any reference to the use of seawater desalination or other potential water sources which would provide diversification, thereby relying solely on the Coosa and Chattahoochee river reservoirs for the future. © 2014 IWA Publishing.

  6. Employing Si solar cell technology to increase efficiency of ultra-thin Cu(In,Ga)Se2 solar cells

    Science.gov (United States)

    Vermang, Bart; Wätjen, Jörn Timo; Fjällström, Viktor; Rostvall, Fredrik; Edoff, Marika; Kotipalli, Ratan; Henry, Frederic; Flandre, Denis

    2014-01-01

    Reducing absorber layer thickness below 500 nm in regular Cu(In,Ga)Se2 (CIGS) solar cells decreases cell efficiency considerably, as both short-circuit current and open-circuit voltage are reduced because of incomplete absorption and high Mo/CIGS rear interface recombination. In this work, an innovative rear cell design is developed to avoid both effects: a highly reflective rear surface passivation layer with nano-sized local point contact openings is employed to enhance rear internal reflection and decrease the rear surface recombination velocity significantly, as compared with a standard Mo/CIGS rear interface. The formation of nano-sphere shaped precipitates in chemical bath deposition of CdS is used to generate nano-sized point contact openings. Evaporation of MgF2 coated with a thin atomic layer deposited Al2O3 layer, or direct current magnetron sputtering of Al2O3 are used as rear surface passivation layers. Rear internal reflection is enhanced substantially by the increased thickness of the passivation layer, and also the rear surface recombination velocity is reduced at the Al2O3/CIGS rear interface. (MgF2/)Al2O3 rear surface passivated ultra-thin CIGS solar cells are fabricated, showing an increase in short circuit current and open circuit voltage compared to unpassivated reference cells with equivalent CIGS thickness. Accordingly, average solar cell efficiencies of 13.5% are realized for 385 nm thick CIGS absorber layers, compared with 9.1% efficiency for the corresponding unpassivated reference cells. PMID:26300619

  7. Urbanization effects on the hydrology of the Atlanta, Georgia (USA)

    Science.gov (United States)

    Peters, N.E.; Rose, S.

    2001-01-01

    For the period from 1958 to 1996, streamflow and rainfall characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds in the vicinity of Atlanta, Georgia (USA). Water levels in several wells completed in surficial and crystalline-rock aquifers also were evaluated. Annual runoff coefficients (runoff as a fractional percentage of precipitation) ranged from 0.31 to 0.34 and were not significantly different for the urban stream (Peachtree Creek). Peak flows for the largest 25 stormflows at Peachtree Creek were 30% to 80% greater than peak flows for the other streams. A 2-day storm recession constant for Peachtree Creek was much larger, that is streamflow decreased more rapidly than for the other streams. Average low flow of Peachtree Creek was 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of storm water and the paving of groundwater recharge areas. The timing of groundwater level variations was similar annually in each well, reflecting the seasonal recharge. Although water level monitoring only began during the late 1970s and early 1980s for the two urban wells, water levels in these wells have been declining compared to non-urban wells since then. The water level decline is attributed to decreased groundwater recharge in the urban watersheds due to increased imperviousness and related rapid storm runoff. Likewise, the increased urbanization from the 1960s to the 1990s of the Peachtree Creek watershed produced more runoff than urbanization in the less urbanized Big Creek and Sweetwater Creek watersheds.

  8. Health impact assessment of the Atlanta BeltLine.

    Science.gov (United States)

    Ross, Catherine L; Leone de Nie, Karen; Dannenberg, Andrew L; Beck, Laurie F; Marcus, Michelle J; Barringer, Jason

    2012-03-01

    Although a health impact assessment (HIA) is a tool that can provide decision makers with recommendations to promote positive health impacts and mitigate adverse health impacts of proposed projects and policies, it is not routinely conducted on most major projects or policies. To make health a decision criterion for the Atlanta BeltLine, a multibillion-dollar transit, trails, parks, and redevelopment project. An HIA was conducted in 2005-2007 to anticipate and influence the BeltLine's effect on health determinants. Changes in access and equity, environmental quality, safety, social capital, and physical activity were forecast, and steps to maximize health benefits and reduce negative effects were recommended. Key recommendations included giving priority to the construction of trails and greenspace rather than residential and retail construction, making health an explicit goal in project priority setting, adding a public health professional to decision-making boards, increasing the connectivity between the BeltLine and civic spaces, and ensuring that affordable housing is built. BeltLine project decision makers have incorporated most of the HIA recommendations into the planning process. The HIA was cited in the awarding of additional funds of $7,000,000 for brownfield clean-up and greenspace development. The project is expected to promote the health of local residents more than in the absence of the HIA. This report is one of the first HIAs to tie specific assessment findings to specific recommendations and to identifiable impacts from those recommendations. The lessons learned from this project may help others engaged in similar efforts. Copyright © 2012. Published by Elsevier Inc.

  9. 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 ...

  10. A Dynamic Optimization Technique for Siting the NASA-Clark Atlanta Urban Rain Gauge Network (NCURN)

    Science.gov (United States)

    Shepherd, J. Marshall; Taylor, Layi

    2003-01-01

    NASA satellites and ground instruments have indicated that cities like Atlanta, Georgia may create or alter rainfall. Scientists speculate that the urban heat island caused by man-made surfaces in cities impact the heat and wind patterns that form clouds and rainfall. However, more conclusive evidence is required to substantiate findings from satellites. NASA, along with scientists at Clark Atlanta University, are implementing a dense, urban rain gauge network in the metropolitan Atlanta area to support a satellite validation program called Studies of PRecipitation Anomalies from Widespread Urban Landuse (SPRAWL). SPRAWL will be conducted during the summer of 2003 to further identify and understand the impact of urban Atlanta on precipitation variability. The paper provides an. overview of SPRAWL, which represents one of the more comprehensive efforts in recent years to focus exclusively on urban-impacted rainfall. The paper also introduces a novel technique for deploying rain gauges for SPRAWL. The deployment of the dense Atlanta network is unique because it utilizes Geographic Information Systems (GIS) and Decision Support Systems (DSS) to optimize deployment of the rain gauges. These computer aided systems consider access to roads, drainage systems, tree cover, and other factors in guiding the deployment of the gauge network. GIS and DSS also provide decision-makers with additional resources and flexibility to make informed decisions while considering numerous factors. Also, the new Atlanta network and SPRAWL provide a unique opportunity to merge the high-resolution, urban rain gauge network with satellite-derived rainfall products to understand how cities are changing rainfall patterns, and possibly climate.

  11. The U.S. Geological Survey and City of Atlanta water-quality and water-quantity monitoring network

    Science.gov (United States)

    Horowitz, Arthur J.; Hughes, W. Brian

    2006-01-01

    Population growth and urbanization affect the landscape, and the quality and quantity of water in nearby rivers and streams, as well as downstream receiving waters (Ellis, 1999). Typical impacts include: (1) disruption of the hydrologic cycle through increases in the extent of impervious surfaces (e.g., roads, roofs, sidewalks) that increase the velocity and volume of surface-water runoff; (2) increased chemical loads to local and downstream receiving waters from industrial sources, nonpoint-source runoff, leaking sewer systems, and sewer overflows; (3) direct or indirect soil contamination from industrial sources, power-generating facilities, and landfills; and (4) reduction in the quantity and quality of aquatic habitats. The City of Atlanta's monitoring network consists of 21 long-term sites. Eleven of these are 'fully instrumented' to provide real-time data on water temperature, pH, specific conductance, dissolved oxygen, turbidity (intended as a surrogate for suspended sediment concentration), water level (gage height, intended as a surrogate for discharge), and precipitation. Data are transmitted hourly and are available on a public Web site (http://ga.water.usgs.gov/). Two sites only measure water level and rainfall as an aid to stormwater monitoring. The eight remaining sites are used to assess water quality.

  12. Green roof adoption in atlanta, georgia: the effects of building characteristics and subsidies on net private, public, and social benefits.

    Science.gov (United States)

    Mullen, Jeffrey D; Lamsal, Madhur; Colson, Greg

    2013-10-01

    This research draws on and expands previous studies that have quantified the costs and benefits associated with conventional roofs versus green roofs. Using parameters from those studies to define alternative scenarios, we estimate from a private, public, and social perspective the costs and benefits of installing and maintaining an extensive green roof in Atlanta, GA. Results indicate net private benefits are a decreasing function of roof size and vary considerably across scenarios. In contrast, net public benefits are highly stable across scenarios, ranging from $32.49 to $32.90 m(-2). In addition, we evaluate two alternative subsidy regimes: (i) a general subsidy provided to every building that adopts a green roof and (ii) a targeted subsidy provided only to buildings for which net private benefits are negative but net public benefits are positive. In 6 of the 12 general subsidy scenarios the optimal public policy is not to offer a subsidy; in 5 scenarios the optimal subsidy rate is between $20 and $27 m(-2); and in 1 scenario the optimal rate is $5 m(-2). The optimal rate with a targeted subsidy is between $20 and $27 m(-2) in 11 scenarios and no subsidy is optimal in the twelfth. In most scenarios, a significant portion of net public benefits are generated by buildings for which net private benefits are positive. This suggests a policy focused on information dissemination and technical assistance may be more cost-effective than direct subsidy payments.

  13. Racial Differences in Partnership Attributes, Typologies, and Risk Behaviors Among Men Who Have Sex With Men in Atlanta, Georgia.

    Science.gov (United States)

    White, Darcy; Grey, Jeremy A; Gorbach, Pamina M; Rothenberg, Richard B; Sullivan, Patrick S; Rosenberg, Eli S

    2017-05-01

    The role of main partnerships in shaping HIV transmission dynamics among men who have sex with men (MSM) has gained recognition in recent studies, but there is little evidence that existing definitions of partnership type are accurate or have consistent meaning for all men. Using data collected from 2011 to 2013 on 693 partnerships described by 193 Black and White MSM in Atlanta, GA, partnership attributes and risk behaviors were examined and compared by race, stratified in two ways: (1) by commonly used definitions of partnerships as "main" or "casual" and (2) by a new data-driven partnership typology identified through latent class analysis (LCA). Racial differences were analyzed using chi-square, Fisher's exact, and Wilcoxon-Mann-Whitney tests. Black participants were less likely to report condomless anal sex (CAS) within partnerships they labeled as main, yet they were also less likely to describe these partnerships as "primary" on a parallel question. In contrast, within strata defined by the LCA-derived typology, most partnership attributes were comparable and the likelihood of CAS was equivalent by race. These findings suggest that classification of partnerships as main or casual does not accurately capture the partnership patterns of MSM, resulting in differential misclassification by race. Future studies and interventions should refine and utilize more evidence-based typologies.

  14. Characterization and Modeling of DHBT in InP/GaAsSb Technology for the Design and Fabrication of a Ka Band MMIC Oscillator

    Directory of Open Access Journals (Sweden)

    S. Laurent

    2012-01-01

    Full Text Available This paper presents the design of an MMIC oscillator operating at a 38 GHz frequency. This circuit was fabricated by the III–V Lab with the new InP/GaAsSb Double Heterojunction Bipolar Transistor (DHBT submicronic technology (We=700 nm. The transistor used in the circuit has a 15 μm long two-finger emitter. This paper describes the complete nonlinear modeling of this DHBT, including the cyclostationary modeling of its low frequency (LF noise sources. The specific interest of the methodology used to design this oscillator resides in being able to choose a nonlinear operating condition of the transistor from an analysis in amplifier mode. The oscillator simulation and measurement results are compared. A 38 GHz oscillation frequency with 8.6 dBm output power and a phase noise of −80 dBc/Hz at 100 KHz offset from carrier have been measured.

  15. A concise guide for the determination of less-studied technology-critical elements (Nb, Ta, Ga, In, Ge, Te) by inductively coupled plasma mass spectrometry in environmental samples

    Science.gov (United States)

    Filella, Montserrat; Rodushkin, Ilia

    2018-03-01

    There is an increasing demand for analytical techniques able to measure so-called 'technology-critical elements', a set of chemical elements increasingly used in technological applications, in environmental matrices. Nowadays, inductively coupled plasma-mass spectrometry (ICP-MS) has become the technique of choice for measuring trace element concentrations. However, its application is often less straightforward than often assumed. The hints and drawbacks of ICP-MS application to the measurement of a set of less-studied technology-critical elements (Nb, Ta, Ga, In, Ge and Te) is discussed here and concise guidelines given.

  16. Underlying Factors Related to the Atlanta Cheating Scandal: An Autoethnographic Account

    Science.gov (United States)

    Beal, Emma Mumphery

    2012-01-01

    In this study I used autoethnography to analyze fifty years of African-American educational history in Georgia. The impetus for the study was the Atlanta cheating scandal, widely interpreted as a character problem for individual teachers and administrators. As a lifelong resident of Georgia, a student, a public school teacher, and a parent, it…

  17. 75 FR 73969 - Approval and Promulgation of Implementation Plans; Extension of Attainment Date for the Atlanta...

    Science.gov (United States)

    2010-11-30

    .... Jane Spann or Ms. Sara Waterson, Regulatory Development Section, Air Planning Branch, Air, Pesticides...., Atlanta, Georgia 30303-8960. The telephone number for Ms. Spann is (404) 562-9029. Ms. Spann can also be reached via electronic mail at spann[email protected] . The telephone number for Ms. Waterson is (404) 562...

  18. Social Support and Social Network Ties among the Homeless in a Downtown Atlanta Park

    Science.gov (United States)

    Reitzes, Donald C.; Crimmins, Timothy J.; Yarbrough, Johanna; Parker, Josie

    2011-01-01

    This study applies a typology of social support with 3 categories of social networks to investigate social ties and their benefits for homeless people. Data were derived from a 2-year long series of participant observations of homeless or precariously housed people who came regularly to a downtown Atlanta public park. The findings are as follows:…

  19. Newcastle disease B1 vaccine strain in wild rock pigeons in Atlanta, Georgia

    Science.gov (United States)

    From June to October of 2012, samples were collected from wild Rock Pigeons (Columba livia) in urban neighborhoods of Atlanta, Georgia to ascertain the prevalence of pigeon paramyxovirus serotype-1 (PPMV-1). PPMV-1 strains are a subset of avian paramyxovirus serotype-1 (APMV-1) commonly isolated fro...

  20. Mixed Messages in Media Coverage of Bilingual Education: The Case of Atlanta, Georgia

    Science.gov (United States)

    Tarasawa, Beth

    2008-01-01

    As the increasing number of Latino and Asian immigrants to the Atlanta area has escalated tensions over occupational, residential, and educational resources, research has begun to examine opposition to bilingual education as an extension of anti-immigrant prejudice and as a measure of perceived threat. This study uses content analysis to compare…

  1. 75 FR 15415 - Expansion of Foreign-Trade Zone 26, Atlanta, Georgia, Area

    Science.gov (United States)

    2010-03-29

    ... DEPARTMENT OF COMMERCE Foreign-Trade Zones Board [Order No. 1670] Expansion of Foreign-Trade Zone 26, Atlanta, Georgia, Area Pursuant to its authority under the Foreign-Trade Zones Act of June 18, 1934, as amended (19 U.S.C. 81a-81u), the Foreign-Trade Zones Board (the Board) adopts the following...

  2. Overkill: Black Lives and the Spectacle of the Atlanta Cheating Scandal

    Science.gov (United States)

    Royal, Camika; Dodo Seriki, Vanessa

    2018-01-01

    This article examines the 2015 Atlanta cheating scandal trials and sentencing. Using critical race theory, the authors argue that cheating is a natural outgrowth of market-based school reform and that racial realism will always lead to scrutiny of Black performance. The sentences of these Black educators is overkill, rooted in anti-Blackness, and…

  3. 77 FR 24440 - Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year...

    Science.gov (United States)

    2012-04-24

    ... ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 52 [EPA-R04-OAR-2010-0021(b); FRL-9661-9] Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year Emissions Inventory AGENCY... 2002 base year emissions inventory portion of the state implementation plan (SIP) revision submitted by...

  4. GaN-Based High-k Praseodymium Oxide Gate MISFETs with P2S5/(NH42SX + UV Interface Treatment Technology

    Directory of Open Access Journals (Sweden)

    Chao-Wei Lin

    2012-01-01

    Full Text Available This study examines the praseodymium-oxide- (Pr2O3- passivated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs with high dielectric constant in which the AlGaN Schottky layers are treated with P2S5/(NH42SX + ultraviolet (UV illumination. An electron-beam evaporated Pr2O3 insulator is used instead of traditional plasma-assisted chemical vapor deposition (PECVD, in order to prevent plasma-induced damage to the AlGaN. In this work, the HEMTs are pretreated with P2S5/(NH42SX solution and UV illumination before the gate insulator (Pr2O3 is deposited. Since stable sulfur that is bound to the Ga species can be obtained easily and surface oxygen atoms are reduced by the P2S5/(NH42SX pretreatment, the lowest leakage current is observed in MIS-HEMT. Additionally, a low flicker noise and a low surface roughness (0.38 nm are also obtained using this novel process, which demonstrates its ability to reduce the surface states. Low gate leakage current Pr2O3 and high-k AlGaN/GaN MIS-HEMTs, with P2S5/(NH42SX + UV illumination treatment, are suited to low-noise applications, because of the electron-beam-evaporated insulator and the new chemical pretreatment.

  5. Summary of Needs and Opportunities from the 2011 Residential Energy Efficiency Stakeholders Meeting: Atlanta, Georgia -- March 16-18, 2011

    Energy Technology Data Exchange (ETDEWEB)

    2011-05-01

    This summary report outlines needs and issues for increasing energy efficiency of new and existing U.S homes, as identified at the U.S Department of Energy Building America program Spring 2011 stakeholder meeting in Atlanta, Georgia.

  6. Modeling the Effect of Onsite Wastewater Treatment Systems on Nitrate Load Using SWAT in an Urban Watershed of Metropolitan Atlanta, Georgia

    Science.gov (United States)

    Hoghooghi, N.; Radcliffe, D. E.; Habteselassie, M.; Jeong, J.

    2016-12-01

    Onsite wastewater treatment systems (OWTSs) can be a source of nitrogen (N) pollution in both surface and ground waters. In Metropolitan Atlanta, GA more than 26% of homes are on OWTSs. The objective of this study was to estimate the effect of OWTS, including failing systems, on NO3- load in an urban watershed in Metropolitan Atlanta using the Soil Water Assessment Tool (SWAT) model. Big Haynes Creek watershed has a drainage area of 44-km2 with mainly urban land use (67%) and most of the homes use OWTS. A USGS gage station where stream flow was measured daily and nitrate (NO3-) concentrations were measured approximately monthly was selected as the outlet. The model was simulated from 1 January 2003 to 31 December 2014. Overall, the model showed satisfactory daily stream flow and NO3- loads with Nash-Sutcliffe coefficients of 0.62 and 0.58 for the calibration period, and 0.67 and 0.33 for the validation period, respectively at the outlet of the Big Haynes watershed. OWTS caused an average increase in NO3- load of about 23% at the watershed scale and 29% at the sub-basin outlet with the highest density of OWTS. Failing OWTS were estimated to be 1% of the total systems and did not have a large impact on stream flow or NO3- load. The NO3- load was 74% of the total N load in the watershed, suggesting the important effect of OWTS on stream loads in urban watersheds.

  7. Development of a new thin film technology for PV systems: Open-system CCSVT process for production of ZnSe/CuGaSe{sub 2} hetero diodes. Final report; Entwicklung einer neuen Duennschichttechnologie fuer die Photovoltaik: CCSVT-Verfahren im offenen System zur Herstellung von ZnSe/CuGaSe{sub 2}-Heterodioden. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Lux-Steiner, M.C.; Jaeger-Waldau, A.

    2000-07-01

    A new technology for fast, large-surface deposition of high-quality semiconducting thin films for PV systems. The new technology, CSVT (close-space vapour transport), is based on a combination of VPE (vapour phase epitaxy) in open systems and CVT (chemical vapour phase transport) in closed systems. The two-source CVD experiments with two different transport gases, i.e. Cu{sub 2}Se with iodine and Ga{sub 2}Se{sub 3} with HCl, enabled controlled variation of the Cu:Ga ratio in the gaseous phase. The solar cells produced had efficiencies of more than 4%. The best solar cell produced had an efficiency of 4.8% and an open terminal voltage of 863 mV. [German] Ziel des Vorhabens war die Entwicklung einer neuen Technologie zur schnellen, grossflaechigen Abscheidung von qualitativ hochstehenden, halbleitenden Duennschichten fuer die Photovoltaik. Das Konzept des neuen Abscheideverfahrens, CSVT (close-space vapour transport) im offenen System, basiert auf einer Kombination der etablierten Methoden VPE (vapour phase epitaxy) im offenen und CVT (chemical vapour phase transport) im geschlossenen System. Die 2-Quellen-CVD-Experimente mit den zwei unterschiedlichen Transportgasen (Cu{sub 2}Se mit Iod; Ga{sub 2}Se{sub 3} mit HCl) ermoeglichten die kontrollierte Variation des Cu:Ga=Verhaeltnisses in der Gasphase. Bisher konnten so Solarzellen mit Wirkungsgraden ueber 4% hergestellt werden, wobei bei der bisher besten Solarzelle ein Wirkungsgrad von {eta}=4.8% und eine offene Klemmenspannung von V{sub oc}=863 mV erreicht wurde. (orig.)

  8. Impacts of the use of spent nuclear fuel burnup credit on DOE advanced technology legal weight truck cask GA-4 fleet size

    International Nuclear Information System (INIS)

    Mobasheran, A.S.; Boshoven, J.; Lake, B.

    1995-01-01

    The object of this paper is to study the impact of full and partial spent fuel burnup credit on the capacity of the Legal Weight Truck Spent Fuel Shipping Cask (GA-4) and to determine the numbers of additional spent fuel assemblies which could be accommodated as a result. The scope of the study comprised performing nuclear criticality safety scoping calculations using the SCALE-PC software package and the 1993 spent fuel database to determine logistics for number of spent fuel assemblies to be shipped. The results of the study indicate that more capacity than 2 or 3 pressurized water reactor assemblies could be gained for GA-4 casks when burnup credit is considered. Reduction in GA-4 fleet size and number of shipments are expected to result from the acceptance of spent fuel burnup credit

  9. Atlanta Gas Light opts for an in-house AM/FM

    International Nuclear Information System (INIS)

    Hull, S.R.

    1993-01-01

    Atlanta Gas Light Co. has completed facilities conversion for the first of nine planned implementations of its automated mapping/facilities management mapping/facilities management system, the Facilities and Land Base Automated Mapping Environment or FLAME. Facilities conversion is generally the most costly and time-consuming phase of an AM/FM project. Many companies decide to rely totally on outside expertise for this phase because of the complexity of the process an the resources required to complete it. Atlanta Gas Light decided to take an alternate approach by performing the facilities conversion process in-house for the first implementation, than having an outside vendor carrying out a future implementation and compare the two

  10. Fútbol, etnicidad y otredad: el Club Atlético Atlanta de Buenos Aires

    Directory of Open Access Journals (Sweden)

    Raanan Rein

    2014-06-01

    While most historians would agree as to the centrality of soccer in Latin American societies, very little has been written on ethnicity and sports in such immigrant societies as Argentina and Brazil. This article focuses on the Club Atlético Atlanta, located in the neighborhood of Villa Crespo. Although populated by various ethnic groups, Villa Crespo has long been considered a Jewish neighborhood. During the second half of the 20th century, there has been a conspicuous Jewish presence among the fans, administrators and presidents of the Atlanta soccer club, to the extent that fans of rival teams often chant anti-Semitic slogans during matches. For the first immigrant generation, belonging to this club was a way of becoming Argentines. For the next generation, it was a way of maintaining ethnic Jewish identity, while for the third it has become a family tradition.

  11. «Space and illusion». Exhibit in the superior art museum Atlanta – USA

    OpenAIRE

    Scogin, Mack; Clark, Chuck

    1980-01-01

    This Exhibit, carried out under the auspices of several cultural organizations of the city of Atlanta, intends to offer a distorted vision of space at the same time as it is real. It has been designed as a labyrinth of rooms in which various special effects are set up, such as: mirrors, lights, sound, shadow, movements, etc. Among the different rooms, the following stand out: the illuminated room, with shadows that appear and disappear on its walls; the perspective room, where the len...

  12. Applying IRSS Theory: The Clark Atlanta University Exemplar

    Science.gov (United States)

    Payton, Fay Cobb; Suarez-Brown, Tiki L.; Smith Lamar, Courtney

    2012-01-01

    The percentage of underrepresented minorities (African-American, Hispanic, Native Americans) that have obtained graduate level degrees within computing disciplines (computer science, computer information systems, computer engineering, and information technology) is dismal at best. Despite the fact that academia, the computing workforce,…

  13. The Metropolitan Atlanta community adolescent rapid testing initiative study: closing the gaps in HIV care among youth in Atlanta, Georgia, USA.

    Science.gov (United States)

    Camacho-Gonzalez, Andres F; Gillespie, Scott E; Thomas-Seaton, LaTeshia; Frieson, Krystal; Hussen, Sophia A; Murray, Ashley; Gaul, Zaneta; Leong, Traci; Graves, Chanda; Sutton, Madeline Y; Chakraborty, Rana

    2017-07-01

    To determine the effectiveness of the Metropolitan Atlanta community adolescent rapid testing initiative (MACARTI) intervention relative to standard of care (SOC), in achieving early diagnosis, linkage, and retention among HIV-infected youth ages 18-24 years. MACARTI was a pilot single-center, prospective, nonrandomized study. MACARTI combined nontraditional venue HIV testing, motivational interviewing, and case management. We collected demographic, clinical variables and calculated linkage and appointment adherence rates. We obtained SOC data from an adolescent HIV clinic. Longitudinal data were analyzed using inverse propensity treatment-weighted linear growth models; medians, interquartile ranges (IQR), means, and 95% confidence intervals are provided. MACARTI screened 435 participants and identified 49 (11.3%) HIV infections. The SOC arm enrolled 49 new HIV-infected individuals. The 98 participants, (49 in each arm) were: 85% men; 91% Black; mean age = 21 years (SD : 1.8). Overall, 63% were linked within 3 months of diagnosis; linkage was higher for MACARTI compared to SOC (96 vs. 57%, P youth in Atlanta, USA. MACARTI may serve as an effective linkage and care model for clinics serving HIV-infected youth.

  14. Prevalence and descriptive epidemiology of Lennox-Gastaut syndrome among Atlanta children.

    Science.gov (United States)

    Trevathan, E; Murphy, C C; Yeargin-Allsopp, M

    1997-12-01

    To determine the prevalence and descriptive epidemiology of Lennox-Gastaut Syndrome (LGS) among metropolitan Atlanta children. We conducted a population-based study of LGS as part of the Metropolitan Atlanta Developmental Disabilities Study (MADDS) using a multiple-source surveillance system for epilepsy and developmental disabilities. Children were defined as having LGS if they had onset of multiple seizure types before age 11 years, with at least one seizure type resulting in falls, and an EEG demonstrating slow spike-wave complexes (<2.5 Hz). Mental retardation (MR) was not used as a diagnostic criterion. The lifetime prevalence of LGS at age 10 years was 0.26/1,000. Ninety-one percent of those with LGS had MR (IQ < or = 70), and 39% had a history of infantile spasms (IS). A comparison of children with LGS and those with multiple seizure types without slow spike-wave complexes demonstrated that those with LGS were more likely to have MR, history of IS, and multiple disabilities (MR, cerebral palsy, blindness, hearing impairment). Seventeen percent of all children in Atlanta with profound MR (IQ < 20) had LGS. LGS accounts for only 4% of all childhood epilepsy, yet is a significant contributor to childhood morbidity.

  15. A Remote Sensing Approach for Urban Environmental Decision-Making: An Atlanta, Georgia Case Study

    Science.gov (United States)

    Quattrochi, Dale A.; Luvall, Jeffrey C.; Rickman, Douglas L.; Laymon, Charles A.; Estes, Maurice G., Jr.; Howell, Burgess F.; Arnold, James E. (Technical Monitor)

    2002-01-01

    Unquestionably, urbanization causes tremendous changes in land cover and land use, as well as impacting a host of environmental characteristics. For example, unlike natural surfaces, urban surfaces have very different thermal energy properties whereby they store solar energy throughout the day and continue to release it as heat well after sunset. This effect, known as the 'Urban Heat Island', serves as a catalyst for chemical reactions from vehicular exhaust and industrial activities leading to the deterioration in air quality, especially exacerbating the production of ground level ozone. 'Cool Community' strategies that utilize remote sensing data, are now being implemented as a way to reduce the impacts of the urban heat island and its subsequent environmental impacts. This presentation focuses on how remote sensing data have been used to provide descriptive and quantitative data for characterizing the Atlanta, Georgia metropolitan area - particularly for measuring surface energy fluxes, such as the thermal or "heat" energy that emanates from different land cover types across the Atlanta urban landscape. In turn, this information is useful for developing a better understanding of how the thermal characteristics of the city surface affect the urban heat island phenomena and, ultimately, air quality and other environmental parameters over the Atlanta metropolitan region. Additionally, this paper also provides insight on how remote sensing, with its synoptic approach, can be used to provide urban planners, local, state, and federal government officials, and other decision-makers, as well as the general public, with information to better manage urban areas as sustainable environments.

  16. Atlanta Centennial Olympic Games and Paralympic Games event study, 1996. Final report, July 1996--August 1996

    Energy Technology Data Exchange (ETDEWEB)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCCs), one Transit Information Center (TIC), The Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) Rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The 1996 Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on-line in time for the Olympic Games. This report presents the findings of the 1996 Olympic and Paralympic Games Events Study--a compilation of findings of system performance, the benefits realized, and the lessons learned during their operations over the event period. The study assessed the performance of the various Travel Demand Management (TDM) plans employed for Olympic Games traffic management.

  17. Evaluation of two-year Jewish genetic disease screening program in Atlanta: insight into community genetic screening approaches.

    Science.gov (United States)

    Shao, Yunru; Liu, Shuling; Grinzaid, Karen

    2015-04-01

    Improvements in genetic testing technologies have led to the development of expanded carrier screening panels for the Ashkenazi Jewish population; however, there are major inconsistencies in current screening practices. A 2-year pilot program was launched in Atlanta in 2010 to promote and facilitate screening for 19 Jewish genetic diseases. We analyzed data from this program, including participant demographics and outreach efforts. This retrospective analysis is based on a de-identified dataset of 724 screenees. Data were obtained through medical chart review and questionnaires and included demographic information, screening results, response to outreach efforts, and follow-up behavior and preferences. We applied descriptive analysis, chi-square tests, and logistic regression to analyze the data and compare findings with published literature. The majority of participants indicated that they were not pregnant or did not have a partner who was pregnant were affiliated with Jewish organizations and reported 100 % AJ ancestry. Overall, carrier frequency was 1 in 3.9. Friends, rabbis, and family members were the most common influencers of the decision to receive screening. People who were older, had a history of pregnancy, and had been previously screened were more likely to educate others (all p influencers who then encouraged screening in the target population. Educating influencers and increasing overall awareness were the most effective outreach strategies.

  18. 76 FR 37781 - Foreign-Trade Zone 26; Atlanta, GA; Application for Temporary/Interim Manufacturing Authority...

    Science.gov (United States)

    2011-06-28

    ..., grinder, hammer, sander, planer, router and screw driver kits (HTSUS 8467.29, duty-free); and, gasoline... (HTSUS 8507.80, 3.4%); armatures (HTSUS 8503.00, free-6.5%); tool bags (HTSUS 4202.92, 3.4-20%); driver... polymers (HTSUS 3903.19, 6.5%); polyamides (HTSUS 3908.10, 6.3%); resins (HTSUS 8543.70, free-2.6%); and...

  19. 76 FR 45771 - Foreign-Trade Zone 26-Atlanta, GA; Application for Manufacturing Authority; Makita Corporation of...

    Science.gov (United States)

    2011-08-01

    ... abroad (representing 64% of the value of the finished product) include: batteries; armatures; tool bags...; vinyl tubes; labels; plastic bags; water tanks; plastic grips; rubber knobs and handles; plastic cases; dust bag assemblies; tool belts; grinding wheels; tapping screws; lock lever connectors; cotters and...

  20. 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.

  1. Impacts of Combined Cooling, Heating and Power Systems, and Rainwater Harvesting on Water Demand, Carbon Dioxide, and NOx Emissions for Atlanta.

    Science.gov (United States)

    James, Jean-Ann; Sung, Sangwoo; Jeong, Hyunju; Broesicke, Osvaldo A; French, Steven P; Li, Duo; Crittenden, John C

    2018-01-02

    The purpose of this study is to explore the potential water, CO 2 and NO x emission, and cost savings that the deployment of decentralized water and energy technologies within two urban growth scenarios can achieve. We assess the effectiveness of urban growth, technological, and political strategies to reduce these burdens in the 13-county Atlanta metropolitan region. The urban growth between 2005 and 2030 was modeled for a business as usual (BAU) scenario and a more compact growth (MCG) scenario. We considered combined cooling, heating and power (CCHP) systems using microturbines for our decentralized energy technology and rooftop rainwater harvesting and low flow fixtures for the decentralized water technologies. Decentralized water and energy technologies had more of an impact in reducing the CO 2 and NO x emissions and water withdrawal and consumption than an MCG growth scenario (which does not consider energy for transit). Decentralized energy can reduce the CO 2 and NO x emissions by 8% and 63%, respectively. Decentralized energy and water technologies can reduce the water withdrawal and consumption in the MCG scenario by 49% and 50% respectively. Installing CCHP systems on both the existing and new building stocks with a net metering policy could reduce the CO 2 , NO x , and water consumption by 50%, 90%, and 75% respectively.

  2. U.S. Department of Energy, National Energy Technology Laboratory Solid-State Lighting Core Technologies Light Emitting Diodes on Semipolar Bulk GaN Substrate with IQE > 80% at 150 A/cm2 and 100 0C

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Arpan [Soraa, Inc., Fremont, CA (United States); David, Aurelien [Soraa, Inc., Fremont, CA (United States); Grundmann, Michael [Soraa, Inc., Fremont, CA (United States); Tyagi, Anurag [Soraa, Inc., Fremont, CA (United States); Craven, Michael [Soraa, Inc., Fremont, CA (United States); Hurni, Christophe [Soraa, Inc., Fremont, CA (United States); Cich, Michael [Soraa, Inc., Fremont, CA (United States)

    2015-03-31

    GaN is a crucial material for light-emitting diodes (LEDs) emitting in the violet-to-green range. Despite its good performance, it still suffers from significant technical limitations. In particular, the efficiency of GaN-based LEDs decreases at high current (“current droop”) and high temperature (“temperature droop”). This is problematic in some lighting applications, where a high-power operation is required. This program studied the use of particular substrates to improve the efficiency of GaN-based LEDs: bulk semipolar (SP) GaN substrates. These substrates possess a very high material quality, and physical properties which are distinctly different from legacy substrates currently used in the LED industry. The program focused on the development of accurate metrology to quantify the performance of GaN-based LEDs, and on improvement to LED quality and design on SP substrates. Through a thorough optimization process, we demonstrated violet LEDs with very high internal quantum efficiency, exceeding 85% at high temperature and high current. We also investigated longer-wavelength blue emitters, but found that the limited strain budget was a key limitation.

  3. Optical and digital GaAs technologies for signal-processing applications; Proceedings of the Meeting, Orlando, FL, Apr. 16-18, 1990

    Science.gov (United States)

    Bendett, Mark P.; Butler, Daniel H., Jr.; Prabhakar, Arati; Yang, Andrew

    1990-10-01

    Practical problems that need to be solved for the introduction of optical modules into processing systems are reviewed. Some papers deal with the state of the art in such key devices as Bragg cells, spatial light modulators, and fast CCDs. Issues unique to optical packaging are also highlightened. New architectures to enable real-time operations are demonstrated, and optical interconnects for parallel processors are discussed. Particular attention is given to the status and operational advantages of government-sponsored efforts to upgrade existing military systems with digital GaAs signal processors and the state of the art in computer-aided design and advanced system architectures.

  4. The revised Atlanta criteria 2012 altered the classification, severity assessment and management of acute pancreatitis.

    Science.gov (United States)

    Huang, Jie; Qu, Hong-Ping; Zheng, Yun-Feng; Song, Xu-Wei; Li, Lei; Xu, Zhi-Wei; Mao, En-Qiang; Chen, Er-Zhen

    2016-06-01

    The Atlanta criteria for acute pancreatitis (AP) has been revised recently. This study was to evaluate its practical value in classification of AP, the severity assessment and management. The clinical features, severity classification, outcome and risk factors for mortality of 3212 AP patients who had been admitted in Ruijin Hospital from 2004 to 2011 were analyzed based on the revised Atlanta criteria (RAC) and the original Atlanta criteria (OAC). Compared to the OAC group, the incidence of severe acute pancreatitis (SAP) was decreased by approximately one half (13.9% vs 28.2%) in the RAC group. The RAC presented a lower sensitivity but higher specificity, and its predictive value for severity and poor outcome was higher than those of the OAC. The proportion of SAP diagnosis and ICU admission in the early phase in the RAC group was significantly lower than that in the OAC group (Pacute necrotic collection and walled-off necrosis. Compared to the OAC, the acute physiology and chronic health evaluation II (APACHE II) score, Ranson score, idiopathic etiology, respiratory failure and laparotomy debridement were not risk factors of death in contrast to walled-off necrosis. Interestingly, hypertriglyceridemia-related SAP had good outcomes in both groups. The RAC showed a higher predictive value for severity and poorer outcome than the OAC. However, the RAC resulted in fewer ICU admissions in the early phase due to its lower sensitivity for diagnosis of SAP. Among SAP cases, older age, high CTSI, renal and cardiovascular failure, complications of acute necrotic collection and walled-off necrosis were independent risk factors for mortality.

  5. Reassessment of biogenic volatile organic compound emissions in the Atlanta area

    International Nuclear Information System (INIS)

    Geron, C.D.; Pierce, T.E.; Guenther, A.B.

    1995-01-01

    Localized estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for photochemical oxidant simulation models. Since forest tree species are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rates. A new system is used to estimate these emissions in the Atlanta area for specific tree genera at hourly and county levels. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis data and an associated urban vegetation survey are used to estimate canopy occupancy by genus in the Atlanta area. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Lraf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera-level estimates are then aggregated to county and regional levels for input into air quality models and for comparison with (1) the regulatory model currently used and (2) previous estimates for the Atlanta area by local researchers. Estimated hourly emissions from the three approaches during a documented ozone event day are compared. The proposed model yields peak diurnal isoprene emission rates that are over a factor of three times higher than previous estimates. This results in total BVOC emission rates that are roughly a factor of two times higher than previous estimates. These emissions are compared with observed emissions from forests of similar composition. Possible implications for oxidant events are discussed. (author)

  6. Status of AlGaN based focal plane array for near UV imaging and strategy to extend this technology to far-UV by substrate removal

    Science.gov (United States)

    Reverchon, Jean-Luc; Gourdel, Yves; Robo, Jean-Alexandre; Truffer, Jean-Patrick; Costard, Eric; Brault, Julien; Duboz, Jean-Yves

    2017-11-01

    The fast development of nitrides has given the opportunity to investigate AlGaN as a material for ultraviolet detection. Such AlGaN based camera presents an intrinsic spectral selectivity and an extremely low dark current at room temperature. Firstly, we will present results on focal plane array of 320x256 pixels with a pitch of 30μm. The peak responsivity is around 280nm (solar-blind), 310nm and 360nm. These results are obtained in a standard SWIR supply chain (readout circuit, electronics). With the existing near-UV camera grown on sapphire, the short wavelength cutoff is due to a window layer improving the material quality of the active layer. The ultimate shortest wavelength would be 200nm due to sapphire substrate. We present here the ways to transfer the standard design of Schottky photodiodes from sapphire to silicon substrate. We will show the capability to remove the silicon substrate, and etch the window layer in order to extend the band width to lower wavelengths.

  7. Fabrication and improvement of nanopillar InGaN/GaN light-emitting diodes using nanosphere lithography

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Ou, Yiyu; Zhan, Teng

    2015-01-01

    Surface-patterning technologies have enabled the improvement of currently existinglight-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency ofgreen GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars onInGaN∕GaN quantum-well LEDs. By ...

  8. Optimization of Electrochemically Deposited Highly Doped ZnO Bilayers on Ga-Rich Chalcopyrite Selenide for Cost-Effective Photovoltaic Device Technology

    Directory of Open Access Journals (Sweden)

    Dimitra N. Papadimitriou

    2016-11-01

    Full Text Available High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO were successively electrodeposited in the form of columnar structures preferentially oriented along the ( 10 1 ¯ 1 crystallographic direction from aqueous solution of zinc nitrate (Zn(NO32 at negative electrochemical potential of EC = (−0.8–(−1.2 V and moderate temperature of 80 °C on gallium rich (30% Ga chalcopyrite selenide Cu(In,GaSe2 (CIGS with chemically deposited ZnSe buffer (ZnSe/Cu(In,GaSe2/Mo/glass. The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ ~10−5 Ω·cm; the respective carrier concentration of the order 1022 cm−3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N2 flux regulation. The hydrostatic compressive strain due to Al3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl3 dopant was εh = −0.046 and the respective stress σh = −20 GPa. The surface reflectivity of maximum 5% over the scanned region of 180–900 nm and the (optical band gap of Eg = 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD Al:ZnO bilayers.

  9. A spatial analysis of lightning strikes and precipitation in the greater Atlanta, Georgia (USA) region

    Science.gov (United States)

    Rose, Leanna Shea

    This study examines patterns of cloud-to-ground flash enhancement and precipitation for the greater Atlanta, Georgia region. Previous research documented greater annual average flash densities (6 to 8 km-2/yr), and more flash days northeast of the city. Precipitation enhancement has also been observed through the use of both ground-based gauge and spaceborne radar data. Using an approach based in cartographic visualization and GIS, a climatology is developed to identify and characterize possible causal mechanisms and variability in flash production. To delineate how prevailing winds contribute to this hotspot, lightning flashes were selected for weak forcing conditions during the summer months (May through September, 1995 through 2003). The steering winds for the events that lower flashes in the northeast hotspot were clustered according to wind speed and direction to isolate variability in flash production around the city. Flash events were coupled to rainfall data (NARR) to visualize associated precipitation production. The spatial patterning of precipitation and cloud-to-ground lightning enhancement around Atlanta is indicative of urban alteration of convective processes. Downwind areas of increased flash activity and precipitation accumulation shifted around the urban area in accordance with steering winds from several directions. This research demonstrates the need for contextual analysis of urban lightning and precipitation patterns that accounts for the variability of localized conditions.

  10. Using synoptic weather types to predict visitor attendance at Atlanta and Indianapolis zoological parks

    Science.gov (United States)

    Perkins, David R.

    2018-01-01

    Defining an ideal "tourism climate" has been an often-visited research topic where explanations have evolved from global- to location-specific indices tailored to tourists' recreational behavior. Unfortunately, as indices become increasingly specific, they are less translatable across geographies because they may only apply to specific activities, locales, climates, or populations. A key need in the future development of weather and climate indices for tourism has been a translatable, meteorologically based index capturing the generalized ambient atmospheric conditions yet considering local climatology. To address this need, this paper tests the applicability of the spatial synoptic classification (SSC) as a tool to predict visitor attendance response in the tourism, recreation, and leisure (TRL) sector across different climate regimes. Daily attendance data is paired with the prevailing synoptic weather condition at Atlanta and Indianapolis zoological parks from September 2001 to June 2011, to review potential impacts ambient atmospheric conditions may have on visitor attendances. Results indicate that "dry moderate" conditions are most associated with high levels of attendance and "moist polar" synoptic conditions are most associated with low levels of attendance at both zoological parks. Comparing visitor response at these zoo locations, visitors in Indianapolis showed lower levels of tolerance to synoptic conditions which were not "ideal." Visitors in Indianapolis also displayed more aversion to "polar" synoptic regimes while visitors in Atlanta displayed more tolerance to "moist tropical" synoptic regimes. Using a comprehensive atmospheric measure such as the SSC may be a key to broadening application when assessing tourism climates across diverse geographies.

  11. GA-Gammon

    DEFF Research Database (Denmark)

    Irineo-Fuentes, Oscar; Cruz-Cortes, Nareli; Rodriguez-Henriquez, Francisco

    2006-01-01

    of the best board positions during a game. Best GA-Gammon individuals so obtained were tested in separated 5000-game tournaments against Pubeval itself, and Fuzzeval, a fuzzy controller-based player. Our experimental results indicate that the best individuals generated by GA-Gammon show similar performance...... than Pubeval. Their winning rates are tied. Furthermore, GA-Gammon consistently outperforms Fuzzeval....

  12. High-Efficiency, High-Temperature, Ultra-Lightweight GaP-Based Solar Cells, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of this proposal is to study and demonstrate novel GaAsNP/GaP/AlGaP technology for use in extreme photovoltaic (PV) energy conversion. NASA and the...

  13. High-Efficiency, High-Temperature, Ultra-Lightweight GaP-Based Solar Cells, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of this proposal is to study and demonstrate novel GaAsNP/GaP/AlGaP technology for use in extreme photovoltaic (PV) energy conversion. NASA and the...

  14. Properties of GaP/ZnO heterostructures for photovoltaics

    International Nuclear Information System (INIS)

    Kovac, J.; Buc, D.; Brath, T.; Kovac, J. jr.; Caplovicova, M.; Elias, P.; Hasenohrl, S.; Novak, J.

    2012-01-01

    In this paper, we discuss the deposition of ZnO thin layers on GaP substrate and GaP nanowires by RF magnetron sputtering and their influence on the structural properties. The main goal of this work is to find the optimal technology for deposition very thin ZnO layers by RF magnetron sputtering with defined parameters to cover round GaP nanowires surface prepared by MOVPE technology. (authors)

  15. Electrical characteristics of AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes irradiated with protons

    Science.gov (United States)

    Sin, Yongkun; Presser, Nathan; Foran, Brendan; LaLumondiere, Stephen; Lotshaw, William; Moss, Steven C.

    2014-03-01

    AlGaN-GaN high electron mobility transistors (HEMTs) are most suitable for commercial and military applications requiring high voltage, high power, and high efficiency operation. In recent years, leading AlGaN HEMT manufacturers have reported encouraging reliability of these devices, but their long-term reliability especially in the space environment still remains a major concern. In addition, degradation mechanisms in AlGaN HEMT devices are still not well understood, and a large number of traps and defects present both in the bulk and at the surface lead to undesirable characteristics. Study of reliability and radiation effects of AlGaN-GaN HEMTs is therefore necessary before GaN HEMT technology is successfully employed in satellite communication systems. For the present study, we investigated electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons. We studied two types of MOCVD-grown AlGaN HEMTs on semi-insulating SiC substrates (HEMT-1 and HEMT-2) as well as MOCVD-grown Al0.27Ga 0.73N Schottky diodes on conducting SiC substrates. Our HEMT-1 structure consisted of a GaN cap, AlGaN/AlN barrier, and 2 μm GaN buffer layers. Our HEMT-2 structure consisting of undoped AlGaN barrier and GaN buffer layers grown on an AlN nucleation layer showed a charge sheet density of ~1013/cm2 and a Hall mobility of ~1500 cm2 /V.sec. Our HEMT-1 devices had a Pt-Au Schottky gate length of 0.2 μm, a total gate width of 200-400 μm periphery, and SiNx passivation. Electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes were compared before and after they were proton irradiated with different energies and fluences. Current-mode deep level transient spectroscopy (DLTS) and capacitance-mode DLTS were employed to study pre-proton irradiation trap characteristics in the AlGaN-GaN HEMTs and AlGaN Schottky diodes, respectively. Focused ion beam (FIB) was employed to prepare both cross-sectional and plan view TEM samples for defect

  16. Describing Peripancreatic Collections According to the Revised Atlanta Classification of Acute Pancreatitis: An International Interobserver Agreement Study.

    Science.gov (United States)

    Bouwense, Stefan A; van Brunschot, Sandra; van Santvoort, Hjalmar C; Besselink, Marc G; Bollen, Thomas L; Bakker, Olaf J; Banks, Peter A; Boermeester, Marja A; Cappendijk, Vincent C; Carter, Ross; Charnley, Richard; van Eijck, Casper H; Freeny, Patrick C; Hermans, John J; Hough, David M; Johnson, Colin D; Laméris, Johan S; Lerch, Markus M; Mayerle, Julia; Mortele, Koenraad J; Sarr, Michael G; Stedman, Brian; Vege, Santhi Swaroop; Werner, Jens; Dijkgraaf, Marcel G; Gooszen, Hein G; Horvath, Karen D

    2017-08-01

    Severe acute pancreatitis is associated with peripancreatic morphologic changes as seen on imaging. Uniform communication regarding these morphologic findings is crucial for accurate diagnosis and treatment. For the original 1992 Atlanta classification, interobserver agreement is poor. We hypothesized that for the revised Atlanta classification, interobserver agreement will be better. An international, interobserver agreement study was performed among expert and nonexpert radiologists (n = 14), surgeons (n = 15), and gastroenterologists (n = 8). Representative computed tomographies of all stages of acute pancreatitis were selected from 55 patients and were assessed according to the revised Atlanta classification. The interobserver agreement was calculated among all reviewers and subgroups, that is, expert and nonexpert reviewers; interobserver agreement was defined as poor (≤0.20), fair (0.21-0.40), moderate (0.41-0.60), good (0.61-0.80), or very good (0.81-1.00). Interobserver agreement among all reviewers was good (0.75 [standard deviation, 0.21]) for describing the type of acute pancreatitis and good (0.62 [standard deviation, 0.19]) for the type of peripancreatic collection. Expert radiologists showed the best and nonexpert clinicians the lowest interobserver agreement. Interobserver agreement was good for the revised Atlanta classification, supporting the importance for widespread adaption of this revised classification for clinical and research communications.

  17. Bagla JS (3) 216 (GA)

    Indian Academy of Sciences (India)

    Admin

    Ahmed Asma (5) 455, (6) 610 (GA). Ananthasuresh G K (6) 530, (9) 849 (GA). Arakeri Jaywant H (1) 32 (GA). Arunan E (12) 1210; (4) 346 (FA). Athreya K B (1) 66 (GA); (4) 384 (TIO). Bagla J S (3) 216 (GA). Balaji C (12) 1171 (GA). Balaram P (5) 416 (GA). Bhanu K S (11) 1119 (TIO). Bhat B V Rajarama (10) 970 (GA).

  18. Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

    Science.gov (United States)

    Grady, R.; Bayram, C.

    2017-07-01

    In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga(1-X)N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga(1-X)N/GaN heterojunction is formed through intentional δ-doping part of the Al X Ga(1-X)N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga(1-X)N barrier; δ-doping location (within the Al X Ga(1-X)N barrier), δ-doped Al X Ga(1-X)N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga(1-X)N barrier results in a normally-off behavior whereas Al X Ga(1-X)N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology.

  19. Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes

    International Nuclear Information System (INIS)

    Zhang Yi-Jun; Zou Ji-Jun; Wang Xiao-Hui; Chang Ben-Kang; Qian Yun-Sheng; Zhang Jun-Ju; Gao Pin

    2011-01-01

    In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoemission behaviour, namely the activation process and quantum yield decay, between the two typical types of III—V compound photocathodes have been investigated using a multi-information measurement system. The activation experiment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs—O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes. (interdisciplinary physics and related areas of science and technology)

  20. Effect of Ga seeding layer on formation of epitaxial Y-shaped GaN nanoparticles on silicon

    Science.gov (United States)

    Fedorov, V. V.; Bolshakov, A. D.; Mozharov, A. M.; Sapunov, G. A.; Shtrom, I. V.; Kirilenko, D. A.; Sitnikova, A. A.; Mukhin, I. S.

    2017-11-01

    Silicon and aluminium nitrides, commonly used as buffer layers for GaN growth on Si are wide gap insulators, preventing barrier free charge-carrier transport across the heterojunction and limiting the functionality of GaN-on-silicon technology. In this work we explore possibility of direct growth of GaN on Si nano-heterostructures by PA-MBE with use of Ga-nanodroplets as seeds. It is demonstrated that use of seeding layer can result in formation of Y-shaped planar GaN nanoparticles (GaN tripods) along with commonly observed GaN nanowires. Growth mechanism, morphology and structural characterization of GaN/Si nano-heterostructures is discussed.

  1. Minority Stress and Intimate Partner Violence Among Gay and Bisexual Men in Atlanta.

    Science.gov (United States)

    Stephenson, Rob; Finneran, Catherine

    2017-07-01

    Intimate partner violence (IPV) rates are disproportionately high among sexual minority populations. Few studies have examined the plausible relationship between minority stress and IPV among men who have sex with men. This study examines the associations between IPV and three indicators of minority stress: internalized homophobia, sexuality-based discrimination, and racism, in a large venue-based sample of gay and bisexual men from Atlanta, USA. Each of the minority stress measures was found to be significantly associated with increased odds of self-reporting any form of receipt of IPV. Significant associations were also identified between perpetration of IPV and minority stressors, with most types of IPV perpetration linked to internalized homophobia. This study confirms findings in a growing body of research supporting the relationship between minority stress and increased prevalence of IPV among men who have sex with men, and points to the need to address structural factors in IPV prevention programs for male-male couples.

  2. Atlanta 10 x 20 NTMS area: Alabama and Georgia. Data report

    International Nuclear Information System (INIS)

    Jones, P.L.

    1979-08-01

    Results of ground water and stream sediment reconnaissance in the National Topographic Map Series (NTMS) Atlanta 1 0 x 2 0 quadrangle are presented. Stream sediment samples were collected from small streams at 1312 sites or at a nominal density of one site per 13 square kilometers in rural areas. Ground water samples were collected at 951 sites or at a nominal density of one site per 18 square kilometers. Neutron activation analysis results are given for uranium and 16 other elements in sediments, and for uranium and 8 other elements in ground water and surface water. Field measurements and observations are reported for each site. Analytical data and field measurements are presented in tables and maps. Statistical summaries of data and a brief description of results are given. A generalized geologic map and a summary of the geology of the area are included

  3. UNDERSTANDING THE INTERNATIONAL CONSENSUS FOR ACUTE PANCREATITIS: CLASSIFICATION OF ATLANTA 2012.

    Science.gov (United States)

    Souza, Gleim Dias de; Souza, Luciana Rodrigues Queiroz; Cuenca, Ronaldo Máfia; Jerônimo, Bárbara Stephane de Medeiros; Souza, Guilherme Medeiros de; Vilela, Vinícius Martins

    2016-01-01

    Contrast computed tomography and magnetic resonance imaging are widely used due to its image quality and ability to study pancreatic and peripancreatic morphology. The understanding of the various subtypes of the disease and identification of possible complications requires a familiarity with the terminology, which allows effective communication between the different members of the multidisciplinary team. Demonstrate the terminology and parameters to identify the different classifications and findings of the disease based on the international consensus for acute pancreatitis ( Atlanta Classification 2012). Search and analysis of articles in the "CAPES Portal de Periódicos with headings "acute pancreatitis" and "Atlanta Review". Were selected 23 articles containing radiological descriptions, management or statistical data related to pathology. Additional statistical data were obtained from Datasus and Population Census 2010. The radiological diagnostic criterion adopted was the Radiology American College system. The "acute pancreatitis - 2012 Rating: Review Atlanta classification and definitions for international consensus" tries to eliminate inconsistency and divergence from the determination of uniformity to the radiological findings, especially the terminology related to fluid collections. More broadly as "pancreatic abscess" and "phlegmon" went into disuse and the evolution of the collection of patient fluids can be described as "acute peripancreatic collections", "acute necrotic collections", "pseudocyst" and "necrosis pancreatic walled or isolated". Computed tomography and magnetic resonance represent the best techniques with sequential images available for diagnosis. Standardization of the terminology is critical and should improve the management of patients with multiple professionals care, risk stratification and adequate treatment. A tomografia computadorizada contrastada e a ressonância magnética são exames amplamente utilizados no estudo da

  4. A Study of School Leaders and How They Impact Classroom Use of Technology

    Science.gov (United States)

    Downs, Robert

    2011-01-01

    The purpose of this study was to examine the relationship between a principal's personality type and a school's classroom use of technology. Myers Briggs Type Indicator data was collected from 48 principals in a large suburban district in the Metro Atlanta area, as well as, observational data documenting student use of technology. The Georgia…

  5. Wavelength Red-Shift of Long Wavelength InGaN/GaN Multi-Quantum Well by Using an InGaN Underlying Layer

    International Nuclear Information System (INIS)

    Li-Rong, Huang; Feng, Wen; Liang-Zhu, Tong; De-Xiu, Huang

    2009-01-01

    Long-wavelength GaN based light-emitting diodes are of importance in full color displays, monolithic white light- emitting diodes and solid-state lighting, etc. However, their epitaxial growth faces great challenges because high indium (In) compositions of InGaN are difficult to grow. In order to enhance In incorporation and lengthen the emission wavelength of a InGaN/GaN multi-quantum well (MQW), we insert an InGaN underlying layer underneath the MQW. InGaN/GaN MQWs with various InGaN underlying layers, such as graded In y Ga 1−y N material with linearly increasing In content, or In y Ga 1−y N with fixed In content but different thicknesses, are grown by metal-organic chemical vapor deposition. Experimental results demonstrate the enhancement of In incorporation and the emission wavelength redshift by the insertion of an InGaN underlying layer. (cross-disciplinary physics and related areas of science and technology)

  6. Urban partnership agreement and congestion reduction demonstration programs : lessons learned on congestion pricing from the Seattle and Atlanta household travel behavior surveys.

    Science.gov (United States)

    2014-04-01

    This paper presents lessons learned from household traveler surveys administered in Seattle and Atlanta as part of the evaluation of the Urban Partnership Agreement and Congestion Reduction Demonstration Programs. The surveys use a two-stage panel su...

  7. 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)

  8. From Practice to Profession. Dimension 2007. Selected Proceedings of the 2007 Joint Conference of the Southern Conference on Language Teaching, the Foreign Language Association of Georgia, and the Southeastern Association for Language Laboratory Technology

    Science.gov (United States)

    Van Houton, Jacque Bott; Gascoigne, Carolyn; Arnold, Nike; Johnson, Catherine T.; Thomas, Patricia; Fountain, Anne; Fountain, Catherine; Cheatham, Rosalie M.; Sanatullov, Marat; Sanatullova-Allison, Elvira; Cherry, C. Maurice, Ed.; Bradley, Lee, Ed.

    2007-01-01

    "Dimension" is the annual volume containing the selected, refereed, edited Proceedings of each year's conference. "From Practice to Profession" was the announced theme of the annual conference of the Southern Conference on Language Teaching (SCOLT), held March 1-3, 2007, at the Atlanta (GA) Renaissance Hotel, in partnership…

  9. Preventing the repetition: Or, what Los Angeles' experience in water management can teach Atlanta about urban water disputes

    Science.gov (United States)

    Feldman, David L.

    2009-04-01

    Southern California's water history is an epic story with larger-than-life characters and ambitions and abundant hubris. Students of water policy might reasonably ask: Does this story, while unique to greater Los Angeles, hold lessons for other metropolises experiencing water conflict caused by explosive growth? We examine this question by considering similarities between the challenges facing Atlanta, Georgia, one of the nation's fastest growing cities in the 21st century, with those of Los Angeles. We focus on junctures where important decisions regarding water were made and how these decisions continue to challenge both cities' futures. Atlanta's financial, cultural, and environmental imprint on its surrounding region share remarkable similarities with Los Angeles' influence trajectory: it is the largest city in the southeast, a principal transportation and business hub, and it is embroiled in water conflict with nearby communities and adjoining states.

  10. 75 FR 66378 - Public Meeting of the Presidential Commission for the Study of Bioethical Issues

    Science.gov (United States)

    2010-10-28

    ... approximately 11:30 a.m. ADDRESSES: Emory Conference Center Hotel, 1615 Clifton Road, Atlanta, GA 30329. Phone... Conference Center Hotel, Atlanta, GA. The meeting will be open to the public with attendance limited to space... technological innovation. In undertaking these duties, the Commission will examine specific bioethical, legal...

  11. The Risk of West Nile Virus Infection Is Associated with Combined Sewer Overflow Streams in Urban Atlanta, Georgia, USA

    OpenAIRE

    Vazquez-Prokopec, Gonzalo M.; Vanden Eng, Jodi L.; Kelly, Rosmarie; Mead, Daniel G.; Kolhe, Priti; Howgate, James; Kitron, Uriel; Burkot, Thomas R.

    2010-01-01

    Background At present, the factors favoring transmission and amplification of West Nile Virus (WNV) within urban environments are poorly understood. In urban Atlanta, Georgia, the highly polluted waters of streams affected by combined sewer overflow (CSO) represent significant habitats for the WNV mosquito vector Culex quinquefasciatus. However, their contribution to the risk of WNV infection in humans and birds remains unclear. Objectives Our goals were to describe and quantify the spatial d...

  12. Effects of urbanization on streamflow in the Atlanta area (Georgia, USA): A comparative hydrological approach

    Science.gov (United States)

    Rose, S.; Peters, N.E.

    2001-01-01

    For the period from 1958 to 1996, streamflow characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds within a 20 000 km2 region in the vicinity of Atlanta, Georgia: In the Piedmont and Blue Ridge physiographic provinces of the southeastern USA. Water levels in several wells completed in surficial and crystalline-rock aquifers were also evaluated. Data were analysed for seven US Geological Survey (USGS) stream gauges, 17 National Weather Service rain gauges, and five USGS monitoring wells. Annual runoff coefficients (RCs; runoff as a fractional percentage of precipitation) for the urban stream (Peachtree Creek) were not significantly greater than for the less-urbanized watersheds. The RCs for some streams were similar to others and the similar streams were grouped according to location. The RCs decreased from the higher elevation and higher relief watersheds to the lower elevation and lower relief watersheds: Values were 0.54 for the two Blue Ridge streams. 0.37 for the four middle Piedmont streams (near Atlanta), and 0.28 for a southern Piedmont stream. For the 25 largest stormflows, the peak flows for Peachtree Creek were 30% to 100% greater then peak flows for the other stream. The storm recession period for the urban stream was 1-2 days less than that for the other streams and the recession was characterized by a 2-day storm recession constant that was, on average, 40 to 100% greater, i.e. streamflow decreased more rapidly than for the other streams. Baseflow recession constants ranged from 35 to 40% lower for Peachtree Creek than for the other streams; this is attributed to lower evapotranspiration losses, which result in a smaller change in groundwater storage than in the less-urbanized watersheds. Low flow of Peachtree Creek ranged from 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of stormwater and the paving of groundwater

  13. High Spatial Resolution Thermal Infrared Remote Sensing Data for Analysis of the Atlanta, Georgia, Urban Heat Island Effect and Its Impacts on the Environment

    Science.gov (United States)

    Quattrochi, Dale A.

    2007-01-01

    The twenty-first century is the first "urban century" according to the United Nations Development Program. The focus of cities reflects awareness of the growing percentage of the world's population that lives in urban areas. In environmental terms, cities are the original producers of many of the global problems related to waste disposal, air and water pollution, and associated environmental and ecological challenges. Expansion of cities, both in population and areal extent, is a relentless process. In 2000, approximately 3 billion people representing about 40% of the global population, resided in urban areas. Urban population will continue to rise substantially over the next several decades according to UN estimates, and most of this growth will Occur in developing countries. The UN estimates that by 2025, 60% of the world's population will live in urban areas. As a consequence, the number of"megacities" (those cities with populations of 10 million inhabitants or more) will increase by 100 by 2025. Thus, there is a critical need to understand urban areas and what their impacts are on environmental, ecological and hydrologic resources, as well as on the local, regional, and even global climate. One of the more egregious side effects of urbanization is the increase in surface and air temperatures that lead to deterioration in air quality. In the United States, under the more stringent air quality guidelines established by the U.S. Environmental Protection Agency in 1997, nearly 300 counties in 34 states will not meet these new air quality standards for ground level ozone. Mitigation of the urban heat island (UHI) effect is actively being evaluated as a possible way to reduce ground ozone levels in cities and assist states in improving air quality. Foremost in the analysis of how the UHI affects air quality and other environmental factors is the use of remote sensing technology and data to characterize urban land covers in sufficient detail to quantifiably measure

  14. Technology.

    Science.gov (United States)

    Online-Offline, 1998

    1998-01-01

    Focuses on technology, on advances in such areas as aeronautics, electronics, physics, the space sciences, as well as computers and the attendant progress in medicine, robotics, and artificial intelligence. Describes educational resources for elementary and middle school students, including Web sites, CD-ROMs and software, videotapes, books,…

  15. Metamagnetism in Ce(Ga,Al)2

    Indian Academy of Sciences (India)

    Metamagnetism in Ce(Ga,Al)2. K G SURESH1,∗. , S RADHA2 and A K NIGAM3. 1Department of Physics, Indian Institute of Technology, Mumbai 400 076, India. 2Department of Physics, Mithibai College, Mumbai 400 056, India. 3Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India. ∗.

  16. "Everyone called me grandma": Public housing demolition and relocation among older adults in Atlanta.

    Science.gov (United States)

    Keene, Danya E; Ruel, Erin

    2013-01-01

    Over the last few decades public and political dissatisfaction with public housing projects and an increasing emphasis on poverty deconcentration has led to the demolition of public housing in cities across the country. A significant body of literature has examined experiences of relocation from public housing and their implications for the well-being of individuals and communities. While much of this literature has focused on young or middle-aged adults and children, older adults have also been affected by demolition and relocation. The displacement of older adults raises a new set of age and life-course specific concerns for the well-being of this population. In this paper, we analyze the relocation narratives of 25 former public housing residents in Atlanta, Georgia. Our analysis focuses on the loss of geographically rooted communities of kinship, support and belonging that many participants, particularly those who have aged in place, attribute to their former developments. Participants describe many material and psychosocial benefits associated with living in communities that were "like families" and where they often held important roles as respected elders. While some were satisfied with their moves, others describe the dispersal of these "families" as a deeply felt loss. While some were able to draw on support from children and grandchildren in their new homes, others describe experiences of profound isolation after relocation.

  17. Solar hot water system installed at Day's Lodge, Atlanta, Georgia

    Energy Technology Data Exchange (ETDEWEB)

    None

    1980-09-01

    The solar energy hot water system installed in the Days Inns of America, Inc., Day's Lodge I-85 and Shallowford Road, NE Atlanta, Georgia is described. This system is one of eleven systems planned under this grant and was designed to provide for 81% of the total hot water demand. There are two separate systems, each serving one building of the lodge (total of 65 suites). The entire system contains only potable city water. The 1024 square feet of Grumman Sunstream Model 332 liquid flat plate collectors and the outside piping drains whenever the collector plates approach freezing or when power is interrupted. Solar heated water from the two above ground cement lined steel tanks (1000 gallon tank) is drawn into the electric domestic hot water (DHW) tanks as hot water is drawn. Electric resistance units in the DHW tanks top off the solar heated water, if needed, to reach thermostat setting. Operation of this system was begun in August, 1979. The solar components were partly funded ($18,042 of $36,084 cost) by the Department of Energy.

  18. Susceptibility to Heat-Related Fluid and Electrolyte Imbalance Emergency Department Visits in Atlanta, Georgia, USA

    Directory of Open Access Journals (Sweden)

    Leila Heidari

    2016-10-01

    Full Text Available Identification of populations susceptible to heat effects is critical for targeted prevention and more accurate risk assessment. Fluid and electrolyte imbalance (FEI may provide an objective indicator of heat morbidity. Data on daily ambient temperature and FEI emergency department (ED visits were collected in Atlanta, Georgia, USA during 1993–2012. Associations of warm-season same-day temperatures and FEI ED visits were estimated using Poisson generalized linear models. Analyses explored associations between FEI ED visits and various temperature metrics (maximum, minimum, average, and diurnal change in ambient temperature, apparent temperature, and heat index modeled using linear, quadratic, and cubic terms to allow for non-linear associations. Effect modification by potential determinants of heat susceptibility (sex; race; comorbid congestive heart failure, kidney disease, and diabetes; and neighborhood poverty and education levels was assessed via stratification. Higher warm-season ambient temperature was significantly associated with FEI ED visits, regardless of temperature metric used. Stratified analyses suggested heat-related risks for all populations, but particularly for males. This work highlights the utility of FEI as an indicator of heat morbidity, the health threat posed by warm-season temperatures, and the importance of considering susceptible populations in heat-health research.

  19. Dietary intake and overweight and obesity among persons living with HIV in Atlanta Georgia.

    Science.gov (United States)

    Hernandez, Dominica; Kalichman, Seth; Cherry, Chauncey; Kalichman, Moira; Washington, Christopher; Grebler, Tamar

    2017-06-01

    In the U.S., there has been a rise in overweight and obesity among persons living with HIV (PLWH). The aim of this study was to examine dietary intake and body mass index (BMI) in PLWH in Atlanta Georgia relative to the U.S. Dietary intake among PLWH was compared with recommended standards as well as estimated dietary intake for adults in the U.S. Over 31% of the study participants were overweight [BMI = 25-29.9 kg/m 2 ], and 33.1% obese [BMI ≥ 30 kg/m 2 ]. Results indicated significant dietary differences between participants in our sample and U.S. daily recommendations for adults as well as estimated intakes of the U.S. Both males and females consumed more percentage of energy from fat and less fiber as well as fruit and vegetables servings than what is recommended. Results suggest that overweight and obesity are an additional health burden to PLWH in our sample and that their daily dietary practices are not meeting the U.S. government-recommended nutritional standards.

  20. Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

    Science.gov (United States)

    Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

    2016-12-01

    Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

  1. GaAs/GaSb nanowire heterostructures grown by MOVPE

    DEFF Research Database (Denmark)

    Jeppsson, Mattias; Dick, Kimberly A.; Wagner, Jakob Birkedal

    2008-01-01

    We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast...... to most other III–V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter...... increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa–GaSb or AuGa2–GaSb pseudo-binaries of the Au–Ga–Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the {1 1¯ 0} side facets....

  2. GaN based nanorods for solid state lighting

    Science.gov (United States)

    Li, Shunfeng; Waag, Andreas

    2012-04-01

    In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

  3. Magnitudes, nature, and effects of point and nonpoint discharges in the Chattahoochee River Basin, Atlanta to West Point Dam, Georgia

    Science.gov (United States)

    Stamer, J.K.; Cherry, Rodney N.; Faye, R.E.; Kleckner, R.L.

    1979-01-01

    During the period April 1975 to June 1978, the U.S. Geological Survey conducted a river-quality assessment of the Upper Chattahoochee River basin in Georgia. One objective of the study was to assess the magnitudes, nature, and effects of point and non-point discharges in the Chattahoochee River basin from Atlanta to the West Point Dam. On an average annual basis and during the storm period of March 1215, 1976, non-point-source loads for most constituents analyzed were larger than point-source loads at the Whitesburg station, located on the Chattahoochee River about 40 river miles downstream of Atlanta. Most of the non-point-source constituent loads in the Atlanta-to-Whitesburg reach were from urban areas. Average annual point-source discharges accounted for about 50 percent of the dissolved nitrogen, total nitrogen, and total phosphorus loads, and about 70 percent of the dissolved phosphorus loads at Whitesburg. During weekends, power generation at the upstream Buford Dam hydroelectric facility is minimal. Streamflow at the Atlanta station during dry-weather weekends is estimated to be about 1,200 ft3/s (cubic feet per second). Average daily dissolved-oxygen concentrations of less than 5.0 mg/L (milligrams per liter) occurred often in the river, about 20 river miles downstream from Atlanta during these periods from May to November. During a low-flow period, June 1-2, 1977, five municipal point sources contributed 63 percent of the ultimate biochemical oxygen demand, 97 percent of the ammonium nitrogen, 78 percent of the total nitrogen, and 90 percent of the total phosphorus loads at the Franklin station, at the upstream end of West Point Lake. Average daily concentrations of 13 mg/L of ultimate biochemical oxygen demand and 1.8 mg/L of ammonium nitrogen were observed about 2 river miles downstream from two of the municipal point sources. Carbonaceous and nitrogenous oxygen demands caused dissolved-oxygen concentrations between 4.1 and 5.0 mg/L to occur in a 22-mile

  4. S-Band AlGaN/GaN power amplifier MMIC with over 20 Watt output power

    NARCIS (Netherlands)

    van Heijningen, M; Visser, G.C.; Wurfl, J.; van Vliet, Frank Edward

    2008-01-01

    Abstract This paper presents the design of an S-band HPA MMIC in AlGaN/GaN CPW technology for radar TR-module application. The trade-offs of using an MMIC solution versus discrete power devices are discussed. The MMIC shows a maximum output power of 38 Watt at 37% Power Added Efficiency at 3.1 GHz.

  5. Cubic AlGaN/GaN Hetero-Junction Field-Effect Transistors with Normally-on and Normally-off Characteristics

    International Nuclear Information System (INIS)

    Tschumak, E.

    2010-01-01

    The growth of cubic group III-nitrides is a direct way to eliminate polarization effects, which inherently limit the fabrication of normally-off hetero-junction field-effect transistors (HFETs) in GaN technology. HFET structures were fabricated of non-polar cubic AlGaN/GaN hetero layers grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001). The electrical insulation of 3C-SiC was realized by Ar + implantation before c-AlGaN/GaN growth. HFETs with normally-off and normally-on characteristics were fabricated of cubic AlGaN/GaN. Capacitance-voltage characteristics of the gate contact were performed to detect the electron channel at the c-AlGaN/GaN hetero-interface.

  6. Technology

    Directory of Open Access Journals (Sweden)

    Xu Jing

    2016-01-01

    Full Text Available The traditional answer card reading method using OMR (Optical Mark Reader, most commonly, OMR special card special use, less versatile, high cost, aiming at the existing problems proposed a method based on pattern recognition of the answer card identification method. Using the method based on Line Segment Detector to detect the tilt of the image, the existence of tilt image rotation correction, and eventually achieve positioning and detection of answers to the answer sheet .Pattern recognition technology for automatic reading, high accuracy, detect faster

  7. GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell

    Science.gov (United States)

    Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh B.; Huffaker, Diana L.; Hubbard, Seth M.

    2017-12-01

    Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.

  8. GaN: Defect and Device Issues

    Energy Technology Data Exchange (ETDEWEB)

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  9. GaAs Gate Dynamic Memory Technology

    Science.gov (United States)

    1992-06-01

    be solved by using an all- impanted the peripheral circuitry, cell as shown in Fig. 8. The p implant beneath the storage node confines o the Mes the...annealed in a computer-controlled AG Associ- grown at temperatures that are much lower than those ates mini -pulse rapid thermal processor. The anneals

  10. 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

  11. Feasibility and availability of 68Ga-labelled peptides

    International Nuclear Information System (INIS)

    Decristoforo, Clemens; Pickett, Roger D.; Verbruggen, Alfons

    2012-01-01

    68 Ga has attracted tremendous interest as a radionuclide for PET based on its suitable half-life of 68 min, high positron emission yield and ready availability from 68 Ge/ 68 Ga generators, making it independent of cyclotron production. 68 Ga-labelled DOTA-conjugated somatostatin analogues, including DOTA-TOC, DOTA-TATE and DOTA-NOC, have driven the development of technologies to provide such radiopharmaceuticals for clinical applications mainly in the diagnosis of somatostatin receptor-expressing tumours. We summarize the issues determining the feasibility and availability of 68 Ga-labelled peptides, including generator technology, 68 Ga generator eluate postprocessing methods, radiolabelling, automation and peptide developments, and also quality assurance and regulatory aspects. 68 Ge/ 68 Ga generators based on SnO 2 , TiO 2 or organic matrices are today routinely supplied to nuclear medicine departments, and a variety of automated systems for postprocessing and radiolabelling have been developed. New developments include improved chelators for 68 Ga that could open new ways to utilize this technology. Challenges and limitations in the on-site preparation and use of 68 Ga-labelled peptides outside the marketing authorization track are also discussed. (orig.)

  12. Feasibility and availability of ⁶⁸Ga-labelled peptides.

    Science.gov (United States)

    Decristoforo, Clemens; Pickett, Roger D; Verbruggen, Alfons

    2012-02-01

    (68)Ga has attracted tremendous interest as a radionuclide for PET based on its suitable half-life of 68 min, high positron emission yield and ready availability from (68)Ge/(68)Ga generators, making it independent of cyclotron production. (68)Ga-labelled DOTA-conjugated somatostatin analogues, including DOTA-TOC, DOTA-TATE and DOTA-NOC, have driven the development of technologies to provide such radiopharmaceuticals for clinical applications mainly in the diagnosis of somatostatin receptor-expressing tumours. We summarize the issues determining the feasibility and availability of (68)Ga-labelled peptides, including generator technology, (68)Ga generator eluate postprocessing methods, radiolabelling, automation and peptide developments, and also quality assurance and regulatory aspects. (68)Ge/(68)Ga generators based on SnO(2), TiO(2) or organic matrices are today routinely supplied to nuclear medicine departments, and a variety of automated systems for postprocessing and radiolabelling have been developed. New developments include improved chelators for (68)Ga that could open new ways to utilize this technology. Challenges and limitations in the on-site preparation and use of (68)Ga-labelled peptides outside the marketing authorization track are also discussed.

  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. GaSb-related materials for TPV cells

    Science.gov (United States)

    Mauk, M. G.; Andreev, V. M.

    2003-05-01

    A survey of materials options and technologies for GaSb-related thermophotovoltaic (TPV) cells is presented, followed by an overview of device design principles and issues. This device technology has been developed for thermal-to-electric generator systems with thermal emitter infrared sources operated in the 1000-1200 °C range. Significant results for the growth, material characterization and device performance of TPV cells based on InGaAsSb, InGaSb, AlGaAsSb and InAsSbP fabricated by LPE, MOCVD, MBE and diffusion methods are reviewed. For single-junction TPV cells, epitaxial heterostructures with a ~0.53 eV bandgap InGaAsSb base layer and wide-bandgap AlGaAsSb or GaSb window/cladding layers (all closely lattice matched to a GaSb substrate) represent the state of the art. As an alternative, a low-cost Zn-diffusion technology for fabrication of InGaAsSb p-n homojunction structures has been developed for producing the high efficiency TPV cells. External quantum yields as high as 90% at wavelengths (around 2000 nm wavelength), and response edges to about 2400 nm wavelength have been obtained with these TPV cells. Multijunction tandem TPV devices based on GaSb top cells and InGaAsSb bottom cells provide even higher performance. TPV cells based on InAsSbP, also reviewed here, have spectral responses in wavelengths in the 2.5-3.5 mum range, and thus provide a means for utilizing radiation from thermal emitters with lower temperatures.

  15. In0.5Ga0.5As self-assembled quantum dots on GaP/Si

    Science.gov (United States)

    Song, Yuncheng

    P SAQDs integrated on exact Si (001). In situ RHEED observation of In0.5Ga 0.5As SAQDs on GaP/Si showed the same transitions as In0.5Ga 0.5As on bulk GaP, indicating similar growth kinetics for In0.5 Ga0.5As on GaP/Si and bulk GaP. In0.5Ga0.5 As SAQD stacks on both substrates yielded nearly identical photoluminescence spectra, with peak position, peak-width, and integrated intensity varying by broad-area lasers at low temperature. Though attempts in developing In0.5Ga0.5As SAQD lasers on GaP showed no stimulated emission, the devices studied here nevertheless hold great promise for future improvement. The In0.5Ga0.5As/GaP SAQDs takes advantage of the scalability and reliability of monolithic integration while avoiding material issues inherent to the use of dilute nitrides and relaxed buffers on Si. The In0.5Ga0.5As/GaP SAQDs in this thesis could have a major technological impact by providing a new pathway for integration of efficient laser diodes on Si.

  16. Multibias and thermal behavior of microwave GaN and GaAs based HEMTs

    Science.gov (United States)

    Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

    2016-12-01

    Multibias and thermal characterizations on 0.25 μm × (2 × 100) μm AlGaN/GaN/SiC HEMT and 0.5 μm × (2 × 100) μm AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance RTH of 7.1, 8.2 and 9.4 °C mm/W for the GaN device was estimated at 25, 75 and 150 °C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage VT, Schottky barrier height ϕb, sheet charge densities of two dimensional electron gas ns, and capacitance under the gate Cg are exactly opposite in the two devices; whereas the knee voltage Vk, on resistance Ron, and series resistance Rseries are shows similar trend. The multi-bias and thermal behavior of the output current Ids, output conductance gds, transconductance gm, cut-off frequency ft, maximum frequency fmax, effective velocity of electron, veff and field dependent mobility, μ demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications.

  17. From Olympia to Atlanta: a cultural-historical perspective on diet and athletic training.

    Science.gov (United States)

    Grivetti, L E; Applegate, E A

    1997-05-01

    Greek and Roman writers described diet and training of Olympic athletes. Lucian (A.D. 120-ca. 180) described distance and speed work in runners; Galen (A.D. 131-201) recommended ball-related exercises to train vision and the body; Philostratos (A.D. 170-249) suggested cross training by endurance running, weight training, and wrestling with animals. The ancient Greek training system, the tetrad (eta tau epsilon tau rho alpha sigma), was a four-day cycle with each day devoted to a different activity. Diogenes Laertius (died A.D. 222) wrote that Greek athletes trained on dried figs, moist cheese and wheat; then the pattern changed and focused on meat. Epictetus (2nd century A.D.) wrote that Olympic victors avoided desserts and cold water and took wine sparingly. Philostratos deprecated athletic diet in his era, a pattern based on white bread sprinkled with poppy seeds, fish and pork. Americans at the XIth Olympiad in Berlin (1936) consumed beefsteak with average daily intake of 125 grams of butter or cotton oil, three eggs, custard for dessert and 1.5 L of milk. The American pattern at Berlin was characterized by ad libitum intake of white bread, dinner rolls, fresh vegetables and salads. At Atlanta, more than 5 million meals will be served during the Olympic festival. The highly varied menu will include fresh vegetables and dips; fruits, cheeses and breads; salads; pasta, rice and fruit salads; soups; meat and seafood entrees; hot vegetables; desserts; and beverages. American Southern specialties will be served.

  18. Responses of urban heat island in Atlanta to different land-use scenarios

    Science.gov (United States)

    Fu, Peng; Weng, Qihao

    2017-06-01

    The urban heat island (UHI) effect changes heat and water cycles in urban areas, and has been accused of elevating energy consumption, deteriorating living environment, and increasing mortality rates. Understanding various UHI effects necessitates a systematic modeling approach. A major problem in UHI simulations is that urban areas were either considered to have only one category of land use/cover or outdated in land use/cover patterns due to the lack of high resolution data. Therefore, this study aims at integrating up-to-date remotely sensed land use/cover data with the Weather Research and Forecasting (WRF/UCM)/Urban Canopy Model modeling systems to simulate surface temperature patterns in Atlanta, Georgia. In addition, three land-use scenarios, i.e., spontaneous scenario (SS), concentrated scenario (CS), and local policy scenario (LPS), were designed and incorporated into the modeling. Five numerical experiments were conducted by using the Weather Research and Forecasting (WRF) model to explore the impact of urbanization-induced land-cover changes on temperature patterns. Land use and land-cover patterns under all three scenarios suggested that urban growth would continue through in-filling development and outward expansion. Compared to temperature simulations in 2011, temperature maps corresponding to the three urban growth scenarios showed warmer and cooler temperature patterns outside and inside the urban core, respectively. Analysis of the mean diurnal temperature cycle suggested that the highest temperature difference of 3.9 K was observed between 2011 and the LPS, and occurred around 22:00 local time. Overall, the simulations showed different UHI effects respond to the land-use scenarios in the summer. It is recommended for urban managers and policy makers to reflect on the potential impacts of alternative urban growth policies on thermal environment.

  19. Racial disparities in travel time to radiotherapy facilities in the Atlanta metropolitan area.

    Science.gov (United States)

    Peipins, Lucy A; Graham, Shannon; Young, Randall; Lewis, Brian; Flanagan, Barry

    2013-07-01

    Low-income women with breast cancer who rely on public transportation may have difficulty in completing recommended radiation therapy due to inadequate access to radiation facilities. Using a geographic information system (GIS) and network analysis we quantified spatial accessibility to radiation treatment facilities in the Atlanta, Georgia metropolitan area. We built a transportation network model that included all bus and rail routes and stops, system transfers and walk and wait times experienced by public transportation system travelers. We also built a private transportation network to model travel times by automobile. We calculated travel times to radiation therapy facilities via public and private transportation from a population-weighted center of each census tract located within the study area. We broadly grouped the tracts by low, medium and high household access to a private vehicle and by race. Facility service areas were created using the network model to map the extent of areal coverage at specified travel times (30, 45 and 60 min) for both public and private modes of transportation. The median public transportation travel time to the nearest radiotherapy facility was 56 min vs. approximately 8 min by private vehicle. We found that majority black census tracts had longer public transportation travel times than white tracts across all categories of vehicle access and that 39% of women in the study area had longer than 1 h of public transportation travel time to the nearest facility. In addition, service area analyses identified locations where the travel time barriers are the greatest. Spatial inaccessibility, especially for women who must use public transportation, is one of the barriers they face in receiving optimal treatment. Published by Elsevier Ltd.

  20. [A comparison between the revision of Atlanta classification and determinant-based classification in acute pancreatitis].

    Science.gov (United States)

    Wu, D; Lu, B; Xue, H D; Lai, Y M; Qian, J M; Yang, H

    2017-12-01

    Objective: To compare the performance of the revision of Atlanta classification (RAC) and determinant-based classification (DBC) in acute pancreatitis. Methods: Consecutive patients with acute pancreatitis admitted to a single center from January 2001 to January 2015 were retrospectively analyzed. Patients were classified into mild, moderately severe and severe categories based on RAC and were simultaneously classified into mild, moderate, severe and critical grades according to DBC. Disease severity and clinical outcomes were compared between subgroups. The receiver operating curve (ROC) was used to compare the utility of RAC and DBC by calculating the area under curve (AUC). Results: Among 1 120 patients enrolled, organ failure occurred in 343 patients (30.6%) and infected necrosis in 74 patients(6.6%). A total of 63 patients (5.6%) died. Statistically significant difference of disease severity and outcomes was observed between all the subgroups in RAC and DBC ( Pacute pancreatitis (with both persistent organ failure and infected necrosis) had the most severe clinical course and the highest mortality (19/31, 61.3%). DBC had a larger AUC (0.73, 95% CI 0.69-0.78) than RAC (0.68, 95% CI 0.65-0.73) in classifying ICU admissions ( P= 0.031), but both were similar in predicting mortality( P= 0.372) and prolonged ICU stay ( P= 0.266). Conclusions: DBC and RAC perform comparably well in categorizing patients with acute pancreatitis regarding disease severity and clinical outcome. DBC is slightly better than RAC in predicting prolonged hospital stay. Persistent organ failure and infected necrosis are risk factors for poor prognosis and presence of both is associated with the most dismal outcome.

  1. GaN transistors for efficient power conversion

    CERN Document Server

    Lidow, Alex; de Rooij, Michael; Reusch, David

    2014-01-01

    The first edition of GaN Transistors for Efficient Power Conversion was self-published by EPC in 2012, and is currently the only other book to discuss GaN transistor technology and specific applications for the technology. More than 1,200 copies of the first edition have been sold through Amazon or distributed to selected university professors, students and potential customers, and a simplified Chinese translation is also available. The second edition has expanded emphasis on applications for GaN transistors and design considerations. This textbook provides technical and application-focused i

  2. Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

    International Nuclear Information System (INIS)

    Grady, R; Bayram, C

    2017-01-01

    In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga (1−X) N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga (1−X) N/GaN heterojunction is formed through intentional δ -doping part of the Al X Ga (1−X) N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga (1−X) N barrier; δ -doping location (within the Al X Ga (1−X) N barrier), δ-doped Al X Ga (1−X) N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga (1−X) N barrier results in a normally-off behavior whereas Al X Ga (1−X) N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology. (paper)

  3. Social, economic, and political processes that create built environment inequities: perspectives from urban African Americans in Atlanta.

    Science.gov (United States)

    Redwood, Yanique; Schulz, Amy J; Israel, Barbara A; Yoshihama, Mieko; Wang, Caroline C; Kreuter, Marshall

    2010-01-01

    Growing evidence suggests that the built environment features found in many high-poverty urban areas contribute to negative health outcomes. Both built environment hazards and negative health outcomes disproportionately affect poor people of color. We used community-based participatory research and Photovoice in inner-city Atlanta to elicit African Americans' perspectives on their health priorities. The built environment emerged as a critical factor, impacting physical and mental health outcomes. We offer a conceptual model, informed by residents' perspectives, linking social, economic, and political processes to built environment and health inequities. Research, practice, and policy implications are discussed within an environmental justice framework.

  4. The Atlanta Urban Heat Island Mitigation and Air Quality Modeling Project: How High-Resoution Remote Sensing Data Can Improve Air Quality Models

    Science.gov (United States)

    Quattrochi, Dale A.; Estes, Maurice G., Jr.; Crosson, William L.; Khan, Maudood N.

    2006-01-01

    The Atlanta Urban Heat Island and Air Quality Project had its genesis in Project ATLANTA (ATlanta Land use Analysis: Temperature and Air quality) that began in 1996. Project ATLANTA examined how high-spatial resolution thermal remote sensing data could be used to derive better measurements of the Urban Heat Island effect over Atlanta. We have explored how these thermal remote sensing, as well as other imaged datasets, can be used to better characterize the urban landscape for improved air quality modeling over the Atlanta area. For the air quality modeling project, the National Land Cover Dataset and the local scale Landpro99 dataset at 30m spatial resolutions have been used to derive land use/land cover characteristics for input into the MM5 mesoscale meteorological model that is one of the foundations for the Community Multiscale Air Quality (CMAQ) model to assess how these data can improve output from CMAQ. Additionally, land use changes to 2030 have been predicted using a Spatial Growth Model (SGM). SGM simulates growth around a region using population, employment and travel demand forecasts. Air quality modeling simulations were conducted using both current and future land cover. Meteorological modeling simulations indicate a 0.5 C increase in daily maximum air temperatures by 2030. Air quality modeling simulations show substantial differences in relative contributions of individual atmospheric pollutant constituents as a result of land cover change. Enhanced boundary layer mixing over the city tends to offset the increase in ozone concentration expected due to higher surface temperatures as a result of urbanization.

  5. Annealing of GaN under high pressure of nitrogen

    CERN Document Server

    Porowski, S; Kolesnikov, D; Lojkowski, W; Jager, V; Jäger, W; Bogdanov, V; Suski, T; Krukowski, S

    2002-01-01

    Gallium nitride, aluminum nitride and indium nitride are basic materials for blue optoelectronic devices. The essential part of the technology of these devices is annealing at high temperatures. Thermodynamic properties of the Ga-N system and their consequences to application of high nitrogen pressure for the annealing of GaN based materials are summarized. The diffusion of Zn, Mg and Au in high dislocation density heteroepitaxial GaN/Al sub 2 O sub 3 layers will be compared with the diffusion in dislocation-free GaN single crystals and homoepitaxial layers. It will be shown that high dislocation density can drastically change the diffusion rates, which strongly affects the performance of nitride devices. Inter-diffusion of Al, Ga and In in AlGaN/GaN and InGaN/GaN quantum well (QW) structures will be also considered. It will be shown that in contrast to stability of metal contacts, which is strongly influenced by dislocations, the inter-diffusion of group III atoms in QW structures is not affected strongly by...

  6. Evaluation of stream water quality in Atlanta, Georgia, and the surrounding region (USA)

    Science.gov (United States)

    Peters, N.E.; Kandell, S.J.

    1999-01-01

    A water-quality index (WQI) was developed from historical data (1986-1995) for streams in the Atlanta Region and augmented with 'new' and generally more comprehensive biweekly data on four small urban streams, representing an industrial area, a developed medium-density residential area and developing and developed low-density residential areas. Parameter WQIs were derived from percentile ranks of individual water-quality parameter values for each site by normalizing the constituent ranks for values from all sites in the area for a base period, i.e. 1990-1995. WQIs were developed primarily for nutrient-related parameters due to data availability. Site WQIs, which were computed by averaging the parameter WQIs, range from 0.2 (good quality) to 0.8 (poor quality), and increased downstream of known nutrient sources. Also, annual site WQI decreases from 1986 to 1995 at most long-term monitoring sites. Annual site WQI for individual parameters correlated with annual hydrological characteristics, particularly runoff, precipitation quantity, and water yield, reflecting the effect of dilution on parameter values. The WQIs of the four small urban streams were evaluated for the core-nutrient-related parameters, parameters for specific dissolved trace metal concentrations and sediment characteristics, and a species diversity index for the macro-invertebrate taxa. The site WQI for the core-nutrient-related parameters used in the retrospective analysis was, as expected, the worst for the industrial area and the best for the low-density residential areas. However, macro-invertebrate data indicate that although the species at the medium-density residential site were diverse, the taxa at the site were for species tolerant of degraded water quality. Furthermore, although a species-diversity index indicates no substantial difference between the two low-density residential areas, the number for macro-invertebrates for the developing area was much less than that for the developed area

  7. Effects of Urbanization on Stream Water Quality in the City of Atlanta, Georgia, USA

    Science.gov (United States)

    Peters, N. E.

    2009-05-01

    A long-term stream water-quality monitoring network was established in the City of Atlanta (COA) during 2003 to assess baseline water-quality conditions and the effects of urbanization on stream water quality. Routine hydrologically-based manual stream sampling, including several concurrent manual point and equal width increment sampling, was conducted approximately 12 times per year at 21 stations, with drainage areas ranging from 3.7 to 232 km2. Eleven of the stations are real-time (RT) water-quality stations having continuous measures of stream stage/discharge, pH, dissolved oxygen, specific conductance, water temperature, and turbidity, and automatic samplers for stormwater collection. Samples were analyzed for field parameters, and a broad suite of water-quality and sediment-related constituents. This paper summarizes an evaluation of field parameters and concentrations of major ions, minor and trace metals, nutrient species (nitrogen and phosphorus), and coliform bacteria among stations and with respect to watershed characteristics and plausible sources from 2003 through September 2007. The concentrations of most constituents in the COA streams are statistically higher than those of two nearby reference streams. Concentrations are statistically different among stations for several constituents, despite high variability both within and among stations. The combination of routine manual sampling, automatic sampling during stormflows, and real-time water-quality monitoring provided sufficient information about the variability of urban stream water quality to develop hypotheses for causes of water-quality differences among COA streams. Fecal coliform bacteria concentrations of most individual samples at each station exceeded Georgia's water-quality standard for any water-usage class. High chloride concentrations occur at three stations and are hypothesized to be associated with discharges of chlorinated combined sewer overflows, drainage of swimming pool(s), and

  8. 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...

  9. Thermal instability of GaSb surface oxide

    Science.gov (United States)

    Tsunoda, K.; Matsukura, Y.; Suzuki, R.; Aoki, M.

    2016-05-01

    In the development of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, the surface leakage current at the mesa sidewall must be suppressed. To achieve this requirement, both the surface treatment and the passivation layer are key technologies. As a starting point to design these processes, we investigated the GaSb oxide in terms of its growth and thermal stability. We found that the formation of GaSb oxide was very different from those of GaAs. Both Ga and Sb are oxidized at the surface of GaSb. In contrast, only Ga is oxidized and As is barely oxidized in the case of GaAs. Interestingly, the GaSb oxide can be formed even in DI water, which results in a very thick oxide film over 40 nm after 120 minutes. To examine the thermal stability, the GaSb native oxide was annealed in a vacuum and analyzed by XPS and Raman spectroscopy. These analyses suggest that SbOx in the GaSb native oxide will be reduced to metallic Sb above 300°C. To directly evaluate the effect of oxide instability on the device performance, a T2SL p-i-n photodetector was fabricated that has a cutoff wavelength of about 4 μm at 80 K. As a result, the surface leakage component was increased by the post annealing at 325°C. On the basis of these results, it is possible to speculate that a part of GaSb oxide on the sidewall surface will be reduced to metallic Sb, which acts as an origin of additional leakage current path.

  10. GaN-on-silicon high-electron-mobility transistor technology with ultra-low leakage up to 3000 V using local substrate removal and AlN ultra-wide bandgap

    Science.gov (United States)

    Dogmus, Ezgi; Zegaoui, Malek; Medjdoub, Farid

    2018-03-01

    We report on extremely low off-state leakage current in AlGaN/GaN-on-silicon metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) up to a high blocking voltage. Remarkably low off-state gate and drain leakage currents below 1 µA/mm up to 3 kV have been achieved owing to the use of a thick in situ SiN gate dielectric under the gate, and a local Si substrate removal technique combined with a cost effective 15-µm-thick AlN dielectric layer followed by a Cu deposition. This result establishes a manufacturable state-of-the-art high-voltage GaN-on-silicon power transistors while maintaining a low specific on-resistance of approximately 10 mΩ·cm2.

  11. They "miss more than anything their normal life back home": masculinity and extramarital sex among Mexican migrants in Atlanta.

    Science.gov (United States)

    Hirsch, Jennifer S; Muñoz-Laboy, Miguel; Nyhus, Christina M; Yount, Kathryn M; Bauermeister, José A

    2009-03-01

    Gender has been recognized as a significant influence on sexual health behaviors. Labor migration presents an important context of vulnerability for sexual health. To understand how the context of migration affects risk-related practices, both cultural and social aspects of gender need to be explored. In the quantitative part of a mixed-methods study conducted in 1999 in Atlanta, 187 Mexican migrant men were asked about their demographic characteristics; sexual history; migration motivations; substance use; social support; leisure-time activities; and ideas about masculinity, sexuality and marriage. Multivariate regression analyses were conducted to test the association between these domains and men's number of partners since their arrival in Atlanta. Number of partners was positively associated with owning a home in Mexico; number of trips back to Mexico; social network size; having had a sex worker as a partner; and going out dancing and to strip clubs on weekends (coefficients, 0.3-4.1). It was negatively associated with age, education, contact with social network members and feeling that sex is tied to emotional intimacy (-0.4 to -1.0). Programs must acknowledge and target migrant men's social networks and the spaces in which they may encounter risky sexual situations. Multilevel strategies, such as the development of more health-enhancing community spaces and the promotion of safer sexual practices should form part of comprehensive efforts to reduce sexual risk among migrant men.

  12. Social vulnerability to heat in Greater Atlanta, USA: spatial pattern of heat, NDVI, socioeconomics and household composition

    Science.gov (United States)

    Sim, Sunhui

    2017-10-01

    The purpose of the article is evaluating spatial patterns of social vulnerability to heat in Greater Atlanta in 2015. The social vulnerability to heat is an index of socioeconomic status, household composition, land surface temperature and normalized differential vegetation index (NDVI). Land surface temperature and NDVI were derived from the red, NIR and thermal infrared (TIR) of a Landsat OLI/TIRS images collected on September 14, 2015. The research focus is on the variation of heat vulnerability in Greater Atlanta. The study found that heat vulnerability is highly clustered spatially, resulting in "hot spots" and "cool spots". The results show significant health disparities. The hotspots of social vulnerability to heat occurred in neighborhoods with lower socioeconomic status as measured by low education, low income and more poverty, greater proportion of elderly people and young children. The findings of this study are important for identifying clusters of heat vulnerability and the relationships with social factors. These significant results provide a basis for heat intervention services.

  13. Reduced pressure MOVPE growth and characterization of GaAs/GaAlAs heterostructures using a triethylgallium source

    Science.gov (United States)

    Norris, P.; Black, J.; Zemon, S.; Lambert, G.

    1984-09-01

    The technologically important GaAs/GaAlAs materials system has been explored via reduced pressure MOVPE using a triethylgallium source. The growth system was designed for rapid responsein order to attain sharp interfaces and is load-locked to minimize contamination from atmospheric sources. GaAs/GaAlAs epilayers have been grown over the temperature range 625-750°C at pressure between 25 and 100 Torr. Photoluminescence (PL) measurements on GaAs and GaAlAs show sharp excitonic structure indicative of high purity. Hall and C - V carrier concentration profiling results confirm this. These high purity GaAs epilayers exhibit evidence of residual Mg acceptors and GaAlAs has a high radiative efficiency due to the use of an In-Ga-Al eutectic trap. Controlled doping experiments on multilayer structures have been performed using a SiH 4 dopant source and wide range dilution system. Epilayer surfaces are essentially featureless under interference contrast microscopic examination; however, "oval defects" originating at epilayer interfaces are still observed. Multiple quantum well (MQW) structures have been fabricated, without growth interruption, as a diagnostic aid in evaluating MOVPE system dynamic response. PL characterization of MQW structures with 6.5 nm well widths indicate high-quality abrupt heterointerfaces.

  14. Mercury(II) selective sensors based on AlGaN/GaN transistors

    International Nuclear Information System (INIS)

    Asadnia, Mohsen; Myers, Matthew; Akhavan, N.D.; O'Donnell, Kane; Umana-Membreno, Gilberto A.; Mishra, U.K.; Nener, Brett; Baker, Murray; Parish, Giacinta

    2016-01-01

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg 2+ . This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg 2+ concentrations. At pH 2.8 in a 10 −2  M KNO 3 ion buffer, a detection limit below 10 −8  M and a linear response range between 10 −8  M-10 −4  M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10 −7  M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10 −7  M and 10 −6  M in 10 −2  M Cd(NO 3 ) 2 and 10 −2  M Pb(NO 3 ) 2 ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg 2+ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. - Highlights: • This work is the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. • The sensor utilised an AlGaN/GaN transistor by functionalising the gate area with a polyvinyl chloride (PVC) based membrane. • The sensor showed a rapid and linear response between 10 −8 M-10 −4 M for Hg 2+ detection at pH 2.8 in a 10 −2 M KNO 3 ion buffer. • Detection limits of approximately 10 −7 M and 10 −6 M in 10 −2 M Cd(NO 3 ) 2 and 10 −2 M Pb(NO 3 ) 2 ion buffers

  15. Unipolar Vertical Transport in GaN/AlGaN/GaN Heterostructures

    OpenAIRE

    Nath, D. N.; Park, P. S.; Yang, Z. C.; Rajan, S.

    2013-01-01

    In this letter, we report on unipolar vertical transport characteristics in c-plane GaN/AlGaN/GaN heterostructures. Vertical current in heterostructures with random alloy barriers was found to be independent of dislocation density and heterostructure barrier height, and significantly higher than theoretical estimates. Percolation-based transport due to random alloy fluctuations in the ternary AlGaN is suggested as the dominant transport mechanism, and confirmed through experiments showing tha...

  16. ASSOCIATIONS BETWEEN OUTDOOR PARTICULATE (PM2.5) CONCENTRATIONS AND GASEOUS CO-POLLUTANT EXPOSURE LEVELS FOR COPD AND MI COHORTS IN ATLANTA, GA

    Science.gov (United States)

    Epidemiological studies indicate that daily ambient particulate matter (PM2.5) concentrations are associated with increased mortality, hospital admissions, and respiratory and cardiovascular effects. It is possible that the observed significant associations are the result of c...

  17. 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

  18. The effects of concentrated system on the electrical parameters of GaInP/GaAs solar cell

    Science.gov (United States)

    Kınacı, Barış

    2017-02-01

    III-V concentrator solar cells are suitable materials in order to reduce the cost of photovoltaic electricity. By using Fresnel lens in concentrating photovoltaic technology is an effective way to entirely use the sunlight. In the present study, the research on the efficiency analysis of the GaInP/GaAs concentrated solar cell structure with AlGaAs tunnel junction was performed. The electrical output parameters of this structure were determined by concentrated system with Fresnel lens. The current-voltage measurements of concentrated solar cell were carried out at room temperature under both dark and air mass 1.5 global radiations. The parameters of GaInP/GaAs concentrated solar cell at 1 Sun and at 32 Suns are compared. It is obtained that the integration of the concentrated system on the solar cell structure improves the device performance by ≈7.5%.

  19. A Study of the Role of Clouds in the Relationship Between Land Use/Land Cover and the Climate and Air Quality of the Atlanta Area

    Science.gov (United States)

    Kidder, Stanley Q.; Hafner, Jan

    2001-01-01

    The goal of Project ATLANTA is to derive a better scientific understanding of how land cover changes associated with urbanization affect climate and air quality. In this project the role that clouds play in this relationship was studied. Through GOES satellite observations and RAMS modeling of the Atlanta area, we found that in Atlanta (1) clouds are more frequent than in the surrounding rural areas; (2) clouds cool the surface by shading and thus tend to counteract the warming effect of urbanization; (3) clouds reflect sunlight, which might other wise be used to produce ozone; and (4) clouds decrease biogenic emission of ozone precursors, and they probably decrease ozone concentration. We also found that mesoscale modeling of clouds, especially of small, summertime clouds, needs to be improved and that coupled mesoscale and air quality models are needed to completely understand the mediating role that clouds play in the relationship between land use/land cover change and the climate and air quality of Atlanta. It is strongly recommended that more cities be studied to strengthen and extend these results.

  20. Changes in Incidence and Antifungal Drug Resistance in Candidemia: Results From Population-Based Laboratory Surveillance in Atlanta and Baltimore, 2008–2011

    Science.gov (United States)

    Cleveland, Angela Ahlquist; Farley, Monica M.; Harrison, Lee H.; Stein, Betsy; Hollick, Rosemary; Lockhart, Shawn R.; Magill, Shelley S.; Derado, Gordana; Park, Benjamin J.; Chiller, Tom M.

    2015-01-01

    Background Candidemia is common and associated with high morbidity and mortality; changes in population-based incidence rates have not been reported. Methods We conducted active, population-based surveillance in metropolitan Atlanta, Georgia, and Baltimore City/County, Maryland (combined population 5.2 million), during 2008–2011. We calculated candidemia incidence and antifungal drug resistance compared with prior surveillance (Atlanta, 1992–1993; Baltimore, 1998–2000). Results We identified 2675 cases of candidemia with 2329 isolates during 3 years of surveillance. Mean annual crude incidence per 100 000 person-years was 13.3 in Atlanta and 26.2 in Baltimore. Rates were highest among adults aged ≥65 years (Atlanta, 59.1; Baltimore, 72.4) and infants (aged candidemia epidemiology over the past 2 decades. Adults aged ≥65 years replaced infants as the highest incidence group; adjusted incidence has declined significantly in infants. Use of antifungal prophylaxis, improvements in infection control, or changes in catheter insertion practices may be contributing to these declines. Further surveillance for antifungal resistance and efforts to determine effective prevention strategies are needed. PMID:22893576

  1. Effects of an HOV-2 to HOT-3 conversion on traveler behavior : evidence from a panel study of the I-85 corridor in Atlanta.

    Science.gov (United States)

    2014-04-01

    This paper uses a two-stage panel survey approach, with roughly 1,600 respondent : households, to analyze the impacts of a federally sponsored variable tolling : program on the I-85 corridor northeast of Atlanta. The focus is on corridor : users d...

  2. Long wavelength MSM photodetectors fabricated on InGaNAs

    Science.gov (United States)

    Gouin, François; Noad, Julian; Higgins, Erle; Coulas, David

    2006-02-01

    Recently there has been a great deal of interest in the growth of dilute nitride quaternary alloys, such as InGaNAs, on GaAs substrates for the fabrication of GaAs-based components and optoelectronic integrated circuits. The addition of indium to the binary compound GaAs produces a ternary with a lower bandgap and larger lattice constant. The incorporation of nitrogen in this ternary further decreases the bandgap while reducing the lattice constant. This makes it possible to grow material lattice-matched to a GaAs substrate but with a narrower bandgap offering the possibility of growing materials suitable for opto-electronic devices on a GaAs substrate while operating at wavelengths used in long-distance optical communications. These devices can then be integrated with mature GaAs device technologies (MESFET, HBT) in photoreceivers and receivers/transmitters for improved functionality and reliability, lower cost, reduced size, etc. We have fabricated metal-semiconductor-metal (MSM) photodetectors on 1-μm thick In .1Ga .9N .03As .97 epilayers, a composition that results in a bandgap in the 1.3 μm region. We report on the DC characteristics, frequency dependence and wavelength dependence of the photoresponse. The results are compared to MSMs fabricated on GaAs. The temporal response is not as fast as that of GaAs MSMs and may be related to low carrier mobility. This shortcoming has been reported as the cause for the lower-than-expected efficiency of solar cells fabricated using this quarternary. The effect of growth conditions and thermal processing on detector characteristics such as bandwidth and dark current were investigated. The challenges associated with the use of InGaNAs in photodetectors (such as defects, response speed, requirement for thermal anneal) will be discussed.

  3. The development of integrated chemical microsensors in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    CASALNUOVO,STEPHEN A.; ASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; BACA,ALBERT G.; HIETALA,S.L.

    1999-11-01

    Monolithic, integrated acoustic wave chemical microsensors are being developed on gallium arsenide (GaAs) substrates. With this approach, arrays of microsensors and the high frequency electronic components needed to operate them reside on a single substrate, increasing the range of detectable analytes, reducing overall system size, minimizing systematic errors, and simplifying assembly and packaging. GaAs is employed because it is both piezoelectric, a property required to produce the acoustic wave devices, and a semiconductor with a mature microelectronics fabrication technology. Many aspects of integrated GaAs chemical sensors have been investigated, including: surface acoustic wave (SAW) sensors; monolithic SAW delay line oscillators; GaAs application specific integrated circuits (ASIC) for sensor operation; a hybrid sensor array utilizing these ASICS; and the fully monolithic, integrated SAW array. Details of the design, fabrication, and performance of these devices are discussed. In addition, the ability to produce heteroepitaxial layers of GaAs and aluminum gallium arsenide (AlGaAs) makes possible micromachined membrane sensors with improved sensitivity compared to conventional SAW sensors. Micromachining techniques for fabricating flexural plate wave (FPW) and thickness shear mode (TSM) microsensors on thin GaAs membranes are presented and GaAs FPW delay line and TSM resonator performance is described.

  4. Mercury(II) selective sensors based on AlGaN/GaN transistors.

    Science.gov (United States)

    Asadnia, Mohsen; Myers, Matthew; Akhavan, N D; O'Donnell, Kane; Umana-Membreno, Gilberto A; Mishra, U K; Nener, Brett; Baker, Murray; Parish, Giacinta

    2016-11-02

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg 2+ . This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg 2+ concentrations. At pH 2.8 in a 10 -2  M KNO 3 ion buffer, a detection limit below 10 -8  M and a linear response range between 10 -8  M-10 -4  M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10 -7  M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10 -7  M and 10 -6  M in 10 -2  M Cd(NO 3 ) 2 and 10 -2  M Pb(NO 3 ) 2 ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg 2+ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.

  5. Phase 2 Remedial Investigation Report Army Materials Technology Laboratory, Task Order 1 Remedial Investigation/Feasibility Study, Volume 5 - Appendices K-V

    Science.gov (United States)

    1994-05-01

    and severe gastrointestinal damage. Therapeutic administration of mercury salts (forK its diuretic and antiseptic properties) has resulted in nephrotic...Toxicological profile for mercury . Atlanta, GA: Agency for Toxic Substances and Disease Registry. E Andres P. 1984. IgA-IgG disease in the intestine of...RADIOLOGICAL APPENDIX R - DETAILED TOXICITY SUMMARIES APPENDIX S - MISCELLANEOUS INFORMATION APPENDIX T - PATHWAY ELIMINATIONS APPENDIX U - QUALITY

  6. Reflectivity modulator based on GaSb/GaAs heterostructure

    International Nuclear Information System (INIS)

    Rabbaa, S

    2017-01-01

    A structure of gallium antimonide (GaSb) and gallium arsenide (GaAs) wafers is built to modulate light reflectivity at CO 2 laser wavelength. A quantum well composed of GaSb/GaAs heterojunction with highly doped GaAs up to 3×10 18 cm -3 is inserted inside a layer structure. A grating of periodic structure of GaAs and gold layer is added just below the substrate. Gsolver software is used to determine the reflectivity of incident light with the existence of free carriers. A voltage is applied to the doped layer to deplete the free electrons and the reflectivity is determined again. The significant difference in reflectivity between the two cases can be used to build a light reflectivity modulator device. (paper)

  7. The interplay of blocking properties with charge and potential redistribution in thin carbon-doped GaN on n-doped GaN layers

    Science.gov (United States)

    Koller, Christian; Pobegen, Gregor; Ostermaier, Clemens; Huber, Martin; Pogany, Dionyz

    2017-07-01

    In carbon-doped GaN (GaN:C) buffers used in a GaN-on-Si technology, the buffer is embedded in between transition and channel layers. This makes the analysis of buffer properties difficult due to e.g., carrier injection from or potential drop at these adjacent layers. Here, we analyze capacitance- and current-voltage characteristics of 200-300 nm thick GaN:C ([C] = 1019 cm-3) layers which are embedded between a top metal electrode and bottom n-doped GaN (n-GaN). Such structures allow a better potential control in GaN:C and thus determination of the band diagram quantitatively. The accumulation of negative charge (concentration up to 6 × 1017 cm-3) with bias is observed in GaN:C at both polarities. For biases Vappl GaN:C near to its interface with n-GaN so that GaN:C exhibits no potential drop and blocks leakage current. For Vappl > +1.7 V, accumulated negative charges in GaN:C raise an energy barrier of ˜1.1 eV for electron injection from n-GaN to GaN:C. This causes a potential drop in GaN:C leading to a significant leakage current increase. The Fermi level pinning in GaN:C at a commonly referred acceptor at EV + 0.7(±0.2) eV is extracted only from electrostatic considerations. The occupancy change of carbon acceptors is attributed to trapping processes where the dislocation-related conductive paths are supposed to be involved in carrier transport from the top metal electrode to the carbon defect.

  8. School principals’ perceptions of their roles and responsibilities in the city of Rzeszów and Atlanta area

    Directory of Open Access Journals (Sweden)

    Tak Cheung Chan

    2018-03-01

    Full Text Available By comparing the roles and responsibilities of principals from the city of Rzeszow (Poland and the Atlanta area (Georgia, U.S.A., this study contributes to a better understanding of school leadership in the two countries. Participating principals included 148 from the United States of America, and 74 from Poland. A researcher designed a Likert-scale questionnaire on the roles and responsibilities of principals in seven leadership areas: character, professional knowledge, professional skills, administrative style, administrative duties, personnel management, and student affairs management. This was supplemented by a survey of three open-ended questions on the principals’ major responsibilities, challenges, and fulfillment. The multivariate analysis of covariance was used for data analyses with gender and age as control covariates. The results of the data analysis indicated significant differences between Poland and the United States in overall responses and three leadership areas: principals’ knowledge, styles, and duties.

  9. Recommendations for nutrition interventions with overweight African-American adolescents and young adults at the Atlanta Job Corps Center.

    Science.gov (United States)

    Dannelly, Jennifer McLeod; Kicklighter, Jana R; Hopkins, Barbara L; Rivers, Brenda A

    2005-02-01

    Focus groups were used to gain insight into the nutrition-related attitudes and motivations of overweight African-American adolescents and young adults enrolled in the Atlanta Job Corps Center in preparation for designing an effective and culturally appropriate nutrition intervention for this population. Eighteen students and 18 staff members participated in six different focus groups. Focus group themes suggest that an intervention with this target group should address overeating, proper diet composition, emotional eating, long-term consequences of a poor diet, group work, and incentives. Limiting food portions, offering healthy, appealing food choices, and displaying nutritional content of foods in the cafeteria were also suggested. It was also suggested that the intervention should be ongoing and led by someone who is patient, supportive, and has overcome an overweight problem. An intervention based on these recommendations can be specifically tailored to this target group and, potentially, be effective in changing dietary behaviors and lifestyle.

  10. Analysis of the thermal behavior of AlGaN/GaN HEMTs

    International Nuclear Information System (INIS)

    Russo, Salvatore; D’Alessandro, Vincenzo; Costagliola, Maurizio; Sasso, Grazia; Rinaldi, Niccolò

    2012-01-01

    Highlights: ► The thermal behavior of advanced multifinger AlGaN/GaN HEMTs grown on SiC is analyzed. ► The study is performed through accurate FEM simulations and DC/dynamic measurements. ► The FEM analysis is supported by an in-house tool devised for a smart mesh generation. ► Illustrative technology/layout guidelines to minimize the thermal issues are provided. - Abstract: The thermal behavior of state-of-the-art multifinger AlGaN/GaN HEMTs grown on SiC is thoroughly analyzed under steady-state and dynamic conditions. Accurate 3-D FEM simulations – based on a novel in-house tool devised to automatically build the device mesh – are performed using a commercial software to explore the influence of various layout and technological solutions on the temperature field. An in-house routine is employed to determine the Foster/Cauer networks suited to describe the dynamic heat propagation through the device structure. To conclude, various experimental techniques are employed to assess the thermal resistance and to allow the monitoring of the thermal impedance versus time of the transistors under test.

  11. Investigation of a GaN Nucleation Layer on a Patterned Sapphire Substrate

    International Nuclear Information System (INIS)

    Wu Meng; Zeng Yi-Ping; Wang Jun-Xi; Hu Qiang

    2011-01-01

    A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale. (cross-disciplinary physics and related areas of science and technology)

  12. GaN Power Stage for Switch-mode Audio Amplification

    DEFF Research Database (Denmark)

    Ploug, Rasmus Overgaard; Knott, Arnold; Poulsen, Søren Bang

    2015-01-01

    Gallium Nitride (GaN) based power transistors are gaining more and more attention since the introduction of the enhancement mode eGaN Field Effect Transistor (FET) which makes an adaptation from Metal-Oxide Semiconductor (MOSFET) to eGaN based technology less complex than by using depletion mode Ga......N FETs. This project seeks to investigate the possibilities of using eGaN FETs as the power switching device in a full bridge power stage intended for switch mode audio amplification. A 50 W 1 MHz power stage was built and provided promising audio performance. Future work includes optimization of dead...

  13. Changes in density of on-premises alcohol outlets and impact on violent crime, Atlanta, Georgia, 1997-2007.

    Science.gov (United States)

    Zhang, Xingyou; Hatcher, Bonnie; Clarkson, Lydia; Holt, James; Bagchi, Suparna; Kanny, Dafna; Brewer, Robert D

    2015-05-28

    Regulating alcohol outlet density is an evidence-based strategy for reducing excessive drinking. However, the effect of this strategy on violent crime has not been well characterized. A reduction in alcohol outlet density in the Buckhead neighborhood of Atlanta from 2003 through 2007 provided an opportunity to evaluate this effect. We conducted a community-based longitudinal study to evaluate the impact of changes in alcohol outlet density on violent crime in Buckhead compared with 2 other cluster areas in Atlanta (Midtown and Downtown) with high densities of alcohol outlets, from 1997 through 2002 (preintervention) to 2003 through 2007 (postintervention). The relationship between exposures to on-premises retail alcohol outlets and violent crime were assessed by using annual spatially defined indices at the census block level. Multilevel regression models were used to evaluate the relationship between changes in exposure to on-premises alcohol outlets and violent crime while controlling for potential census block-level confounders. A 3% relative reduction in alcohol outlet density in Buckhead from 1997-2002 to 2003-2007 was associated with a 2-fold greater reduction in exposure to violent crime than occurred in Midtown or Downtown, where exposure to on-premises retail alcohol outlets increased. The magnitude of the association between exposure to alcohol outlets and violent crime was 2 to 5 times greater in Buckhead than in either Midtown or Downtown during the postintervention period. A modest reduction in alcohol outlet density can substantially reduce exposure to violent crime in neighborhoods with high density of alcohol outlets. Routine monitoring of community exposure to alcohol outlets could also inform the regulation of alcohol outlet density, consistent with Guide to Community Preventive Services recommendations.

  14. Investigation Into the Use of Satellite Data in Aiding Characterization of Particulate Air Quality in the Atlanta, Georgia Metropolitan Area

    Science.gov (United States)

    Alston, Erica J.; Sokolik, Irina, N.; Doddridge, Bruce G.

    2011-01-01

    Poor air quality episodes occur often in metropolitan Atlanta, Georgia. The primary focus of this research is to assess the capability of satellites as a tool in characterizing air quality in Atlanta. Results indicate that intra-city PM2.5 concentrations show similar patterns as other U.S. urban areas, with the highest concentrations occurring within the city. Both PM2.5 and MODIS AOD show more increases in the summer than spring, yet MODIS AOD doubles in the summer unlike PM2.5. A majority of OMI AI is below 0.5. Using this value as an ambient measure of carbonaceous aerosols in the urban area, aerosol transport events can be identified. Our results indicate that MODIS AOD is well correlated with PM2.5 on a yearly and seasonal basis with correlation coefficients as high as 0.8 for Terra and 0.7 for Aqua. A possible alternative view of the PM2.5 and AOD relationship is seen through the use of AOD thresholds. These probabilistic thresholds provide a means to describe the AQI through the use of past AOD for a specific area. We use the NAAQS to classify the AOD into different AQI codes, and probabilistically determine thresholds of AOD that represent the majority of a specific AQI category. For example, the majority 80% of moderate AQI days have AOD values between 0.5 - 0.6. The development of thresholds could be a tool used to evaluate air quality from the use of satellites in regions where there are sparse ground-based measurements of PM2.5.

  15. Thin film GaP for solar cell application

    Science.gov (United States)

    Morozov, I. A.; Gudovskikh, A. S.; Kudryashov, D. A.; Nikitina, E. V.; Kleider, J.-P.; Myasoedov, A. V.; Levitskiy, V.

    2016-08-01

    A new approach to the silicon based heterostructures technology consisting of the growth of III-V compounds (GaP) on a silicon substrate by low-temperature plasma enhanced atomic layer deposition (PE-ALD) is proposed. The basic idea of the method is to use a time modulation of the growth process, i.e. time separated stages of atoms or precursors transport to the growing surface, migration over the surface, and crystal lattice relaxation for each monolayer. The GaP layers were grown on Si substrates by PE-ALD at 350°C with phosphine (PH3) and trimethylgallium (TMG) as sources of III and V atoms. Scanning and transmission electron microscopy demonstrate that the grown GaP films have homogeneous amorphous structure, smooth surface and a sharp GaP/Si interface. The GaP/Si heterostructures obtained by PE-ALD compare favourably to that conventionally grown by molecular beam epitaxy (MBE). Indeed, spectroscopic ellipsometry measurements indicate similar interband optical absorption while photoluminescence measurements indicate higher charge carrier effective lifetime. The better passivation properties of GaP layers grown by PE-ALD demonstrate a potential of this technology for new silicon based photovoltaic heterostructure

  16. Determination of provincial logistics capability for South African provinces

    CSIR Research Space (South Africa)

    Mashoko, L

    2012-10-10

    Full Text Available Production January 2013/ Vol. 39 Life cycle inventory of electricity cogeneration from bagasse in the South African sugar industry L. Mashoko a , C. Mbohwa b,* , V.M. Thomas c,d a Logistics and Quantitative Methods, CSIR Built Environment..., Georgia Institute of Technology, Atlanta, GA 30332, USA d School of Public Policy, Georgia Institute of Technology, Atlanta, GA 30332, USA Abstract The South African sugar industry has a potential for cogeneration of steam and electricity using...

  17. Photoelectrochemical studies of InGaN/GaN MQW photoanodes

    Science.gov (United States)

    Butson, Joshua; Reddy Narangari, Parvathala; Krishna Karuturi, Siva; Yew, Rowena; Lysevych, Mykhaylo; Tan, Hark Hoe; Jagadish, Chennupati

    2018-01-01

    The research interest in photoelectrochemical (PEC) water splitting is ever growing due to its potential to contribute towards clean and portable energy. However, the lack of low energy band gap materials with high photocorrosion resistance is the primary setback inhibiting this technology from commercialisation. The ternary alloy InGaN shows promise to meet the photoelectrode material requirements due to its high chemical stability and band gap tunability. The band gap of InGaN can be modulated from the UV to IR regions by adjusting the In concentration so as to absorb the maximum portion of the solar spectrum. This paper reports on the influence of In concentration on the PEC properties of planar and nanopillar (NP) InGaN/GaN multi-quantum well (MQW) photoanodes, where NPs were fabricated using a top-down approach. Results show that changing the In concentration, while having a minor effect on the PEC performance of planar MQWs, has an enormous impact on the PEC performance of NP MQWs, with large variations in the photocurrent density observed. Planar photoanodes containing MQWs generate marginally lower photocurrents compared to photoanodes without MQWs when illuminated with sunlight. NP MQWs with 30% In generated the highest photocurrent density of 1.6 mA cm-2, 4 times greater than that of its planar counterpart and 1.8 times greater than that of the NP photoanode with no MQWs. The InGaN/GaN MQWs also slightly influenced the onset potential of both the planar and NP photoanodes. Micro-photoluminescence, diffuse reflectance spectroscopy and IPCE measurements are used to explain these results.

  18. ITER TASK T252 (1995):Gamma radiation testing of a GaAs operational amplifier for instrument applications

    International Nuclear Information System (INIS)

    Hiemstra, D.

    1996-03-01

    The purpose of this 1995 ITER task was : to build an improved operational amplifier using GaAs MESFET technology, to build a reference voltage subcircuit using GaAs MESFET technology and to investigate the potential of GaAs HBT's to improve the noise performance of the GaAs MESFET operational amplifier. This work addresses the need for instrumentation-grade components to read sensors in an experimental fusion reactor, where the anticipated total dose for a useful service life is 3Grad(GaAs). It is an extension of our 1994 work. 3 tabs., 6 figs

  19. 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

  20. GaN High Power Devices

    Energy Technology Data Exchange (ETDEWEB)

    PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P.; CHO,H.; GILA,B.P.; JOHNSON,J.W.; MONIER,C.; ABERNATHY,C.R.; HAN,JUNG; BACA,ALBERT G.; CHYI,J.-I.; LEE,C.-M.; NEE,T.-E.; CHUO,C.-C.; CHI,G.C.; CHU,S.N.G.

    2000-07-17

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN heterojunction bipolar transistors, GaN heterostructure and metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  1. Y ogananda CS (10) 8 (GA)

    Indian Academy of Sciences (India)

    Chinese remainder theorem (2) 78 (CR). Chlamydomonas (5) 22 (GA). Cholesterol (2) 74 (GA). Chromium compound (9) 72 (FA). Cananga odorata Hook! & Thoms. (11) (FT). Cicca disticha L. Syn. C.Acida Merr (2) (FT). Circadian rhythm (5) 10, 14, 32, (GA). Circadian rhythms (5) 22 (GA). Claim size distribution (10) 49 (GA).

  2. High Concentration InGaN/GaN Multi-Quantum Well Solar Cells with a Peak Open-Circuit Voltage of 2.45 V

    International Nuclear Information System (INIS)

    Zhang Dong-Yan; Zheng Xin-He; Li Xue-Fei; Wu Yuan-Yuan; Wang Jian-Feng; Yang Hui

    2012-01-01

    We report InGaN/GaN multi-quantum well (MQW) solar cells with a comparatively high open-circuit voltage and good concentration properties. The open circuit voltage (V oc ) keeps increasing logarithmically with concentration ratio until 60 suns. The peak V oc of InGaN/GaN MQW solar cells, which has a predominant peak wavelength of 456 nm from electroluminescence measurements, is found to be 2.45 V when the concentration ratio reaches 333×. Furthermore, the dependence of conversion efficiency and fill factor on concentration ratio are analyzed. (cross-disciplinary physics and related areas of science and technology)

  3. The 2018 GaN power electronics roadmap

    Science.gov (United States)

    Amano, H.; Baines, Y.; Beam, E.; Borga, Matteo; Bouchet, T.; Chalker, Paul R.; Charles, M.; Chen, Kevin J.; Chowdhury, Nadim; Chu, Rongming; De Santi, Carlo; Merlyne De Souza, Maria; Decoutere, Stefaan; Di Cioccio, L.; Eckardt, Bernd; Egawa, Takashi; Fay, P.; Freedsman, Joseph J.; Guido, L.; Häberlen, Oliver; Haynes, Geoff; Heckel, Thomas; Hemakumara, Dilini; Houston, Peter; Hu, Jie; Hua, Mengyuan; Huang, Qingyun; Huang, Alex; Jiang, Sheng; Kawai, H.; Kinzer, Dan; Kuball, Martin; Kumar, Ashwani; Boon Lee, Kean; Li, Xu; Marcon, Denis; März, Martin; McCarthy, R.; Meneghesso, Gaudenzio; Meneghini, Matteo; Morvan, E.; Nakajima, A.; Narayanan, E. M. S.; Oliver, Stephen; Palacios, Tomás; Piedra, Daniel; Plissonnier, M.; Reddy, R.; Sun, Min; Thayne, Iain; Torres, A.; Trivellin, Nicola; Unni, V.; Uren, Michael J.; Van Hove, Marleen; Wallis, David J.; Wang, J.; Xie, J.; Yagi, S.; Yang, Shu; Youtsey, C.; Yu, Ruiyang; Zanoni, Enrico; Zeltner, Stefan; Zhang, Yuhao

    2018-04-01

    Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

  4. Photoluminescence Studies of Rare Earth (Er, Eu, Tm) in situ Doped GaN

    Science.gov (United States)

    2003-01-01

    lighting technology , and optical communications. We are currently investigating the photoluminescence (PL) properties of RE (Er, Eu, Tm)-doped GaN thin-films prepared by solid-source molecular beam epitaxy. The most intense visible PL under above-gap excitation is observed from GaN:Eu (red: 622 nm) followed by GaN:Er (green: 537 nm, 558 nm), and then GaN:Tm (blue: 479 nm). In this paper, we present spectroscopic results on the Ga-flux dependence of the Er3+ PL properties from GaN:Er and we report on the identification of different Eu3+ centers in GaN:Eu

  5. Urban Growth Areas, This Layer represents the current Urbanized Area for Atlanta as defined by the U.S. Census Bureau. An Urbanized Area is a concept used by the U.S. Census Bureau to measure the population, land area and population density of a built-up or continuously deve, Published in 2000, 1:100000 (1in=8333ft) scale, Atlanta Regional Commission.

    Data.gov (United States)

    NSGIC Regional | GIS Inventory — Urban Growth Areas dataset current as of 2000. This Layer represents the current Urbanized Area for Atlanta as defined by the U.S. Census Bureau. An Urbanized Area...

  6. 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.

  7. New Decay Studies of 66Ga

    Science.gov (United States)

    Kumar, Suresh; Ahmad, I.; Carpenter, M. P.; Chen, J.; Greene, J. P.; Kondev, F. G.; Zhu, S.

    2014-03-01

    High-energy γ rays with energies up to 5.0 MeV are emitted in the radioactive decay of 66Ga (T1/2 = 9.49 h). Thus, this radionuclide appears to be a suitable candidate for energy and efficiency calibrations of high-resolution, γ-ray spectrometers that are employed in studies of very neutron-rich nuclei which have large Qβ values. In addition, accurate emission probabilities of this isotope are of interest to medical imaging applications, owing to the existence of large β+ decay branches, which need to be characterized with better accuracy. Decay studies of 66Ga were initiated using the γ-ray spectroscopy technique. The source was produced by means of the 66Zn(p,n) reaction at a beam energy of 12 MeV. Singles and γ - γ coincidences measurements were carried out using a single Ge detector and Gammasphere, respectively. The previously known 66Ga decay scheme was extended and many new γ rays were placed in the daughter nuclide 66Zn. The work at ANL was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. S. Kumar acknowledges support from the Indo-US Science and Technology Forum for the award of a Research Fellowship.

  8. Effects of combined gate and ohmic recess on GaN HEMTs

    Directory of Open Access Journals (Sweden)

    Sunil Kumar

    2016-09-01

    Full Text Available AlGaN/GaN, because of their superior material properties, are most suitable semiconductor material for High Electron Mobility Transistors (HEMTs. In this work we investigated the hidden physics behind these materials and studied the effect of recess technology in AlGaN/GaN HEMTs. The device under investigation is simulated for different recess depth using Silvaco-Atlas TCAD. Recess technology improves the performance of AlGaN/GaN HEMTs. We considered three kinds of recess technology gate, ohmic and combination of gate and ohmic. Gate recess improves transconductance gm but it reduces the drain current Id of the device under investigation. Ohmic recess improves the transconductance gm but it introduces leakage current Ig in the device. In order to use AlGaN/GaN for high voltage operation, both the transconductance and the drain current should be reasonably high which is obtained by combining both gate and ohmic recess technologies. A good balance in transconductance and drain current is achieved by combining both gate and ohmic recess technologies without any leakage current.

  9. GaN/AlGaN nanostructures for intersubband optoelectronics

    Energy Technology Data Exchange (ETDEWEB)

    Tchernycheva, M.; Macchadani, H.; Nevou, L.; Mangeney, J.; Julien, F.H. [Institut d' Electronique Fondamentale, UMR 8622 CNRS, University Paris Sud XI, 91405 Orsay (France); Kandaswamy, P.K.; Wirthmueller, A.; Monroy, E. [CEA-Grenoble, INAC/SP2M/NPSC, 17 rue des Martyrs, 38054 Grenoble (France); Vardi, A.; Schacham, S.; Bahir, G. [Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

    2010-06-15

    We have investigated intraband absorptions in GaN/AlN QDs for ultrafast all-optical switching applications at telecommunication wavelengths. Using time-resolved pump-probe experiments the electron lifetime in the excited state of the QDs is measured to be 165 fs. Intraband absorption saturation experiments reveal a record low switching energy. We then investigate quantum cascade ISB photodetectors based on GaN/AlGaN QWs and show that mesa devices with 17 x 17 {mu}m{sup 2} size provide a frequency response above 10 GHz at 1.5 {mu}m wavelength. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  10. 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

  11. Sensing by means of nonlinear optics with functionalized GaAs/AlGaAs photonic crystals.

    Science.gov (United States)

    Estephan, Elias; Bajoni, Daniele; Saab, Marie-Belle; Cloitre, Thierry; Aulombard, Roger; Larroque, Christian; Andreani, Lucio Claudio; Liscidini, Marco; Malvezzi, Andrea Marco; Gergely, Csilla

    2010-06-15

    We report on specific functionalization of GaAs/AlGaAs photonic structures for molecular sensing via the optical second harmonic generation signal in the visible range exhibited by these nanostructures. Functionalization has been achieved by peptides selected by the phage display technology, revealing specific recognition for semiconducting surfaces. These small peptides when biotinylated serve for controlled placement of biotin onto the substrate to capture then streptavidin. Functionalization (with biotinylated peptide) and molecular recognition (of streptavidin) events both result in enhancing the nonlinear optical response of the samples. Adsorption and infiltration of biomolecules into the GaAs/AlGaAs photonic structure were monitored by atomic force and scanning electron microscopy combined with Energy Dispersive X-ray spectroscopy. We demonstrate that once functionalized with specific peptides, photonic structures could be used as miniature biosensors down to femtomolar detection sensitivity, by monitoring changes in the second harmonic signal when molecules are captured. Our results prove the outstanding sensitivity of the nonlinear approach in biosensing with photonic crystal waveguides as compared to linear absorption techniques on the same samples. The present work is expected to pioneer development of a new class of extremely small affinity-based biosensors with high sensitivity and demonstrates that photonic structures support device functionality that includes strongly confined and localized nonlinear radiation emission and detection processes.

  12. 31% European InGaP/GaAs/InGaAs Solar Cells for Space Application

    Directory of Open Access Journals (Sweden)

    Campesato Roberta

    2017-01-01

    Full Text Available We report a triple junction InGaP/GaAs/InGaNAs solar cell with efficiency of ~31% at AM0, 25 °C fabricated using a combined molecular beam epitaxy (MBE and metal-organic chemical vapour deposition (MOCVD processes. The prototype cells comprise of InGaNAs (Indium Gallium Nitride Arsenide bottom junction grown on a GaAs (Gallium Arsenide substrate by MBE and middle and top junctions deposited by MOCVD. Repeatable cell characteristics and uniform efficiency pattern over 4-inch wafers were obtained. Combining the advantages offered by MBE and MOCVD opens a new perspective for fabrication of high-efficiency space tandem solar cells with three or more junctions. Results of radiation resistance of the sub-cells are also presented and critically evaluated to achieve high efficiency in EOL conditions.

  13. Source apportionment of submicron organic aerosol collected from Atlanta, Georgia, during 2014-2015 using the aerosol chemical speciation monitor (ACSM)

    Science.gov (United States)

    Rattanavaraha, Weruka; Canagaratna, Manjula R.; Budisulistiorini, Sri Hapsari; Croteau, Philip L.; Baumann, Karsten; Canonaco, Francesco; Prevot, Andre S. H.; Edgerton, Eric S.; Zhang, Zhenfa; Jayne, John T.; Worsnop, Douglas R.; Gold, Avram; Shaw, Stephanie L.; Surratt, Jason D.

    2017-10-01

    The Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was redeployed at the Jefferson Street (JST) site in downtown Atlanta, Georgia (GA) for 1 year (March 20, 2014-February 08, 2015) to chemically characterize non-refractory submicron particulate matter (NR-PM1) in near real-time and to assess whether organic aerosol (OA) types and amounts change from year-to-year. Submicron organic aerosol (OA) mass spectra were analyzed by season using multilinear engine (ME-2) to apportion OA subtypes to potential sources and chemical processes. A suite of real-time collocated measurements from the Southeastern Aerosol Research and Characterization (SEARCH) network was compared with ME-2 factor solutions to aid in the interpretation of OA subtypes during each season. OA tracers measured from high-volume filter samples using gas chromatography interfaced with electron ionization-mass spectrometry (GC/EI-MS) also aided in identifying OA sources. The initial application of ME-2 to the yearlong ACSM dataset revealed that OA source apportionment by season was required to better resolve sporadic OA types. Spring and fall OA mass spectral datasets were separated into finer periods to capture potential OA sources resulting from non-homogeneous emissions during transitioning periods. NR-PM1 was highest in summer (16.7 ± 8.4 μg m-3) and lowest in winter (8.0 ± 5.7 μg m-3), consistent with prior studies. OA dominated NR-PM1 mass (56-74% on average) in all seasons. Hydrocarbon-like OA (HOA) from primary emissions was observed in all seasons, averaging 5-22% of total OA mass. Strong correlations of HOA with carbon monoxide (CO) (R = 0.71-0.88) and oxides of nitrogen (NOx) (R = 0.55-0.79) indicated that vehicular traffic was the likely source. Biomass burning OA (BBOA) was observed in all seasons, with lower contributions (2%) in summer and higher in colder seasons (averaging 8-20% of total OA mass). BBOA correlated strongly with levoglucosan (R = 0.78-0.95) during colder seasons

  14. Exposición «espacios e ilusiones» en el museo superior de arte, Atlanta - EE. UU.

    OpenAIRE

    Scogin, Mack; Clark, Chuck

    1980-01-01

    This Exhibit, carried out under the auspices of several cultural organizations of the city of Atlanta, intends to offer a distorted vision of space at the same time as it is real. It has been designed as a labyrinth of rooms in which various special effects are set up, such as: mirrors, lights, sound, shadow, movements, etc. Among the different rooms, the following stand out: the illuminated room, with shadows that appear and disappear on its walls; the perspective room, where the...

  15. Influences of stress on the properties of GaN/InGaN multiple quantum well LEDs grown on Si (111) substrates

    Science.gov (United States)

    Liu, Ming-Gang; Yang, Yi-Bin; Xiang, Peng; Chen, Wei-Jie; Han, Xiao-Biao; Lin, Xiu-Qi; Lin, Jia-Li; Luo, Hui; Liao, Qiang; Zang, Wen-Jie; Wu, Zhi-Sheng; Liu, Yang; Zhang, Bai-Jun

    2015-06-01

    The influences of stress on the properties of InGaN/GaN multiple quantum wells (MQWs) grown on silicon substrate were investigated. The different stresses were induced by growing InGaN and AlGaN insertion layers (IL) respectively before the growth of MQWs in metal-organic chemical vapor deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements demonstrated that the InGaN IL introduced an additional tensile stress in n-GaN, which released the strain in MQWs. It is helpful to increase the indium incorporation in MQWs. In comparison with MQWs without the IL, the wavelength shows a red-shift. AlGaN IL introduced a compressive stress to compensate the tensile stress, which reduces the indium composition in MQWs. PL measurement shows a blue-shift of wavelength. The two kinds of ILs were adopted to InGaN/GaN MQWs LED structures. The same wavelength shifts were also observed in the electroluminescence (EL) measurements of the LEDs. Improved indium homogeneity with InGaN IL, and phase separation with AlGaN IL were observed in the light images of the LEDs. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 51177175), the National Basic Research Program of China (Grant Nos. 2010CB923201 and 2011CB301903), the Ph. D. Program Foundation of the Ministry of Education of China (Grant No. 20110171110021), the International Science and Technology Collaboration Program of China (Grant No. 2012DFG52260), the National High Technology Research and Development Program of China (Grant No. 2014AA032606), the International Science and Technology Collaboration Program of Guangdong Province, China (Grant No. 2013B051000041), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics (Grant No. IOSKL2014KF17).

  16. Metamorphic GaAs/GaAsBi Heterostructured Nanowires.

    Science.gov (United States)

    Ishikawa, Fumitaro; Akamatsu, Yoshihiko; Watanabe, Kentaro; Uesugi, Fumihiko; Asahina, Shunsuke; Jahn, Uwe; Shimomura, Satoshi

    2015-11-11

    GaAs/GaAsBi coaxial multishell nanowires were grown by molecular beam epitaxy. Introducing Bi results in a characteristic nanowire surface morphology with strong roughening. Elemental mappings clearly show the formation of the GaAsBi shell with inhomogeneous Bi distributions within the layer surrounded by the outermost GaAs, having a strong structural disorder at the wire surface. The nanowire exhibits a predominantly ZB structure from the bottom to the middle part. The polytipic WZ structure creates denser twin defects in the upper part than in the bottom and middle parts of the nanowire. We observe room temperature cathodoluminescence from the GaAsBi nanowires with a broad spectral line shape between 1.1 and 1.5 eV, accompanied by multiple peaks. A distinct energy peak at 1.24 eV agrees well with the energy of the reduced GaAsBi alloy band gap by the introduction of 2% Bi. The existence of localized states energetically and spatially dispersed throughout the NW are indicated from the low temperature cathodoluminescence spectra and images, resulting in the observed luminescence spectra characterized by large line widths at low temperatures as well as by the appearance of multiple peaks at high temperatures and for high excitation powers.

  17. HTGR technology development: status and direction

    International Nuclear Information System (INIS)

    Kasten, P.R.

    1982-01-01

    During the last two years there has been an extensive and comprehensive effort expended primarily by General Atomic (GA) in generating a revised technology development plan. Oak Ridge National Laboratory (ORNL) has assisted in this effort, primarily through its interactions over the past years in working together with GA in technology development, but also through detailed review of the initial versions of the technology development plan as prepared by GA. The plan covers Fuel Technology, Materials Technology (including metals, graphite, and ceramics), Plant Technology (including methods, safety, structures, systems, heat exchangers, control and electrical, and mechanical), and Component Design Verification and Support areas

  18. Reliability of GaAs processes for space applications

    OpenAIRE

    Peray, J.F; Fiers, C.; Crudo, P.; Jacobelli, C.

    1992-01-01

    This paper reviews the reliability of GaAs MMICs processes for low noise and power applications in future space systems. Each technology and library element were evaluated in terms of reliability. Results present main data of each process and an understanding of the causes of each failure modes. Improvements methodology is explained and first results are showed.

  19. Status of GaAs solar cell production

    Science.gov (United States)

    Yeh, Milton; Ho, Frank; Iles, Peter A.

    1989-01-01

    Recent experience in producing GaAs solar cells, to meet the full requirements of space-array manufacturers is reviewed. The main problems have been in extending MOCVD technology to provide high throughput of high quality epitaxial layers, and to integrate the other important factors needed to meet the full range of user requirements. Some discussion of evolutionary changes is also given.

  20. Mercury(II) selective sensors based on AlGaN/GaN transistors

    Energy Technology Data Exchange (ETDEWEB)

    Asadnia, Mohsen, E-mail: mohsen.asadnia@mq.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Department of Engineering, Macquarie University, NSW 2109 (Australia); Myers, Matthew [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); CSIRO Energy Flagship, Kensington, Western Australia 6151 (Australia); Akhavan, N.D. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); O' Donnell, Kane [Department of Imaging and Applied Physics, Curtin University, Bentley, Western Australia 6102 (Australia); Umana-Membreno, Gilberto A. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Mishra, U.K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93106 (United States); Nener, Brett [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Baker, Murray [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Parish, Giacinta [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia)

    2016-11-02

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg{sup 2+}. This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg{sup 2+} concentrations. At pH 2.8 in a 10{sup −2} M KNO{sub 3} ion buffer, a detection limit below 10{sup −8} M and a linear response range between 10{sup −8} M-10{sup −4} M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10{sup −7} M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10{sup −7} M and 10{sup −6} M in 10{sup −2} M Cd(NO{sub 3}){sub 2} and 10{sup −2} M Pb(NO{sub 3}){sub 2} ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg{sup 2+} solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. - Highlights: • This work is the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. • The sensor utilised an AlGaN/GaN transistor by functionalising the gate area with a polyvinyl chloride (PVC) based membrane. • The sensor showed a rapid and linear response between 10{sup −8} M-10{sup −4} M for Hg{sup 2+} detection at pH 2.8 in a 10{sup −2} M KNO{sub 3} ion buffer. • Detection limits of

  1. Conduction, reverse conduction and switching characteristics of GaN E-HEMT

    DEFF Research Database (Denmark)

    Sørensen, Charlie; Lindblad Fogsgaard, Martin; Christiansen, Michael Noe

    2015-01-01

    In this paper switching and conduction characterization of the GS66508P-E03 650V enhancement mode gallium nitride (GaN) transistor is described. GaN transistors are leading edge technology and as so, their characteristics are less than well documented. The switching characteristics are found using...

  2. Organic compounds assessed in Chattahoochee River water used for public supply near Atlanta, Georgia, 2004-05

    Science.gov (United States)

    Hughes, W. Brian; Younker, Cristal L.

    2011-01-01

    An investigation by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program characterized the occurrence of 266 organic compounds in source water and finished water from the Chattahoochee River, which is the main water-supply source for the Atlanta metropolitan area. Source water is stream water collected at a surface-water intake prior to water treatment, and finished water is water that has passed through treatment processes prior to distribution. Samples were collected approximately monthly during 2004-05 and included 15 paired source-water and finished-water samples. Samples were collected during winter-spring high flow and summer-fall low flow, but storm events were not targeted during this Source Water-Quality Assessment (SWQA) study. Samples were analyzed for pesticides and degradates, gasoline hydrocarbons, solvents, disinfection by-products, personal care and domestic-use products, and other organic compounds. Community water systems are required to monitor regulated organic compounds under the Safe Drinking Water Act of 1996 (U.S. Environmental Protection Agency, 1998); however, most compounds included in this study are not regulated by Federal drinking-water standards (U.S. Environmental Protection Agency, 2007a). The Chattahoochee River study is part of an ongoing NAWQA investigation of community water systems across the United States. Additional details about the national study are given in Carter and others (2007).

  3. Value of the revised Atlanta classification (RAC) and determinant-based classification (DBC) systems in the evaluation of acute pancreatitis.

    Science.gov (United States)

    Wang, Xiaolei; Qin, Li; Cao, Jingli

    2017-11-03

    Since increasing acute pancreatitis (AP) severity is significantly associated with mortality, accurate and rapid determination of severity is crucial for effective clinical management. This study investigated the value of the revised Atlanta classification (RAC) and the determinant-based classification (DBC) systems in stratifying severity of acute pancreatitis. This retrospective observational cohort study included 480 AP patients. Patient demographics and clinical characteristics were recorded. The primary outcome was mortality, and secondary outcomes were admission to intensive care unit (ICU), duration of ICU stay, and duration of hospital stay. Based on the RAC classification, there were 295 patients with mild AP (MAP), 146 patients with moderate-to-severe AP (MSAP), and 39 patients with severe AP (SAP). Based on the DBC classification, there were 389 patients with MAP, 41 patients with MSAP, 32 patients with SAP, and 18 patients with critical AP (CAP). ROC curve analysis showed that the DBC system had a significantly higher accuracy at predicting organ failure compared to the RAC system (p < .001). Multivariate regression analysis showed that age and ICU stay were independent risk factors of mortality. The DBC system had a higher accuracy at predicting organ failure. Age and ICU stay were significantly associated with risk of death in AP patients. A classification of CAP by the DBC system should warrant close attention, and rapid implementation of effective measures to reduce mortality.

  4. 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.

  5. Long-term trends and weekday-to-weekend differences in ozone, its precursors, and other secondary pollutants in Atlanta, Georgia

    Science.gov (United States)

    Pollack, I. B.; Ryerson, T. B.; Baumann, K.; Edgerton, E. S.; De Gouw, J. A.; Gilman, J.; Graus, M.; Holloway, J.; Lerner, B. M.; Neuman, J. A.; Roberts, J. M.; Veres, P. R.; Warneke, C.; Trainer, M.; Parrish, D. D.

    2013-12-01

    In an environment rich in biogenic volatile organic compounds (VOCs), decreasing concentrations of ozone (-1.3 % yr-1) and other secondary pollutants (-8.2 % yr-1 for nitric acid, HNO3; and -7.9 % yr-1 for peroxyacetyl nitrate, PAN) in Atlanta, Georgia over the past fifteen years are primarily attributed to decreases in local emissions of nitrogen oxides (NOx=NO+NO2). Large reductions in abundances of NOx in the Southeast U.S. over the years (-8.0 % yr-1 for total reactive nitrogen, NOy) are the direct result of control strategies implemented to reduced emissions from electric-power generation plants and on-road motor vehicles. Here, we compile an extensive historical data set of trace gas measurements spanning fifteen years between 1998 and 2013 from a surface monitoring network site in downtown Atlanta (i.e. the SEARCH network Jefferson Street site) and research aircraft (e.g. the 2013 Southeast Atmosphere Study and 1999 Southern Oxidants Study aboard the NOAA P-3 aircraft). With this data set we confirm and extend long-term trends and weekday-to-weekend differences in ozone, its precursors, and other secondary pollutants during summertime in Atlanta. Long-term changes in abundances and enhancement ratios of secondary oxidation products indicate changes in pollutant formation chemistry in Atlanta resulting from the significant decrease in NOx precursor emissions over the past fifteen years. The most noteworthy changes include: 1) an increase in enhancement ratios of odd oxygen (Ox=O3+NO2) to (PAN+HNO3) of +5.5 % yr-1 indicating an increase in ozone production efficiency by a factor of 2 over the fifteen year period, 2) no significant change in the fraction of oxidized NOx out of NOy over time indicating little change in the extent of photochemical processing of the NOx emissions, and 3) a flip in observed ozone concentrations from higher average ozone on weekends to higher average ozone on weekdays after 2004. The observations for Atlanta will also be contrasted

  6. Robust AlGaN/GaN Low Noise Amplifier MMICs for C-, Ku- and Ka-Band Space Applications

    NARCIS (Netherlands)

    Suijker, E.M.; Rodenburg, M.; Hoogland, J.A.; van Heijningen, M; Seelmann-Eggebert, M.; Quay, R.; Bruckner, P.; van Vliet, Frank Edward

    2009-01-01

    Abstract The high power capabilities in combination with the low noise performance of gallium nitride (GaN) makes this technology an excellent choice for robust receivers. This paper presents the design and measured results of three different LNAs, which operate in C-, Ku-, and Ka-band. The designs

  7. High speed, low noise ultraviolet photodetectors based on GaN p-i-n and AlGaN(p)-GaN(i)-GaN(n) structures

    Energy Technology Data Exchange (ETDEWEB)

    Xu, G.; Salvador, A.; Botchkarev, A.E.; Kim, W.; Lu, C.; Tang, H. [Illinois Univ., Urbana, IL (United States). Mater. Res. Lab. and Coordinated Sci.; Morkoc, H. [Illinois Univ., Urbana, IL (United States). Mater. Res. Lab. and Coordinated Sci.]|[Air Force Wright Lab., Wright Patterson, AFB, OH (United States)]|[Dept. of Electrical Eng., Virginia Commonwealth Univ., Richmond, VA (United States); Smith, G.; Estes, M.; Dang, T. [Air Force Wright Lab., Wright Patterson, AFB, OH (United States); Wolf, P. [Air Force Inst. of Tech., Wright-Patterson AFB, OH (United States). Dept. of Engineering Physics

    1998-08-01

    We have investigated the spectral response of front surface illuminated GaN, AlGaN/GaN and AlGaN p-i-n ultraviolet photodetectors grown by reactive molecular beam epitaxy on sapphire substrates. The GaN homojunction p-i-n photodiode exhibited a peaked response at 364 nm the origin of which is not yet clear. This response was absent in the AlGaN/GaN heterojunction p-i-n detectors. The maximum responsivity for the unbiased GaN and AlGaN/GaN is 0.07 and 0.12 A/W, respetively, and occurs at 364 nm. The responsivity drops by more than 3 orders of magnitude near 390 nm. The AlGaN homojunction p-i-n on the other hand has a peak responsivity of 0.08 A/W at 340 nm. The noise equivalent power of 4 pW and 8.3 pW were obtained for the GaN and AlGaN/GaN photodiodes respectively. We measured extremely fast decay times of 12 ns for the AlGaN/GaN and 29 ns for the GaN photodiodes. (orig.) 5 refs.

  8. Ivestigation of an InGaN - GaN nanowire heterstructure

    Energy Technology Data Exchange (ETDEWEB)

    Limbach, Friederich; Gotschke, Tobias; Stoica, Toma; Calarco, Raffaella; Gruetzmacher, Detlev [Institute of Bio- and Nanosystems (IBN-1), Research Center Juelich GmbH, Juelich (Germany); JARA-Fundamentals of Future Information Technology, Juelich (Germany); Sutter, Eli; Ciston, Jim [Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY (United States); Cusco, Ramon; Artus, Luis [Institut Jaume Almera, Consell Superior d' Investigacions Cientifiques (CSIC), Barcelona, Catalonia (Spain); Kremling, Stefan; Hoefling, Sven; Worschech, Lukas [University Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wuerzburg (Germany)

    2011-07-01

    InGaN/GaN nanowire (NW) heterostructures grown by molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multi-faceted InGaN cap wrapping the top part of the GaN NW. Transmission electron microscopy images taken from different parts of a InGaN/GaN nanowire show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it. Photoluminescence spectra of these heterostructure NW ensembles show an emission peak at 2.1 eV. However, {mu}-PL spectra measured on single nanowires reveal much sharper luminescence peaks. A Raman analysis reveals a variation of the In content between 20 % and 30 %, in agreement with PL and TEM investigations.

  9. Study of Adsorption Property of Ga(III) onto Strongly Basic Resin for Ga Extraction from Bayer Liquor

    Science.gov (United States)

    Zhao, Zhuo; Yang, Yongxiang; Lu, Hao; Hua, Zhongsheng; Ma, Xiaoling

    Ion-exchange is the main technology used in industry for gallium recovery from Bayer liquor, the largest gallium production resource. However, the co-extraction of vanadium and the degradation of resins are the major issues. Further investigations related to fundamental theory are needed. This paper reports the study of the adsorption properties of a strongly basic resin having a combination of one =NOH group and another active group -NH2 for Ga(III) extraction. The influence of operational conditions such as contact time, initial Ga(III) concentration and temperature on Ga(III) adsorption were extensively investigated. The results revealed that the resin has high adsorption capacity and Ga(III) selectivity. The optimal adsorption condition was obtained at temperatures of 40-50°C and contact time of 40-60 min. The Ga(III) adsorption data on the resin fit well with the pseudo second-order kinetics. Langmuir and Freundlich models were used to describe Ga(III) adsorption isotherms on the resin.

  10. 'Nikkei Global Environment Technology Prize' awarded to the joint research group on regeneration of tropical forest; Nettairin saisei kyodo kenkyu ga 'Nikkei chikyu kankyo gijutsusho' wo jusho

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, T. [Kansai Electric Power Co. Inc., Osaka (Japan)

    1998-11-10

    The tropical forest regeneration technology research group of Kansai Electric Power Company and Kansai Environment Center has been performing the research and development of tropical forest regeneration technology jointly with Indonesia since fiscal 1992. The group was awarded with the Global Environment Technology Prize from Nihon Keizai Shimbun, Inc. As a result of stringent examination on 97 applications, being two times as many as in usual years, the group received high evaluation on the originality, reality and possibility of proliferation of its research, and impacts given to the societies. Two other groups were also selected. The achievements were reported by the representative of the group in the award commemoration lecture at the global environment economist summit held by the Nikkei press the same day. Conventionally, afforestation done with considerable efforts has often been lost by forest fires and slash-and-burn farming, whereas the present research aims at establishing a comprehensive afforestation technology considering social and economic aspects, and CO2 fixation. As one of the choices of flexible measures as a result of the effect of forests having been recognized in COP3, frameworks for utilizing the mechanisms of joint implementation and clean resource development were introduced. Ever increasing expectations are placed on the achievements of the present research works. (NEDO)

  11. Temperature Dependence of GaN HEMT Small Signal Parameters

    OpenAIRE

    Ali M. Darwish; Amr A. Ibrahim; H. Alfred Hung

    2011-01-01

    This study presents the temperature dependence of small signal parameters of GaN/SiC HEMTs across the 0–150°C range. The changes with temperature for transconductance ( m ), output impedance ( d s and d s ), feedback capacitance ( d g ), input capacitance ( g s ), and gate resistance ( g ) are measured. The variations with temperature are established for m , d s , d s , d g , g s , and g in the GaN technology. This information is useful for MMIC designs....

  12. Gallium arsenide (GaAs) quantum photonic waveguide circuits

    Science.gov (United States)

    Wang, Jianwei; Santamato, Alberto; Jiang, Pisu; Bonneau, Damien; Engin, Erman; Silverstone, Joshua W.; Lermer, Matthias; Beetz, Johannes; Kamp, Martin; Höfling, Sven; Tanner, Michael G.; Natarajan, Chandra M.; Hadfield, Robert H.; Dorenbos, Sander N.; Zwiller, Val; O'Brien, Jeremy L.; Thompson, Mark G.

    2014-09-01

    Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9±1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6±1.3% and 84.4±1.5% respectively were demonstrated in Mach-Zehnder interferometers exploiting the electro-optic Pockels effect. This work paves the way for a fully integrated quantum technology platform based on the GaAs material system.

  13. Technology of gallium nitride crystal growth

    CERN Document Server

    Ehrentraut, Dirk; Bockowski, Michal

    2010-01-01

    This book deals with the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production. Leading experts from industry and academia report in a very comprehensive way on the current state-of-the-art of the growth technologies and optical and structural properties of the GaN crystals are compared.

  14. Analysis and modelling of GaN Schottky-based circuits at millimeter wavelengths

    International Nuclear Information System (INIS)

    Pardo, D; Grajal, J

    2015-01-01

    This work presents an analysis of the capabilities of GaN Schottky diodes for frequency multipliers and mixers at millimeter wavelengths. By using a Monte Carlo (MC) model of the diode coupled to a harmonic balance technique, the electrical and noise performances of these circuits are investigated. Despite the lower electron mobility of GaN compared to GaAs, multipliers based on GaN Schottky diodes can be competitive in the first stages of multiplier chains, due to the excellent power handling capabilities of this material. The performance of these circuits can be improved by taking advantage of the lateral Schottky diode structures based on AlGaN/GaN HEMT technology. (paper)

  15. Development of methods for the purification of {sup 67}Ga and {sup 68}Ga for biomolecules labeling; Desenvolvimento de metodos de purificacao do {sup 67}Ga e {sup 68}Ga para a marcacao de biomoleculas

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Renata Ferreira

    2012-07-01

    For more than fifty years, the long-lived {sup 68}Ge/{sup 68}Ga generators have been in development, obtaining {sup 68}Ga without the need of having in house cyclotron, which is a considerable convenience for PET centers that have no nearby cyclotrons. {sup 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 {sup 68}Ge/{sup 68}Ga generators still contains high levels of long lived {sup 68}Ge, besides other metallic impurities, which competes with {sup 68}Ga with a consequent reduction of the labeling yield of biomolecules, such as Fe{sup 3+} and Zn{sup 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 {sup 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. {sup 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

  16. Photoluminescence studies of rare earth (Er, Eu, Tm) in situ doped GaN

    International Nuclear Information System (INIS)

    Hoemmerich, U.; Nyein, Ei Ei; Lee, D.S.; Heikenfeld, J.; Steckl, A.J.; Zavada, J.M.

    2003-01-01

    The emission properties of rare earth (RE)-doped GaN are of significant current interest for applications in full color displays, white lighting technology, and optical communications. We are currently investigating the photoluminescence (PL) properties of RE (Er, Eu, Tm)-doped GaN thin-films prepared by solid-source molecular beam epitaxy. The most intense visible PL under above-gap excitation is observed from GaN:Eu (red: 622 nm) followed by GaN:Er (green: 537 nm, 558 nm), and then GaN:Tm (blue: 479 nm). In this paper, we present spectroscopic results on the Ga-flux dependence of the Er 3+ PL properties from GaN:Er and we report on the identification of different Eu 3+ centers in GaN:Eu through high-resolution PL excitation (PLE) studies. In addition, we observed an enhancement of the blue Tm 3+ PL from AlGaN:Tm compared to GaN:Tm. Intense blue PL from Tm 3+ ions was also obtained from AlN:Tm under below-gap pumping

  17. Simulating unsteady transport of nitrogen, biochemical oxygen demand, and dissolved oxygen in the Chattahoochee River downstream from Atlanta, Georgia

    Science.gov (United States)

    Jobson, Harvey E.

    1985-01-01

    As part of an intensive water-quality assessment of the Chattahoochee River, repetitive water-quality measurements were made at 12 sites along a 69-kilometer reach of the river downstream of Atlanta, Georgia. Concentrations of seven constituents (temperature, dissolved oxygen, ultimate carbonaceous biochemical oxygen demand (BOD), organic nitrogen, ammonia, nitrite, and nitrate) were obtained during two periods of 36 hours, one starting on August 30, 1976, and the other starting on May 31, 1977. The study reach contains one large and several small sewage outfalls and receives the cooling water from two large powerplants. An unsteady water-quality model of the Lagrangian type was calibrated using the 1977 data and verified using the 1976 data. The model provided a good means of interpreting these data even though both the flow and the pollution loading rates were highly unsteady. A kinetic model of the cascade type accurately described the physical and biochemical processes occurring in the river. All rate coefficients, except reaeration coefficients and those describing the resuspension of BOD, were fitted to the 1977 data and verified using the 1976 data. The study showed that, at steady low flow, about 38 percent of the BOD settled without exerting an oxygen demand. At high flow, this settled BOD was resuspended and exerted an immediate oxygen demand. About 70 percent of the ammonia extracted from the water column was converted to nitrite, but the fate of the remaining 30 percent is unknown. Photosynthetic production was not an important factor in the oxygen balance during either run.

  18. Baseline Prevalence of Birth Defects Associated with Congenital Zika Virus Infection - Massachusetts, North Carolina, and Atlanta, Georgia, 2013-2014.

    Science.gov (United States)

    Cragan, Janet D; Mai, Cara T; Petersen, Emily E; Liberman, Rebecca F; Forestieri, Nina E; Stevens, Alissa C; Delaney, Augustina; Dawson, April L; Ellington, Sascha R; Shapiro-Mendoza, Carrie K; Dunn, Julie E; Higgins, Cathleen A; Meyer, Robert E; Williams, Tonya; Polen, Kara N D; Newsome, Kim; Reynolds, Megan; Isenburg, Jennifer; Gilboa, Suzanne M; Meaney-Delman, Dana M; Moore, Cynthia A; Boyle, Coleen A; Honein, Margaret A

    2017-03-03

    Zika virus infection during pregnancy can cause serious brain abnormalities, but the full range of adverse outcomes is unknown (1). To better understand the impact of birth defects resulting from Zika virus infection, the CDC surveillance case definition established in 2016 for birth defects potentially related to Zika virus infection* (2) was retrospectively applied to population-based birth defects surveillance data collected during 2013-2014 in three areas before the introduction of Zika virus (the pre-Zika years) into the World Health Organization's Region of the Americas (Americas) (3). These data, from Massachusetts (2013), North Carolina (2013), and Atlanta, Georgia (2013-2014), included 747 infants and fetuses with one or more of the birth defects meeting the case definition (pre-Zika prevalence = 2.86 per 1,000 live births). Brain abnormalities or microcephaly were the most frequently recorded (1.50 per 1,000), followed by neural tube defects and other early brain malformations † (0.88), eye abnormalities without mention of a brain abnormality (0.31), and other consequences of central nervous system (CNS) dysfunction without mention of brain or eye abnormalities (0.17). During January 15-September 22, 2016, the U.S. Zika Pregnancy Registry (USZPR) reported 26 infants and fetuses with these same defects among 442 completed pregnancies (58.8 per 1,000) born to mothers with laboratory evidence of possible Zika virus infection during pregnancy (2). Although the ascertainment methods differed, this finding was approximately 20 times higher than the proportion of one or more of the same birth defects among pregnancies during the pre-Zika years. These data demonstrate the importance of population-based surveillance for interpreting data about birth defects potentially related to Zika virus infection.

  19. A comparison of traditional food and health strategies among Taiwanese and Chinese immigrants in Atlanta, Georgia, USA.

    Science.gov (United States)

    Jiang, Sandy; Quave, Cassandra L

    2013-08-27

    Ethnobotanical studies on the use of plants amongst migrant populations are of great relevance to public health. Traditional health strategies, which incorporate plants as medicines, foods, or both - can play an important role in individual well-being. However, at the same time, migrant populations' traditional knowledge of such practices may be under a state of greater threat of decline due to factors such as limited access to the plant materials and physical isolation from the homeland, which serves as the primary living reservoir for this knowledge. In this study, we conducted a medical ethnobotanical survey focusing on a comparison of local medicinal food and health strategies with members of two Asian immigrant populations in metro-Atlanta: Chinese and Taiwanese. Snowball sampling techniques were employed to recruit 83 study participants, 57 of which were included in the final analysis. Semi-structured interview techniques were used to question participants about their beliefs and usage of the yin yang system, usage of Chinese herbs and medicinal foods, preference and usage of Eastern and Western medicines, and gardening for medicinal foods. Comparison of the two groups demonstrated a remarkable difference in health strategies concerning medicinal plant use, including statistically significant differences in beliefs concerning yin and yang, uses of Eastern versus Western medicine, and gardening for medicinal foods. Domestic health strategies in the form of medicinal foods play an important role in local health practices, especially among the Taiwanese participants. The collective desire for the use of both Eastern and Western medicine by both groups highlights the important role that cultural competency training will play in preparing allopathic health practitioners to serve increasingly diverse patient populations in the US.

  20. RCQ-GA: RDF Chain Query Optimization Using Genetic Algorithms

    Science.gov (United States)

    Hogenboom, Alexander; Milea, Viorel; Frasincar, Flavius; Kaymak, Uzay

    The application of Semantic Web technologies in an Electronic Commerce environment implies a need for good support tools. Fast query engines are needed for efficient querying of large amounts of data, usually represented using RDF. We focus on optimizing a special class of SPARQL queries, the so-called RDF chain queries. For this purpose, we devise a genetic algorithm called RCQ-GA that determines the order in which joins need to be performed for an efficient evaluation of RDF chain queries. The approach is benchmarked against a two-phase optimization algorithm, previously proposed in literature. The more complex a query is, the more RCQ-GA outperforms the benchmark in solution quality, execution time needed, and consistency of solution quality. When the algorithms are constrained by a time limit, the overall performance of RCQ-GA compared to the benchmark further improves.

  1. Synthesis of In0.1Ga0.9N/GaN structures grown by MOCVD and MBE for high speed optoelectronics

    KAUST Repository

    Alshehri, Bandar

    2016-06-07

    In this work, we report a comparative investigation of InxGa1-xN (SL) and InxGa1-xN/GaN (MQW) structures with an indium content equivalent to x=10%. Both structures are grown on (0001) sapphire substrates using MOCVD and MBE growth techniques. Optical properties are evaluated for samples using PL characteristics. Critical differences between the resulting epitaxy are observed. Microstructures have been assessed in terms of crystalline quality, density of dislocations and surface morphology. We have focused our study towards the fabrication of vertical PIN photodiodes. The technological process has been optimized as a function of the material structure. From the optical and electrical characteristics, this study demonstrates the benefit of InGaN/GaN MQW grown by MOCVD in comparison with MBE for high speed optoelectronic applications.

  2. Second annual clean coal technology conference: Proceedings

    International Nuclear Information System (INIS)

    1993-01-01

    The Second Annual Clean Coal Technology Conference was held at Atlanta, Georgia, September 7--9, 1993. The Conference, cosponsored by the US Department of Energy (USDOE) and the Southern States Energy Board (SSEB), seeks to examine the status and role of the Clean Coal Technology Demonstration Program (CCTDP) and its projects. The Program is reviewed within the larger context of environmental needs, sustained economic growth, world markets, user performance requirements and supplier commercialization activities. This will be accomplished through in-depth review and discussion of factors affecting domestic and international markets for clean coal technology, the environmental considerations in commercial deployment, the current status of projects, and the timing and effectiveness of transfer of data from these projects to potential users, suppliers, financing entities, regulators, the interested environmental community and the public. Individual papers have been entered separately

  3. Fecal-coliform bacteria concentrations in streams of the Chattahoochee River National Recreation Area, Metropolitan Atlanta, Georgia, May-October 1994 and 1995

    Science.gov (United States)

    Gregory, M. Brian; Frick, Elizabeth A.

    2000-01-01

    Introduction: The Metropolitan Atlanta area has been undergoing a period of rapid growth and development. The population in the 10-county metropolitan area almost doubled from about 1.5 million people in 1970 to 2.9 million people in 1995 (Atlanta Regional Commission, written commun., 2000). Residential, commercial, and other urban land uses more than tripled during the same period (Frick and others, 1998). The Chattahoochee River is the most utilized water resource in Georgia. The rapid growth of Metropolitan Atlanta and its location downstream of the headwaters of the drainage basin make the Chattahoochee River a vital resource for drinking-water supplies, recreational opportunities, and wastewater assimilation. In 1978, the U.S. Congress declared the natural, scenic, recreation, and other values of 48 miles of the Chattahoochee River from Buford Dam to Peachtree Creek to be of special national significance. To preserve this reach of the Chattahoochee River, the U.S. Congress created the Chattahoochee River National Recreational Area (CRNRA), which includes the Chattahoochee River downstream from Buford Dam to the mouth of Peachtree Creek and a series of park areas adjacent to the river in northern Metropolitan Atlanta Even with this protection, waters of the Chattahoochee River and many of its tributaries in Metropolitan Atlanta did not meet water-quality standards set for designated uses during 1994 and 1995 (fig. 1 and table 1). Much of the degradation of water quality has been associated with areas undergoing rapid urban growth and sprawling suburban development. The resulting conversion of mostly forested land to urban land has multiple adverse effects on water quality. Degradation of water quality may be caused by a number of factors including an increase in nutrient concentrations, sediment and sedimentbound contaminant concentrations (e.g., metals and pesticides) (Frick and others, 1998), and fecal-coliform bacteria concentrations (Center for Watershed

  4. Measuring the thermal conductivity of the GaN buffer layer in AlGaN/GaN HEMTs

    OpenAIRE

    Power, Maire; Pomeroy, James W; Otoki, Yohei; Tanaka, Takeshi; Wada, Jiro; Kuzuhara, Masaaki; Jantz, Wolfgang; Souzis, Andrew; Kuball, Martin H H

    2015-01-01

    The thermal conductivity of the GaN buffer layer in AlGaN/GaN devices can be determined by measuring the vertical temperature gradient through this layer. In this work, diamond micro-thermometers and standard micro-Raman thermography were used to determine the surface and volumetric depth average temperature, respectively, of the carbon-doped GaN buffer layer in AlGaN/GaN transistors. By comparing measured temperatures with finite element thermal simulation, a thermal conductivity of 200 ± 20...

  5. Projecting Future Urbanization with Prescott College's Spatial Growth Model to Promote Environmental Sustainability and Smart Growth, A Case Study in Atlanta, Georgia

    Science.gov (United States)

    Estes, Maurice G., Jr.; Crosson, William; Limaye, Ashutosh; Johnson, Hoyt; Quattrochi, Dale; Lapenta, William; Khan, Maudood

    2006-01-01

    Planning is an integral element of good management and necessary to anticipate events not merely respond to them. Projecting the quantity and spatial distribution of urban growth is essential to effectively plan for the delivery of city services and to evaluate potential environmental impacts. The major drivers of growth in large urban areas are increasing population, employment opportunities, and quality of life attractors such as a favorable climate and recreation opportunities. The spatial distribution of urban growth is dictated by the amount and location of developable land, topography, energy and water resources, transportation network, climate change, and the existing land use configuration. The Atlanta region is growing very rapidly both in population and the consumption of forestland or low-density residential development. Air pollution and water availability are significant ongoing environmental issues. The Prescott Spatial Growth Model (SGM) was used to make growth projections for the metropolitan Atlanta region to 2010,2020 and 2030 and results used for environmental assessment in both business as usual and smart growth scenarios. The Prescott SGM is a tool that uses an ESRI ArcView extension and can be applied at the parcel level or more coarse spatial scales and can accommodate a wide range of user inputs to develop any number of growth rules each of which can be weighted depending on growth assumptions. These projections were used in conjunction with meteorological and air quality models to evaluate future environmental impacts. This presentation will focus on the application of the SGM to the 13-County Atlanta Regional Commission planning jurisdiction as a case study. The SGM will be described, including how rule sets are developed and the decision process for allocation of future development to available land use categories. Data inputs required to effectively run the model will be discussed. Spatial growth projections for ten, twenty, and thirty

  6. Mitigating Structural Defects in Droop-Minimizing InGaN/GaN Quantum Well Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Zhibo; Chesin, Jordan; Singh, Akshay; Nelson, Erik; Wildeson, Isaac; Deb, Parijat; Armstrong, Andrew; Stach, Eric; Gradecak, Silvija

    2016-12-01

    Modern commercial InGaN/GaN blue LEDs continue to suffer from efficiency droop, a reduction in efficiency with increasing drive current. External quantum efficiency (EQE) typically peaks at low drive currents (< 10 A cm2) and drops monotonically at higher current densities, falling to <85% of the peak EQE at a drive current of 100 A cm2. Mitigating droop-related losses will yield tremendous gains in both luminous efficacy (lumens/W) and cost (lumens/$). Such improvements are critical for continued large-scale market penetration of LED technologies, particularly in high-power and high flux per unit area applications. However, device structures that reduce droop typically require higher indium content and are accompanied by a corresponding degradation in material quality which negates the droop improvement via enhanced Shockley-Read-Hall (SRH) recombination. In this work, we use advanced characterization techniques to identify and classify structural defects in InGaN/GaN quantum well (QW) heterostructures that share features with low-droop designs. Using aberration-corrected scanning transmission electron microscopy (Cs-STEM), we find the presence of severe well width fluctuations (WWFs) in a number of low droop device architectures. However, the presence of WWFs does not correlate strongly with external quantum efficiency nor defect densities measured via deep level optical spectroscopy (DLOS). Hence, performance losses in the heterostructures of interest are likely dominated by nanoscale point or interfacial defects rather than large-scale extended defects.

  7. 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

  8. Comparison Between Revised Atlanta Classification and Determinant-Based Classification for Acute Pancreatitis in Intensive Care Medicine. Why Do Not Use a Modified Determinant-Based Classification?

    Science.gov (United States)

    Zubia-Olaskoaga, Felix; Maraví-Poma, Enrique; Urreta-Barallobre, Iratxe; Ramírez-Puerta, María-Rosario; Mourelo-Fariña, Mónica; Marcos-Neira, María-Pilar

    2016-05-01

    To compare the classification performance of the Revised Atlanta Classification, the Determinant-Based Classification, and a new modified Determinant-Based Classification according to observed mortality and morbidity. A prospective multicenter observational study conducted in 1-year period. Forty-six international ICUs (Epidemiology of Acute Pancreatitis in Intensive Care Medicine study). Admitted to an ICU with acute pancreatitis and at least one organ failure. Modified Determinant-Based Classification included four categories: In group 1, patients with transient organ failure and without local complications; in group 2, patients with transient organ failure and local complications; in group 3, patients with persistent organ failure and without local complications; and in group 4, patients with persistent organ failure and local complications. A total of 374 patients were included (mortality rate of 28.9%). When modified Determinant-Based Classification was applied, patients in group 1 presented low mortality (2.26%) and morbidity (5.38%), patients in group 2 presented low mortality (6.67%) and high morbidity (60.71%), patients in group 3 presented high mortality (41.46%) and low morbidity (8.33%), and patients in group 4 presented high mortality (59.09%) and morbidity (88.89%). The area under the receiver operator characteristics curve of modified Determinant-Based Classification for mortality was 0.81 (95% CI, 0.77-0.85), with significant differences in comparison to Revised Atlanta Classification (0.77; 95% CI, 0.73-0.81; p Determinant-Based Classification (0.77; 95% CI, 0.72-0.81; p Determinant-Based Classification was 0.80 (95% CI, 0.73-0.86), with significant differences in comparison to Revised Atlanta Classification (0.63, 95% CI, 0.57-0.70; p Determinant-Based Classification (0.81, 95% CI, 0.74-0.88; nonsignificant). Modified Determinant-Based Classification identified four groups with different clinical presentation in patients with acute pancreatitis in

  9. Modeling on oxide dependent 2DEG sheet charge density and threshold voltage in AlGaN/GaN MOSHEMT

    Science.gov (United States)

    Panda, J.; Jena, K.; Swain, R.; Lenka, T. R.

    2016-04-01

    We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas (2DEG) density and surface potential for AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMT). The developed model includes important parameters like polarization charge density at oxide/AlGaN and AlGaN/GaN interfaces, interfacial defect oxide charges and donor charges at the surface of the AlGaN barrier. The effects of two different gate oxides (Al2O3 and HfO2) are compared for the performance evaluation of the proposed MOSHEMT. The MOSHEMTs with Al2O3 dielectric have an advantage of significant increase in 2DEG up to 1.2 × 1013 cm-2 with an increase in oxide thickness up to 10 nm as compared to HfO2 dielectric MOSHEMT. The surface potential for HfO2 based device decreases from 2 to -1.6 eV within 10 nm of oxide thickness whereas for the Al2O3 based device a sharp transition of surface potential occurs from 2.8 to -8.3 eV. The variation in oxide thickness and gate metal work function of the proposed MOSHEMT shifts the threshold voltage from negative to positive realizing the enhanced mode operation. Further to validate the model, the device is simulated in Silvaco Technology Computer Aided Design (TCAD) showing good agreement with the proposed model results. The accuracy of the developed calculations of the proposed model can be used to develop a complete physics based 2DEG sheet charge density and threshold voltage model for GaN MOSHEMT devices for performance analysis.

  10. Rentgenovskaja diagnostika psevdomorfnoj AlGaAs/InGaAs/GaAs – kompozicii

    Czech Academy of Sciences Publication Activity Database

    Subbotin, I. A.; Čujev, M. A.; Pašajev, E. M.; Imamov, R. M.; Galiev, G. B.; Tichomirov, S. A.; Kacerovský, Pavel

    2007-01-01

    Roč. 52, č. 4 (2007), s. 638-644 ISSN 0023-4761 R&D Projects: GA ČR GA202/06/1315 Grant - others:RFFI(RU) 05-02-17585; NŠ(RU) 5133.2006.2 Institutional research plan: CEZ:AV0Z20670512 Source of funding: O - operačné programy ; O - operačné programy Keywords : diffraction * semiconductor thin films * X-ray spetrometers Subject RIV: BM - Solid Matter Physics ; Magnetism

  11. Coulomb excitation of 73Ga

    CERN Document Server

    Diriken, J; Balabanski, D; Blasi, N; Blazhev, A; Bree, N; Cederkäll, J; Cocolios, T E; Davinson, T; Eberth, J; Ekström, A; Fedorov, D V; Fedosseev, V N; Fraille, L M; Franchoo, S; Georgiev, G; Gladnishki, K; Huyse, M; Ivanov, O V; Ivanov, V S; Iwanicki, V; Jolie, J; Konstantinopoulos, T; Kröll, Th; Krücken, R; Köster, U; Lagoyannis, A; Bianco, G Lo; Maierbeck, P; March, B A; Napiarkowski, P; Patronis, N; Pauwels, D; Reiter, P; Seliverstov, M; Sletten, G; Van de Walle, J; Van Duppen, P; Voulot, D; Walters, W B; Warr, N; Wenander, F; Wrzosek, K

    2010-01-01

    The B(E2; Ii ! If ) values for transitions in 71Ga and 73Ga were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL-detector array and B(E2; Ii->If ) values were obtained from the yields normalized to the known strength of the 2+ -> 0+ transition in the 120Sn target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity towards lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes which indicated a structural change in this isotopical chain between N = 40 and N = 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2- spin and parity for the ground state, the extracted results revealed evidence for a 1/2-; 3/2- doublet near the ground state in 73 31Ga...

  12. High quantum efficiency ultraviolet/blue AlGaN /InGaN photocathodes grown by molecular-beam epitaxy

    Science.gov (United States)

    Leopold, D. J.; Buckley, J. H.; Rebillot, P.

    2005-08-01

    Enormous technological breakthroughs have been made in optoelectronic devices through the use of advanced heteroepitaxial-semiconductor crystal-growth techniques. This technology is being extended toward enhanced ultraviolet/blue single-photon detection through the design and fabrication of atomically tailored heteroepitaxial GaAlN /GaInN photocathode device structures. The AlGaN /InGaN system is ideal because the band gap can be tailored over an energy range from 0.8 to 6.2 eV and epitaxial thin-film layers can be grown directly on optically transparent sapphire substrates. Although a single p-type GaN layer activated with cesium can produce reasonably high quantum efficiency in the ultraviolet wave band, a more complex design is necessary to achieve high levels extending into the blue region. In the present work, band-gap engineering concepts have been utilized to design heterostructure photocathodes. The increased level of sophistication offered by this approach has been exploited in an attempt to precisely control photoelectron transport to the photocathode surface. Thin heterostructure layers designed for transmission-mode detection were fabricated by molecular-beam epitaxy. A quantum efficiency of 40% at 250 nm was achieved using a thin, compositionally graded GaN /InGaN layer, epitaxially grown on a sapphire substrate. Further improvements are anticipated through continued optimization, defect reduction, and more complex photocathode designs.

  13. InGaAs focal plane array developments and perspectives

    Science.gov (United States)

    Rouvié, A.; Coussement, J.; Huet, O.; Truffer, J. P.; Pozzi, M.; Oubensaid, E. H.; Hamard, S.; Chaffraix, V.; Costard, E.

    2015-05-01

    SWIR spectral band is an attractive domain thanks to its intrinsic properties. Close to visible wavelengths, SWIR images interpretation is made easier for field actors. Besides complementary information can be extracted from SWIR band and bring significant added value in several fields of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). Among the various new technologies able to detect SWIR wavelengths, InGaAs appears as a key technology. Initially developed for optical telecommunications, this material guaranties performances, stability and reliability and is compatible with attractive production capacity. Thanks to high quality material, very low dark current levels can be achieved at ambient temperature. Then uncooled operation can be set up, allowing compact and low power systems. Since the recent transfer of InGaAs imaging activities from III-Vlab, Sofradir provides a framework for the production activity with the manufacturing of high performances products: CACTUS320 SW. The developments towards VGA format with 15μm pixel pitch, lead today to the industrialization of a new product: SNAKE. On one side, the InGaAs detection array presents high performances in terms of dark current and quantum efficiency. On the other side, the low noise ROIC has different additional functionalities. Then this 640x512 @ 15μm sensor appears as well suited to answer the needs of a wide range of applications. In this paper, we will present the Sofradir InGaAs technology, the performances of our last product SNAKE and the perspectives of InGaAs new developments.

  14. 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.

  15. Alternating-Current InGaN/GaN Tunnel Junction Nanowire White-Light Emitting Diodes.

    Science.gov (United States)

    Sadaf, S M; Ra, Y-H; Nguyen, H P T; Djavid, M; Mi, Z

    2015-10-14

    The current LED lighting technology relies on the use of a driver to convert alternating current (AC) to low-voltage direct current (DC) power, a resistive p-GaN contact layer to inject positive charge carriers (holes) for blue light emission, and rare-earth doped phosphors to down-convert blue photons into green/red light, which have been identified as some of the major factors limiting the device efficiency, light quality, and cost. Here, we show that multiple-active region phosphor-free InGaN nanowire white LEDs connected through a polarization engineered tunnel junction can fundamentally address the afore-described challenges. Such a p-GaN contact-free LED offers the benefit of carrier regeneration, leading to enhanced light intensity and reduced efficiency droop. Moreover, through the monolithic integration of p-GaN up and p-GaN down nanowire LED structures on the same substrate, we have demonstrated, for the first time, AC operated LEDs on a Si platform, which can operate efficiently in both polarities (positive and negative) of applied voltage.

  16. Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

    Science.gov (United States)

    Vlasov, A. S.; Khvostikov, V. P.; Karlina, L. B.; Sorokina, S. V.; Potapovich, N. S.; Shvarts, M. Z.; Timoshina, N. Kh.; Lantratov, V. M.; Mintairov, S. A.; Kalyuzhnyi, N. A.; Marukhina, E. P.; Andreev, V. M.

    2013-07-01

    A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5-50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio K c = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400-800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.

  17. Phase equilibria in Sm-Ga-S ternary system according to SmGa2-GaS, SmGa2-SmS, Sm3S4-Ga2S3, SmS-GaS, Sm-GaS cross sections

    International Nuclear Information System (INIS)

    Alieva, O.A.; Aliev, O.M.; Ehjnullaev, A.V.

    1993-01-01

    Phase equilibria in ternary system Sm-Ga-S over cross sections SmGa 2 -GaS, SmGa 2 -SmS, SmS-GaS, Sm 3 S 4 -Ga 2 S 3 , Sm-GaS have been studied for the first time using the methods of physicochemical analysis, their T-x projections were plotted. The cross sections SmGa 2 -GaS, SmGa 2 -SmS, Sm 3 S 4 -Ga 2 S 3 and SmS-GaS are quasibinary, while Sm-GaS is nonquasibinary one. Formation of two ternary compounds of the composition Sm 4 GaS 5 and Sm 5 Ga 2 S 5 was ascertained by peritectic reactions

  18. Improvement of breakdown characteristics of an AlGaN/GaN HEMT with a U-type gate foot for millimeter-wave power application

    International Nuclear Information System (INIS)

    Kong Xin; Wei Ke; Liu Guo-Guo; Liu Xin-Yu

    2012-01-01

    In this study, the physics-based device simulation tool Silvaco ATLAS is used to characterize the electrical properties of an AlGaN/GaN high electron mobility transistor (HEMT) with a U-type gate foot. The U-gate AlGaN/GaN HEMT mainly features a gradually changed sidewall angle, which effectively mitigates the electric field in the channel, thus obtaining enhanced off-state breakdown characteristics. At the same time, only a small additional gate capacitance and decreased gate resistance ensure excellent RF characteristics for the U-gate device. U-gate AlGaN/GaN HEMTs are feasible through adjusting the etching conditions of an inductively coupled plasma system, without introducing any extra process steps. The simulation results are confirmed by experimental measurements. These features indicate that U-gate AlGaN/GaN HEMTs might be promising candidates for use in millimeter-wave power applications. (interdisciplinary physics and related areas of science and technology)

  19. GaAs, AlGaAs and InGaP Tunnel Junctions for Multi-Junction Solar Cells Under Concentration: Resistance Study

    International Nuclear Information System (INIS)

    Wheeldon, Jeffrey F.; Valdivia, Christopher E.; Walker, Alex; Kolhatkar, Gitanja; Hall, Trevor J.; Hinzer, Karin; Masson, Denis; Riel, Bruno; Fafard, Simon; Jaouad, Abdelatif; Turala, Artur; Ares, Richard; Aimez, Vincent

    2010-01-01

    The following four TJ designs, AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs are studied to determine minimum doping concentration to achieve a resistance of -4 ω·cm 2 and a peak tunneling current suitable for MJ solar cells up to 1500-suns concentration (operating current of 21 A/cm 2 ). Experimentally calibrated numerical models are used to determine how the resistance changes as a function of doping concentration. The AlGaAs/GaAs TJ design is determined to require the least doping concentration to achieve the specified resistance and peak tunneling current, followed by the GaAs/GaAs, and AlGaAs/AlGaAs TJ designs. The AlGaAs/InGaP TJ design can only achieve resistances >5x10 -4 ωcm 2 .

  20. Dose rate hardening of As Ga components by buffer layers with hetero structure Ga As/Ga Al As

    International Nuclear Information System (INIS)

    Dupont-Nivet, E.; Coic, Y.M.; Frijlink, P.; Nicolas, J.L.

    1989-01-01

    Radiation resistance of gallium arsenide components is improved by incorporation between the substrate and the active layer a potential barrier with GaAlAs which has a greater forbidden band than GaAs [fr

  1. 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.

  2. 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

  3. 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.

  4. High performance resonant tunnelling structures on GaAs substrates

    Science.gov (United States)

    Riechert, H.; Bernklau, D.; Reithmaier, J.-P.; Schnell, R. D.

    1990-03-01

    GaAs-based resonant tunneling structures of high quality were grown by molecular beam epitaxy. Room temperature peak-to-valley ratios of 4.8 for a GaAs/AlGaAs double barrier quantum well, 4.1 for GaAs/AlGaAs with InGaAs quantum well and 5.9 for GaAs/AlGaAs with adjacent InGaAs 'prewell' were obtained, in connection with reasonable peak current densities.

  5. Improvement of electrostatic discharge characteristics of InGaN/GaN MQWs light-emitting diodes by inserting an n+-InGaN electron injection layer and a p-InGaN/GaN hole injection layer

    International Nuclear Information System (INIS)

    Jia, Chuanyu; Zhong, Cantao; Yu, Tongjun; Wang, Zhe; Tong, Yuzhen; Zhang, Guoyi

    2012-01-01

    To improve the electrostatic discharge properties of InGaN/GaN LEDs, an n + -InGaN electron injection layer and a p-InGaN/GaN hole injection layer were inserted beneath and above the InGaN/GaN MQWs. The influences of activated donor concentration in n + -InGaN and acceptor concentration in p-InGaN/GaN and on the depletion width and the internal capacitance of GaN-based n + -P LED have been investigated. Our research results indicated that the capacitance of GaN-based n + -P LED is mainly determined by the depletion width which is dependent on the activated acceptor concentration N A in the p-InGaN/GaN hole injection layer. The relationship between the internal capacitance of InGaN–LEDs and the electrostatic discharge (ESD) properties was also investigated. It was found that the LEDs with large internal capacitance were more resistant to external ESD impulses. With optimized LED structures with n + -InGaN layer and a p-InGaN/GaN SLs, the HBM-ESD pass yield at −1500 V reached 95%, much higher than the value of 15% in reference samples without inserting layers above. (paper)

  6. 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.

  7. 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

  8. Graphene-GaN Schottky Photodiodes

    Data.gov (United States)

    National Aeronautics and Space Administration — Graphene-GaN Schottky Photodiodes is the development of the world's first graphene-based GaN Schottky device that has the potential to achieve a much greater total...

  9. Exposición «espacios e ilusiones» en el museo superior de arte, Atlanta - EE. UU.

    Directory of Open Access Journals (Sweden)

    Scogin, Mack

    1980-10-01

    Full Text Available This Exhibit, carried out under the auspices of several cultural organizations of the city of Atlanta, intends to offer a distorted vision of space at the same time as it is real. It has been designed as a labyrinth of rooms in which various special effects are set up, such as: mirrors, lights, sound, shadow, movements, etc. Among the different rooms, the following stand out: the illuminated room, with shadows that appear and disappear on its walls; the perspective room, where the length of the vestibule can be easily mistaken; the nature room, where different animal species are seen by T.V., etc.

    Esta Exposición, realizada bajo los auspicios de varias organizaciones culturales de la ciudad de Atlanta, pretende ofrecer una visión distorsionada del espacio a la vez que real. Se ha concebido como un laberinto de salas en las que existen diversos efectos especiales tales como: espejos, luces, sonidos, sombras, movimientos, etc. Entre las diversas salas destacan: la Iluminada, en cuyos muros aparecen y desaparecen sombras; la de perspectiva, en la que se equivoca fácilmente la longitud del vestíbulo; la de la naturaleza, en la que mediante T.V. se ven distintas especies de animales; etc.

  10. GaN nanowire Schottky barrier diodes

    OpenAIRE

    Sabui, Gourab; Zubialevich, Vitaly Z.; White, Mary; Pampili, Pietro; Parbrook, Peter J.; McLaren, Mathew; Arredondo-Arechavala, Miryam; Shen, Z. John

    2017-01-01

    A new concept of vertical gallium nitride (GaN) Schottky barrier diode based on nanowire (NW) structures and the principle of dielectric REduced SURface Field (RESURF) is proposed in this paper. High-threading dislocation density in GaN epitaxy grown on foreign substrates has hindered the development and commercialization of vertical GaN power devices. The proposed NW structure, previously explored for LEDs offers an opportunity to reduce defect density and fabricate low cost vertical GaN pow...

  11. Monolithic GaAs surface acoustic wave chemical microsensor array

    Energy Technology Data Exchange (ETDEWEB)

    HIETALA,VINCENT M.; CASALNUOVO,STEPHEN A.; HELLER,EDWIN J.; WENDT,JOEL R.; FRYE-MASON,GREGORY CHARLES; BACA,ALBERT G.

    2000-03-09

    A four-channel surface acoustic wave (SAW) chemical sensor array with associated RF electronics is monolithically integrated onto one GaAs IC. The sensor operates at 690 MHz from an on-chip SAW based oscillator and provides simple DC voltage outputs by using integrated phase detectors. This sensor array represents a significant advance in microsensor technology offering miniaturization, increased chemical selectivity, simplified system assembly, improved sensitivity, and inherent temperature compensation.

  12. 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

  13. 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

  14. Adaptive and active materials: selected papers from the ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 12) (Stone Mountain, GA, USA, 19-21 September 2012)

    Science.gov (United States)

    Seelecke, Stefan; Erturk, Alper; Ounaies, Zoubeida; Naguib, Hani; Huber, John; Turner, Travis; Anderson, Iain; Philen, Michael; Baba Sundaresan, Vishnu

    2013-09-01

    The fifth annual meeting of the ASME/AIAA Smart Materials, Adaptive Structures and Intelligent Systems Conference (SMASIS) was held in beautiful Stone Mountain near Atlanta, GA. It is the conference's objective to provide an up-to-date overview of research trends in the entire field of smart materials systems. This was reflected in keynote speeches by Professor Eduard Arzt (Institute of New Materials and Saarland University, Saarbrücken, Germany) on 'Micro-patterned artificial 'Gecko' surfaces: a path to switchable adhesive function', by Professor Ray H Baughman (The Alan G MacDiarmid NanoTech Institute, University of Texas at Dallas) on 'The diverse and growing family of carbon nanotube and related artificial muscles', and by Professor Richard James (University of Minnesota) on 'The direct conversion of heat to electricity using multiferroic materials with phase transformations'. SMASIS 2012 was divided into eight symposia which span basic research, applied technological design and development, and industrial and governmental integrated system and application demonstrations. • SYMP 1. Development and characterization of multifunctional materials. • SYMP 2. Mechanics and behavior of active materials. • SYMP 3. Modeling, simulation and control of adaptive systems. • SYMP 4. Integrated system design and implementation. • SYMP 5. Structural health monitoring/NDE. • SYMP 6. Bio-inspired materials and systems. • SYMP 7. Energy harvesting. • SYMP 8. Structural and materials logic. This year we were particularly excited to introduce a new symposium on energy harvesting, which has quickly matured from a special track in previous years to an independent symposium for the first time. The subject cuts across fields by studying different materials, ranging from piezoelectrics to electroactive polymers, as well as by emphasizing different energy sources from wind to waves and ambient vibrations. Modeling, experimental studies, and technology applications all

  15. Characteristics of GaN/InGaN Double-Heterostructure Photovoltaic Cells

    Directory of Open Access Journals (Sweden)

    Ming-Hsien Wu

    2012-01-01

    Full Text Available The p-GaN/i-InxGa1−xN/n-GaN double-heterostructure photovoltaic (PV cells have been fabricated and the theoretical photovoltaic properties were also calculated in this work. From theoretical simulation, higher efficiency can be obtained in GaN/InGaN double-heterostructure photovoltaic cells with higher In composition in i-InGaN intrinsic layer. GaN/InGaN double-heterostructure photovoltaic cells with In compositions of 10%, 12%, and 14% were fabricated and characterized for demonstrating with the simulated results. The corresponding photoelectrical conversion efficiency of fabricated GaN/InGaN photovoltaic cells with In compositions of 10%, 12%, and 14% is 0.51%, 0.53%, and 0.32% under standard AM 1.5G measurement condition, respectively. GaN/InGaN photovoltaic cells with In composition of 10% showed high open-circuit voltage (Voc of 2.07 V and fill factor (F.F. of 80.67%. The decrease of Voc and FF was observed as In composition increasing from 10% to 14%. For comparing with the fabricated GaN/InGaN photovoltaic cells, theoretical conversion efficiency of GaN/InGaN photovoltaic cells with In compositions of 10%, 12%, and 14%, is 1.80%, 2.04%, and 2.27%, respectively. The difference of GaN/InGaN photovoltaic properties between theoretical simulation and experimental measurement could be attributed to the inferior quality of InGaN epilayer and GaN/InGaN interface generated as the increase of In composition.

  16. Recessed insulator and barrier AlGaN/GaN HEMT

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 88; Issue 4. Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure for improving DC and RF characteristics ... Keywords. AlGaN/GaN high electron mobility transistor; breakdown voltage; output power density; short channel effect; gate-drain capacitance ...

  17. Luminescence of the InGaN/GaN Blue Light-Emitting Diodes

    Science.gov (United States)

    2000-07-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO 11314 TITLE: Luminescence of the InGaN/GaN Blue Light -Emitting Diodes...ADP011332 UNCLASSIFIED Luminescence of the InGaN/GaN blue light -emitting diodes J. K. Sheu a), T. W. Yeh and G. C. Chi Optical Sciences Center, National

  18. Charge transport study and spectral response of GaSb/GaAs heterojunctions prepared by MOVPE

    Czech Academy of Sciences Publication Activity Database

    Toušková, J.; Kindl, Dobroslav; Samokhin, Jevgen; Toušek, J.; Hulicius, Eduard; Pangrác, Jiří; Šimeček, Tomislav; Výborný, Zdeněk

    2003-01-01

    Roč. 76, - (2003), s. 135-145 ISSN 0927-0248 R&D Projects: GA ČR GA102/99/0414 Institutional research plan: CEZ:AV0Z1010914 Keywords : thermophotovoltaics * GaSb/GaAs heterojunction * charge transport * band diagram Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.188, year: 2003

  19. 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.

  20. Growth and Optimization of 2 Micrometers InGaSb/AlGaSb Quantum-Well-Based VECSELs on GaAs/AlGaAs DBRs

    Science.gov (United States)

    2013-08-01

    active region consists of nine In0.2Ga0.8Sb QWs separated by pump absorbing Al0.25Ga0.75 Sb barriers. An AlSb confinement layer on each side of the...by pump absorbing Al0.25Ga0.75Sb barriers and AlSb top/bottom clad. The key feature of the antimonide VECSEL based on the GaAs/AlGaAs DBRs is the...also enhanced by the AlSb carrier con- finement layers. However, the “ABC” empirical model is not adequate to model the carrier losses at high carrier

  1. Insulated gate and surface passivation structures for GaN-based power transistors

    Science.gov (United States)

    Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu

    2016-10-01

    structures as well as different characterization methods, including our own photo-assisted C-V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology.

  2. Insulated gate and surface passivation structures for GaN-based power transistors

    International Nuclear Information System (INIS)

    Yatabe, Zenji; Asubar, Joel T; Hashizume, Tamotsu

    2016-01-01

    variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C – V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology. (topical review)

  3. A review of Ga2O3 materials, processing, and devices

    Science.gov (United States)

    Pearton, S. J.; Yang, Jiancheng; Cary, Patrick H.; Ren, F.; Kim, Jihyun; Tadjer, Marko J.; Mastro, Michael A.

    2018-03-01

    Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (ɛ) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

  4. Electrodynamic Tethers and E-Sails as Active Experiment Testbeds and Technologies in Space

    Science.gov (United States)

    Gilchrist, B. E.; Wiegmann, B.; Johnson, L.; Bilen, S. G.; Habash Krause, L.; Miars, G.; Leon, O.

    2017-12-01

    of electric sail propulsion systems," 53rd AIAA/SAE/ASEE Joint Propulsion Conf., 10-12 July 2017, Atlanta, GA.

  5. Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan

    2011-07-14

    The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.

  6. 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).

  7. Characterization of NIR InGaAs imager arrays for the JDEM SNAPmission concept

    Energy Technology Data Exchange (ETDEWEB)

    Seshadri, S.; Cole, M.D.; Hancock, B.; Ringold, P.; Wrigley, C.; Bonati, M.; Brown, M.G.; Schubnell, M.; Rahmer, G.; Guzman, D.; Figer,D.; Tarle, G.; Smith, R.M.; Bebek, C.

    2006-05-23

    We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP. However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future astronomy applications.

  8. 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.

  9. GaAsP/InGaP heterojunction bipolar transistors grown by MOCVD

    Science.gov (United States)

    Heidelberger, Christopher; Fitzgerald, Eugene A.

    2017-01-01

    Heterojunction bipolar transistors with GaAsxP1-x bases and collectors and InyGa1-yP emitters were grown on GaAs substrates via metalorganic chemical vapor deposition, fabricated using conventional techniques, and electrically tested. Four different GaAsxP1-x compositions were used, ranging from x = 0.825 to x = 1 (GaAs), while the InyGa1-yP composition was adjusted to remain lattice-matched to the GaAsP. DC gain close to or exceeding 100 is measured for 60 μm diameter devices of all compositions. Physical mechanisms governing base current and therefore current gain are investigated. The collector current is determined not to be affected by the barrier caused by the conduction band offset between the InGaP emitter and GaAsP base. While the collector current for the GaAs/InGaP devices is well-predicted by diffusion of electrons across the quasi-neutral base, the collector current of the GaAsP/InGaP devices exceeds this estimate by an order of magnitude. This results in higher transconductance for GaAsP/InGaP than would be estimated from known material properties.

  10. 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 63-80 at.% 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.% 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. (Auth.)

  11. Magnetic coupling in Fe/(Ga,Mn)As based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sperl, M.; Soda, M.; Eigenmann, F.; Utz, M.; Woltersdorf, G.; Bougeard, D.; Back, C.H. [Institut fuer Experimentelle Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Torelli, P.; Panaccione, G. [Laboratorio Nazionale TASC, INFM-CNR, in Area Science Park, S.S. 14, Km 163.5, I-34012 Trieste (Italy); Polesya, S. [Department of Chemistry, Ludwig-Maximilians University Munich (Germany)

    2011-07-01

    (Ga,Mn)As is one of the most promising diluted magnetic semiconductors (DMS) for spintronics due to the compatibility with the GaAs MBE technology. Despite the promising features (Ga,Mn)As has a Curie temperature well below room temperature limiting its possible applications. One potential direction to tailor novel properties of DMS thus making integration in real devices feasible is to exploit interface effects in highly controlled heterostructures (HS). Following this route FM behaviour of Mn at room temperature in both epitaxial and non-epitaxial Fe/(Ga,Mn)As interfaces has been demonstrated. We report results obtained with Synchrotron Radiation techniques, where we were able to monitor the evolution of the magnetic coupling between Fe and Mn as a function of Mn doping, temperature and thickness. In particular, XMCD experiments show a peculiar thickness dependence of the room temperature magnetic coupling between Fe and Mn, namely a switching from antiparallel to parallel, thus opening the possibility of controlling the magnetization state of the interface.

  12. Growth of GaN on ZnO for solid state lighting applications

    Science.gov (United States)

    Li, Nola; Park, Eun-Hyun; Huang, Yong; Wang, Shenjie; Valencia, Adriana; Nemeth, Bill; Nause, Jeff; Ferguson, Ian

    2006-08-01

    In this work, ZnO has been investigated as a substrate technology for GaN-based devices due to its close lattice match, stacking order match, and similar thermal expansion coefficient. Since MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. Our aim is to grow low defect density GaN for efficient phosphor free white emitters. However, there are a number of issues that need to be addressed for the MOCVD growth of GaN on ZnO. The thermal stability of the ZnO substrate, out-diffusion of Zn from the ZnO into the GaN, and H II back etching into the substrate can cause growth of poor quality GaN. Cracks and pinholes were seen in the epilayers, leading to the epi-layer peeling off in some instances. These issues were addressed by the use of H II free growth and multiple buffer layers to remove the cracking and reduce the pinholes allowing for a high quality GaN growth on ZnO substrate.

  13. Hybrid laser technology for creation of doped biomedical layers

    Czech Academy of Sciences Publication Activity Database

    Jelínek, Miroslav; Bačáková, Lucie; Remsa, Jan; Kocourek, Tomáš; Mikšovský, Jan; Písařík, Petr; Vandrovcová, Marta; Filová, Elena; Kubinová, Šárka

    2016-01-01

    Roč. 4, Jan (2016), s. 98-104 ISSN 2327-6045 R&D Projects: GA ČR(CZ) GA15-05864S; GA ČR(CZ) GA15-01558S Institutional support: RVO:68378271 ; RVO:67985823 ; RVO:68378041 Keywords : hybrid laser technology * biomaterials * thin Films * doped Layers * DLC Subject RIV: BM - Solid Matter Physics ; Magnetism; JJ - Other Materials (FGU-C)

  14. Controllable process of nanostructured GaN by maskless inductively coupled plasma (ICP) etching

    International Nuclear Information System (INIS)

    Zhao, Yanfei; Wang, Hu; Shen, Yang; Huang, Zengli; Zhang, Jian; Dingsun, An; Zhang, Wei; Li, Jiadong

    2017-01-01

    This work improved the anisotropically etching profile of GaN with Cl 2 ICP by adjusting etching pressure and gas flow. High etching rate is achieved by lowering pressure and gas flow instead of increasing etching power. High etching power is unfavorable because it may cause physical damages on the surface. In addition, it is noticed that the material of the carrier, used for holding samples during etching, has significant effects on the morphology and profile of the etched GaN surface. A smooth and large-area GaN surface was achieved by proper ICP etching with a big piece of Si carrier; whereas, with other kinds of carriers, various nano-structures were formed on the GaN surfaces after etching. In fact, it is the etching resistance of carrier materials that impacts the surface profile of etched GaN. Needle-like and grass-like nanostructures on etched GaN surfaces were observed with Al and sapphire carriers, of which the process is very similar to RIE-grass or black-silicon technology. This controllable maskless dry-etching process for the GaN nanostructured surface may show more potential applications in GaN devices. (paper)

  15. Controllable process of nanostructured GaN by maskless inductively coupled plasma (ICP) etching

    Science.gov (United States)

    Zhao, Yanfei; Wang, Hu; Zhang, Wei; Li, Jiadong; Shen, Yang; Huang, Zengli; Zhang, Jian; Dingsun, An

    2017-11-01

    This work improved the anisotropically etching profile of GaN with Cl2 ICP by adjusting etching pressure and gas flow. High etching rate is achieved by lowering pressure and gas flow instead of increasing etching power. High etching power is unfavorable because it may cause physical damages on the surface. In addition, it is noticed that the material of the carrier, used for holding samples during etching, has significant effects on the morphology and profile of the etched GaN surface. A smooth and large-area GaN surface was achieved by proper ICP etching with a big piece of Si carrier; whereas, with other kinds of carriers, various nano-structures were formed on the GaN surfaces after etching. In fact, it is the etching resistance of carrier materials that impacts the surface profile of etched GaN. Needle-like and grass-like nanostructures on etched GaN surfaces were observed with Al and sapphire carriers, of which the process is very similar to RIE-grass or black-silicon technology. This controllable maskless dry-etching process for the GaN nanostructured surface may show more potential applications in GaN devices.

  16. High Quantum Efficiency AlGaN/InGaN Photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Buckley, James H. [Washington Univ., St. Louis, MO (United States). Physics Dept.; Leopold, Daniel [Washington Univ., St. Louis, MO (United States). Physics Dept.

    2009-11-24

    High efficiency photon counting detectors in use today for high energy particle detection applications have a significant spectral mismatch with typical sources and have a number of practical problems compared with conventional bialkali photomultiplier tubes. Numerous high energy physics experiments that employ scintillation light detectors or Cherenkov detectors would benefit greatly from photomultipliers with higher quantum efficiencies. The need for extending the sensitivity of photon detectors to the blue and UV wavebands comes from the fact that both Cherenkov light and some scintillators have an emission spectrum which is peaked at short wavelengths. This research involves the development of high quantum efficiency, high gain, UV/blue photon counting detectors based on AlGaN/InGaN photocathode heterostructures grown by molecular beam epitaxy (MBE). The work could eventually lead to nearly ideal light detectors with a number of distinct advantages over existing technologies for numerous applications in high-energy physics and particle astrophysics. Potential advantages include much lower noise detection, better stability and radiation resistance than other cathode structures, very low radioactive background levels for deep underground experiments and high detection efficiency of individual UV-visible photons. We are also working on the development of photocathodes with intrinsic gain, initially improving the detection efficiency of hybrid semiconductor-vacuum tube devices, and eventually leading to an all-solid-state photomultiplier device.

  17. Lattice location of Mn in GaAs and GaN

    CERN Document Server

    De Coster, Arnaud; Vantomme, André; Temst, Kristiaan

    The field of dilute magnetic semiconductors (DMS) has seen a lot of development in the past decades, both from a fundamental interest in the link between magnetic and conducting properties and with an eye to potential applications in computer technology. While the presence of semiconducting properties and magnetism in a given material is not out of the ordinary, DMS materials stand out because the charge carriers actually mediate between magnetic moments in the lattice, causing the ferromagnetic ordering. These magnetic moments and charge carriers are supplied by transition-metal (TM) dopants in a classic semiconductor. The location where these dopants are incorporated will determine if they will act as either an acceptor or donor and how they will couple to other magnetic moments. Hence, in order to achieve a better understanding of DMS, accurate knowledge of the lattice location the TM takes up in the crystal is vital. In this thesis the lattice location of Mn in GaAs and GaN is studied, two model materials...

  18. Lattice location of Mn in GaAs and GaN

    CERN Document Server

    De Coster, Arnaud; Vantomme, André; Temst, Kristiaan

    The field of dilute magnetic semiconductors (DMS) has seen a lot of development in the past decades, both from a fundamental interest in the linkage of magnetic and conducting properties and with an eye to potential applications in computer technology. While the presence of semiconducting properties and magnetism in a given material is not out of the ordinary, DMS materials stand out because the charge carriers actually mediate between magnetic moments in the lattice, causing the ferromagnetic ordering. These magnetic moments and charge carriers are supplied by transition-metal (TM) dopants in a classic semiconductor. The location where these dopants are incorporated will determine if they will act as either an acceptor or donor and how they will couple to other magnetic moments. Hence, in order to achieve a better understanding of DMS, accurate knowledge of the lattice location the TM takes up in the crystal is vital. In this thesis the lattice location of Mn in GaAs and GaN is studied, two model materials f...

  19. The Effects of Interdot Spacing and Dot Size on the Performance of InGaAs/GaAs QDIBSC

    Directory of Open Access Journals (Sweden)

    Sayeda Anika Amin

    2017-01-01

    Full Text Available In0.53Ga0.47As/GaAs-based quantum dot intermediate band solar cells (QDIBSCs have been designed and optimized for the next generation photovoltaic technology. The wave behavior of charge carriers inside the dot and their barrier have been analyzed with different dot sizes and interdot spacing. The device characteristics such as short circuit current density, Jsc, open circuit voltage, Voc, and conversion efficiency, η, have been evaluated. Based on the behavior of electron wave function, it is found that varying the dot spacing leads to a change in the IB width and in the density of states, whereas varying the size of dots leads to a formation of a second IB. For a fixed dot spacing, two ranges of dot sizes vary the number of IBs in In0.53Ga0.47As/GaAs QDIBSC. Smaller dots of a size ranging from 2 nm to 5 nm form a single IB while larger dots of a size ranging from 6 nm to 9 nm can produce 2 IBs. The efficiency of 2 IBs close to 1 IB suggests that formation of multiple IBs can possibly enhance the device efficiency.

  20. GaN nanostructure-based light emitting diodes and semiconductor lasers.

    Science.gov (United States)

    Viswanath, Annamraju Kasi

    2014-02-01

    GaN and related materials have received a lot of attention because of their applications in a number of semiconductor devices such as LEDs, laser diodes, field effect transistors, photodetectors etc. An introduction to optical phenomena in semiconductors, light emission in p-n junctions, evolution of LED technology, bandgaps of various semiconductors that are suitable for the development of LEDs are discussed first. The detailed discussion on photoluminescence of GaN nanostructures is made, since this is crucial to develop optical devices. Fabrication technology of many nanostructures of GaN such as nanowires, nanorods, nanodots, nanoparticles, nanofilms and their luminescence properties are given. Then the optical processes including ultrafast phenomena, radiative, non-radiative recombination, quantum efficiency, lifetimes of excitons in InGaN quantum well are described. The LED structures based on InGaN that give various important colors of red, blue, green, and their design considerations to optimize the output were highlighted. The recent efforts in GaN technology are updated. Finally the present challenges and future directions in this field are also pointed out.

  1. Green light emission by InGaN/GaN multiple-quantum-well microdisks

    International Nuclear Information System (INIS)

    Hsu, Yu-Chi; Lo, Ikai; Shih, Cheng-Hung; Pang, Wen-Yuan; Hu, Chia-Hsuan; Wang, Ying-Chieh; Tsai, Cheng-Da; Chou, Mitch M. C.; Hsu, Gary Z. L.

    2014-01-01

    The high-quality In x Ga 1−x N/GaN multiple quantum wells were grown on GaN microdisks with γ-LiAlO 2 substrate by using low-temperature two-step technique of plasma-assisted molecular beam epitaxy. We demonstrated that the hexagonal GaN microdisk can be used as a strain-free substrate to grow the advanced In x Ga 1−x N/GaN quantum wells for the optoelectronic applications. We showed that the green light of 566-nm wavelength (2.192 eV) emitted from the In x Ga 1−x N/GaN quantum wells was tremendously enhanced in an order of amplitude higher than the UV light of 367-nm wavelength (3.383 eV) from GaN

  2. 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.

  3. Comparative study of GaN and GaAs photocathodes

    Science.gov (United States)

    Qiao, Jianliang; Chang, Benkang; Yang, Zhi; Tian, Si; Gao, Youtang

    2008-02-01

    Taking GaAs and GaN as representation, negative electron affinity (NEA) photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive long-wave threshold, great potential to extend the long-wave spectral response waveband. Therefore it plays more and more important effect in high performance image intensifiers and polarized electron sources. GaN NEA photocathode and GaAs NEA photocathode are very similar because they all belong to III-V compound. But, GaN photocathode and GaAs photocathode have many difference in such aspects as preparation process, activation manners, stability and application field etc. In this paper, using the multi-information measurement and evaluation system of photocathode, the preparation processes of native reflection-mode GaN photocathode and GaAs photocathode are studied. The different activation manners of GaN photocathode and GaAs photocathode are compared and analyzed. The spectral response and stability of the two kind of photocathode are compared also. The experiments indicate: the atomically clean degree of NEA photocathode surface and the structure of activation layer are the main factors that influence photocathode sensitivity and stability after activation. GaN photocathode and GaAs photocathode have good NEA property and large quantum yield. Compare with GaAs photocathode, GaN photocathode has high stability, and the decay of the quantum yield is comparatively slow.

  4. Wet etching of AlGaN/GaN photocathode grown by MOCVD

    Science.gov (United States)

    Hao, Guanghui; Chang, Benkang; Cheng, Hongchang

    2013-08-01

    The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). And one of two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, and the GaN thickness of them are 7nm and 2.5nm respectively. And etch speed of GaN are got in molten KOH at about 400°C. Then the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave. And the quantum efficiency decline with the GaN thickness decrease.

  5. 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.

  6. Studies of adsorber materials for preparing 68Ge/68Ga generators

    International Nuclear Information System (INIS)

    Brambilla, Tania de Paula

    2013-01-01

    The 68 Ga is a promising radionuclide for nuclear medicine, decaying by positron emission with an abundance of 89%, with physical half-life of 68 minutes, which is compatible with the pharmacokinetics of many biomolecules and low molecular weight substrates. Another important feature is its availability through a generator system, where the parent radionuclide, 68 Ge (t 1/2 = 270.95 days) is adsorbed on a column and the daughter, 68 Ga, is eluted in an ionic form 68Ga 3+ . The development of 68 Ge/ 68 Ga generators began in the 60s, but its clinical use began to be acceptable and relevant only recently. The method of separation of 68 Ge and 68 Ga most used is the ion-exchange chromatographic system, due to its practical operation, but other generator systems have been proposed, such as solvent extraction and evaporation technique. Currently, 68 Ge/ 68 Ga generators are commercially available using inorganic matrices columns prepared with TiO 2 or SnO 2 as well using organic resin. The efficiency of 68 Ga elution ranges from 70% to 80%, decreasing over time. The 68 Ge breakthrough varies from 10 -2 to10 -3 % or lower in a fresh generator, but there is an increase in the levels of contamination after long periods of use. Even with all the technological advances in the development of 68 Ge/ 68 Ga generators in the past decades, the 68 Ga eluted from commercial generators is not suitable for direct use in humans and some improvements in the systems need to be made to reduce the 68 Ge breakthrough and chemical impurities levels. The main objective of this work was to develop a 68 Ge/ 68 Ga generator system is which 68 Ga could be eluted with quality required for clinical use. The chemical behavior of Ge and Ga was evaluated on various inorganic adsorbents materials. Two types of 68 Ge/ 68 Ga generator systems were developed using TiO 2 as adsorbent material: elution system with manual pressure and vacuum controlled. The efficiencies of the generators were similar to

  7. GaN-on-Silicon - Present capabilities and future directions

    Science.gov (United States)

    Boles, Timothy

    2018-02-01

    Gallium Nitride, in the form of epitaxial HEMT transistors on various substrate materials, is the newest and most promising semiconductor technology for high performance devices in the RF, microwave, and mmW arenas. This is particularly true for GaN-on-Silicon based devices and MMIC's which enable both state-of-the-art high frequency functionality and the ability to scale production into large wafer diameter CMOS foundries. The design and development of GaN-on-Silicon structures and devices will be presented beginning with the basic material parameters, growth of the required epitaxial construction, and leading to the fundamental operational theory of high frequency, high power HEMTs. In this discussion comparisons will be made with alternative substrate materials with emphasis on contrasting the inherent advantages of a silicon based system. Theory of operation of microwave and mmW high power HEMT devices will be presented with special emphasis on fundamental limitations of device performance including inherent frequency limiting transit time analysis, required impedance transformations, internal and external parasitic reactance, thermal impedance optimization, and challenges improved by full integration into monolithic MMICs. Lastly, future directions for implementing GaN-on-Silicon into mainstream CMOS silicon semiconductor technologies will be discussed.

  8. InGaN High-Temperature Photovoltaic Cells

    Science.gov (United States)

    Starikov, David

    2015-01-01

    This Phase II project developed Indium-Gallium-Nitride (InGaN) photovoltaic cells for high-temperature and high-radiation environments. The project included theoretical and experimental refinement of device structures produced in Phase I as well as modeling and optimization of solar cell device processing. The devices have been tested under concentrated air mass zero (AM0) sunlight, at temperatures from 100 degC to 250 degC, and after exposure to ionizing radiation. The results are expected to further verify that InGaN can be used for high-temperature and high-radiation solar cells. The large commercial solar cell market could benefit from the hybridization of InGaN materials to existing solar cell technology, which would significantly increase cell efficiency without relying on highly toxic compounds. In addition, further development of this technology to even lower bandgap materials for space applications would extend lifetimes of satellite solar cell arrays due to increased radiation hardness. This could be of importance to the Departmentof Defense (DoD) and commercial satellite manufacturers.

  9. Spatial Growth Modeling and High Resolution Remote Sensing Data Coupled with Air Quality Modeling to Assess the Impact of Atlanta, Georgia on the Local and Regional Environment

    Science.gov (United States)

    Quattrochi, Dale A.; Estes, Maurice G., Jr.; Crosson, William; Johnson, Hoyt; Khan, Maudood

    2006-01-01

    The growth of cities, both in population and areal extent, appears as an inexorable process. Urbanization continues at a rapid rate, and it is estimated that by the year 2025, 60 percent of the world s population will live in cities. Urban expansion has profound impacts on a host of biophysical, environmental, and atmospheric processes within an urban ecosystems perspective. A reduction in air quality over cities is a major result of these impacts. Because of its complexity, the urban landscape is not adequately captured in air quality models such as the Community Multiscale Air Quality (CMAQ) model that is used to assess whether urban areas are in attainment of EPA air quality standards, primarily for ground level ozone. This inadequacy of the CMAQ model to sufficiently respond to the heterogeneous nature of the urban landscape can impact how well the model predicts ozone levels over metropolitan areas and ultimately, whether cities exceed EPA ozone air quality standards. We are exploring the utility of high-resolution remote sensing data and urban spatial growth modeling (SGM) projections as improved inputs to a meteorological/air quality modeling system focusing on the Atlanta, Georgia metropolitan area as a case study. These growth projections include business as usual and smart growth scenarios out to 2030. The growth projections illustrate the effects of employing urban heat island mitigation strategies, such as increasing tree canopy and albedo across the Atlanta metro area, which in turn, are used to model how air temperature can potentially be moderated as impacts on elevating ground-level ozone, as opposed to not utilizing heat island mitigation strategies. The National Land Cover Dataset at 30m resolution is being used as the land use/land cover input and aggregated to the 4km scale for the MM5 mesoscale meteorological model and the CMAQ modeling schemes. Use of these data has been found to better characterize low density/suburban development as compared

  10. Thirty-five years after Stonewall: an exploratory study of satisfaction with police among gay, lesbian, and bisexual persons at the 34th Annual Atlanta Pride Festival.

    Science.gov (United States)

    Gillespie, Wayne

    2008-01-01

    The gay rights movement began in the summer of 1969 when gay men rioted against police for raiding a bar known as the Stonewall Inn. In the succeeding 35 years, very little research has explored the relationship between police organizations and gay, lesbian, bisexual, and transgendered (GLBT) communities. The purpose of this study is to describe the attitudes that GLBT persons currently hold toward police. Subjects were sampled from the 34th Annual Atlanta Pride Festival and asked to complete a self-administered questionnaire. Of the 179 GLBT participants, the vast majority reported high satisfaction with community policing practices at this event. Moreover, age, household income, victimization, security presence, and identification with gay-themed media significantly predicted attitudes toward police.

  11. Remote Sensing and Spatial Growth Modeling Coupled with Air Quality Modeling to Assess the Impact of Atlanta, Georgia on the Local and Regional Environment

    Science.gov (United States)

    Quattrochi, Dale A.; Estes, Maurice G., Jr.; Crosson, William; Khan, Maudood

    2006-01-01

    The growth of cities, both in population and areal extent, appears as an inexorable process. Urbanization continues at a rapid rate, and it is estimated that by the year 2025, 80 percent of the world s population will live in cities. Directly aligned with the expansion of cities is urban sprawl. Urban expansion has profound impacts on a host of biophysical, environmental, and atmospheric processes. A reduction in air quality over cities is a major result of these impacts. Strategies that can be directly or indirectly implemented to help remediate air quality problems in cities and that can be accepted by political decision makers and the general public are now being explored to help bring down air pollutants and improve air quality. The urban landscape is inherently complex and this complexity is not adequately captured in air quality models, particularly the Community Multiscale Air Quality (CMAQ) model that is used to assess whether urban areas are in attainment of EPA air quality standards, primarily for ground level ozone. This inadequacy of the CMAQ model to sufficiently respond to the heterogeneous nature of the urban landscape can impact how well the model predicts ozone pollutant levels over metropolitan areas and ultimately, whether cities exceed EPA ozone air quality standards. We are exploring the utility of high-resolution remote sensing data and urban spatial growth modeling (SGM) projections as improved inputs to the meteorology component of the CMAQ model focusing on the Atlanta, Georgia metropolitan area as a case study. These growth projections include "business as usual" and "smart growth" scenarios out to 2030. The growth projections illustrate the effects of employing urban heat island mitigation strategies, such as increasing tree canopy and albedo across the Atlanta metro area, which in turn, are used to model how ozone and air temperature can potentially be moderated as impacts on elevating ground-level ozone, as opposed to not utilizing heat

  12. AlGaN/GaN current aperture vertical electron transistors with regrown channels

    OpenAIRE

    Ben-Yaacov, I; Seck, Y K; Mishra, U K; DenBaars, S P

    2004-01-01

    AlGaN/GaN current aperture vertical electron transistors with regrown aperture and source regions have been fabricated and tested. A 2 mum thick GaN:Si drain region followed by a 0.4 mum GaN:Mg current-blocking layer were grown by metalorganic chemical vapor deposition on a c-plane sapphire substrate. Channel apertures were etched, and a maskless regrowth was performed to grow unintentionally doped GaN inside the aperture as well as above the insulating layer, and to add an AlGaN cap layer. C...

  13. Perceived stress following race-based discrimination at work is associated with hypertension in African-Americans. The metro Atlanta heart disease study, 1999-2001.

    Science.gov (United States)

    Din-Dzietham, Rebecca; Nembhard, Wendy N; Collins, Rakale; Davis, Sharon K

    2004-02-01

    There is increasing evidence of an association between stress related to job strain and hypertension. However little data exist on stress from racism and race-based discrimination at work (RBDW). The objective of this study was to investigate whether blood pressure (BP) outcomes are positively associated with stressful racism towards African-Americans from non-African-Americans as well as RBDW from other African-Americans. The metro Atlanta heart disease study was a population-based study which included 356 African-American men and women, aged >/=21 years, residing in metropolitan Atlanta, Georgia during 1999-2001. Perceived stress was self-reported by 197 participants for racism from non-African-Americans and 95 for RBDW from other African-Americans. Sitting systolic (SBP) and diastolic (DBP) BP were taken at a clinic visit and was the average of the last two of three BP measures. Hypertension was self-reported as physician-diagnosed high BP on 2 or more visits. Logistic and least-squares linear regression models were fit accordingly and separately for each type of stress, adjusting for age, gender, body mass index, and coping abilities. The likelihood of hypertension significantly increased with higher levels of perceived stress following racism from non-African-Americans, but not from RBDW from other African-Americans; adjusted odd ratios (95% CI) were 1.4 (1.0, 1.9) and 1.2 (0.8, 1.5) per unit increment of stress. The adjusted magnitude of SBP and DBP increase between low and very high level of stress, conversely, was greater when RBDW originated from African-Americans than racism from non-African-Americans. Stressful racism and RBDW encounters are associated with increased SBP and DBP and increased likelihood of hypertension in African-Americans. Future studies with a larger sample size are warranted to further explore these findings for mechanistic understanding and occupational policy consideration regarding stress risk reduction.

  14. Photoemission of graded-doping GaN photocathode

    Science.gov (United States)

    Fu, Xiao-Qian; Chang, Ben-Kang; Wang, Xiao-Hui; Li, Biao; Du, Yu-Jie; Zhang, Jun-Ju

    2011-03-01

    We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×1017 cm-3. The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile. Project supported by the National Natural Science Foundation of China (Grant No. 60871012) and the Research Fund of Nanjing University of Science and Technology (Grant No. 2010ZYTS032).

  15. 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

  16. Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Harmatha, Ladislav, E-mail: ladislav.harmatha@stuba.sk; Ľubica, Stuchlíková; Juraj, Racko; Juraj, Marek; Juraj, Pecháček; Peter, Benko; Michal, Nemec; Juraj, Breza

    2014-09-01

    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{sub 0.2}GaN{sub 0.8}/GaN Schottky heterostructure. - Abstract: The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al{sub 2}O{sub 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{sub 0.2}GaN{sub 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.

  17. Multi-stacked GaSb/GaAs type-II quantum nanostructures for application to intermediate band solar cells

    Science.gov (United States)

    Shoji, Yasushi; Tamaki, Ryo; Okada, Yoshitaka

    2017-06-01

    We have investigated the performance of 10-layer stacked GaSb/GaAs quantum dot (QD) and quantum ring (QR) solar cells (SCs) having a type-II band alignment. For both SCs, the external quantum efficiency (EQE) increased in the longer wavelength region beyond GaAs bandedge wavelength of λ > 870 nm due to an additive contribution from GaSb/GaAs QD or QR layers inserted in the intrinsic region of p-i-n SC structure. The EQE of GaSb/GaAs QRSC was higher than that of QDSC at room temperature and the photoluminescence intensity from GaSb/GaAs QRs was stronger compared with GaSb/GaAs QDs. These results indicate that crystal quality of GaSb/GaAs QRs is superior to that of GaSb/GaAs QDs. Furthermore, a photocurrent production due to two-step photo-absorption via GaSb/GaAs QD states or QR states, ΔEQE was measured at low temperature and the ratio of two-step absorption to total carrier extraction defined as ΔEQE / (ΔEQE + EQE), was higher for GaSb/GaAs QRSC than that of QDSC. The ratio of GaSb/GaAs QRSC exceeds 80% over the wavelength region of λ = 950 - 1250 nm. This suggests that two-step absorption process is more dominant for carrier extraction from GaSb/GaAs QR structure.

  18. Liquidus surface of Sm-Ga-S system

    International Nuclear Information System (INIS)

    Alieva, O.A.; Aliev, O.M.

    1989-01-01

    Using methods of physicochemic alanalysis for the first time phase diagrams of SmS-Ga 2 S 3 , Sm 2 S 3 -Ga 2 S 3 , SmS-GaS, Sm-GaS, SmGa 2 -SmS, SmGa 2 -GaS, GaS-SmGa 2 S 4 , Sm 3 S 4 -Ga 2 S 3 , Sm 2 S 3 -GaS, Sm 3 S 4 -SmGa 2 S 4 cross sections are studied and the projection of the liquidus surface of the Sm-Ga-S ternary system is plotted. It is found that there exist 6 ternary compounds in the system (SmGa 2 S 4 , SmGaS 3 , SmGa 4 S 7 , Sm 4 GaS 5 , Sm 3 Ga 2 S 5 , Sm 6 Ga 10/3 S 14 ) and, besides, found solid solutions based on GaS, Ga 2 S 3 and SmGa 2 S 4

  19. Characteristics of GaN material and application in UV detection

    Science.gov (United States)

    Qiao, Jianliang; Xu, Yuan; Wang, Xiaohui; Qian, Yunsheng; Chang, Benkang

    2012-10-01

    For the characteristics such as wide bandgap, low dielectric constant, ability to bear high temperature, ability to resist radiation etc., GaN material can be used for UV solar blind detection in very rigorous environments. But for a long time, the preparation technology for GaN material has been still keeping it from being used extensively. GaN photocathode with good future is developed slowly in the field of UV detection. The key method of obtaining effective photoemission is to reduce the vacuum energy level of GaN emission surface, make it lower than bulk conduction band minimum. Negative electron affinity (NEA) GaN photocathode can convert the light under 365 nm to the photoelectrons that can be sent to the free space. The surface potential of NEA GaN photocathode is made up of two straight line sections with different slope. As the first dipole layer, [GaN(Mg):Cs] dipole brings 3.0 eV decline of the vacuum energy level, make the GaN photocathode surface obtain about -1.0 eV effective negative electron affinity. The second dipole O-Cs makes effective electron affinity reduce further to - 1.2 eV. The results show: near 37% quantum efficiency can be gotten at the wavelength 200 nm for reflection-mode GaN photocathode, and the quantum efficiency reaches up to 13% at 290 nm in transmission mode. The large quantum efficiency and high stability are very good properties for UV detection devices employing GaN photoemitter.

  20. SITE TECHNOLOGY CAPSULE: SUBSURFACE VOLATILIZATION AND VENTILATION SYSTEM (SVVS)

    Science.gov (United States)

    The Subsurface Volatilization and Ventilation System is an integrated technology used for attacking all phases of volatile organic compound (VOC) contamination in soil and groundwater. The SVVS technology promotes insitu remediation of soil and groundwater contaminated with or-ga...

  1. Axial InGaAs/GaAs nanowire separate absorption-multiplication avalanche photodetectors (Conference Presentation)

    Science.gov (United States)

    Huffaker, Diana L.

    2017-05-01

    In0.53Ga0.47As/InP single photon avalanche detectors (SPADs) have a high photon detection efficiency in the near-IR, however the dark count rate is prohibitively high at room temperature. A nanowire-based In0.3Ga0.7As/GaAs SPAD can significantly reduce the DCR through a nearly three order of magnitude reduction in bulk InGaAs volume, as well as by reducing the indium composition for operation at 1064 nm. As a first step, we have successfully grown axial InGaAs/GaAs heterostructures using catalyst-free selective-area epitaxy. We will present the electrical characterization of a vertically oriented nanowire array InGaAs/GaAs SPADs operating at 1064 nm and use 3-dimensional modeling to aid in the analysis.

  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. 67Ga and 66Ga yield in 66,67,68Zn(dxn) reactions

    International Nuclear Information System (INIS)

    Dmitriev, P.P.; Panarin, M.V.; Molin, G.A.; Dmitrieva, Z.P.

    1991-01-01

    Nowadays the 67 Ga (T 1/2 =78.255 h) is one of the most important radionuclides for medicine. The 67,66 Ga yields depending on deuteron energy were measured for thick targets of enriched by 66,67,68 Zn and natural zinc in the reactions: 66 Zn(dn) 67 Ga (thresholdless one), 66 Zn(d2n) 66 Ga (energy threshold of 8.43 MeV), 67 Zn(d2n) 67 Ga (4.13 MeV), 67 Zn(d3n) 66 Ga (15.7 MeV), 68 Zn(d3n) 67 Ga (14.6 MeV). The yields for thick targets were measured for each reaction up to E d ≅ 22 MeV. The yield of 67,66 Ga was also measured for the natural zinc

  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. 3-D GaAs radiation detectors

    CERN Document Server

    Meikle, A R; Ledingham, Kenneth W D; Marsh, J H; Mathieson, K; O'Shea, V; Smith, K M

    2002-01-01

    A novel type of GaAs radiation detector featuring a 3-D array of electrodes that penetrate through the detector bulk is described. The development of the technology to fabricate such a detector is presented along with electrical and radiation source tests. Simulations of the electrical characteristics are given for detectors of various dimensions. Laser drilling, wet chemical etching and metal evaporation were used to create a cell array of nine electrodes, each with a diameter of 60 mu m and a pitch of 210 mu m. Electrical measurements showed I-V characteristics with low leakage currents and high breakdown voltages. The forward and reverse I-V measurements showed asymmetrical characteristics, which are not seen in planar diodes. Spectra were obtained using alpha particle illumination. A charge collection efficiency of 50% and a S/N ratio of 3 : 1 were obtained. Simulations using the MEDICI software package were performed on cells with various dimensions and were comparable with experimental results. Simulati...

  6. 3-D GaAs radiation detectors

    International Nuclear Information System (INIS)

    Meikle, A.R.; Bates, R.L.; Ledingham, K.; Marsh, J.H.; Mathieson, K.; O'Shea, V.; Smith, K.M.

    2002-01-01

    A novel type of GaAs radiation detector featuring a 3-D array of electrodes that penetrate through the detector bulk is described. The development of the technology to fabricate such a detector is presented along with electrical and radiation source tests. Simulations of the electrical characteristics are given for detectors of various dimensions. Laser drilling, wet chemical etching and metal evaporation were used to create a cell array of nine electrodes, each with a diameter of 60 μm and a pitch of 210 μm. Electrical measurements showed I-V characteristics with low leakage currents and high breakdown voltages. The forward and reverse I-V measurements showed asymmetrical characteristics, which are not seen in planar diodes. Spectra were obtained using alpha particle illumination. A charge collection efficiency of 50% and a S/N ratio of 3 : 1 were obtained. Simulations using the MEDICI software package were performed on cells with various dimensions and were comparable with experimental results. Simulations of a nine-electrode cell with 10 μm electrodes with a 25 μm pitch were also performed. The I-V characteristics again showed a high breakdown voltage with a low leakage current but also showed a full depletion voltage of just 8 V

  7. Whole-Body Vibration Assessment of the M9161A1 Truck Trailer

    Science.gov (United States)

    1993-08-01

    Grove, UT 84062 Loral Instrumentation 8401-T Aero Dr. San Diego, CA 92123 Scientific Atlanta 1-T Technology Parkway P.O. Box 105600 Atlanta, GA 30348...ntumnstloat Stanudrds Orgnintion ISO 2631: Cmfort ... Rtled comfort boundry Fatigue ... Fatigua-dscressed proficimy boundsry 1ealth ... Helth and safety...Internatiomna Standurds organization ISO 2631: Comfort ... Reduced comfort bowdery Futipis ... Fatigu-dmcresesd proficiency botwary Health ... Helth and safety

  8. Laser-induced transformation of GaS and GaSe nanosheets to ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Experimental evidence for the transformation of nanosheets of GaS and GaSe into onion struc- tures on UV excimer pulsed laser irradiation is presented. Few-layer GaS and GaSe on Si substrates were exposed to KrF pulsed laser with wavelength of 248 nm and the effect was studied as a function of number of.

  9. Characterization of GaN/AlGaN epitaxial layers grown by ...

    Indian Academy of Sciences (India)

    s and carrier concentration is 4.5 × 1016/cm3. Dislocation density of GaN buffer layer, 2×108/cm2, was measured by AFM after wet etching. The refractive indices of GaN buffer layer at 633 nm is 2.3544 for TE mode and 2.1515 for TM mode. This data demonstrate the quality achieved for GaN and AlGaN epitaxial layers.

  10. 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....

  11. GaN Initiative for Grid Applications (GIGA)

    Energy Technology Data Exchange (ETDEWEB)

    Turner, George [MIT Lincoln Lab., Lexington, MA (United States)

    2015-07-03

    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  12. Molecular beam epitaxy of GaSb on GaAs substrates with AlSb/GaSb compound buffer layers

    International Nuclear Information System (INIS)

    Hao Ruiting; Deng Shukang; Shen Lanxian; Yang Peizhi; Tu Jielei; Liao Hua; Xu Yingqiang; Niu Zhichuan

    2010-01-01

    GaSb films with AlSb/GaSb compound buffer layers were grown by molecular beam epitaxy on GaAs (001) substrates. The crystal quality and optical properties were studied by high resolution transition electron microscopy and low temperature photoluminescence spectra (PL), respectively. It was found that the AlSb/GaSb compound buffer layers can restrict the dislocations into GaSb epilayers. The intensity of PL spectra of GaSb layer becomes large with the increasing the periods of AlSb/GaSb superlattices, indicating that the optical quality of GaSb films is improved.

  13. Element specific investigation of ultrathin Co2MnGa/GaAs heterostructures

    DEFF Research Database (Denmark)

    Claydon, Jill S.; Hassan, Sameh; Damsgaard, Christian Danvad

    2007-01-01

    We have used x-ray magnetic circular dichroism to study the element specific magnetic properties of ultrathin films of the Heusler alloy Co2MnGa at room temperature. Nine films were grown by molecular beam epitaxy on GaAs substrates and engineered to vary in stoichiometry as Co1.86Mn0.99Ga1, Co1...

  14. Ga self-diffusion in isotopically enriched GaAs heterostructures doped with Si and Zn

    Energy Technology Data Exchange (ETDEWEB)

    Norseng, Marshall Stephen [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    This study attempts to advance the modeling of AlGaAs/GaAs/AlAs diffusion by experimental investigation of Ga self-diffusion in undoped, as-grown doped and Zinc diffused structures. We utilize novel, isotopically enriched superlattice and heterostructure samples to provide direct observation and accurate measurement of diffusion with a precision not possible using conventional techniques.

  15. Temperature dependence of lattice parameter of (Ga,Mn)As on GaAs substrate

    Science.gov (United States)

    Matsukura, Fumihiro; Ohno, Hideo

    2015-09-01

    We measure the temperature dependence of the lattice parameter of (Ga,Mn)As by X-ray diffraction. The result shows that the lattice parameter of (Ga,Mn)As shows similar temperature dependence to that of GaAs, and no obvious change is observed in the vicinity of its Curie temperature.

  16. Heterojunction bipolar transistor technology for data acquisition and communication

    Science.gov (United States)

    Wang, C.; Chang, M.; Beccue, S.; Nubling, R.; Zampardi, P.; Sheng, N.; Pierson, R.

    1992-01-01

    Heterojunction Bipolar Transistor (HBT) technology has emerged as one of the most promising technologies for ultrahigh-speed integrated circuits. HBT circuits for digital and analog applications, data conversion, and power amplification have been realized, with speed performance well above 20 GHz. At Rockwell, a baseline AlGaAs/GaAs HBT technology has been established in a manufacturing facility. This paper describes the HBT technology, transistor characteristics, and HBT circuits for data acquisition and communication.

  17. Enhanced lateral heat dissipation packaging structure for GaN HEMTs on Si substrate

    International Nuclear Information System (INIS)

    Cheng, Stone; Chou, Po-Chien; Chieng, Wei-Hua; Chang, E.Y.

    2013-01-01

    This work presents a technology for packaging AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate. The GaN HEMTs are attached to a V-groove copper base and mounted on a TO-3P leadframe. The various thermal paths from the GaN gate junction to the case are carried out for heat dissipation by spreading to protective coating; transferring through the bond wires; spreading in the lateral device structure through the adhesive layer, and vertical heat spreading of silicon chip bottom. Thermal characterization showed a thermal resistance of 13.72 °C/W from the device to the TO-3P package. Experimental tests of a 30 mm gate-periphery single chip packaged in a 5 × 3 mm V-groove Cu base with a 100 V drain bias showed power dissipation of 22 W. -- Highlights: ► An enhanced packaging structure designed for AlGaN/GaN HEMTs on an Si substrate. ► The V-groove copper base is designed on the device periphery surface heat conduction for enhancing Si substrate thermal dissipation. ► The proposed device shows a lower thermal resistance and upgrade in thermal conductivity capability. ► This work provides useful thermal IR imagery information to aid in designing high efficiency package for GaN HEMTs on Si

  18. High quality superconducting NbN thin films on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Marsili, Francesco; Fiore, Andrea [COBRA Research Institute, Eindhoven University of Technology, PO Box 513, NL-5600MB Eindhoven (Netherlands); Gaggero, Alessandro; Leoni, Roberto [Istituto di Fotonica e Nanotecnologie (IFN), CNR, via Cineto Romano 42, I-00156 Roma (Italy); Li, Lianhe H; Surrente, Alessandro [Institute of Photonics and Quantum Electronics (IPEQ), Ecole Polytechnique Federale de Lausanne (EPFL), Station 3, CH-1015 Lausanne (Switzerland); Levy, Francis, E-mail: francesco.marsili@epfl.c [Institute of Condensed Matter Physics (IPMC), Ecole Polytechnique Federale de Lausanne (EPFL), Station 3, CH-1015 Lausanne (Switzerland)

    2009-09-15

    A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature T{sub S} = 400 {sup 0}C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar+N{sub 2} plasma. 5.5 nm thick NbN films on GaAs exhibit T{sub C} = 10.7 K, {Delta}T{sub C} = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

  19. Second annual clean coal technology conference: Proceedings. Volume 1

    Energy Technology Data Exchange (ETDEWEB)

    1993-09-09

    The Second Annual Clean Coal Technology Conference was held at Atlanta, Georgia, September 7--9, 1993. The Conference, cosponsored by the US Department of Energy (USDOE) and the Southern States Energy Board (SSEB), seeks to examine the status and role of the Clean Coal Technology Demonstration Program (CCTDP) and its projects. The Program is reviewed within the larger context of environmental needs, sustained economic growth, world markets, user performance requirements and supplier commercialization activities. This will be accomplished through in-depth review and discussion of factors affecting domestic and international markets for clean coal technology, the environmental considerations in commercial deployment, the current status of projects, and the timing and effectiveness of transfer of data from these projects to potential users, suppliers, financing entities, regulators, the interested environmental community and the public. Individual papers have been entered separately.

  20. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    Science.gov (United States)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    1987-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  1. 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.

  2. Analysis of Interface Scattering in AlGaN/GaN/InGaN/GaN Double-Heterojunction High-Electron-Mobility Transistors

    Science.gov (United States)

    Wang, Lin; Hu, Weida; Chen, Xiaoshuang; Lu, Wei

    2012-08-01

    This paper presents detailed investigations on the direct-current (DC) characteristics of an AlGaN/GaN/InGaN/GaN double-heterojunction high-electron-mobility transistor (DH-HEMT) using two-dimensional numerical analysis. In this work, the hot-electron effect is taken into account and implemented in the hydrodynamic model. The results indicate that carrier transport in this kind of device exhibits properties significantly different from that in a conventional AlGaN/GaN HEMT. Due to imperfections at the GaN/InGaN interface, scattering caused by the interface roughness, phonons, etc. inhibit the negative differential conductance in high electric field. In addition, the velocity increment of electrons around the gate edge is dominated by the overshoot effect rather than the phonon effect. The energy exchange between phonons and electrons, as presented in this paper, illustrates that the dissipated power is just a small portion of the exchanged energy. For further performance improvement, more lattice-matched material with strong polarization for the barrier layer is proposed.

  3. 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...

  4. GA BASED GLOBAL OPTIMAL DESIGN PARAMETERS FOR ...

    African Journals Online (AJOL)

    This article uses Genetic Algorithm (GA) for the global design optimization of consecutive reactions taking place in continuous stirred tank reactors (CSTRs) connected in series. GA based optimal design determines the optimum number of CSTRs in series to achieve the maximum conversion, fractional yield and selectivity ...

  5. Development of GaAs Detectors for Physics at the LHC

    CERN Multimedia

    Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

    2002-01-01

    % RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

  6. Wide bandgap engineering of (AlGa)2O3 films

    International Nuclear Information System (INIS)

    Zhang, Fabi; Saito, Katsuhiko; Tanaka, Tooru; Nishio, Mitsuhiro; Guo, Qixin; Arita, Makoto

    2014-01-01

    Bandgap tunable (AlGa) 2 O 3 films were deposited on sapphire substrates by pulsed laser deposition (PLD). The deposited films are of high transmittance as measured by spectrophotometer. The Al content in films is almost the same as that in targets. The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of (AlGa) 2 O 3 films as it is in good agreement with the bandgap values from transmittance spectra. The measured bandgap of (AlGa) 2 O 3 films increases continuously with the Al content covering the whole Al content range from about 5 to 7 eV, indicating PLD is a promising growth technology for growing bandgap tunable (AlGa) 2 O 3 films.

  7. Demonstration of GaN/InGaN Light Emitting Diodes on (100) β-Ga2O3 Substrates by Metalorganic Chemical Vapour Deposition

    International Nuclear Information System (INIS)

    Zi-Li, Xie; Rong, Zhang; Xiang-Qian, Xiu; Ping, Han; Bin, Liu; Hong, Zhao; Ruo-Lian, Jiang; Yi, Shi; You-Dou, Zheng; Chang-Tai, Xia

    2008-01-01

    The growth and fabrication of GaN/InGaN multiple quantum well (MQW) light emitting diodes (LEDs) on (100) β-Ga 2 O 3 single crystal substrates by metal-organic chemical vapour deposition (MOCVD) technique are reported. x-ray diffraction (XRD) θ – 2θ scan spectroscopy is carried out on the GaN buffer layer grown on a (100) β-Ga 2 O 3 substrate. The spectrum presents several sharp peaks corresponding to the (100) β-Ga 2 O 3 and (004) GaN. High-quality (0002) GaN material is obtained. The emission characteristics of the GaN/InGaN MQW LED are measurement. The first green LED on β-Ga 2 O 3 with vertical current injection is demonstrated. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  8. Electrochemical profiling of heterostructures with multiple quantum wells InGaN/GaN

    International Nuclear Information System (INIS)

    Zubkov, Vasily; Kucherova, Olga; Frolov, Dmitry; Zubkova, Anna

    2013-01-01

    A method of electrochemical capacitance-voltage profiling is used to characterize InGaN/GaN heterostructures with multiple quantum wells. Implementation of pulsed electrochemical etching allowed getting good planarity of etched surface despite of the high density of dislocations in GaN. The quality of etching, optimization of its parameters and independent check of etched depth were controlled by AFM measurements. Concentration profiles of InGaN/GaN QWs structures were evaluated then from capacitance-voltage measurements revealing several quantum wells with a period of 17 nm. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. 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.

  10. Reliability-Limiting Defects in GaN/AlGaN High Electron Mobility Transistors

    Science.gov (United States)

    2011-12-01

    100655. I am extremely thankful to our collaborators at University of California, Santa Barbara , for providing us with the GaN HEMTs, without which...California, Santa Barbara . These devices were grown by molecular beam epitaxy under Ga-rich, N-rich, and NH3-rich conditions. Devices grown using...Köhler, R. Kiefer , R. Quay, M. Baeumber, and L. Kirste, “Growth of AlGaN/GaN based electronic device structures with semi-insulating GaN buffer and AlN

  11. Aluminum gallium nitride (GaN)/GaN high electron mobility transistor-based sensors for glucose detection in exhaled breath condensate.

    Science.gov (United States)

    Chu, Byung Hwan; Kang, Byoung Sam; Hung, Sheng Chun; Chen, Ke Hung; Ren, Fan; Sciullo, Andrew; Gila, Brent P; Pearton, Stephen J

    2010-01-01

    Immobilized aluminum gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs) have shown great potential in the areas of pH, chloride ion, and glucose detection in exhaled breath condensate (EBC). HEMT sensors can be integrated into a wireless data transmission system that allows for remote monitoring. This technology offers the possibility of using AlGaN/GaN HEMTs for extended investigations of airway pathology of detecting glucose in EBC without the need for clinical visits. HEMT structures, consisting of a 3-microm-thick undoped GaN buffer, 30-A-thick Al(0.3)Ga(0.7)N spacer, and 220-A-thick silicon-doped Al(0.3)Ga(0.7)N cap layer, were used for fabricating the HEMT sensors. The gate area of the pH, chloride ion, and glucose detection was immobilized with scandium oxide (Sc(2)O(3)), silver chloride (AgCl) thin film, and zinc oxide (ZnO) nanorods, respectively. The Sc(2)O(3)-gated sensor could detect the pH of solutions ranging from 3 to 10 with a resolution of approximately 0.1 pH. A chloride ion detection limit of 10(-8) M was achieved with a HEMT sensor immobilized with the AgCl thin film. The drain-source current of the ZnO nanorod-gated AlGaN/GaN HEMT sensor immobilized with glucose oxidase showed a rapid response of less than 5 seconds when the sensor was exposed to the target glucose in a buffer with a pH value of 7.4. The sensor could detect a wide range of concentrations from 0.5 nM to 125 microM. There is great promise for using HEMT-based sensors to enhance the detection sensitivity for glucose detection in EBC. Depending on the immobilized material, HEMT-based sensors can be used for sensing different materials. These electronic detection approaches with rapid response and good repeatability show potential for the investigation of airway pathology. The devices can also be integrated into a wireless data transmission system for remote monitoring applications. This sensor technology could use the exhaled breath condensate to measure the

  12. Above room temperature operation of InGaAs/AlGaAs/GaAs quantum cascade lasers

    Science.gov (United States)

    Pierścińska, D.; Gutowski, P.; Hałdaś, G.; Kolek, A.; Sankowska, I.; Grzonka, J.; Mizera, J.; Pierściński, K.; Bugajski, M.

    2018-03-01

    In this work we report on the performance of mid-infrared quantum cascade lasers (QCLs) based on strained InGaAs/AlGaAs grown by molecular beam epitaxy on GaAs substrate. Structures were grown with indium content from 1% to 6% in GaAs quantum wells (QW) and 45% of Al in AlGaAs barrier layers. The design results in strained heterostructure, however, no strain relaxation was observed as documented by x-ray diffraction measurements up to ∼3% of In content in QWs. The investigation of heterostructures and devices was performed, including structural measurements and electrooptical characterization of devices. Devices fabricated from epi wafers with 2.64% of In exhibited performance largely improved over GaAs/AlGaAs QCLs. Roughly two times reduction of the threshold current density was observed at lasing wavelength ∼9.45 μm. The lasers operated in pulsed mode up to T = 50 °C with characteristic temperature T 0 = 115 K. The decrease of the threshold current density has been mainly attributed to the reduction of interface roughness scattering and the increase of activation energy for the escape of carriers from the upper laser level to the 3D continuum. Further increase of In content in QWs resulted in the deterioration of device parameters.

  13. Optically-pumped lasing of semi-polar InGaN/GaN(1122) heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Strittmatter, A.; Teepe, M.; Yang, Z.; Chua, C.; Northrup, J.; Johnson, N.M. [Palo Alto Research Center, Palo Alto, CA (United States); Spiberg, P.; Brown, R.G.W. [Ostendo Technologies, Inc., Carlsbad, CA (United States); Ivantsov, V.; Syrkin, A.; Shapovalov, L.; Usikov, A. [TDI, Inc., an Oxford Instruments Company, Silver Spring, MD (United States)

    2010-07-15

    Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(11-22)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 {mu}m thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicate high crystallographic quality that approaches that of GaN(0001) layers on sapphire. Growth studies on the semi-polar GaN templates established the high efficiency of indium incorporation into InGaN layers, with a wide growth-temperature window up to 800 C for green light emitting structures. Basic LEDs were fabricated with peak emission up to 527 nm wavelength. Further growth studies established conditions for growing reasonably smooth, undoped InGaN/GaN laser heterostructures suitable for optical pumping. Optically-pumped lasing was achieved at wavelengths from 400 nm up to 500 nm. The results demonstrate the viability of semi-polar GaN(11-22) on sapphire templates for long-wavelength nitride laser diodes (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Optical properties of InGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Joo In; Lee, Chang Myung [Korea Research Institute of Standards and Science, Taejon (Korea, Republic of); Leem, Jae Young [Inje Univ., Kimhae (Korea, Republic of); Lim, Ki Soo [Chungbuk National Univ., Cheongju (Korea, Republic of); Han, Il Ki [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2002-03-01

    We have used steady-state and time-resolved photoluminescence to investigate optical properties of In{sub 0.13}Ga{sub 0.87}N/GaN multiple quantum wells (MQW) grown by using metalorganic chemical vapor deposition. The quantum well spectra were explained in terms of the radiative recombination of excitons in the localized states. Exciton formation of the InGaN MQW might be delayed for excitations above the GaN barrier excitation compared with exciton formation in excitations below the GaN barrier. The critical temperature at which nonradiative recombination dominantly occurred was increased under the excitation below the GaN barrier because screening caused by carriers in the GaN barrier vanished.

  15. GaAs quantum dots in a GaP nanowire photodetector

    Science.gov (United States)

    Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

    2018-03-01

    We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p–i–n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor–liquid–solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

  16. 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)

  17. Atomic Layer Epitaxy Dielectric Based GaN MOS Devices and Beyond

    Science.gov (United States)

    Zhou, Hong

    GaN HEMT usually suffers from high Ig and ID current collapse due to its limited Schottky barrier height and high density of surface states. Although GaN MOSHEMT with amorphous gate dielectric is an effective way to suppress the Ig and passivate the surface states, high-quality gate dielectric on GaN MOS devices are still lacking. In this work, single crystalline gate dielectric Mg0.25Ca0.75O, grown by ALE, has been successfully integrated into three kinds of GaN MOSHEMTs, namely InAlN/GaN/SiC, AlGaN/GaN/SiC and AlGaN/GaN/Si MOSHEMTs. With a nearly lattice-matched oxide, the interface quality between the oxide and barrier is significantly improved. Ig is reduced by several orders of magnitudes compared to HEMTs. All three kinds of MOSHEMTs exhibit high ID on/off ratio exceeding 1011, near ideal SS, negligible ID-V GS hysteresis and negligible current collapse. RF small-signal characteristics of AlGaN/GaN/SiC MOSHEMTs show ft/fmax of 101/150 GHz for a Lg of 120 nm device and large-signal characteristics with Pout of 4.18 W/mm for a Lg=150 nm device at f=35 GHz. Enhancement-mode non-recessed AlGaN/GaN/Si fin-MOSHEMTs are also realized through the side-wall depletion of the fin structures. Combining with the high ID, high peak gm, and low Ron, MgCaO turns out to be a new and very promising gate dielectric for GaN MOS technology. Beyond the wide bandgap semiconductor GaN, promising next generation ultra-wide bandgap semiconductor beta-Ga2O3 is also investigated. Piranha solution and PDA were first used to optimize the ALD Al2O3/beta-Ga2O3 interface. Low C-V hysteresis of 0.1 V and Dit=2.3x1011 cm-2˙eV-1 are achieved due to the passivated dangling bonds at the interface. Meanwhile, we have demonstrated a record high ID of 600/450 mA/mm for D/E-mode back-gate GOOI FETs at a beta-Ga2O3 doping concentration of 2.8x1018 cm-3. Following the motivation of chasing higher I D and lower Ron, we have increased the doping concentration to 7.8x1018 cm-3 and the record ID has been

  18. If This Is a "Real" Housewife, Who Are All These Women Around Me?: An Examination of The Real Housewives of Atlanta and the Persistence of Historically Stereotypical Images of Black Women in Popular Reality Television.

    OpenAIRE

    Bunai, Dominique Christabel

    2014-01-01

    Stereotypical images of blacks have persisted throughout multiple forms of media for decades, with one of the most recent arenas being reality television programming. This study examines the Bravo Television network series The Real Housewives of Atlanta to consider the impact of reality television on the image of black women in America today. This increasingly popular show is the most viewed in The Real Housewives franchise, and demonstrates that black women in America do not embody any one h...

  19. 77 FR 75972 - Foreign-Trade Zone 26 - Atlanta, Georgia Notification of Proposed Production Activity Suzuki Mfg...

    Science.gov (United States)

    2012-12-26

    ... Corp. (SMAC), located in Rome, Jonesboro, and Cartersville, Georgia. The notification conforming to the..., 2012. The SMAC facilities are located at: 1520 and 1627 Technology Parkway, NW., Rome (Floyd County...), Georgia. A separate request for subzone designation at the SMAC facilities has been processed under...

  20. The Arabidopsis NPF3 protein is a GA transporter

    DEFF Research Database (Denmark)

    Tal, Iris; Zhang, Yi; Jørgensen, Morten Egevang

    2016-01-01

    Gibberellins (GAs) are plant hormones that promote a wide range of developmental processes. While GA signalling is well understood, little is known about how GA is transported or how GA distribution is regulated. Here we utilize fluorescently labelled GAs (GA-Fl) to screen for Arabidopsis mutants...... deficient in GA transport. We show that the NPF3 transporter efficiently transports GA across cell membranes in vitro and GA-Fl in vivo. NPF3 is expressed in root endodermis and repressed by GA. NPF3 is targeted to the plasma membrane and subject to rapid BFA-dependent recycling. We show that abscisic acid...... (ABA), an antagonist of GA, is also transported by NPF3 in vitro. ABA promotes NPF3 expression and GA-Fl uptake in plants. On the basis of these results, we propose that GA distribution and activity in Arabidopsis is partly regulated by NPF3 acting as an influx carrier and that GA-ABA interaction may...

  1. Understanding the emission impacts of high-occupancy vehicle (HOV) to high-occupancy toll (HOT) lane conversions: Experience from Atlanta, Georgia.

    Science.gov (United States)

    Xu, Yanzhi Ann; Liu, Haobing; Rodgers, Michael O; Guin, Angshuman; Hunter, Michael; Sheikh, Adnan; Guensler, Randall

    2017-08-01

    Converting a congested high-occupancy vehicle (HOV) lane into a high-occupancy toll (HOT) lane is a viable option for improving travel time reliability for carpools and buses that use the managed lane. However, the emission impacts of HOV-to-HOT conversions are not well understood. The lack of emission impact quantification for HOT conversions creates a policy challenge for agencies making transportation funding choices. The goal of this paper is to evaluate the case study of before-and-after changes in vehicle emissions for the Atlanta, Georgia, I-85 HOV/HOT lane conversion project, implemented in October 2011. The analyses employed the Motor Vehicle Emission Simulator (MOVES) for project-level analysis with monitored changes in vehicle activity data collected by Georgia Tech researchers for the Georgia Department of Transportation (GDOT). During the quarterly field data collection from 2010 to 2012, more than 1.5 million license plates were observed and matched to vehicle class and age information using the vehicle registration database. The study also utilized the 20-sec, lane-specific traffic operations data from the Georgia NaviGAtor intelligent transportation system, as well as a direct feed of HOT lane usage data from the State Road and Tollway Authority (SRTA) managed lane system. As such, the analyses in this paper simultaneously assessed the impacts associated with changes in traffic volumes, on-road operating conditions, and fleet composition before and after the conversion. Both greenhouse gases and criteria pollutants were examined. A straight before-after analysis showed about 5% decrease in air pollutants and carbon dioxide (CO 2 ). However, when the before-after calendar year of analysis was held constant (to account for the effect of 1 yr of fleet turnover), mass emissions at the analysis site during peak hours increased by as much as 17%, with little change in CO 2 . Further investigation revealed that a large percentage decrease in criteria

  2. Inductively Coupled Plasma Etching of III-V Semiconductors in BCl(3)-Based Chemistries: Part 1: GaAs, GaN, GaP, GaSb and AlGaAs

    Energy Technology Data Exchange (ETDEWEB)

    Abernathy, C.R,; Han, J.; Hobson, W.S.; Hong, J.; Lambers, E.S.; Lee, J.W.; Maeda, T.; Pearton, S.J.; Shul, R.J.

    1998-12-04

    BC13, with addition of Nz, Ar or Hz, is found to provide smooth anisotropic pattern transfer in GaAs, GaN, GaP, GaSb and AIGriAs under Inductively Coupled Plasma conditions, Maxima in the etch rates for these materials are observed at 33% N2 or 87$'40 Hz (by flow) addition to BC13, whereas Ar addition does not show this behavior. Maximum etch rates are typically much higher for GaAs, Gap, GaSb and AIGaAs (-1,2 @rein) than for GaN (-0.3 ymu'min) due to the higher bond energies of the iatter. The rates decrease at higher pressure, saturate with source power (ion flux) and tend to show maxima with chuck power (ion energy). The etched surfaces remain stoichiometric over abroad range of plasma conditions.

  3. 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

  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. Structural properties of (GaIn)(AsN)/GaAs MQW structures grown by MOVPE

    International Nuclear Information System (INIS)

    Giannini, C.; Carlino, E.; Tapfer, L.; Hoehnsdorf, F.; Koch, J.; Stolz, W.

    2000-01-01

    In this work, the authors investigate the structural properties of (GaIn)(AsN)/GaAs multiple quantum wells (MQW) grown at low temperature by metalorganic vapor phase epitaxy. The structural properties, in particular the In- and N-incorporation, the lattice strain (strain modulation), the structural perfection of the metastable (GaIn)(AsN) material system and the structural quality of the (GaIn)(AsN)/GaAs interfaces are investigated by means of high-resolution x-ray diffraction, transmission electron microscopy (TEM), and secondary ion mass spectrometry. They demonstrate that (GaIn)(AsN) layers of high structural quality can be fabricated up to lattice mismatches of 4%. The experiments reveal that N and In atoms are localized in the quaternary material and no evidences of In-segregation or N-interdiffusion could be found. TEM analyses reveal a low defect density in the highly strained layers, but no clustering or interface undulation could be detected. High-resolution TEM images show that (GaIn)(AsN)/GaAs interfaces are slightly rougher than GaAs/(GaIn)(AsN) ones

  6. Photovoltaic response of InGaN/GaN multi-quantum well solar cells enhanced by inserting thin GaN cap layers

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Zhao, D.G., E-mail: dgzhao@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Jiang, D.S.; Chen, P.; Zhu, J.J.; Liu, Z.S.; Le, L.C.; He, X.G.; Li, X.J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Yang, H. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zhang, Y.T.; Du, G.T. [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130023 (China)

    2015-06-25

    Highlights: • The spectral response of InGaN/GaN MQW solar cells with different LT-cap layer thicknesses was investigated. • Inserting a 0.75 nm-thick LT-cap layer can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells. • A macroscopic optical method was used to investigate the microscopic localization effect and defect density in InGaN QW. • Strong localization effect in InGaN QW is harmful for the formation of high efficiency InGaN/GaN MQW solar cells. - Abstract: Structural properties and photovoltaic response of InGaN/GaN multi-quantum well (MQW) solar cells with low temperature grown GaN cap (LT-cap) layers were investigated. It is found that inserting a thin LT-cap layer (around 0.75 nm) between each InGaN quantum well (QW) and GaN quantum barrier (QB) can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells. This is attributed to the increased optical absorption of InGaN QWs due to higher indium content and thicker InGaN QWs thickness when LT-cap layers are added. However, if the LT-cap layer is too thick, the localization effect is enhanced and the defect density of InGaN QW layers will increase too much. Both of them will result in a reduced photovoltaic response of InGaN/GaN MQW solar cells.

  7. Pseudodirect to Direct Compositional Crossover in Wurtzite GaP/InxGa1–xP Core–Shell Nanowires

    KAUST Repository

    Gagliano, L.

    2016-11-29

    Thanks to their uniqueness, nanowires allow the realization of novel semiconductor crystal structures with yet unexplored properties, which can be key to overcome current technological limits. Here we develop the growth of wurtzite GaP/InGaP core-shell nanowires with tunable indium concentration and optical emission in the visible region from 590 nm (2.1 eV) to 760 nm (1.6 eV). We demonstrate a pseudodirect (δ-δ) to direct (δ-δ) transition crossover through experimental and theoretical approach. Time resolved and temperature dependent photoluminescence measurements were used, which led to the observation of a steep change in carrier lifetime and temperature dependence by respectively one and 3 orders of magnitude in the range 0.28 ± 0.04 ≤ x ≤ 0.41 ± 0.04. Our work reveals the electronic properties of wurtzite InGaP.

  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. 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.

  10. Misfit dislocation-related deep levels in InGaAs/GaAs and GaAsSb/GaAs p-i-n heterostructures and the effect of these on the relaxation time of nonequilibrium carriers

    Science.gov (United States)

    Sobolev, M. M.; Soldatenkov, F. Yu.; Shul'pina, I. L.

    2018-04-01

    A study of deep levels in InGaAs/GaAs and GaAsSb/GaAs p0-i-n0 heterostructures with misfit dislocations and identification of the effective defects responsible for the significant (by up to a factor of 100) decrease in the relaxation time of nonequilibrium carriers in the base layers (and in the related reverse recovery time) of InGaAs/GaAs and GaAsSb/GaAs high-voltage power p-i-n diodes is reported. Experimental capacitance-voltage characteristics and deep-level transient spectroscopy spectra of p+-p0-i-n0-n+ homostructures based on undoped GaAs layers without misfit dislocations and InGaAs/GaAs and GaAsSb/GaAs heterostructures with a homogeneous network of misfit dislocations, all grown by liquid-phase epitaxy, are analyzed. Acceptor defects with deep levels HL2 and HL5 are identified in GaAs epitaxial p0 and n0 layers. Dislocation-related electron and hole deep traps designated as ED1 and HD3 are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The effective recombination centers in the heterostructure layers, to which we attribute the substantial decrease in the relaxation time of nonequilibrium carriers in the base layers of p-i-n diodes, are dislocation-related hole traps that are similar to HD3 and have the following parameters: thermal activation energy Et = 845 meV, carrier capture cross-section σp = 1.33 × 10-12 cm2, concentration Nt = 3.80 × 1014 cm-3 for InGaAs/GaAs and Et = 848 meV, σp = 2.73 × 10-12 cm2, and Nt = 2.40 × 1014 cm-3 for the GaAsSb/GaAs heterostructure. The relaxation time of the concentration of nonequilibrium carriers in the presence of dislocation-related deep acceptor traps similar to HD3 was estimated to be 1.1 × 10-10 and 8.5 × 10-11 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 8.9 × 10-7 s for the GaAs homostructure. These data correspond to the relaxation times of nonequilibrium carriers in the base layers of GaAs, InGaAs/GaAs, and GaAsSb/GaAs high-voltage power p-i-n diodes.

  11. Synthesis and characterization of silicon-doped polycrystalline GaN ...

    Indian Academy of Sciences (India)

    Administrator

    and high frequency devices as well. The main technologi- cal interest in the polycrystalline-based devices stems from its very low-cost production. Among different group. III nitrides, GaN ..... Li Z Q, Chen H, Liu H F, Wan L, Huang Q and Zhou J M. 2001 J. Cryst. Growth 227–228 420. 4. Hasegawa S, Nishida S, Yamashita T ...

  12. Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 55; Issue 3. Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal ... Laser Laboratory, Physics Department, Burdwan University, Burdwan 713 104, India; Centre for Advanced Technology, Indore 452 013, India; Anhui Institute of Optics and Fine ...

  13. 1 GHz GaAs Buck Converter for High Power Amplifier Modulation Applications

    NARCIS (Netherlands)

    Busking, E.B.; Hek, A.P. de; Vliet, F.E. van

    2012-01-01

    A fully integrated 1 GHz buck converter output stage, including on-chip inductor and DC output filtering has been realized, in a standard high-voltage breakdown GaAs MMIC technology. This is a significant step forward in designing highspeed power control of supply-modulated HPAs (high power

  14. GaAs Multiplexers for VLWIR Detector Readout Below 10 Kelvin

    Science.gov (United States)

    Cunningham, T.; Fitzsimmons, M. J.

    1997-01-01

    A multiplexer and buffer based on GaAs JFET technology is presented. This multiplexer operates normally from room temperature down to 4 Kelvin and is suitable for the readout of Very Long Wavelength Infrared Detectors that must be cooled to below 10 Kelvin.

  15. GaN C-band HPA for phased-array applications

    NARCIS (Netherlands)

    Wanum, M. van; Hek, A.P. de; Vliet, F.E. van

    2013-01-01

    In the UMS GH25-10 GaN MMIC technology a Cband high power amplifier (HPA) has been realized. The current design is primarily intended for use in a space-based SAR system with a center frequency of 5.4 GHz and a sweep bandwidth of 100 MHz. To enable reuse of the amplifier in other radar systems such

  16. GA(2)LEN (Global Allergy and Asthma European Network) addresses the allergy and asthma 'epidemic'

    NARCIS (Netherlands)

    Bousquet, J.; Burney, P. G.; Zuberbier, T.; Cauwenberge, P. V.; Akdis, C. A.; Bindslev-Jensen, C.; Bonini, S.; Fokkens, W. J.; Kauffmann, F.; Kowalski, M. L.; Lodrup-Carlsen, K.; Mullol, J.; Nizankowska-Mogilnicka, E.; Papadopoulos, N.; Toskala, E.; Wickman, M.; Anto, J.; Auvergne, N.; Bachert, C.; Bousquet, P. J.; Brunekreef, B.; Canonica, G. W.; Carlsen, K. H.; Gjomarkaj, M.; Haahtela, T.; Howarth, P.; Lenzen, G.; Lotvall, J.; Radon, K.; Ring, J.; Salapatas, M.; Schünemann, H. J.; Szczecklik, A.; Todo-Bom, A.; Valovirta, E.; von Mutius, E.; Zock, J. P.

    2009-01-01

    Allergic diseases represent a major health problem in Europe. They are increasing in prevalence, severity and costs. The Global Allergy and Asthma European Network (GA(2)LEN), a Sixth EU Framework Program for Research and Technological Development (FP6) Network of Excellence, was created in 2005 as

  17. Surface Modification of Sputtered Ga.5In.5Sb Thin Films ISHU ...

    African Journals Online (AJOL)

    MICHAEL

    IR detectors useful for fiber optic communication. Since the efficiency of detector depends very much on the surface properties of the substrate material, improvement of substrate surfaces is a challenging task in device technology. Reports on the improved electrical properties of GaAs and InP surfaces by. Ru3+ modification ...

  18. DFT algorithms for bit-serial GaAs array processor architectures

    Science.gov (United States)

    Mcmillan, Gary B.

    1988-01-01

    Systems and Processes Engineering Corporation (SPEC) has developed an innovative array processor architecture for computing Fourier transforms and other commonly used signal processing algorithms. This architecture is designed to extract the highest possible array performance from state-of-the-art GaAs technology. SPEC's architectural design includes a high performance RISC processor implemented in GaAs, along with a Floating Point Coprocessor and a unique Array Communications Coprocessor, also implemented in GaAs technology. Together, these data processors represent the latest in technology, both from an architectural and implementation viewpoint. SPEC has examined numerous algorithms and parallel processing architectures to determine the optimum array processor architecture. SPEC has developed an array processor architecture with integral communications ability to provide maximum node connectivity. The Array Communications Coprocessor embeds communications operations directly in the core of the processor architecture. A Floating Point Coprocessor architecture has been defined that utilizes Bit-Serial arithmetic units, operating at very high frequency, to perform floating point operations. These Bit-Serial devices reduce the device integration level and complexity to a level compatible with state-of-the-art GaAs device technology.

  19. Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs) Photoconductive Semiconductor Switch (PCSS) Fabrication

    Science.gov (United States)

    2016-09-27

    ARL-TR-7819 ● SEP 2016 US Army Research Laboratory Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs...Laboratory Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs) Photoconductive Semiconductor Switch (PCSS) Fabrication by...Report 3. DATES COVERED (From - To) January 2016–September 2016 4. TITLE AND SUBTITLE Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs

  20. 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

  1. Study on the electrical degradation of AlGaN/GaN MIS-HEMTs induced by residual stress of SiNx passivation

    Science.gov (United States)

    Bai, Zhiyuan; Du, Jiangfeng; Liu, Yong; Xin, Qi; Liu, Yang; Yu, Qi

    2017-07-01

    In this paper, we report a new phenomenon in C-V measurement of different gate length MIS-HEMTs, which can be associated with traps character of the AlGaN/GaN interface. The analysis of DC measurement, frequency dependent capacitance-voltage measurements and simulation show that the stress from passivation layer may induce a decrease of drain output current Ids, an increase of on-resistance, serious nonlinearity of transconductance gm, and a new peak of C-V curve. The value of the peak is reduced to zero while the gate length and measure frequency are increasing to 21 μm and 1 MHz, respectively. By using conductance method, the SiNx/GaN interface traps with energy level of EC-0.42 eV to EC-0.45 eV and density of 3.2 × 1012 ∼ 5.0 × 1012 eV-1 cm-2 is obtained after passivation. According to the experimental and simulation results, formation of the acceptor-like traps with concentration of 3 × 1011 cm-2 and energy level of EC-0.37 eV under the gate on AlGaN barrier side of AlGaN/GaN interface is the main reason for the degradation after the passivation. He is currently an Associate Professor with State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Microelectronics and Solid-State Electronics, UESTC. He is the author of over 30 peer-reviewed journal papers and more than 20 conference papers. He has also hold over 20 patents. His research interests include Gallium Nitride based high-voltage power switching devices, microwave and millimeter-wave power devices and integrated technologies. Dr. Yu was a recipient of the prestigious Award of Science and Technology of China

  2. 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.

  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. Triangle and GA Methods for UAVs Jamming

    Directory of Open Access Journals (Sweden)

    Yu Zhang

    2014-01-01

    Full Text Available We focus on how to jam UAVs network efficiently. The system model is described and the problem is formulated. Based on two properties and a theorem which helps to decide good location for a jammer, we present the Triangle method to find good locations for jammers. The Triangle method is easy to understand and has overall computational complexity of ON2. We also present a genetic algorithm- (GA- based jamming method, which has computational complex of OLMN2. New chromosome, mutation, and crossover operations are redefined for the GA method. The simulation shows that Triangle and GA methods perform better than Random method. If the ratio of jammers’ number to UAVs’ number is low (lower than 1/5 in this paper, GA method does better than Triangle method. Otherwise, Triangle method performs better.

  5. High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Wen-Ping, Gu; Huan-Tao, Duan; Jin-Yu, Ni; Yue, Hao; Jin-Cheng, Zhang; Qian, Feng; Xiao-Hua, Ma

    2009-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current I Dsat , maximal transconductance g m , and the positive shift of threshold voltage V TH at high drain-source voltage V DS . The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with V DS = 20 V and V GS = 0 V applied to the device for 10 4 sec, the SiN passivation decreases the stress-induced degradation of I Dsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of I Dsat , which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  6. 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.

  7. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wang, X. Q., E-mail: wangshi@pku.edu.cn; Shen, B., E-mail: bshen@pku.edu.cn [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Fu, K.; Zhang, B. S. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Ruoshui Road 398, 215123 Suzhou (China); Hashimoto, H.; Yoshikawa, A. [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Ge, W. K. [Department of Physics, Tsinghua University, Beijing 100871 (China)

    2014-04-28

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection.

  8. 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

  9. A Ga 2O 3 passivation technique compatible with GaAs device processing

    Science.gov (United States)

    Hong, M.; Passlack, M.; Mannaerts, J. P.; Harris, T. D.; Schnoes, M. L.; Opila, R. L.; Krautter, H. W.

    1997-04-01

    Electronic and structural properties of ex-situ fabricated Ga 2O 3GaAs interfaces have been investigated. The fabrication comprises thermal desorption of native oxide and subsequent Ga 2O 3 film deposition on (100) GaAs wafers in ultra-high vacuum. Interfacial x-ray photoelectron spectroscopy revealed the absence of As xO y indicating thermodynamic stability of the oxide-GaAs interface. A low interface recombination velocity S of 9000 cm/s equivalent to an interface state density Dit in the upper 10 10 cm -2 eV -1 range has been inferred. The technique provides excellent passivation for GaAs wafers or surfaces exposed to room air and/or processing environments during fabrication of devices such as FETs, HBTs, etc.

  10. Electrical characterization of InGaN/GaN quantum dots by deep level transient spectroscopy

    International Nuclear Information System (INIS)

    Kim, J.S.; Kim, E.K.; Kim, H.J.; Yoon, E.; Park, I.W.; Park, Y.J.

    2004-01-01

    We have investigated the electrical property of InGaN quantum dots (QDs) embedded in GaN layer using capacitance-voltage and deep-level transient spectroscopy (DLTS) measurements. The apparent activation energy was observed 0.43 eV below the conduction band edge of barrier layers in InGaN/GaN QDs system. The capture barrier height of InGaN QDs was measured more than about 0.17 eV, showing the existence of strain between QDs and barrier layers. Thus, the bound state of QDs was estimated as 0.26 eV apart from the conduction band edge of the GaN. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Mid-infrared Photoconductive Response in AlGaN/GaN Step Quantum Wells

    Science.gov (United States)

    Rong, X.; Wang, X. Q.; Chen, G.; Zheng, X. T.; Wang, P.; Xu, F. J.; Qin, Z. X.; Tang, N.; Chen, Y. H.; Sang, L. W.; Sumiya, M.; Ge, W. K.; Shen, B.

    2015-09-01

    AlGaN/GaN quantum structure is an excellent candidate for high speed infrared detectors based on intersubband transitions. However, fabrication of AlGaN/GaN quantum well infrared detectors suffers from polarization-induced internal electric field, which greatly limits the carrier vertical transport. In this article, a step quantum well is proposed to attempt solving this problem, in which a novel spacer barrier layer is used to balance the internal electric field. As a result, a nearly flat band potential profile is obtained in the step barrier layers of the AlGaN/GaN step quantum wells and a bound-to-quasi-continuum (B-to-QC) type intersubband prototype device with detectable photocurrent at atmosphere window (3-5 μm) is achieved in such nitride semiconductors.

  12. Anisotropy of mosaic structure of GaAsP layers grown on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Saka, T. [Daido Institute of Technology, 10-3, Takiharu-cho, Minami-ku, Nagoya 457-8530 (Japan); Kato, T. [Daido Steel Co. Ltd., 2-30, Daido-cho, Minami-ku, Nagoya 457-8545 (Japan); Jin, X.G.; Tanioku, M.; Ujihara, T.; Takeda, Y. [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yamamoto, N.; Nakagawa, Y.; Mano, A.; Okumi, S.; Yamamoto, M.; Nakanishi, T. [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Horinaka, H.; Matsuyama, T. [Faculty of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai 599-8531 (Japan); Yasue, T.; Koshikawa, T. [Fundamental Electronics Research Institute, Osaka Electro-Communication University, 18-8, Hatsu-cho, Neyagawa 572-8530 (Japan)

    2009-08-15

    The crystalline structure of GaAsP layers grown on GaAs and GaP(001) substrates, used for spin polarized photocathodes, has been investigated by X-ray diffraction. The layers on the GaAs substrate possess a mosaic structure observable by X-ray topography and consist of many large blocks. The mosaicity is anisotropic and the distribution of the mosaic is restricted within the (110) plane, and the blocks zigzag around the [110] direction. The layer grown on the GaP substrate was uniform and no mosaic was observed in the topographs. The results indicate that different mechanisms of strain release occur in GaAsP layers for tensile and compressive strains. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  13. Characterization of Inx Ga1-x As-GaAs heterostructures via electron beam techniques

    Science.gov (United States)

    Gomez-Barojas, Estela; Silva-Gonzalez, Rutilo; Serrano-Rojas, Rosa Maria; Vidal-Borbolla, Miguel Angel

    2005-03-01

    In the case of strained superlattices abrupt heterointerfaces are required because compositional fluctuations at heterointerfaces results in uncertainty in both composition and lattice constant. The aim of this work is to study exsitu the surface morphology, the periodicity and elemental composition of a set of 3 InGaAs-GaAs heterostructures grown on GaAs (100) substrates by a molecular beam epitaxy system. The heterostructures are formed by 10 periods of InGaAs-GaAs epitaxially grown on GaAs substrates with nominal thickness of 500 and 1000 å, respectively. The techniques used for this purpose are the scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The In content in the heterostructures is determined from corresponding Auger depth profiles. This work has been supported by VIEP-BUAP, Project No. II53G02.

  14. 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%.

  15. 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%.

  16. Water, Air Emissions, and Cost Impacts of Air-Cooled Microturbines for Combined Cooling, Heating, and Power Systems: A Case Study in the Atlanta Region

    Directory of Open Access Journals (Sweden)

    Jean-Ann James

    2016-12-01

    Full Text Available The increasing pace of urbanization means that cities and global organizations are looking for ways to increase energy efficiency and reduce emissions. Combined cooling, heating, and power (CCHP systems have the potential to improve the energy generation efficiency of a city or urban region by providing energy for heating, cooling, and electricity simultaneously. The purpose of this study is to estimate the water consumption for energy generation use, carbon dioxide (CO2 and NOx emissions, and economic impact of implementing CCHP systems for five generic building types within the Atlanta metropolitan region, under various operational scenarios following the building thermal (heating and cooling demands. Operating the CCHP system to follow the hourly thermal demand reduces CO2 emissions for most building types both with and without net metering. The system can be economically beneficial for all building types depending on the price of natural gas, the implementation of net metering, and the cost structure assumed for the CCHP system. The greatest reduction in water consumption for energy production and NOx emissions occurs when there is net metering and when the system is operated to meet the maximum yearly thermal demand, although this scenario also results in an increase in greenhouse gas emissions and, in some cases, cost. CCHP systems are more economical for medium office, large office, and multifamily residential buildings.

  17. Trends in cytogenetic testing and identification of chromosomal abnormalities among pregnancies and children with birth defects, metropolitan Atlanta, 1968-2005.

    Science.gov (United States)

    Jackson, Jodi M; Crider, Krista S; Rasmussen, Sonja A; Cragan, Janet D; Olney, Richard S

    2012-01-01

    The purpose of this study was to examine changes in the use of cytogenetic testing and identification of chromosomal abnormalities among pregnancies and children with birth defects. Utilizing data from 1968 to 2005 from the Metropolitan Atlanta Congenital Defects Program, we analyzed trends in the frequency and timing (prenatal or postnatal) of cytogenetic testing and the prevalence of recognized chromosome abnormalities among pregnancies and children with birth defects (n = 51,424). Cytogenetic testing of pregnancies and children with birth defects increased from 7.2% in 1968 to 25.0% in 2005, as did the identification of chromosomal abnormalities (2.2% in 1968 to 6.8% in 2005). The use of prenatal cytogenetic testing decreased from 1996 to 2005 among women aged ≥35 years. Identification of chromosomal abnormalities in pregnancies and children with birth defects increased from 1968 to 2005, possibly due to increased testing, improved diagnostic techniques, or increasing maternal age. The decline in prenatal cytogenetic testing observed among mothers aged ≥35 years may be related to the availability of improved prenatal screening techniques, resulting in a reduction in the utilization of invasive diagnostic tests. Published 2011 Wiley Periodicals, Inc. This article is a U.S. Government work and is in the public domain in the USA.

  18. Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

    Science.gov (United States)

    Zhang, Jingzhao; Zhang, Yiou; Tse, Kinfai; Zhu, Junyi

    2018-01-01

    Heterostructures of wurtzite based devices have attracted great research interest because of the tremendous success of GaN in light emitting diodes (LED) industry. High-quality GaN thin films on inexpensive and lattice matched ZnO substrates are both commercially and technologically desirable. Intrinsic wetting conditions, however, forbid such heterostructures as the energy of ZnO polar surfaces is much lower than that of GaN polar surfaces, resulting in 3D growth mode and poor crystal quality. Based on first-principles calculations, we propose the use of surfactant hydrogen to dramatically alter the growth mode of the heterostructures. Stable H-involved surface configurations and interfaces are investigated with the help of our newly developed modelling techniques. The temperature and chemical potential dependence of our proposed strategy, which is critical in experiments, is predicted by applying the experimental Gibbs free energy of H2. Our thermodynamic wetting condition analysis is a crucial step for the growth of GaN on ZnO, and we find that introducing H will not degrade the stability of ZnO substrate. This approach will allow the growth of high-quality GaN thin films on ZnO substrates. We believe that our new strategy may reduce the manufactory cost, improve the crystal quality, and improve the efficiency of GaN-based devices.

  19. Metamagnetism in Ce(Ga,Al)2

    Indian Academy of Sciences (India)

    Abstract. Effect of Al substitution on the magnetic properties of Ce(Ga1−x Alx )2 (x = 0, 0.1 and. 0.5) system has been studied. The magnetic state of CeGa2 is found to be FM with a TC of 8 K, whereas the compounds with x =0.1 and 0.5 are AFM and possess TN of about 9 K. These two com- pounds undergo metamagnetic ...

  20. CBE growth of GaAs/GaAlAs HBTs using the new DEAlH-NMe 3 precursor and all-gaseous dopants

    Science.gov (United States)

    Lane, P. A.; Whitehouse, C. R.; Martin, T.; Houlton, M.; Williams, G. M.; Cullis, A. G.; Gill, S. S.; Dawsey, J. R.; Ball, G.; Hughes, B. T.; Crouch, M. A.; Allenson, M. B.

    1992-05-01

    This paper describes the first reported use of diethylaluminium hydride-trimethylamine adduct (DEAlH-NMe 3) for the growth of GaAs/GaAlAs power heterojunction bipolar transistors (HBTs) by chemical beam epitaxy (CBE). This precursor possesses a significantly higher vapour pressure than the more conventionally used triethylaluminium (TEA), and leads to much less stringent requirements for bubbler and gas-line heating, and also much-improved GaAs/GaAlAs heterojunction definition when no carrier gas is employed. The use of all-gaseous n- and p-type dopants offers significant technological advantages in CBE, and the current paper also provides the first report of the use of hydrogen sulphide for n-type doping of CBE-grown GaAlAs HBT emitter regions. In conclusion, DC and RF data obtained from the heterojunction bipolar transistors fabricated to date are described. A DC gain of 40 has already been measured and encouraging early data obtained from RF-probed devices are also presented.

  1. 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.

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

    Indian Academy of Sciences (India)

    The temperature-dependent PL properties of GaN-rich InGa1−N alloys is investigated and -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 should be the ...

  3. Effect of GaN template thickness and morphology on Al{sub x}Ga{sub 1−x}N (0 < x < 0.2) growth by MOVPE

    Energy Technology Data Exchange (ETDEWEB)

    Halidou, I., E-mail: ibrahim.halidou@fsm.rnu.tn [Université de Monastir, Faculté des Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications (URHEA) 5000 Monastir (Tunisia); Touré, A. [Université de Monastir, Faculté des Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications (URHEA) 5000 Monastir (Tunisia); Fouzri, A. [Université de Monastir, Faculté des Sciences, Laboratoire de Physico-Chimie des Matériaux, Unité de service commun de recherche “High Resolution X-ray Diffractometer”, 5000 Monastir (Tunisia); Ramonda, M. [Laboratoire de Microscopie à Champ Proche, Université de Montpellier II, 34095 Montpellier Cedex 5 (France); El Jani, B. [Université de Monastir, Faculté des Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications (URHEA) 5000 Monastir (Tunisia)

    2013-09-01

    We have grown Al{sub x}Ga{sub 1−x}N/GaN (0 < x < 0.2) films by MOVPE at atmospheric pressure in a home-made vertical reactor. The films were deposited on high temperature GaN templates which were grown on in situ nano-masked (0 0 0 1) sapphire substrates by using Si/N treatment. This process presents advantages of ELO technology without its ex situ complicated steps and induces a transition from 3D mode (initial stage) to 2D growth mode. We investigate systematically the effect of the template thickness and morphology on structural and morphological properties of AlGaN films. Four 0.5 μm-thick Al{sub 0.07}Ga{sub 0.93}N samples grown on different GaN templates have been studied. The HRXD and the AFM results show a better film quality when the AlGaN layer is grown on a 1.3 μm-thick 2D GaN template. It is possible to control the stress in the layers. The crystalline quality is also showed to degrade with Al solid content increase.

  4. Migration characterization of Ga and In adatoms on dielectric surface in selective MOVPE

    Science.gov (United States)

    Chen, Wei-Jie; Han, Xiao-Biao; Lin, Jia-Li; Hu, Guo-Heng; Liu, Ming-Gang; Yang, Yi-Bin; Chen, Jie; Wu, Zhi-Sheng; Liu, Yang; Zhang, Bai-Jun

    2015-11-01

    Migration characterizations of Ga and In adatoms on the dielectric surface in selective metal organic vapor phase epitaxy (MOVPE) were investigated. In the typical MOVPE environment, the selectivity of growth is preserved for GaN, and the growth rate of GaN micro-pyramids is sensitive to the period of the patterned SiO2 mask. A surface migration induced model was adopted to figure out the effective migration length of Ga adatoms on the dielectric surface. Different from the growth of GaN, the selective area growth of InGaN on the patterned template would induce the deposition of InGaN polycrystalline particles on the patterned SiO2 mask with a long period. It was demonstrated with a scanning electron microscope and energy dispersive spectroscopy that the In adatoms exhibit a shorter migration length on the dielectric surface. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 51177175), the National Basic Research Program of China (Grant No. 2011CB301903), the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 20110171110021), the International Sci. & Tech. Collaboration Program of China (Grant No. 2012DFG52260), the International Sci. & Tech. Collaboration Program of Guangdong Province, China (Grant No. 2013B051000041), the Science and Technology Plan of Guangdong Province, China (Grant No. 2013B010401013), the National High Technology Research and Development Program of China (Grant No. 2014AA032606), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics, China (Grant No. IOSKL2014KF17).

  5. 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 d......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...

  6. Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices

    Science.gov (United States)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Osinsky, A. V.; Norris, P. E.; Pearton, S. J.; Van Hove, J.; Wowchak, A.; Chow, P.

    2001-12-01

    Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices are compared to those of similarly doped p-GaN films. It is shown that modulation doping increases the sheet hole concentration by several times. In p-AlGaN/GaN superlattices grown on GaN underlayers, this increase is accompanied by a significant increase in hole mobility which results in a remarkable decrease in sheet resistivity of the structure compared to p-GaN films and this decrease in sheet resistivity should hold up to temperatures exceeding 350 °C. For superlattices prepared on AlGaN underlayers, the mobility decreases compared to p-GaN. In such superlattices, one also observes a strong redshift and a strong broadening of the band edge luminescence peak coming most probably from increased mosaicity and strain which would also explain the observed deterioration of mobility. The magnitude of the redshift in the position of the band edge luminescence band slightly increased upon application of reverse bias which is interpreted as a manifestation of quantum-confined Stark effect.

  7. 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)

  8. 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

  9. Interface electron traps and capacitance characteristics of AlGaN/GaN

    International Nuclear Information System (INIS)

    Osvald, J.

    2012-01-01

    We simulated the charge transport in heterostructures by well-known drift-diffusion approximation. Continuity equations were solved self-consistently with the Poisson equation and we received the electric potential and the charge concentration in every point of the whole device. The AlGaN/GaN structure consisted of 25 nm thick AlGaN barrier layer and 75 nm thick GaN buffer layer. Doping concentration of AlGaN barrier layer was assumed to be 1 · 10 18 cm -3 and for GaN buffer layer we considered two doping concentrations assumed, 1 · 10 17 cm -3 , and 1 · 10 16 cm -3 , the sheet concentration of positive piezoelectric charge at the AlGaN/GaN interface responsible for the 2DEG formation was set to 8 · 10 12 cm -2 . Schottky barrier height at the metal/AlGaN interface was chosen to be 1.3 V. (authors)

  10. 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......-dependent properties to minimize passivation layer removal for electrical contacting is demonstrated. Thorough electrical characterization and analysis of the cell is reported. The electrostatic potential distribution across the radial p-i-n junction GaAs NW is investigated by off-axis electron holography....

  11. 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

  12. 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

    Vascular adhesion protein-1 (VAP-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...... to previously published methods. A simple, robust radiosynthesis of [68 Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non-decay corrected) was identified, 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...

  13. GaAs FETs and novel heteroepitaxial quaternary lasers grown on InP substrates by organometallic chemical vapor deposition

    International Nuclear Information System (INIS)

    Lo, Y.H.; Bhat, R.; Chang-Hasnain, C.; Caneau, C.; Zah, C.E.; Lee, T.P.

    1988-01-01

    This paper reports the GaAs MESFETs and 1.3μm buried hetero-structure lasers with AlGaAs/GaAs lateral confinement layers simultaneously grown by OMCVD and fabricated on InP structures. The 1μm recessed gate MESFET has a transconductance of 220 mS/mm and the novel structured laser has a CW threshold current of 45 mA. The heteroepitaxy technology and devices show great promises for long wavelength opto-electronic integrated circuits

  14. Epitaxial Al{sub x}Ga{sub 1–x}As:Mg alloys with different conductivity types

    Energy Technology Data Exchange (ETDEWEB)

    Seredin, P. V., E-mail: paul@phys.vsu.ru; Lenshin, A. S. [Voronezh State University (Russian Federation); Arsentiev, I. N., E-mail: arsentyev@mail.ioffe.ru; Zhabotinskii, A. V.; Nikolaev, D. N.; Tarasov, I. S.; Shamakhov, V. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Prutskij, Tatiana, E-mail: prutskiy@yahoo.com [Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias (Mexico); Leiste, Harald; Rinke, Monika [Karlsruhe Nano Micro Facility (Germany)

    2017-01-15

    The structural, optical, and energy properties of epitaxial Al{sub x}Ga{sub 1–x}As:Mg/GaAs(100) heterostructures at different levels of doping with Mg are studied by high-resolution X-ray diffraction analysis and Raman and photoluminescence spectroscopies. It is shown that, by choosing the technological conditions of Al{sub x}Ga{sub 1–x}As:Mg alloy production, it is possible to achieve not only different conductivity types, but also substantially different charge-carrier concentrations in an epitaxial film.

  15. Planar Homojunction Gallium Nitride (GaN) P-i-N Device Evaluated for Betavoltaic Energy Conversion: Measurement and Analysis

    Science.gov (United States)

    2016-09-01

    7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) US Army Research Laboratory ATTN: RDRL-SED-E 2800 Powder Mill Road Adelphi, MD 20783-1138...3). 10. Wang G-q, Yang , Liu. Electrical performance of GaN diode as betavoltaic isotope battery energy converter. Atomic Energy Sci and Tech...Conference, Orlando, FL, 2005 Jan 3. 16. Li F , Gao X, Yuan Y, Yuan J, Lu M. GaN PIN betavoltaic nuclear batteries. Science China Technological

  16. 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

  17. Semiconductor technology program: Progress briefs

    Science.gov (United States)

    Galloway, K. F.; Scace, R. I.; Walters, E. J.

    1981-01-01

    Measurement technology for semiconductor materials, process control, and devices, is discussed. Silicon and silicon based devices are emphasized. Highlighted activities include semiinsulating GaAs characterization, an automatic scanning spectroscopic ellipsometer, linewidth measurement and coherence, bandgap narrowing effects in silicon, the evaluation of electrical linewidth uniformity, and arsenicomplanted profiles in silicon.

  18. Intergenerational bargaining in technology adoption

    Czech Academy of Sciences Publication Activity Database

    Jeong, Byeongju

    -, č. 414 (2010), s. 1-61 ISSN 1211-3298 R&D Projects: GA MŠk LC542 Institutional research plan: CEZ:MSM0021620846 Keywords : technology adoption * stagnation * economic integration * political fragmentation Subject RIV: AH - Economics http://www.cerge-ei.cz/pdf/wp/Wp414.pdf

  19. Hole-spin dynamics in p-doped GaAs/AlGaAs heterostructures; Lochspindynamik in p-dotierten GaAs/AlGaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Kugler, Michael

    2012-11-15

    This work investigates the spin dynamics of holes in p-doped GaAs/AlGaAs quantum wells (QW) at low temperatures. To examine the energetic structure of the used samples, PL and PLE-spectroscopy were employed. Time resolved Kerr and Faraday-Rotation (TRKR/FR) and 'Resonant Spin Amplification' (RSA) were used to analyse the spin dynamics. First, the signal formation in TRKR/FR and RSA experiments is discussed taking into account the interconnected charge carrier dynamics and spin dynamics of electrons and holes. An excitation energy dependent sign change of the Kerr signal amplitude could be observed, whose energetic position corresponds to an absorption maximum in PLE experiments. This behavior could be explained by an energy dependent splitting of the spin niveaus, which leads to an energy dependence of the Faraday and Kerr signal. Furthermore, two initialization processes were investigated, which could be used to transfer optically generated spin information into the resident hole spin system. This could be achieved by either applying a magnetic field, or by rapid dephasing of hole spins immediately after excitation. Changes in excitation energy, excitation density or temperature could be used to influence the fast dephasing processes and therefore the initial ratio of hole to electron spins. The complex, interconnected charge carrier and spin dynamics of electrons and holes could be accurately reproduced using a rate equation model. This allowed for the extraction of physically relevant parameters like spin lifetimes and g-factors from RSA and TRKR/FR data. An analytical model that was developed at the Wroclaw University of Technology delivered matching results. In the second part of the experimental work, the dependence of the hole spin lifetime and the hole g-factor on various parameters was analysed. Here, the RSA method could for the first time be applied to two-dimensional hole systems, allowing for new insights into the regime of long lived hole

  20. Fabrication of vertical GaN/InGaN heterostructure nanowires using Ni-Au bi-metal catalysts.

    Science.gov (United States)

    Ha, Ryong; Kim, Sung-Wook; Choi, Heon-Jin

    2013-06-26

    We have fabricated the vertically aligned coaxial or longitudinal heterostructure GaN/InGaN nanowires. The GaN nanowires are first vertically grown by vapor-liquid-solid mechanism using Au/Ni bi-metal catalysts. The GaN nanowires are single crystal grown in the [0001] direction, with a length and diameter of 1 to 10 μm and 100 nm, respectively. The vertical GaN/InGaN coaxial heterostructure nanowires (COHN) are then fabricated by the subsequent deposition of 2 nm of InxGa1-xN shell on the surface of GaN nanowires. The vertical GaN/InGaN longitudinal heterostructure nanowires (LOHN) are also fabricated by subsequent growth of an InGaN layer on the vertically aligned GaN nanowires using the catalyst. The photoluminescence from the COHN and LOHN indicates that the optical properties of GaN nanowires can be tuned by the formation of a coaxial or longitudinal InGaN layer. Our study demonstrates that the bi-metal catalysts are useful for growing vertical as well as heterostructure GaN nanowires. These vertically aligned GaN/InGaN heterostructure nanowires may be useful for the development of high-performance optoelectronic devices.

  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. A Heuristic Approach

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 10; Issue 5 ... Graduate Student School of Physics Georgia Institute of Technology, Atlanta GA 30332-0430, USA. Associate Professor Department of Aerospace Engineering Indian Institute of Technology Bombay, Powai Mumbai 400076, India.

  3. 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.)

  4. Hybrid laser technology for composite coating and medical applications

    Czech Academy of Sciences Publication Activity Database

    Jelínek, Miroslav; Kocourek, Tomáš; Písařík, Petr; Mikšovský, Jan; Remsa, Jan; Mihailescu, I. N.; Kopeček, Jaromír

    2014-01-01

    Roč. 10, č. 1 (2014), s. 1-8 ISSN 1823-3430 R&D Projects: GA ČR(CZ) GA101/09/0702; GA MŠk LD12069 Institutional support: RVO:68378271 Keywords : hybrid technology * pulsed laser deposition * biocompatible composites * doped coating * composite coating Subject RIV: BM - Solid Matter Physics ; Magnetism http://web.usm.my/jes/pastIssue.html

  5. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    International Nuclear Information System (INIS)

    Hodges, C.; Pomeroy, J.; Kuball, M.

    2014-01-01

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate

  6. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    Energy Technology Data Exchange (ETDEWEB)

    Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Pomeroy, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  7. 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 ...

  8. Optical quenching of X-ray photoconductor based on GaN

    International Nuclear Information System (INIS)

    Yan Changsheng; Fu Kai; Wang Guo; Lu Min

    2011-01-01

    X-ray photoconductor based on GaN have been made by using advanced semiconductor microfabrication technology. Optical quenching phenomenon of GaN X-ray detector was presented. The photocurrent had a mutation when the fluorescent light was turned on and off. Experiments have been carried out to analyze the optical quenching and current mutation phenomenons. The results have indicated that optical quenching effect associates with a hole trap and recombination centers, while the current mutation results from a UV light which excited the electron from valence band to conduction band. (authors)

  9. Modeling and Design of Graphene GaAs Junction Solar Cell

    Directory of Open Access Journals (Sweden)

    Yawei Kuang

    2015-01-01

    Full Text Available Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work.

  10. Report of the George A. Towns Elementary School solar heating and cooling project, Atlanta, Georgia. United States special format report

    Energy Technology Data Exchange (ETDEWEB)

    1976-07-01

    The design, construction, and performance analysis of an experimental solar heating and cooling system to accommodate a building of approximately 3,000 m/sup 2/ in area are described. The objectives of the experiment are to: make a significant contribution to solar design, technology, and acceptability; conduct an advanced experiment on an integrated large-scale solar heating and cooling system, determine its performance, reliability, and maintainability, and compare these actual results with predicted performance; identify subsystem interface problems that cannot adequately be predicted by theoretical analysis; operationally test major components and identify improvements required; and identify cost reducing materials and techniques which may improve the economic viability of solar heating and cooling systems. (WDM)

  11. Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures using capacitance deep level optical spectroscopy

    OpenAIRE

    Armstrong, A; Chakraborty, A; Speck, J S; DenBaars, S P; Mishra, U K; Ringel, S A

    2006-01-01

    Deep levels were observed using capacitance deep level optical spectroscopy (DLOS) in an AlGaN/GaN heterostructure equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AlGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AlGaN- and GaN-related defects, and the latter emphasizes defects residing in the GaN. A band gap state at E-c-3.85 eV was unambigu...

  12. 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

  13. Characterization of GaN/AlGaN epitaxial layers grown by ...

    Indian Academy of Sciences (India)

    of the native substrate, GaN epitaxial layers are generally grown on sapphire or. SiC substrate with lattice and thermal mismatch. Growth of GaN epitaxial layers on such substrates, by using a low-temperature nucleation layer demonstrated a good crystal quality [4]. Remarkable improvement in epitaxial material quality is.

  14. 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...

  15. Sub-monolayer Deposited InGaAs/GaAs Quantum Dot Heterostructures and Lasers

    DEFF Research Database (Denmark)

    Xu, Zhangcheng

    2004-01-01

    are two different methods of growing self-assembled QDs. In the case of SK growth, which has been widely used for lattice mis-matched materials, such as In(Ga)As/Ga(Al)As, coherent three dimensional (3D) islands form on top of a wetting layer to relax the strain energy. However,in the case of SML...

  16. 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)

  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. 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

  19. Measurement of strain in InGaN/GaN nanowires and nanopyramids

    DEFF Research Database (Denmark)

    Stankevic, Tomas; Mickevicius, Simas; Nielsen, Mikkel Schou

    2015-01-01

    the individual facet planes. The strained lattice constants were found from the positions of the Bragg peaks. Vegard's law and Hooke's law for an anisotropic medium were applied in order to find the composition and strain in the InGaN shells. A range of nanowire samples with different InGaN shell thicknesses...

  20. 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.

  1. 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.

  2. 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...

  3. Capture and release of carriers in InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Porte, Henrik; Daghestani, N.

    2009-01-01

    We observe the ultrafast capture and release of charge carriers in InGaAs/GaAs quantum dots (QDs) at room-temperature with time-resolved terahertz spectroscopy. For excitation into the barrier states, a decay of the photoinduced conductivity, due to capture of carriers into the nonconducting QD...

  4. Deep defects in GaN/AlGaN/SiC hererostructures

    Czech Academy of Sciences Publication Activity Database

    Kindl, Dobroslav; Hubík, Pavel; Krištofik, Jozef; Mareš, Jiří J.; Výborný, Zdeněk; Leys, M.R.; Boeykens, S.

    2009-01-01

    Roč. 105, č. 9 (2009), 093706/1-093706/8 ISSN 0021-8979 R&D Projects: GA ČR GA202/07/0525 Institutional research plan: CEZ:AV0Z10100521 Keywords : nitrides * silicon carbide * deep levels * DLTS Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.072, year: 2009

  5. Excitonic complexes in GaN/(Al,Ga)N quantum dots

    International Nuclear Information System (INIS)

    Elmaghraoui, D; Triki, M; Jaziri, S; Muñoz-Matutano, G; Leroux, M; Martinez-Pastor, J

    2017-01-01

    Here we report a theoretical investigation of excitonic complexes in polar GaN/(Al,Ga)N quantum dots (QDs). A sum rule between the binding energies of charged excitons is used to calculate the biexciton binding energy. The binding energies of excitonic complexes in GaN/AlN are shown to be strongly correlated to the QD size. Due to the large hole localization, the positively charged exciton energy is found to be always blueshifted compared to the exciton one. The negatively charged exciton and the biexciton energy can be blueshifted or redshifted according to the QD size. Increasing the size of GaN/AlN QDs makes the identification of charged excitons difficult, and the use of an Al 0.5 Ga 0.5 N barrier can be advantageous for clear identification. Our theoretical results for the binding energy of exciton complexes are also confronted with values deduced experimentally for InAs/GaAs QDs, confirming our theoretical prediction for charged excitonic complexes in GaN/(Al,Ga)N QDs. Finally, we realize that the trends of excitonic complexes in QDs are significantly related to competition between the local charge separation (whatever its origin) and the correlation effect. Following our findings, entangled photons pairs can be produced in QDs with careful control of their size in order to obtain zero exciton–biexciton energy separation. (paper)

  6. Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Lü Ling; Zhang Jin-Cheng; Xue Jun-Shuai; Ma Xiao-Hua; Zhang Wei; Bi Zhi-Wei; Zhang Yue; Hao Yue

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10 15 cm −2 . The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance—voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  7. Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

    Science.gov (United States)

    Lü, Ling; Zhang, Jin-Cheng; Xue, Jun-Shuai; Ma, Xiao-Hua; Zhang, Wei; Bi, Zhi-Wei; Zhang, Yue; Hao, Yue

    2012-03-01

    AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 1015 cm-2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance—voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.

  8. 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...

  9. Investigation of Photovoltaic Properties of Single Core-Shell GaN/InGaN Wires.

    Science.gov (United States)

    Messanvi, A; Zhang, H; Neplokh, V; Julien, F H; Bayle, F; Foldyna, M; Bougerol, C; Gautier, E; Babichev, A; Durand, C; Eymery, J; Tchernycheva, M

    2015-10-07

    We report the investigation of the photovoltaic properties of core-shell GaN/InGaN wires. The radial structure is grown on m-plane {11̅00} facets of self-assembled c̅-axis GaN wires elaborated by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. The conversion efficiency of wires with radial shell composed of thick In0.1Ga0.9N layers and of 30× In0.18Ga0.82N/GaN quantum wells are compared. We also investigate the impact of the contact nature and layout on the carrier collection and photovoltaic performances. The contact optimization results in an improved conversion efficiency of 0.33% and a fill factor of 83% under 1 sun (AM1.5G) on single wires with a quantum well-based active region. Photocurrent spectroscopy demonstrates that the response ascribed to the absorption of InGaN/GaN quantum wells appears at wavelengths shorter than 440 nm.

  10. AlGaN/GaN-based HEMT on SiC substrate for microwave ...

    Indian Academy of Sciences (India)

    The AlGaN/GaN-based high electron mobility transistors (HEMTs) are attracting much research interest worldwide because of their high density of states (DOS), high elec- tron saturation drift velocity, large band gap, high breakdown voltage, high electric field. DOI: 10.1007/s12043-012-0290-9; ePublication: 20 June 2012.

  11. 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

  12. Sharp interfaces in p+-AlGaAs/n-GaAs epitaxial structures obtained by MOCVD

    Directory of Open Access Journals (Sweden)

    Vakiv N. M.

    2014-06-01

    Full Text Available The complexity of forming sharp and high-quality boundaries in p+AlGaAs/n-GaAs systems by MOCVD method is caused by differing on 80—120°С optimal crystallization temperature of GaAs layers and n-AlGaAs solid solutions. A method of forming qualitative hetero boundaries under conditions of continuous growth at changing crystallization temperature from 600—700°C has been developed. It has been determined that the crystallization of p+-AlGaAs: Zn solid solution layer on the surface of n-GaAs:Si layer, with increasing the crystallization temperature in the temperature range of 600—760°C at a rate 8—10 °C/min allows to crystallize sharp impurity boundary between the layers of p- and n-type conductivity. The method of forming sharp hetero boundaries in p-GaAs:Zn/n-GaAs:Si systems can be used for manufacturing wide range of epitaxial structures.

  13. 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.

  14. Threshold Voltage Instability in Al2O3/GaN/AlGaN/GaN Metal-Insulator-Semiconductor High-Electron Mobility Transistors

    Science.gov (United States)

    Huang, Sen; Yang, Shu; Roberts, John; Chen, Kevin J.

    2011-11-01

    The threshold voltage (Vth) instability in GaN-based metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current-voltage (I-V), high-frequency capacitance-voltage (C-V) (HFCV), and quasi-static C-V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques.

  15. Improved light output power in GaN-based vertical light-emitting diodes with p-AlInGaN/GaN superlattices

    International Nuclear Information System (INIS)

    Kim, Su Jin; Son, Sung Hun; Kim, Tae Geun

    2012-01-01

    In this paper, we report the effect of p-type AlGaInN/GaN superlattices (SLs) as electron blocking layers (EBLs) on the optical properties of vertical light-emitting diodes (VLEDs). Using p-AlGaInN/GaN SLs in VLEDs, we have achieved significant improvements in the output power and the external quantum efficiency (EQE) as compared to VLEDs using p-AlGaInN EBL and p-AlGaN EBL. The forward voltages at 350 mA were calculated to be 4.1, 4.3, and 4.4 V for VLEDs with p-AlInGaN/GaN SLs, p-AlInGaN, and p-AlGaN EBLs, respectively. When p-AlInGaN/GaN SLs were inserted as the EBLs, the light-output power and the EQE were also improved by 16.8% and 17.3% at 350 mA, respectively, as compared to those with p-AlGaN EBLs.

  16. Laser-Combined Scanning Tunneling Microscopy on the Carrier Dynamics in Low-Temperature-Grown GaAs/AlGaAs/GaAs

    Directory of Open Access Journals (Sweden)

    Yasuhiko Terada

    2011-01-01

    Full Text Available We investigated carrier recombination dynamics in a low-temperature-grown GaAs (LT-GaAs/AlGaAs/GaAs heterostructure by laser-combined scanning tunneling microscopy, shaken-pulse-pair-excited STM (SPPX-STM. With the AlGaAs interlayer as a barrier against the flow of photocarriers, recombination lifetimes in LT-GaAs of 4.0 ps and GaAs of 4.8 ns were successfully observed separately. We directly demonstrated the high temporal resolution of SPPX-STM by showing the recombination lifetime of carriers in LT-GaAs (4.0 ps in the range of subpicosecond temporal resolution. In the carrier-lifetime-mapping measurement, a blurring of recombination lifetime up to 50 nm was observed at the LT-GaAs/AlGaAs boundary, which was discussed in consideration of the screening length of the electric field from the STM probe. The effect of the built-in potential on the signal, caused by the existence of LT-GaAs/AlGaAs/GaAs boundaries, was discussed in detail.

  17. 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.)

  18. 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.

  19. 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

  20. 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.)