bluuebunny/crossref_metadata_2025_split huggingface dataset:
Weak Antilocalization in Polarization-Doped AlGaN/GaN Heterostructures
Authors: Thillosen Nicolas Henri , Schäpers Thomas , Kaluza Nicoleta , Hardtdegen Hilde , Guzenko Vitaliy 
Published: April 2011

AbstractThe properties of AlGaN/GaN heterostructures have been a subject of great activity because of their application in high frequency, high power, and high temperature devices. Magnetotransport measurements give the possibility to study the properties of a two-dimensional electron gas. Indeed, Shubnikov-de Haas oscillations of a two-dimensional electron gas can be observed at high magnetic fields. Moreover, magnetoresistance measurements close to zero magnetic field give the possibility to investigate the weak localization and weak antilocalization arising from AlGaN/GaN heterostructures. The latter is related to the spin-orbit interaction on the spin of the carriers present in these heterostructures and is a key-feature of the spin-transistor proposed by Datta and Das [1]. As a matter of fact, the spin orientation between the electrodes of this novel device should be manipulated by the controllable strength of the spin-orbit interaction in the two-dimensional electron gas. In order to obtain information on spin-orbit effects in AlGaN/GaN heterostructures we therefore analyzed the weak antilocalization observed in the magnetoresistance.Polarization-doped AlGaN/GaN heterostructures were grown by metalorganic vapor phase epitaxy (MOVPE) on the (0001) surface of sapphire substrates. First a 3 mm-thick GaN buffer layer was grown, followed by a Al0.3Ga0.7N layer with a thickness of 20 nm. Magnetotransport measurements were performed over a magnetic field range from –50 mT to +50 mT at various temperatures between 0.1 and 18 K. The Hall-bars were prepared by optical lithography and Ar+-ion-beam-etching technique. The metals used for the ohmic contacts were Ti/Al/Ni/Au. The mobility and carrier concentration in the single occupied subband were obtained from the Shubnikov-de Haas oscillations with the respective values of 9100 cm2/Vs and 6.2×1012 cm-2.In our case, the Shubnikov-de Haas oscillations of the two-dimensional electron gas reveal the occupation of a single subband in the nearly triangular quantum well. At low magnetic field, weak localization as well as weak antilocalization were observed, showing that strong spin-orbit interaction is present in our structures. A previous report [2] explained the weak-antilocalization as being related to the intersubband scattering due to the occupation of a second subband in a modulation-doped quantum well. We show that weak antilocalization is also present in a polarization-doped quantum well with a single subband being occupied. In this perspective, temperature-dependent weak antilocalization measurements will be presented and analyzed using adequate theoretical models. Finally, the relevant scattering times like elastic scattering time, dephasing time as well as spin-orbit scattering time have been extracted. [1] S. Datta and B. Das, Appl. Phys. Lett. Vol. 56, pp. 665-667, 1990. [2] J. Lu et al., Appl. Phys. Lett., Vol. 85, pp. 3125-3127, 2004
Polarization-Induced 3-Dimensional Electron Slabs in Graded AlGaN Layers
Authors: Simon John , Wang Kejia , Xing Huili , Jena Debdeep , Rajan Siddharth 
Published: April 2011

AbstractBy compositionally grading AlGaN layers over different thicknesses, high mobility electron gases are produced by polarization-induced doping. Temperature dependent Hall and capacitance-voltage measurements were performed on these AlGaN layers, and two degrees of freedom are found for choosing the carrier concentration of these slabs. Carrier mobilities determined from Hall measurements are observed to be much higher than impurity doped structures of similar carrier densities. Alloy and phonon scattering are determined to be the major contributors limiting the mobility of the electron in the graded layers. This form of polarization-induced doping offers an attractive alternative to the traditional doping techniques, and may be used for highly conductive AlGaN layers with high Al composition, both for lateral and vertical transport.
ZnCdO/ZnMgO and ZnO/AlGaN Heterostructures for UV and Visible Light Emitters
Authors: Osinsky Andrei , Dong Jianwei , Xie J. Q. , Hertog B. , Dabiran A. M. , Chow P. P. , Pearton S. J. , Norton D. P. , Look D. C. , Schoenfeld W. , Lopatiuk O. , Chernyak L. , Cheung M. , Cartwright A.N. , Gerhold M. 
Published: April 2011

AbstractThis paper reviews of some of the progress made in the development of ZnO-based light emitting diodes (LEDs). n-ZnO/p-AlGaN-based heterostructures have been successfully for the fabrication of UV emitting LEDs that have operated at temperatures up to 650K, suggesting an excitonic origin for the optical transitions. RF-plasma-assisted molecular beam epitaxy has been used to grow epitaxial CdxZn1-xO films on GaN/sapphire structure. These films have a single-crystal wurtzite structure as demonstrated by structural and compositional analysis. High quality CdxZn1-xO films were grown with up to x=0.78 mole fraction as determined by RBS and SIMS techniques. Optical emission ranging from purple (Cd0.05Zn0.95O) to yellow (Cd0.29Zn0.71O) was observed. Compositional fluctuations in a Cd0.16Zn0.84O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ∼0.5 μm diameter were seen on the intensity maps. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd0.16Zn0.84O film.
Time-resolved Spectroscopy of Excitons Bound at Shallow Neutral Donors in HVPE GaN
Authors: Monemar Bo , Paskov P. P. , Bergman J. P. , Malinauskas T. , Jarasiunas K. , Toropov A. A. , Shubina T. V. , Usui A. 
Published: April 2011

AbstractTime-resolved photoluminescence (TRPL) spectroscopy has been performed in the temperature range 2 K to 300 K on thick (300 μm – 1 mm) nominally undoped bulk HVPE grown GaN layers. The PL spectra are dominated by the free excitons (FEs) and the two neutral donor bound excitons (DBEs) at about 3.4712 eV and 3.4721 eV at 2 K, assigned to the residual O and Si donors, respectively. The zero-phonon decay curves for both FEs and DBEs are nonexponential, with a fast initial decay and a slower tail at longer times. The initial decay time of the FE is about 130 ps at 2 K in such samples, the corresponding initial decay time for the DBEs for O and Si is close to 300 ps. The different lines corresponding to the so called two-electron transitions for the DBE show a different behaviour, with a longer decay time than the corresponding principal DBE states. The LO phonon replicas of the DBEs also have a decay time in excess of 1 ns in lightly doped samples.
Growth of Large AlN Single Crystals Along the [0001] Direction
Authors: Herro Ziad Georges , Zhuang Dejin , Schlesser Raoul , Collazo Ramon , Sitar Zlatko 
Published: April 2011

AbstractWe have demonstrated growth of large AlN single crystals using (0001)-oriented AlN seeds. Boules with a diameter of 15 mm and length up to 12 mm were obtained from 5 mm seeds. Step flow growth was observed on both Al and N-polar surfaces. N-polar face was suitable for growth within a large window of growth parameters while the Al-polar seeds yielded high-quality crystals only at low supersaturation.
Dislocation Reduction and Structural Properties of GaN layers Grown on N+-implanted AlN/Si (111) Substrates
Authors: Jamil Muhammad , Grandusky James R , Jindal Vibhu , Tripathi Neeraj , Sandvik Fatemeh Shahedipour 
Published: April 2011

AbstractAn alternative scheme to the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been previously introduced that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. Here, the effects of N+ ion implantation of AlN/Si (111) substrate on the structural and optical properties of the overgrown GaN epilayers have been investigated. Temperature dependent photoluminescence has been used to investigate the impact of the implantation conditions (energy and dose) on optical and structural quality of the GaN overgrown layers. A correlation between PL and high resolution x-ray diffraction (XRD) of the overgrown GaN layers show that the lowest FWHM of bandedge, the highest bandedge to deep defect blue luminescence band ratio, and the lowest symmetric rocking curve FWHM are achieved for the optimized implantation conditions. This correlates well with the results of etch pit density measurement showing an order of magnitude reduction in threading dislocation defect density
Structural and optical properties of MOCVD InAlN epilayers
Authors: Hernández S. , Wang K. , Amabile D. , Nogales E. , Pastor D. , Cuscó R. , Artús L. , Martin R.W. , O'Donnell K.P. , Watson I.M. , Network RENiBEl 
Published: April 2011

AbstractWe have studied the structural and optical properties of InAlN alloys with compositions nearly lattice-matched to GaN. Scanning electron microscopy measurements reveals a good overall surface quality, with some defect structures distributed across the surface whose density increases with the InN concentration. On the other hand, Raman scattering experiments show three peaks in the frequency range between 500 and 900 cm-1, which have been assigned to InN-like and AlN-like E2 modes and A1(LO) mode of the InAlN. These results agree with theoretical calculations previously reported where two-mode and one-mode behavior was predicted for the E and A(LO) modes, respectively. Photoluminescence and photoluminescence excitation allowed us to determine the emission and absorption energies of the InAlN epilayers. Both energies display a redshift as the InN fraction increases. We find a roughly linear increase of the Stokes shift with InN fraction, with Stokes shift values of ≈0.5 eV in the composition range close to the lattice-matched condition.
SiH4 exposure of GaN surfaces: A useful tool for highlighting dislocations
Authors: Oliver Rachel , Kappers Menno J. , Sumner Joy , Datta Ranjan , Humphreys Colin J. 
Published: April 2011

AbstractFast-turnaround, accurate methods for the assessment of threading dislocation densities in GaN are an essential research tool. Here, we present an in-situ surface treatment for use in MOVPE (metal-organic vapour phase epitaxy) growth, in which GaN is exposed to a SiH4 flux at 860 °C in the presence of NH3. Subsequent characterisation by atomic force microscopy shows that the treatment is effective in increasing edge and mixed/screw dislocation pit sizes on both n- and p-type material, and on partially coalesced GaN layers.
Comparative investigation of quantum-dot-like localization centers in InGaN quantum well and quantum dot structures
Authors: Sebald Kathrin , Lohmeyer Henning , Gutowski Jürgen , Yamaguchi Tomohiro , Hommel Detlef 
Published: April 2011

AbstractWe present comparative micro-photoluminescence measurements on InGaN/GaN quantum well and quantum dot samples. Single sharp emission lines were investigated for both kinds of samples as a function of temperature and excitation density. For the sharp emission lines of the quantum dots and the strong localization centers in the quantum well samples comparable experimental findings were obtained such as the independence of their spectral position of the excitation density and the observation of binding and antibinding multiexcitonic states giving clear evidence for the quantum dot nature of localization centers.
Stresses experienced by AlN films grown on sapphire
Authors: Bai Jie , Bai J. , Tassev V.L. , Lal Nakarmi M. , Sun W. , Huang X. , Dudley M. , Zhang H. , F. Bliss D. , Lin J. , Jiang H. , Yang J. , Asif Khan M. 
Published: April 2011

AbstractThe evolution of stress during the MOCVD growth of AlN thin films on sapphire substrates under both low and high temperature conditions has been evaluated. The final stress state of the films is assumed to consist of the summation of stresses from three different sources: (1) the stress which arises from residual lattice mismatch between film and substrate i.e. that which persists after partial relaxation by misfit dislocation formation. The extent of relaxation is determined from High Resolution TEM analysis of the substrate/film interface; (2) the stress arising from the coalescence of the 3D islands nucleated in this high mismatch epitaxy process. This requires knowledge of the island sizes just prior to coalescence and this was provided by AFM studies of samples grown under the conditions of interest; and (3) the stress generated during post-growth cooling which arises from the differences in thermal expansion coefficient between AlN and sapphire. The final resultant stress, comprising the summation of stresses arising from these three sources, is found to be tensile in the sample grown at lower temperature and compressive in the sample grown at higher temperature. These results are in general qualitative agreement with results of TEM and High resolution X-ray diffraction (HRXRD) studies, which show evidence for tensile and compressive stresses in the low temperature and high temperature cases, respectively.
Study of ELOG GaN for Application in the Fabrication of Micro-channels for Optoelectronic Devices
Authors: Rodak Lee E , Berry Ann N J , Kasarla Kalyan Reddy , Yang Nanying , Korakakis D 
Published: April 2011

AbstractGallium Nitride (GaN) is a promising wide band gap semiconductor material for many optoelectronic applications, especially in the near UV range. Over the past several years, an extensive technical effort has been focused on improving the quality of GaN films through various overgrowth techniques such as epitaxial lateral overgrowth (ELOG), facet controlled epitaxial lateral overgrowth (FACELO), and Pendeoepitaxy. ELOG has been shown to reduce the density of threading dislocations by up to five orders of magnitude [1], however a complete physical model describing lateral overgrowth is needed in order to take full advantage of the process. A lateral overgrowth model will allow for the design and fabrication of three dimensional structures that can lead to novel devices and also to efficient biosensors by integrating micro and nano channels on the same chip as the optoelectronic components.A two-step process has been used to successfully control the geometry of overgrown GaN. Conditions have been identified which give a reduced lateral growth rate, in order to allow expansion of the {112n} plane to form vertical sidewalls and for the design of channel width. These geometries are being examined for possible application in laser diode and micro-channel fabrication for integrating bio-agent detection modules.
Environmental Assessment of Micro/Nano Production in a Life Cycle Perspective
Authors: Olsen Stig , Jørgensen Michael Søgaard 
Published: April 2011

AbstractThe concept of life cycle assessment (LCA) is build upon the object of assessment, namely the functional unit, i.e. all impacts etc. are related to a specific service or function in the society. In a LCA context, the assessment of emerging technologies like Nanotechnology is challenging due to a number of knowledge gaps. It may not be known exactly what is the function (or functional unit) or what the technology may substitute and production may still be at an experimental level, raising questions about technology or materials choice.For prospective LCA studies methodologies like “consequential LCA” may be useful because future changes are taken into account. However, it still does not suffice for emerging technologies. In a recent “Green Technology Foresight” project a methodology was developed based on five elements: Life-cycle thinking, systems approach, a broad dialogue based understanding of the environment, precaution as a principle and finally, prevention as preferred strategy. When assessing emerging technologies three levels should be considered. First order effects are connected directly to production, use and disposal. Second order are effects from interaction with other parts of the economy from more intelligent design and management of processes, products, services, product chains etc. and the effect on the stocks of products. An example could be dematerialisation. Rebound effects may be considered as third order effects, like when efficiency gains stimulate new demands, which balances or overcompensates the savings.In the Micro/Nano Production area a range of new possibilities arise both within applications, production technology and materials. The Department of Manufacturing Engineering and Management at The Technical University of Denmark has staked on a joint effort in manufacturing engineering and environmental assessment for eco efficiency improvement. A review of knowledge and studies on environmental assessments in the micro/nano technology area is performed and will be used to further detail the general framework for assessment outlined above to be more specific for micro/nano production.
Addressing Environmetal Issues for the Automotive Industry
Authors: Papasavva Stella 
Published: April 2011

AbstractThe integration of environmental, social, and economic (ESE) objectives into business decisions and future planning is the path towards sustainable development. The goal of this paper is to address the environmental component of sustainable development within the automotive industry based on the Life Cycle Analysis and Well-to-Wheels approach.Life Cycle Analysis (LCA) is very relevant for making the concept of environmental sustainability operational because environmental impacts have to be examined from a 'cradle-to-grave' perspective. Life cycle analysis is an analytical tool that quantifies energy consumption and emissions associated with the raw material extraction, processing of materials, manufacturing, use phase, and end-of-life (reuse, recycling, and disposal) of products. The potential impact of current production and consumption patterns, on the future availability of non-renewable resources, can also be evaluated within the LCA framework. Thus, LCA provides an effective way for industry to support better management of natural resources, in order to maximize economic benefits and minimize environmental burdens.Well-to-Wheel (WtW) analysis is a subset of a complete LCA because it quantifies the environmental burdens associated only with the fuel production and its consumption during the driving time of a vehicle. Well-to-Wheel studies mainly provide energy use and air emissions inventories.This paper provides the results obtained from two major studies conducted at General Motors R&D Center. The first is a LCA study that assesses the environmental emissions associated with four alternative automotive paint processes and seven different paint formulations. The second is a WtW study that addresses 18 different combinations of alternative fuels and vehicle engines.Considering that the use phase of the vehicle contributes more than 80% of its life cycle energy consumption, and that the automotive paint process is the most energy intensive component of the manufacturing phase in any given vehicle, the results presented in this paper are noteworthy for environmental sustainability considerations relevant to the automotive industry.
Hydrogen as Fuel for Urban Transportation Environmental Footprint of Different Hydrogen Production Routes and the Influence on the Total Life Cycle of FC Powered Transportation Systems: An LCA Case Study within CUTE
Authors: Binder Marc , Faltenbacher Michael , Fischer Matthias 
Published: April 2011

AbstractFuel cells have the potential to offer an alternative propulsion system to convential internal combustion engines used in transportation at the present time. As a result fuel cells may provide consumers a cleaner and more efficient technology. Fuel cells are powered with hydrogen fuel which can be produced from various energy sources, which include renewable sources of energy or conventional fossil fuel. Thus, the emerging hydrogen infrastructure needs to be addressed carefully.A consortium of industries, research institutes and several European cities launched the EU-project CUTE (Clean Urban Transport in Europe), whose aim is not only to develop and demonstrate 30 fuel cell busses and the accompanying infrastructure in 10 European cities, but also assess the environmental impacts. Within the project scope the potential of fuel cell powered transport systems for reducing environmental influences such as greenhouse effect, improving the quality of the atmosphere and conserving fossil resources is assessed. This first large scale test run of fuel cell transportation systems is the best possible information base to give real life numbers about environmental impacts of a fuel cell system including hydrogen used as fuel.Meanwhile the use of hydrogen fuel is mostly considered as environmental friendly. However a statement about the actual environmental impacts is only possible by regarding the entire Life Cycle of the hydrogen, which include its production and use. Within CUTE different routes of the hydrogen production have been assessed: hydrogen production via electrolysis and steam reforming, considering different boundary conditions, e.g. country specific energy production/ supply, different ways for electricity production (e.g. wind power, geothermal energy etc.) etc.This presentation will show the environmental footprint of these routes (Life Cycle Assessment results), which enable the comparison of the environmental impacts of the different hydrogen production routes and the transportation system considering the total life cycle (production of FC bus, operation and end of life) along with diesel and natural gas as “conventional” fuels for bus operation.
A Life Cycle Analysis of Hydrogen Production for Buildings and Vehicles
Authors: Tupper Kendra , Kreider Jan F 
Published: April 2011

AbstractAspects of the hydrogen economy are addressed by quantifying impacts and costs associated with a hydrogen-based energy infrastructure. It is recommended that hydrogen (H2) is produced from Solar Thermochemical (STC) Cycles and Wind Electrolysis, with the possible use of Steam Methane Reforming (SMR) to aid in the creation of a hydrogen infrastructure. Despite high impact assessment results from SimaPro, the external costs associated with Biomass gasification are shown to be comparable with those for Wind Electrolysis. Thus, biomass-produced hydrogen could also be a viable alternative, especially in areas ideally suited to the growth of energy crops. Finally, the most influential life cycle stages are the Construction of the FCV and Hydrogen Production (except for the environmentally benign wind electrolysis). For the Wind/Electrolysis case, the majority of impacts come from plant construction.
Grinding and Separation of The Cellular Phone Housing
Authors: Jung Woo-Hyuk , Tortorella Nathan , Beatty Charles L. , McCarthy Stephen P. 
Published: April 2011

AbstractThe front covers of Motorola cellular phone housings, which were composed of 62.2 wt% of polycarbonate (PC) /acrylonitrile-butadiene-styrene (ABS), were ground and separated from the undesired materials using sink-float methods. The sink-float methods in water and salt were used to remove the floating materials such as the adhesive strips and the foams, and to separate the metal parts where the recovery ratios were 92.8 and 40.5 %, respectively. The separation of residual wires and button rubbers, which could not be done by the sink-float process in water, was preformed using V-Stat Triboelectric Separator (Outokumpu Technology) of a roll separator that also provided the effective methods to separate the ground metals that had existed in the printed circuit boards where the recovery weight ratio of metal parts was 19 wt%. The separated PC/ABS’s could be compounded with the ground circuit boards or the thermoplastic elastomer called Engage®, or the reactive species of glycidyl methacrylate (GMA).