British Library Electronic Table of Contents (United Kingdom)

We carried out theoretical analyses based on ab initio calculations that incorporate free energy of the vapor phase in order to determine the initial growth process of cubic GaN on GaN (001)-(4x1). The results suggest that a N-adsorbed structure appears at the initial growth stage and then Ga adsorbs on the N-adsorbed GaN (001)-(4x1) surface. Considering this process, we performed Monte Carlo simulations. The results suggest that the maximum point of Ga coverage after supplying a Formula Not Shown monolayer of atoms shifted toward a Ga-rich condition from V/III=1.0.

British Library Electronic Table of Contents (United Kingdom)

We carried out theoretical analyses based on ab initio calculations incorporates in which free energy of the vapor phase is incorporated in order to determine the initial growth kinetics of c-GaN on GaN(001)-(4x1). The feasibility of the theoretical approach had been confirmed by calculations of Ga adsorption-desorption transition temperature and transition beam equivalent pressures on the GaAs(001)-(4x2)b2 surface in our previous work [Y. Kangawa, T. Ito, A. Taguchi, K. Shiraishi, T. Ohachi, Surf. Sci. 493 (2001) 178]. The results of calculations suggest that no Ga adsorption occurs on the initial surface under typical growth conditions but that a Ga adsorption site appears after N adsorption on GaN(001)-(4x1). That is, in the initial growth stage of c-GaN on GaN(001)-(4x1), a N-adsorbed ...

Energy Technology Data Exchange (ETDEWEB)

In recent years, there has been increasing demand for resource-recycling of waste plastic, especially due to the introduction of legislation on recycling of materials used for packages of household goods. Methods of recycling waste plastic from household goods are currently still under development, and appropriate techniques to deal with such waste are required. Toshiba has developed a technique to dehydrochlorinate plastic containing polyvinyl chloride (PVC). This paper introduces our petrolization and dehydrochlorination system for waste plastic containing PVC. (author)

International Nuclear Information System (INIS)

GaN and Al_1_-_xGa_xN films were grown by the method of ECR-MBE. Absorption constants as a function of wavelength were determined from transmission measurements. Photoconducting detectors were fabricated from these films and characterized in terms of their spectral response and photoconductive gain. Mobility-lifetime products were determined from the measurement of photoconductive gain. The resistivity and mobility-lifetime products of the films were varied from 10--10"9 ohm-cm and 10"-"3--10"-"8 cm"2/V respectively by changing the microwave power in the ECR discharge from 20--60 watts. The change in the mobility-lifetime product is attributed to change in the lifetimes of the photogenerated carriers. This assumption is supported by direct measurement of detector response times. Finally, the authors report for the first time, the detection of alpha particles using GaN detectors.

Energy Technology Data Exchange (ETDEWEB)

Activated charcoal which is the desulfurizing agent for the fuel cell plant can be used only at the normal temperature, and it must be placed upstream of the fuel gas, increasing the displacement flow of the fuel gas processed in the desulfurizer. In addition, a large quantity of activated charcoal must be filled or the frequency of its exchange must be increased because activated charcoal used at the normal temperature has little sulfur absorbing capacity. This invention is concerned with provision of a desulfurizer in the downstream of the fuel gas compressor of the fuel cell plant to remove sulfur content in the fuel gas by this desulfurizer. As a result, the displacement flow of the processing gas is decreased to increase the processing capacity of the desulfurizing agent. In addition, hydrogen recycling can be eliminated to realize compact arrangement of the equipment and economization of energy consumption. Metal oxide based desulfurizers of copper, iron, zinc, manganese, etc. ...

Energy Technology Data Exchange (ETDEWEB)

The authors report on the nano-fabrication of GaN/AlGaN device structures using focused ion beam (FIB) etching, illustrated on a GaN/AlGaN heterostructure field effect transistor (HFET). Pillars as small as 20nm to 300nm in diameter were fabricated from the GaN/AlGaN HFET. Micro-photoluminescence and UV micro-Raman maps were recorded from the FIB-etched pattern to assess its material quality. Photoluminescence was detected from 300nm-size GaN/AlGaN HFET pillars, i.e., from the AlGaN as well as the GaN layers in the device structure, despite the induced etch damage. Properties of the GaN and the AlGaN layers in the FIB-etched areas were mapped using UV Micro-Raman spectroscopy. Damage introduced by FIB-etching was assessed. The fabricated nanometer-size GaN/AlGaN structures were found to be of good quality. The results demonstrate the potential of FIB-etching for the nano-fabrication of III-V nitride devices.

International Nuclear Information System (INIS)

We describe the growth, fabrication, and characterization of an ultraviolet (UV) photoconductive detector based on In_xAl_yGa_1_-_x_-_yN quaternary alloy that is lattice matched to GaN. The detector consisted of 0.1 #mu#m In_xAl_yGa_1_-_x_-_yN alloy grown on 0.5-1.0 #mu#m GaN epilayer by metalorganic chemical vapor deposition. With varying indium concentration, the cut-off wavelength of the In_xAl_yGa_1_-_x_-_yN detectors could be varied to the deep UV range. The most important and intriguing result is that the responsivity of the In_xAl_yGa_1_-_x_-_yN quaternary alloy exceeded that of AlGaN alloy of a comparable cutoff wavelength by a factor of five. This makes the nitride quaternary alloy very important material for solar blind UV detectors applications particularly in the deep UV range where Al rich AlGaN alloys have problems with low quantum efficiency and cracks due in part to lattice mismatch with GaN. The advantages ...

International Nuclear Information System (INIS)

The highest equilibrium free-carrier doping concentration possible in a given material is limited by the ''pinning energy'' which shows a remarkable universal alignment in each class of semiconductors. Our first-principles total energy calculations reveal that equilibrium n -type doping is ultimately limited by the spontaneous formation of close-shell acceptor defects: the 3- -charged cation vacancy in AlN, GaN, InP, and GaAs and the 1- -charged DX center in AlAs, AlP, and GaP. This explains the alignment of the pinning energies and predicts the maximum equilibrium doping levels in different materials. (c) 2000 The American Physical Society

Energy Technology Data Exchange (ETDEWEB)

By ab-initio calculation we show that the (Ga,Fe)N ground state may be changed from anti-ferromagnetic to ferromagnetic by acceptor defect like Ga vacancies. The electronic structures are calculated by using the Korringa-Kohn-Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that we can increase the magnetic moment of Fe in p-type GaN by oxygen co-doping. Mechanism of exchange interactions between magnetic ions in p-type (Ga,Fe)N is also studied. The effect of external magnetic field on the electronic structure of (Ga, Fe)N and p-type (Ga, Fe)N is investigated.

Energy Technology Data Exchange (ETDEWEB)

Four HVDC (high voltage DC) {+-} 250kV submarine OF (oil-filled) cables are to be installed each capable of 1.4-million kW for one dipole channel and two returns for forwarding to Yura Switchyard a part of the power to be generated by a Tachibanawan coal-fired power plant to open in 2000. The first cable is now being laid. They are to cover a distance of 48km on the sea bottom, and their 190mm diameter is the largest in the world and this decreases the required number of cables for a reduction in the construction cost. The installation is executed by use of a dedicated cable laying ship loaded with cables. The ship is equipped with five thruster screws by adjusting which a cable is fed into the sea and laid on the bottom with high positional accuracy in all directions, and with a 10m-accurate DPS (Dynamic Positioning System) besides GPS (Global Positioning System). Operating on the sea bottom is a simultaneous laying/burying machine which buries the cable 2-3m deep in the sea bottom. ...

Energy Technology Data Exchange (ETDEWEB)

Ion Beam Induced Luminescence (IBIL) and Ion Beam Induced Charge Collection (IBICC) have been applied in the study of the luminescence emission efficiency and investigation of the homogeneity of the luminescence emission in phosphors. The IBIL imaging was performed by using sharply focused ion beams or broad/partially-focused ion beams. The luminescence emission homogeneity in samples was examined to reveal possible distributed crystal-defects that may lead to the inhomogeneity of the luminescence emission in samples.The purpose of the study is to search for suitable luminescent thin films that have high homogeneity of luminescence emission, large IBIL efficiency under heavy ion excitation, and can be placed as a thin layer on the top of microelectronic devices to be analyzed with Ion Photon Emission Microscopy (IPEM). The emission yield was found to be low for organic materials, due to saturation of the light output dependence on the energy deposition of heavy ions. The emission yield ...

International Nuclear Information System (INIS)

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III - V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other. [copyright] 2001 American Institute of ...

Science.gov (United States)

The zinc-blende (ZB) and wurtzite (W) structures are the most common crystal forms of binary octet semiconductors. In this work we have developed a simple scaling that systematizes the {ital T}=0 energy difference {Delta}{ital E}{sub W{minus}ZB} between W and ZB for all simple binary semiconductors. We have first calculated the energy difference {Delta}{ital E}{sub W{minus}ZB}{sup LDF}({ital AB}) for AlN, GaN, InN, AlP, AlAs, GaP, GaAs, ZnS, ZnSe, ZnTe, CdS, C, and Si using a numerically precise implementation of the first-principles local-density formalism (LDF), including structural relaxations. We then find a {ital linear} scaling between {Delta}{ital E}{sub W{minus}ZB}{sup LDF}({ital AB}) and an atomistic orbital-radii coordinate {ital {tilde R}}({ital A},{ital B}) that depends only on the properties of the free atoms {ital A} and {ital B} making up the binary compound {ital AB}. Unlike classical structural coordinates (electronegativity, atomic sizes, electron ...

International Nuclear Information System (INIS)

The optical, electromagnetic and mechanical properties of thin films (TFs) are directly correlated to their morphology at the nanoscale. This, in concert with the fact that new deposition techniques are enabling the growth of thin films with very complex morphologies, there is an increasing interest in model-based simulation (MBS) for the design of engineering structures (including nanostructures), and increasing computer speeds are beginning to make MBS an effective design tool capable of bridging the nanoscale with the continuum scale, has made it increasingly important to understand how the nanostructure of a thin film impacts its properties at all length scales. The authors have developed the capability to determine the mechanical properties of thin films with amorphous nanostructure by combining molecular dynamics, i.e., position of particles (e.g., atoms or molecules) and their interatomic potential(s), with continuum mechanics principles. This work concerns the application of ...

Energy Technology Data Exchange (ETDEWEB)

The purpose of the present work is to investigate the effects of matrix resin and fiber content on the behavior of fatigue crack propagation in continuous-glass-fiber-mat reinforced CP-resin composites. For this purpose, ductile matrix resin and brittle one are used. These two kinds of resins have the characteristic that the elastic modulus and tensile strength are nearly the same with each other while the elongation is different. The composite specimens are made of these resins and continuous grass fiber mat of 20 wt.% and 60 wt% fiber contents. The fatigue crack propagation test was conducted by using the tapered DCB specimens to control the stress intensity factor range, {delta}K, during the test. The results obtained are as follows; (1) The relation between the crack propagation rate, da/dN, and {delta}K for all the present materials is shown by a straight line in logarithmic representation. (2) For the composites of 20 wt.% fiber content, the da/dN of the ductile matrix composite ...