bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative Differential Resistivity in GaN Metal-Semiconductor-Metal Photoconductors
Authors: Huang Z.C. , Chen J.C. , Zheng Youdou , Mott D.B. 
Published: April 2011

ABSTRACTWe have observed a negative differential resistivity (NDR) in metal-semiconductor-metal (M-S-M) photoconductor made from unintentionally doped GaN grown by metalorganic chemical vapor deposition. The threshold field for the onset of NDR was found to be independent of the spacing of M-S-M fingers, and was measured to be 1.91×105 V/cm for GaN with an n-type carrier concentration of 1014 cm−3. We believe that the observed NDR is due to transferred electron effect in GaN. The threshold field value is very close to the value obtained from the theoretical simulation. This observation, to the best of our knowledge, is the first experimental evidence of transferred-electron effects in GaN, which is important in understanding GaN energy band structure and in the application of Gunn-effect devices using GaN materials.
Ion Implantation Doping and High Temperature Annealing of GaN
Authors: Zolper J. C. , Hagerott crawford M. , Howard A. J. , Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Yuan C. , Stalls R. A. , Ramer J. , Hersee S. D. , Wilson R. G. 
Published: April 2011

ABSTRACTThe III-V nitride-containing semiconductors InN, GaN, and AIN and their ternary alloys are the focus of extensive research for application to visible light emitters and as the basis for high temperature electronics. Recent advances in ion implantation doping of GaN and studies of the effect of rapid thermal annealing up to 1100 °C are making new device structures possible. Both p- and n-type implantation doping of GaN has been achieved using Mg co-implanted with P for p-type and Si-implantation for n-type. Electrical activation was achieved by rapid thermal anneals in excess of 1000 °C. Atomic force microscopy studies of the surface of GaN after a series of anneals from 750 to 1100 °C shows that the surface morphology gets smoother following anneals in Ar or N2. The photoluminescence of the annealed samples also shows enhanced bandedge emission for both annealing ambients. For the deep level emission near 2.2 eV, the sample annealed in N2 shows slightly reduced emission while the sample annealed in Ar shows increased emission. These annealing results suggest a combination of defect interactions occur during the high temperature processing.
Ion Damage and Annealing of Epitaxial Gallium Nitride and Comparison With GaAs/AlGaAs Materials
Authors: Tan H.H. , Williams J.S. , Yuan C. , Pearton S.J. 
Published: April 2011

ABSTRACTIon damage build up has been measured by ion channeling in good quality epitaxial GaN films on sapphire. GaN is found to be remarkably resistant to ion damage, with extremely efficient dynamic defect annihilation occurring at liquid nitrogen temperature during ion implantation. When disorder does accumulate at doses around 1016cm−2 of 90 keV Si ions, the surface appears to be a strong sink for damage build up and possibly the nucleation of amorphous layers. Once ion disorder has been produced in GaN, it is extremely difficult to remove by annealing. GaN exhibits disordering and annealing behaviour which is somewhat similar to that in high Al-content AlGaAs.
Growth of Silicon-Doped and High Quality, Highly Resistive GaN for FET Applications
Authors: Doverspike K. , Wickenden A.E. , Binari S.C. , Gaskill D.K. , Freitas J.A. 
Published: April 2011

ABSTRACTWe have shown the ability to grow thin, high mobility, GaN channel layers on high quality, highly resistive GaN. The growth, characteristics, and device results of two types of MESFET structures were discussed. The first device structure consists of a 2000Ǻ, 2 × 1017cm−3 Si-doped channel layer, grown on 3µm of highly resistive GaN, while die second structure (recessed-gate MESFET) had a 1000Ǻ, 1 × 1018cm−3 Si-doped, n+ capping layer deposited on a 2000Ǻ, 2 × 1017cm−3 Si-doped channel layer. The first MESFET structure was operational at 500°C which is the highest reported operating temperature for a GaN device while the recessed-gate MESFET had a gmas high as 41mS/mm, which is the highest reported value for a GaN MESFET.
Pulsed Laser Ablation Growth and Doping of Epitaxial Compound Semiconductor Films
Authors: Lowndes Douglas H. , Rouleau Christopher M. , Geohegan D. B. , Puretzky A. A. , Strauss M. A. , Pedraza A. J. , Park J. W. , Budai J. D. , Poker D. B. 
Published: April 2011

ABSTRACTPulsed laser ablation (PLA) has several characteristics that are potentially attractive for the growth and doping of chemically complex compound semiconductors including (1) stoichiometric (congruent) transfer of composition from target to film, (2) the use of reactive gases to control film composition and/or doping via energetic-beam-induced reactions, and (3) low-temperature nonequilibrium phase formation in the laser-generated plasma “plume.” However, the electrical properties of compound semiconductors are far more sensitive to low concentrations of defects than are the oxide metals/ceramics for which PLA has been so successful. Only recently have doped epitaxial compound semiconductor films been grown by PLA. Fundamental studies are being carried out to relate film electrical and microstructural properties to the energy distribution of ablated species, to the temporal evolution of the ablation pulse in ambient gases, and to beam-assisted surface and/or gas-phase reactions. In this paper we describe results of ex situ Hall effect, high-resolution x-ray diffraction, transmission electron microscopy, and Rutherford backscattering measurements that are being used in combination with in situ RHEED and time-resolved ion probe measurements to evaluate PLA for growth of doped epitaxial compound semiconductor films and heterostructures. Examples are presented and results analyzed for doped II–VI, I–III–VI, and column-Ill nitride materials grown recently in this and other laboratories.
Fabrication of CDS Thin Films Using Continuous Wave Laser Evaporation
Authors: Tenpas E.W. , Vuong K. D. , Orloff S. , Fagan J.G. , Wu V. , Wang X.W. 
Published: April 2011

ABSTRACTWe report new results on continuous wave Nd: YAG laser deposition of Cadmium Sulfide (CdS) thin films. Substrates were soda-lime silicate (SLS) glass, silica glass, silicon, alumina, and copper coated formvar sheets. As-deposited films were characteristically mixtures of cubic and hexagonal phases. X-ray diffraction analysis reveals that two different grain size groups are present. As revealed by SEM micrographs, films had smooth surface morphology. Transmission electron microscopy analysis reveals that grain sizes were extremely small. Also, semiconductive behavior was noted.
Deposition of Diamond-Like Carbon Films by Excimer Lasers Using Frozen Source Gases
Authors: Hanabusa Mitsugu , Tsujihara Kiyohito , Zhengxin Liu , Ishihara Seiji , Uchida Hironaga 
Published: April 2011

ABSTRACTWe deposited diamond-like carbon (DLC) films, using frozen acetylene and acetone as the target of laser ablation. The frozen gases were dissociated by an ArF laser and a KrF laser. The DLC films were deposited on quartz substrates below 300°C. We measured the Raman spectra to identify the deposited films as DLC. The films showed the broad Raman peak at 1540 cm-1. The number of particles mixed into the deposits was controlled by laser power densities. By using the ArF laser for frozen acetylene we could reduce the hydrogen concentration in the films, which showed a high degree of dissociation of the source gas. The oxygen content was kept at the same level in the films deposited from frozen acetone as from frozen acetylene. The present results suggested the importance of energetic and charged species ejected from the frozen gas target.
Applications of Laser Processing for Sensors and Actuators
Authors: Meunier M. , Izquierdo R. , Shen B. , Lecours A. , Allard M. , Bergeron A. , Hanus F. , Boughabah S. , Ivanov D. , Currie J.F. , Laude L. , Yelon A. 
Published: April 2011

ABSTRACTThe fabrication of sensors and actuators requires new materials with multicomponent stoichiometry as well as new three-dimensional microstructures. We present several potential applications of laser processing for the fabrication of sensors and actuators. The first example concerns gas sensors which require ionic conductor multicomponent ceramics whose stoichiometry is not maintained by conventional sputtering methods. We have successfully employed pulsed laser deposition (PLD) for producing high quality NASICON (Na SuperIonic CONductor) thin films. XPS measurements show that all elements are transferred from a target of Na1+xZr2SixP3-xO12, (where 0 < x < 3 ) to the substrate, and that the composition of the thin film is very close to that of the target. Electrical measurements show good ionic conductivity. Thus, these films are suitable for the fabrication of electrochemical gas sensors. Since such ceramic thin films are very sensitive to liquids, wet etching is prohibited, and patterning is done using laser ablation. For other applications, a laser micromachining technique has been developed to make tunnels and cavities in Si under SiO2 films, based on the laser-induced CI2 etching of Si and high chlorine Si/SiO2 etch rate ratios. Tunnels with length of up to 3 mm and cavities of 100×100 cm2 were successfully fabricated in SiO2/Si bilayer samples. These are usable in microfluidic or gas pressure measurement systems.
Synthesis of Thin Films of Size Selected Silicon Nanocrystallites Using Pulsed Laser Ablation Supersonic
Authors: Werwa E. , Kolenbrander K.D. 
Published: April 2011

ABSTRACTThin films composed of size selected silicon nanocrystallites have been fabricated and their photoluminescence behavior has been studied. The silicon nanocrystallites were produced using a pulsed laser ablation supersonic expansion source. This source typically generates silicon clusters of many different sizes, which leads to photoluminescence spectra with a large fiill width at half maximum. To best utilize our gas phase synthesis technique, we have performed size selection of the silicon clusters using a mechanical velocity selection apparatus. Films of these size selected nanocrystallites exhibited photoluminescence spectra which had a smaller full width at half maximum and which were peaked to the blue of the spectra of samples with a broader size distribution. These results suggest that the photoluminescence wavelength of these nanocrystallite thin films is determined by quantum confinement of the electrons and holes in the crystallites.
Raman Spectroscopy Study of Pulsed Laser Induced Structural Transformations in Amorphous Ge Films
Authors: García C. , Prieto A.C. , Jiménez J. , Siegel J. , Solís J. , Afonso C.N. , Chafai M. 
Published: April 2011

ABSTRACTStructural transformations induced in amorphous Ge films by picosecond laser pulses are studied by means of Raman spectroscopy and their dependence on parameters like the pulse fluence or the thermal conductivity of the substrate are analyzed. A correlation length model is used for studying the crystallization process, while the average bond angle distortion is used for determining the state of relaxation of the amorphous phase. Silicon and glass substrates are compared.
Real-Time Optical Monitoring of Tungsten Nucleation During Laser Induced Pyrolytic Cvd
Authors: Zhang Xiafang , Allen Susan D. 
Published: April 2011

ABSTRACTThe nucleation of tungsten on bare Si and SiO2/Si surfaces by Ar ion laser induced CVD has been studied with high speed real-time specular reflection and scattering. Our experimental results show that the induction time of tungsten nucleation decreases with laser power and is longer on thicker SiO2 surfaces than on thin native SiO2 surfaces at the same laser power. The activation energy of tungsten nucleation on native SiO2/Si obtained from an Arrhenius plot of induction time is about 33 kJ/mol at temperatures less than 1000 K and 16 kJ/mol at temperatures higher than 1000 K. The results on bare Si with and without H2 reveal that the initial reaction mechanism appears to be the same in both cases. An Arrhenius plot of induction time shows two different apparent activation energies at different temperature ranges, which suggest that W nucleation is controlled by H atom desorption from the Si surface at temperatures less than 714 K and is dominated by Si atom reduction of WF6 molecules at surface temperatures greater than 800 K.
Laser Direct Writing of Aluminum Conductor Lines from a Liquid Phase Precursor
Authors: Chen Qijun , Allen Susan D. 
Published: April 2011

ABSTRACTAluminum conductor lines were deposited on Si substrates from liquid phase triisobutylaluminum (TIBA) using a scanned argon ion laser. The vertical growth rate of Al lines initially increased, then decreased with increasing dwell time. The maximum vertical growth rate occurred at a particular dwell time depending upon the laser power. Lower vertical growth rates at longer dwell times are propably caused by the depletion of the reactant at the reaction site. A volcano deposit shape was observed, which became more pronounced as dwell time increased. The conductivity of the as-deposited Al lines decreased with increasing dwell time for our experimental conditions. To study the deposition kinetics and calculate the activation energy, the temperature rise on the Si surface was calculated by solving the nonlinear heat equation using finite difference method.
Epitaxial Silicon-Carbon Alloy Growth by Laser Induced Melting and Solidification
Authors: Kramer Kenneth M. , Thompson Michael O. 
Published: April 2011

ABSTRACTIon implantation of carbon into single-crystal silicon followed by excimer laser irradiation was used to create supersaturated, epitaxial SixC1-x. films. Crystallization proceeded from the underlying single-crystal silicon through the carbon containing layers at velocities of approximately 5 m/s. Characterization by high-resolution x-ray diffraction and Fourier-transform infrared absorption indicate that the carbon is found predominantly on substi-tutional lattice sites for concentrations up to 1.4 at.% C. Secondary-ion mass spectrometry profiles and numerical mass transfer calculations were used to estimate the diffusion coefficient of carbon in the liquid as 2-3 × 10−4cm2/s with a segregation coefficient greater than 0.4. Unusual diffusion behavior was observed for the carbon at 1.4 at.% C. At higher concentrations, evidence of SiC precipitates was observed in transmission electron microscope images and FTIR absorption spectra.
Solid State Interfacial Reactions Between Tic Thin Films and Ti3AI Substrates
Authors: Si Weimin , Dudley Michael , Li Pengxing , Wu Renjie 
Published: April 2011

ABSTRACTThe products and kinetics of solid state reactions between TiC and Ti3Al have been investigated using X-ray diffractometry (XRD) and Auger electron spectroscopy (AES) with Ar ion beam sputtering. Diffusion couples were prepared by sputtering TiC thin films onto polished Ti3AI substrates, and then isothermally annealed in vacuum in the temperature range of 800 to 1000°C for 0.25 to 2.25 hours. The thickness of the interfacial reaction layer was obtained from AES elemental concentration depth profiling, while the reaction products were identified from XRD spectra. In the TiC/Ti3Al system, the reaction product was primarily P(Ti3AlC) phase. The growth-rate of the reaction product was fitted to a parabolic growth law (dZ/dt = k1/Z) and the activation energy of the rate constant was about 36.16 kcal/mole. The reaction mechanism will be discussed on the basis of thermodynamical equilibrium in Ti-Al-C ternary system.
Nonisothermal Kinetics Study of Phase Evolution of Zn-Fe Intermetallics
Authors: Uwakweh O. N. C. , Liu Z. T. , Boisson M. 
Published: April 2011

ABSTRACTThrough mechanical alloying of pure elemental powders of Fe and Zn, true homogeneous alloys of Γ (Fe3Zn10), Γ1(Fe5Zn21), δ (FeZn7) and ζ (FeZn13) intermetallic phases are formed. Based on nonisothermal kinetics analyses, the highest activation energies associated with the metastable to stable transformations of these phases are determined as follows: 170±1 kJ/mol, 2 51±2 kJ/mol, 176±1 kJ/mol and 73 7±4 kJ/mol for the Γ, Γ1, δ and ζ-phases, respectively. These values reflect different diffusion/thermally induced processes associated with the transition of each of these phases.
Phase Separation and Crystallization in the Bulk Amorphous Alloy Zr41Ti14Cu12.5Ni10Be22.5
Authors: Macht M.-P. , Wanderka N. , Wiedenmann A. , Wollenberger H. , Wei Q. , Klose S.G. , Sagel A. , Fecht H.J. 
Published: April 2011

ABSTRACTThe decomposition and crystallization above the glass temperature of the bulk metallic glass Zr41Ti14Cu12.5Ni10Be22.5 and the crystallization during solidification of the melt were investigated by means of different analytical methods, including Transmission Electron Microscopy (TEM), Small Angle Neutron Scattering (SANS), Field Ion Microscopy with Atom Probe (FIM/AP).Dependent on the thermal history these phase transitions lead to different phases and different microstructures of the alloy. During annealing above the glass tremperature the decomposition of the alloy into two supercooled liquid phases is observed by the formation of nanosized precipitates, which differ from the matrix by their Be and Ti contents. This decomposition retards significantly the subsequent crystallization, however it does not inhibit the formation of the phases which crystallize if the decomposition is bypassed by appropriate heat treatment. By stepwise crystallization a nanosized microstructure is formed consisting of three metastable phases and of stable Zr2Cu. This microstructure differ significantly from the crystalline equilibrium microstructure resulting from slow cooling of the melt. Crystallization of the amorphous alloy by very fast heating causes totally different microstructures.
Solid-Phase Epitaxial Growth of Amorphized GaAs: The Influence of Microscopic and Macroscopic Non-Stoichiometry
Authors: Belay K.B. , Llewellyn D.J. , Ridgway M.C. 
Published: April 2011

ABSTRACTThe solid-phase epitaxial growth of amorphized GaAs has been characterized to investigate the influence of both microscopic and macroscopic non-stoichiometry on the onset of twinning and subsequent interfacial non-planarity. Microscopic non-stoichiometry or equivalently, chemical disorder on an atomic scale, was produced by implanting samples with equal doses of both Ga and As ions. In such samples, the onset of twinning and interfacial non-planarity where independent of the energy deposited in vacancy production, the latter considered a first estimate of relative differences in microscopic non-stoichiometry between samples. Twinning and interfacial non-planarity are thus independent of microscopic non-stoichiometry or alternatively, microscopic non-stoichiometry may approach saturation over the given dose range. In contrast, macroscopic non-stoichiometry produced by implanting samples with Ga or As ions influenced both the onset of twinning and interfacial non-planarity. Excess Ga was observed to have a greater effect than excess As. The influence of a macroscopic non-stoichiometry may be indicative that the availabiltiy of a lattice constitutent and/or defect is rate-limiting during solid-phase epitaxial growth. Macroscopic non-stoichiometry may also yield preferrential nuclueation sites for twinning and in the presence of excess Ga, molten precipitates could contribute to an observed rapid amorphous-to-crystalline transformation.
Kinetic Study on the Formation of the Aragonite-Like Phase Ba(CuOx)1-Y(CO3)y
Authors: Tomasi A. , Galvanetto E. , Matacotta F.C. , Nozar P. , Scardi P. , Migliori A. 
Published: April 2011

ABSTRACTA systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-500°C, under various atmospheres, by traditional thermal analysis techniques, high temperature X-ray diffraction and high resolution electron microscopy, has permitted to identify and characterise the formation kinetics of a new copper containing phase isomorphic to γ-BaCO3.
Studies on Dynamics of Interfaces in Cu-Ai-Zn-Ni Alloy
Authors: Shen KM. , Huang Y.N. , Zhang Z.F. , Yang Z. , Wang X.M. , Wang Y.N. , Tan S.S. 
Published: April 2011

ABSTRACTAn internal friction peak associated with the viscous motion of interfaces was measured in the 50–150kHz range for the Cu-Al-Zn-Ni sample. The internal friction formula based on the viscous motion of interfaces has been derived. Also, corresponding parameters, which play an important role in shape memory effect such as viscosity coefficient, pinned force constant etc., were obtained.
Effects of High Magnetic Field and Tensile Stress on Martensitic Transformation Behavior and Microstructure At 4 K in Fe-Ni-C Alloys
Authors: Ohtsuka H. , Nagai K. , Kajiwara S. , Kitaguchi H. , Uehara M. 
Published: April 2011

ABSTRACTEffects of high magnetic field and tensile stress on martensitic transformation behavior and microstructure at 4 K have been studied in Fe-31Ni-0.4C and Fe-27Ni-0.8C shape memory alloys. It was found that the critical magnetic field to induce martensitic transformation is between 7.5 T and 10 T. In the case of Fe-27Ni-0.8C, martensitic transformation is stress-induced at lower level of stress in magnetic field than in the case when no magnetic Field is applied. The amount of martensite formed by increasing the magnetic field under constant stress is larger than that formed by increasing the stress in the constant magnetic field.
Critical Behavior of Antiphase Boundaries in Fe-A127% Close to the D03→B2 Order Phase Transition
Authors: Floc'h D. Le , Loiseau A. 
Published: April 2011

ABSTRACTIn this paper, we present the first quantitative determination of the divergence law of the correlation length ξ, when approaching the second order phase transition DO3→B2, by studying the behaviour of the APBs by transmission electron microscopy.
A Study of the Effect of Oxide Structure on the Synthesis of Nanocrystalline Ge from Si1-xGexO2
Authors: Blaser Juliana M. , Caragianis-Broadbridge Christine , Walden Barbara L. , Paine David C. 
Published: April 2011

ABSTRACTIn this study, Si1-xGexO2 was produced by hydrothermal oxidation of Si1-xGex alloys at temperatures of 450–500°C and pressures of 30–40 MPa. The resulting Si1-xGexO2 samples were annealed in forming gas (85/15:N2/H2) and the precipitation and growth of Ge crystallites as a function of oxidation and annealing conditions were investigated using FTIR, Raman spectroscopy, XPS, AFM and high resolution SEM. The particle size distribution through the oxide thickness is accounted for by consideration of the incorporation of hydroxyl groups in the amorphous oxide network and their effect on the rate of diffusion of Ge in the amorphous structure during H2 annealing.
Reentrant Growth in Kinetic Thin-Film Deposition on Stepped Surfaces
Authors: Xiao Rong-Fu 
Published: April 2011

ABSTRACTWe have studied the reentrant growth in kinetic thin-film deposition on stepped surfaces using a Monte Carlo simulation. The results show that the reentrant oscillation of two dimensional nucleation growth occurs as a result of the variation of surface diffusion length with deposition temperature, and that it is a natural phenomenon in kinetic thin-film epitaxy on a substrate with a permanent step source.