bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Annealing of InGaN/GaN Strained-Layer Quantum Well
Authors: Chan Michael C.Y. , Tsang Kwok-On , Li E. Herbert , Denbaars Steven P. 
Published: April 2011

AbstractQuantum well (QW) material engineering has attracted a considerable amount of interest from many people because of its ability to produce a number of optoelectronic devices. QW composition intermixing is a thermal induced interdiffusion of the constituent atoms through the hetero-interface. The intermixing process is an attractive way to achieve the modification of the QW band structure. It is known that the band structure is a fundamental determinant for such electronic and optical properties of materials as the optical gain, the refractive index and the absorption. During the process, the as-grown square-QW compositional profile is modified to a graded profile, thereby altering the confinement profile and the subband structure in the QW. The blue-shifting of the wavelength in the intermixed QW structure is found in this process.In recent years, III-nitride semiconductors have attracted much attention. This is mainly due to their large bandgap range from 1.89eV (wurtzite InN) to 3.44eV (wurtzite GaN). InGaN/GaN quantum well structures have been used to achieve high lumens blue and green light emitting diodes. Such structures also facilitate the production of full colour LED displays by complementing the colour spectrum of available LEDs.In this paper, the effects of thermal annealing on the strained-layer InGaN/GaN QW will be presented. The effects of intermixing on the confinement potential of InGaN/GaN QWs have been theoretically analysed, with sublattices interdiffusion as the basis. This process is described by Fick's law, with constant diffusion coefficients in both the well and the barrier layers. The diffusion coefficients depend on the annealing temperature, time and the activation energy of constituent atoms. The optical properties of intermixed InGaN/GaN QW structure of different interdiffusion rates have been theoretically analyzed for applications of novel optical devices. The photoluminescence studies and the intermixed QW modeling have been used to understand the effects of intermixing.
Thermal Stability of GaN Investigated by Raman Scattering
Authors: Kuball M. , Demangeot F. , Frandon J. , Renucci M.A. , Grandjean N. , Briot O. 
Published: April 2011

AbstractWe have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of the degradation of GaN during high-temperature processing has been demonstrated. GaN samples grown by molecular-beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOCVD) were studied. Characteristic features in the Raman spectrum identify three thermal stability regimes: (1) annealing below 900°C does not affect the GaN Raman spectrum; (2) annealing between 900°C and 1000°C results in the appearance of disorder-induced Raman scattering between the E2 and A1(LO) phonon; (3) annealing at temperatures higher than 1000°C gives rise to distinct Raman modes at 630 cm-1, 656 cm-1 and 770 cm-1. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for an interfacial reaction between GaN and sapphire for annealing temperatures higher than 1000°C.
Study of Thin Films Polarity of Group III Nitrides
Authors: Dovidenko K. , Oktyabrsky S. , Narayan J. , Razeghi M. 
Published: April 2011

AbstractThin films of GaN grown by MOCVD on (0001) sapphire were studied by transmission electron microscopy in order to correlate the observed extended defects with crystal polarity of the films. We propose relatively simple and unambiguous method of polarity determination for wurtzite group III nitrides based on the dependence of the intensity of diffracted beams upon thickness of the specimen. Due to the dynamic scattering by polar structure, the convergent beam electron diffraction patterns lose inversion symmetry and become in fact fingerprints of the structure carrying information about crystal polarity. In this study, we have used the thinnest regions of the specimens (< 15 nm) and multiple diffraction spots in high-symmetry orientation for polarity determination. The films were found to have Ga-polar surfaces, either being unipolar, or containing thin (10-30 nm in diameter) columnar inversion domains (IDs) of N-polarity. The occurrence of IDs was correlated with specific types of dislocation distribution in the films.
Room Temperature Laser Action in Laterally Overgrown GaN Pyramids on (111) Silicon
Authors: Bidnyk S. , Little B. D. , Cho Y. H. , Krasinski J. , Song J. J. , Yang W. , McPherson S. A. 
Published: April 2011

AbstractSingle and multi-mode room temperature laser action was observed in GaN pyramids under strong optical pumping. The 5- and 15-micron-wide hexagonal-based pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal-organic chemical vapor deposition. The pyramids were individually pumped, imaged, and spectrally analyzed through a high magnification optical system using a high density pulsed excitation source. We suggest that the cavity formed in a pyramid is of a ring type, formed by total internal reflections of light off the pyramids' surfaces. The mode spacing of the laser emission was found to be correlated to the size of pyramids. The effects of pyramid geometry and pulse excitation on the nature of laser oscillations inside of the pyramids is discussed.
Base Transit Time in Abrupt GaN/InGaN/GaN and AlGaN/GaN/AlGaN HBTs
Authors: Chiu Shean-Yih , Anwar A. F. M. , Wu Shangli 
Published: April 2011

AbstractBase transit time, τb, in abrupt npn GaN/InGaN/GaN and AlGaN/GaN/AlGaN double heterojunction bipolar transistors (DHBTs) is reported. Base transit time strongly depends not only on the quasi-neutral base width, but also on the low field electron mobility, μn, in the neutral base region and the effective electron velocity, Sc, at the edge of base-collector heterojunction. μn and Sc are temperature-dependent parameters. A unity gain cut-off frequency of 10.6 GHz is obtained in AlGaN/GaN/AlGaN DHBTs and 19.1 GHz in GaN/InGaN/GaN DHBTs for a neutral base width of 0.05um. It is also shown that non-stationary transport is not required to study τb for neutral base width in the range of 0.05um for GaN-based HBTs.
Generation Recombination Noise in GaN Photoconducting Detectors
Authors: Misra M. , Doppalapudi D. , Sampath A.V. , Moustakas T.D. , McDonald P.H. 
Published: April 2011

AbstractLow frequency noise measurements are a powerful tool for detecting deep traps in semiconductor devices and investigating trapping-recombination mechanisms. We have performed low frequency noise measurements on a number of photoconducting detectors fabricated on autodoped n-GaN films grown by ECR-MBE. At room temperature, the noise spectrum is dominated by 1/f noise and thermal noise for low resistivity material and by generation-recombination (G-R) noise for high resistivity material. Noise characteristics were measured as a function of temperature in the 80K to 300K range. At temperatures below 150K, 1/f noise is dominant and at temperatures above 150K, G-R noise is dominant. Optical excitation revealed the presence of traps not observed in the dark, at room temperature.
The Charge Redistributon Accompanying Slip and Cleavage: Electronic Structure Calculations in Alloy Design
Authors: Eberhart M.E. , Woodward C. , Giamei A.F. 
Published: April 2011

AbstractExtracting full information from electronic structure calculations requires the ability to compare differences in bonding between two molecules or solids. Often these comparisons use qualitative models of the chemical bond in an unsuccessful attempt to account for subtle variations in molecular properties. Correlating electronic structure with properties requires an unambiguous and quantifiable description of the chemical bond. Here, we show that such a description is contained within the geometric properties of the charge density, which can be obtained from quantum mechanical calculations. This description is used to rationalize the previously unexplained variation in the mechanical properties of a series of ordered intermetallic alloys. The ease with which this description of chemical bonding can be applied to problems, which have defied simple bonding explanations, suggests that it may be useful in accounting for the properties of any molecular system which arise from the making, breaking, or rearrangement of bonds.
Experimental Analysis of Deformation Induced Microstructure Near a Crack Tip in a Hardened Copper Crystal
Authors: Bastawros A.-F. , Kim K.-S. 
Published: April 2011

AbstractThe incremental in-plane Green-Lagrange strain tensor was measured near a stationary crack tip in a cyclically work-hardened copper single crystal. Measurements were made on the surface of a four-point bend specimen, using a finite-deformation laser moiré interferometer. The measurement showed the existence of a narrow asymptotic field beyond a distance of 300 μm from the crack tip. The inner boundary of the asymptotic zone was almost fixed at acharacteristic distanceahead of the crack tip. This length scale is thought to arise from a microstructural evolution near the crack tip. The inhomogeneous hardening due to glide-band clustering and patchy slip in a small volume near the crack tip triggered such an evolution. The outer boundary of the asymptotic zone radially grew with the increasing load. The deformation field was found to be very sensitive to additional mode II loading.
Quasi-Static Brittle Fracture
Authors: Pfaendtner J. A. , Muthiah R. C. , McMahon C. J. 
Published: April 2011

AbstractRecent work on the phenomenon of diffusion-controlled quasi-static brittle fracture, known as dynamic embrittlement, is reviewed here with reference to sulfur-induced embrittlement of steel, tin-induced embrittlement of Cu-Sn alloys, and oxygen-induced embrittlement of copper-based and nickel-based alloys. The mechanisms of this generic form of intergranular brittle fracture are discussed.
The Influence of Microstructure on the Fracture and Tensile Properties of Die Cast and Thixomolded Magnesium Alloys
Authors: Thoma Paul E. , Hays Colleen , Baik Aekyung 
Published: April 2011

AbstractIn this investigation, the fracture and tensile properties of die cast and thixomolded magnesium alloys are compared and shown to be dependent on the microstructure of the test specimens. The principal features of a die cast structure that inhibit crack propagation and contribute to high ductility are the presence of highly structured primary α-magnesium dendrites and a continuous network of the α-magnesium phase. The lower tensile properties of thixomolded magnesium alloys are attributed to the presence of nodular a-magnesium dendrites. Cracks propagate around the nodular dendrites through the divorced eutectic that surrounds the nodular α-magnesium dendrites. In the thixomolded alloys, there is also a less developed continuous network of the α-magnesium phase.
Effect of Bottom Electrode System on Ferroelectric Properties of Sputter Deposited PZT Capacitors
Authors: Hong Kwon , Yu Yong Sik , Lee Shang Kyoo 
Published: April 2011

AbstractRF magnetron sputter deposited PZT films were prepared on various bottom electrode systems such as Pt/Ti/SiO2/Si, IrO2/SiO2/Si, Pt/IrO2/SiO2/Si and Ir/IrO2/SiO2/Si substrates using the ceramic PZT target with Pb1.1(Zr0.52Ti0.48)O3 composition. In order to obtain single perovskite phase, PZT films were sputter-deposited at room temperature under Ar only plasma condition followed by high temperature annealing under oxygen ambient. Regardless of the bottom electrode system, reasonable ferroelectric properties such as 2Pp, Vc could be obtained by 650°C post annealing. Their values were over 20μ C/cm2 and below ± 1.OV when drive voltage was ± 3V, respectively. Hybrid electrode system, namely, thick Pt or Ir and thin IrO2 shows good leakage current characteristics, of ∼ 10−8A/cm2. Fatigue properties of PZT capacitor depend on the test condition. However, retention after 3×104sec showed a degradation of 15% when writing voltage was −5V irrespective of bottom electrode system. Imprint characteristics also showed good results within ± 1 as a figure of merit (FOM).
Characterization of Ruo2 Films Prepared by Rf Reactive Magnetron Sputtering
Authors: Meng Li-jian , Santos M.P. dos 
Published: April 2011

AbstractRuthenium dioxide films have been prepared by rf reactive magnetron sputtering at different oxygen partial pressures and total sputtering pressures. The films have been characterized by scanning electron microscopy, X-ray diffraction and electrical conductivity. The films prepared at low oxygen partial pressure and total pressure show a strong preferred orientation along the [110] direction. As both pressures increased, the peak intensity decreases. All the films are subject to a compressive stress. As the total pressure is decreased and the oxygen partial pressure is increased, the stress increases. When the total pressure is lower than 6 × 10−3 mbar and the oxygen partial pressure is higher than 1 × 103 mbar, the films peeled off automatically from the substrate because of the high stress. The films prepared at high oxygen partial pressure and high total pressure have a rough surface and those prepared at low pressure show smooth surface. In this paper, these phenomena have been discussed. In addition, the electrical properties of the films are also discussed.
Fabrication of PZT Based Capacitor with SrRuO3 Electrode for Memory Device Applications
Authors: Kumar Ashok , Rahman H. , Shamsuzzoha M. 
Published: April 2011

AbstractStrontium ruthenium oxide (SrRuO3) was deposited on Pt/(100)Si substrates at varying temperatures and 300 mTorr oxygen pressure using the pulsed laser deposition method and was found to be highly crystalline and textured when deposited over 450°C. After achieving highly crystalline SrRuO3 films, capacitors using the ferroelectric material - PZT (PbZr0.5Ti0.48O3) were successfully fabricated on Pt/(100)Si substrates. The ferroelectric properties of the films were determined by the RT66A Standardized Ferroelectric Test System. The structural properties of the films were analyzed by X-ray diffraction. Transmission electron microscopy was used to determine the crystallinity and quality of interfaces among different layers.
The Phase Transition of Bi-Pt Alloys at the Interface of Pt/SrBi2Ta2O9 and its Effect on Interface Roughness
Authors: Shin Dong Suk , Lee Ho Nyung , Kim Yong Tae , Park Young K. , Choi In-Hoon 
Published: April 2011

AbstractPt/SrBi2Ta2O9(SBT)/CeO2/Si (MFIS) structures were investigated for observing the change of electrical properties and morphology of interface of Pt/SBT after post-annealing of Pt top electrodes. The morphology of Pt/SBT interface became smooth and Bi oxide was formed at the bottom of Pt top electrode after post-annealing Pt top electrode. In order to describe the origin of these changes, Bi-oxide/Pt/SiO2/Si structure was investigated with annealing temperatures about the reaction between Bi oxide and Pt. We can describe that the smooth interface of Pt/SBT and the consumption of metallic Bi, which the reason why electrical properties were drastically improved, is induced by the melting of Pt-Bi alloys and formation of Bi-oxide after post-annealing Pt top electrode.
Sol-Gel Growth of High-Quality Pb(Zr,Ti)O3 Films on RUO2 Using Seed Layers
Authors: Norga G. J. , Fè Laura , Wouters D. J. , Bartic A. , Maes H.E. 
Published: April 2011

AbstractNew approaches for improving fatigue performance of sol-gel PZT based ferroelectric capacitors with RuO2 electrodes are discussed. The use of thin (∼5 nm) high-Ti PZT seed layer was found to be effective for improving fatigue performance. For an optimized seedlayer thickness, FECAPs with excellent fatigue characteristics (less than 10% decrease in Pr after 1011 cycles) were obtained.
The Stress State and Domain Structure of Epitaxial PbZr0.2Ti0.8O3 Films on (001) SrTiO3 with and without La0.5Sr0.5CoO3 Electrode Layer
Authors: Alpay S.P. , Nagarajan V. , Bendersky L.A. , Vaudin M.D. , Aggarwal S. , Ramesh R. , Roytburd A.L. 
Published: April 2011

AbstractThe domain structure of the 400 nm thick PbZr0.2Ti0.8O3 (PZT) films with different electrode layer configurations was investigated by x-ray diffraction and transmission electron microscopy. The c-domain fractions of the PZT films with no electrode layer, with a 50 nm electrode layer between the film and the substrate, and with 50 nm electrode layers on top and bottom of the PZT film were found to be equal. This means that depolarizing fields do not affect the polydomain structure of the film. Calculations of the in-plane strains based on the lattice parameters of the La0.5Sr0.5CoO3 (LSCO) layer in the above configurations led to the conclusion that the bottom electrode layer is coherently strained to match the substrate.
Ferroelectric Behavior of Li-Doped ZnO Thin Films on Si(100) by Pulsed Laser Deposition
Authors: Joseph M. , Tabata H. , Tkawai T. 
Published: April 2011

AbstractThin films of Li-doped ZnO of different compositions (Zn1−xLix)O, x=0.1, 0.17 and 0.3 have been prepared on Si(100) substrate for the first time by pulsed laser deposition. These films are characterized for their structural, surface morphology and ferroelectric nature. A memory window of 1.2V has been observed in capacitance-voltage measurement.
The Effect of (Ba,Sr) and (Mn,Fe,W) Dopants on the Microwave Properties of BaxSr1−xTiO3 Thin Films
Authors: Chang Wontae , Horwitz James S. , Kim Won-Jeong , Pond Jeffrey M. , Kirchoefer Steven W. , Chrisey Douglas B. 
Published: April 2011

AbstractSingle phase BaxSr1−xTiO3 (x=0.5 and 0.6) thin films (∼5000Å thick) have been deposited onto (100) MgO single crystal substrate with (Ba,Sr) compensated and/or (Mn,Fe,W) doped targets using pulsed laser deposition (PLD). The room temperature capacitance (C) and dielectric Q (1/tanδ) have been measured at microwave frequencies of I to 20 GHz as a function of electric field (0-80kV/cm). Microstructural defects associated with cation and anion vacancies have been observed in BaxSr1−xTiO3 films. Compensation of the ablation target with excess Ba and Sr tends to increase the dielectric constant and the dielectric Q. A film deposited with (Ba,Sr) compensated target has been obtained with 25% tuning, where % tuning is defined as {(C(0)-C(E))/C(O))×100, and dielectric Q of ∼ 100 at room temperature (1 — 10 GHz) for DC bias field (E=67 kV/cm). A further increase in the dielectric Q is observed by the addition of donor/acceptor dopants such as Mn, Fe, and W (Q≈100-240). The effects of (Ba, Sr) compensation and (Mn,Fe,W) doping on the film structure and dielectric properties are discussed.
Electrode Structures for Integration of Ferroelectric or High Dielectric Constant Films in Semiconductor Devices
Authors: Grill Alfred 
Published: April 2011

AbstractThe preparation of ferroelectric and high-dielectric perovskite materials, which is performed at high temperatures in oxidizing environments, imposes strong limitations on the choice of suitable electrode materials which can be used for integration of these materials with semiconductor devices. Because of the complex compositions of the perovskites and of some of the electrode materials the two can interact and result in the deterioration of the structures. The electrode materials have, therefore, to be used often in combination with suitable barriers which block diffusion of the elements of the perovskite and of the Si device and prevent interactions between the components. These requirements can result in complex, multilayered electrode/barrier structures that can affect the crystallization of the perovskite material and its electrical properties as well as the perovskite properties during subsequent processing steps (e.g. in forming gas anneals). The present paper will review the different electrode/barrier structures that have been proposed for integration of ferroelectric thin films with semiconductor devices and discuss their effects on the properties of ferroelectric and high-dielectric materials.
Dendritic Macromolecules: A Fourth Major Class of Polymer Architecture – New Properties Driven by Architecture
Authors: Tomalia D. A. , Uppuluri S. , Swanson D. R. , Brothers H. M. , Piehler L. T. , Li J. , Meier D. J. , Hagnauer G. L. , Balogh L. 
Published: April 2011

AbstractThis new architectural class of macromolecules has received substantial attention during the past decade. Three dendritic subclasses, which include (a) random hyperbranched (i.e., one-pot ABx, polymerizations), (b) dendritic grafted (i.e., Combburst® polymers) and (c) regular dendrons/dendrimers (e.g., Starburst® dendrimers) have been synthesized and characterized at a well-defined level in our laboratory. It is clear that their precisely controlled, nanoscale dimensions and architecture play critical roles in influencing physical properties and performance characteristics. Furthermore, these parameters have also distinguished dendrimers as fundamental modules for many nanotechnology applications, as well as for the construction of a new class of larger nanoscale entities which we have termed core-shell tecto(dendrimers). This account will overview these activities and focus on certain unique de Gennes dense packing (or congestion phenomena) and nanoscale container properties that have emerged from this novel architecture.
The Hot Carrier Degradation and Device Characteristics with Variation of Pre-Metal Dielectric Materials
Authors: Seo Y. J. , Choi W. S. , Kim S. Y. , Kim C. I. , Chang E. G. , Lee W. S. 
Published: April 2011

AbstractIt is very important to select superior interlayer Pre Metal Dielectric (PMD) materials which can act as a penetration barrier to various impurities created by the Chemical Mechanical Polishing (CMP) processes. In this paper, hot carrier degradation and device characteristics were investigated with material variation of PMD-1 layers, which were split by LP-TEOS, SR-oxide, PE-oxynitride, PE-nitride and PE-TEOS films. It was observed that the PE-oxynitride and PEnitride using plasma was greatly deteriorated in hot carrier effect in comparison with silicon oxide. Consequently, it is clearly shown that silicon oxide turned out to be a better PMD-1 material than both PE-oxynitride and PE-nitride. From the results, it is suggested that LP-TEOS film is the best PMD-1 material among the silicon oxide samples.
Ammonia RF-Plasma Treatment of Tubular ePTFE Vascular Prostheses : A Preliminary Study
Authors: Mantovanil D. , Castonguay M. , Pageaul J. F. , Fiset M. , Laroche G. 
Published: April 2011

AbstractA cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used to modify the internal surface of ePTFE arterial prostheses. The effects of RF-power on the surface chemical composition were characterized by XPS. Results show that the treatment at 20 W, for 250 seconds and under an ammonia pressure of 300 mtorr yielded a good compromise between ablation and substitution phenomena on the surface. With this treatment, fluorine content was decreased, while up to 20 % of the surface atoms were substituted by nitrogen.