bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Stabilization of Non-Stoichiometric GaAs through Beryllium Doping
Authors: Lutz R.C. , Specht P. , Zhao R. , Jeong S. , Bokor J. , Weber E.R.
Published: April 2011

Beryllium-doped, non-stoichiometric GaAs grown by MBE at low temperatures appears superior to its undoped counterpart in several key areas vital to device manufacturing. X-ray diffraction studies have indicated that material grown above 275°C shows complete thermal stability to annealing at temperatures up to 600°C. This behavior is ascribed in part to strain compensation between the small beryllium atoms and the large arsenic antisites. Consequently, outdiffusion of excess arsenic from the non-stoichiometric material into neighboring layers upon annealing or subsequent high temperature growth is expected to be negligible. Short carrier lifetime (<1 psec) and high resistivity (>104 Ω-cm) have been observed in the same as-grown material. Sub-picosecond lifetimes have been measured previously in undoped material, but the low growth temperatures required produce a supersaturation of antisites allowing for significant hopping conductivity through the defect band in as-grown material, and significant arsenic outdiffusion upon annealing. Due to electrical compensation of antisites by beryllium acceptors, materials in which the ionized antisites represent a major fraction of a relatively small total antisite concentration are now made possible by proceeding to higher growth temperatures. Thus, nonstoichiometric GaAs having a beneficial combination of thermal stability, short carrier lifetime and high resistivity can be fabricated
Damage Evolution and Mechanical Failure in Flip-chip Interconnects
Authors: Soperm A. , Wolf I. De , Pozza G. , Ignat M. , Parat G.
Published: April 2011

The analysis of the mechanical behaviour of flip-chip interconections is an essential aspect of the reliability of the devices using this technique. When manufacturing them and during their operation, the interconective systems are submitted to thermal and mechanically induced stresses. By cyclic micromechanical testing and from analysis by micro Raman of singularities, we studied the mechanical response and the failure of samples, consisting of a substrate, the interconections and a chip.

Two sort of low melting point alloys were investigated, with different metallurgies for the pads, holding the interconections.
Stress Evolution during Thermoset Cure
Authors: Mei Yuhai , Yee Albert F. , Wineman Alan S. , Xia Chaodong
Published: April 2011

The residual stress evolution in an epoxy during isothermal curing process has been determined experimentally. It was found that for a certain curing temperature range in which the characteristic time for the molecular motions leading to volume recovery is shorter than the time scale of the experiment, an incremental elastic constitutive equation can be used to describe the mechanical response of the epoxy. It was also found that appreciable residual stresses are developed in a threedimensionally constrained epoxy resin system within the rubbery state.
Analysis of Catastrophic Field Failures Due to Conductive Anodic Filament (CAF) Formation
Authors: Ready W. J. , Smith B.A. , Turbini L.J. , Stock S.R.
Published: April 2011

Under certain environmental conditions, printed wiring boards (PWB) respond to applied voltages by developing subsurface deposits of copper salts extending from anode to cathode along separated fiber / epoxy interfaces. The formation of these deposits, termed conductive anodic filaments (CAF) require high humidity (80%RH) and high voltage gradient (5V/mil). The humidity exposure during the storage environment may cause the failure in the use environment. CAF formation is enhanced by the use of certain hot air solder leveling (HASL) fluids and / or water soluble flux constituents.

In this work, two catastrophic field failures were analyzed. Both failures were related to boards produced in a manufacturing process, which included HASL. One CAF failure occurred between a component through-hole and power plane held at a potential difference of 40V with a 0.005″ nominal spacing. The other occurred on an inner layer of a multi-layer board (MLB) between a via and ground plane held at a potential difference of 320V with 0.015” nominal spacing. The nature of the CAF was analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Ion chromatography (IC) was used to identify residue extracted from a failed board. The failure phenomena known as CAF poses serious longterm reliability concerns in electronic products exposed to adverse and hostile environments, especially those with closely spaced conductors.
The Study on The Under Bump Metallurgy (Ubm) and 63SN-37PB Solder Bumps Interface for Flip Chip Interconnection
Authors: Jang Se-Young , Paik Kyung-Wook
Published: April 2011

In the flip chip interconnection on organic substrates using eutectic Pb/Sn solder bumps, highly reliable Under Bump Metallurgy (UBM) is required to maintain adhesion and solder wettability. Various UBM systems such as l.tm Al/0.2 μm Ti/5 μm Cu, l μm A1/0.2 μm Ti/l μm Cu, 1 μm A1/0.2 μm Ni/1 μm Cu and 1 μm At/10.2μm Pd/l μm Cu, laid under eutectic Pb/Sn solder of low melting point, were investigated with regard to their interfacial reactions and adhesion properties. The effects of numbers of solder reflow and aging time on the growth of intermetallic compounds (IMC) and on the solder ball shear strength were investigated. Good ball shear strength was obtained with 1 μm AI/0.2μm Ti/5μm Cu and 1 μm Al/0.2 μm Ni/l μm Cu even after 4 solder reflows or 7 day aging at 150°C. In contrast, l μm Al/0.2 μm Ti/l μm Cu and l μm A1/0.21μm Pd/μm Cu shows poor ball shear strength. The decrease of the shear strength was mainly due to the direct contact between solder and nonwettable metal such as Ti and Al resulting in a delamination. Thin 1 μm Cu and 0.2 μm Pd diffusion barrier layer were completely consumed by Cu-Sn and Pd-Sn reaction.
Readout of Magnetic Film-Based Memories by Nonlinear-Optical Magnetic Kerr Effect
Authors: Murzina T.V. , Didenko N.V. , Fedyanin A.A. , Melnikov A.V. , Misuryaev T.V. , Aktsipetrov O.A.
Published: April 2011

Magnetic field induced second harmonic generation (MSHG) is suggested as a nonlinear-optical readout for magnetic film-based memories: Systematic studies of the nonlinear-optical magnetic Kerr effect and MSHG interferometry are carried out for (i) magnetic rare-earth iron garnet films, (ii) Gd-containing Langmuir-Blodgett films and (iii) CoxCu1-x granular films. The magneto-induced nonlinear-optical properties of thin films being used for recording the information can be easily distinguished by the MSHG nondestructive probe. An estimation of the signal-to-noise ratio (readout error) shows an acceptable value of the magnetic contrast for this potential readout.
Diluted Magnetic Semiconductor Thin Films and Multilayers
Authors: Furdyna J. K.
Published: April 2011

We review the properties of diluted magnetic semiconductor (DMS) thin films and multilayers, with special attention to their usefulness in magneto-optical device applications. We begin with the most widely studied DMS family, i.e., alloys of II-VI semiconductors involving Mn ions. Prospects and challenges are discussed for achieving II1-xMnxVI-based non-reciprocal devices; and for devices operating in the far infrared. We also consider the unique advantages which DMSs offer for probing the properties of semiconductor heterostructures. We then discuss ferromagnetic DMSs, including those based on the III-V semiconductor family. And we briefly review the status of hybrid ferromagnetic-semiconductor structures achieved through recent advances in epitaxy of new materials.
Magnetization Process in Cr Substituted Diluted Magnetic Semiconductor Films
Authors: Adachi N. , Hirano J. , Yamazaki T. , Okuda T. , Kitazawa H. , Kido G.
Published: April 2011

Cr substituted dilute magnetic semiconductor Cd1-xCrxSe films were grown onto fused silica and sapphire (00 · 1) substrates by vapor deposition technique. The films with wurtzite structure were obtained at composition of 0 ≤ × ≤ 0.66. Saturation magnetization and magnetic susceptibility increased as x increased. In comparison with Mn-DMS system, the initial magnetization curves saturate easily. This tendency is different from most DMS materials in which magnetic ions interact with each other antiferromagnetically. It is possible that ferromagnetic interactions exist in Cd1-xCrxSe.
Effect of Quaternary Ammonium-Modified Montmorillonites on Mechanical Properties of Polypropylene
Authors: Zhang Y. H. , Gong K. C.
Published: April 2011

Hybrids of quaternary ammonium-modified montmorillonites and polypropylene were prepared by melting intercalation. Results of mechanical property measurements show that, tensile strength, modulus and impact strength of PP composites are greatly enhanced simultaneously by a small addition amount of modified montmorillonites.
High-Resolution Transmission Electron Microscope Analysis of Tungsten Carbide Thin Films
Authors: Qin Wentao , Shih W. , Lib J. , James W. , Siriwardaneane H. , Fraundorf P.
Published: April 2011

Electron diffraction patterns and high-resolution transmission electron microscope (HREM) images show that the dominant phase in tungsten carbide thin films grown by plasma enhanced chemical vapor deposition is WC(1−x). The f.c.c crystal structure and the unit cell size of WC(1−x) have been determined via electron powder diffraction. The two largest and most dominant spacings in HREM images are the {111} and {002} spacings of WC(1−x). Cross lattice fringes along the two most densely populated zones of WC(1−x) are seen. The sizes and aspect ratios of nano-crystals have been measured from HREM images. Stereo analysis of individual nano-crystals has been done. Confirmation of the 3-D structure of WC(1−x) via spacings larger than 0.15 nm will require a tilt larger than 35° between images.
Design of Novel Treated Silica Xerogels: Synthesis, Property and Reinforcement in Silicone Elastomers
Authors: Deng Q. , Bums G. T. , Hahn J. R. , Reese C. C. , Preston J. D. , Winchell S. B.
Published: April 2011

Treated silica xerogels with controlled porosity and surface area were prepared by the in-situ treatment of hydrogels with hexamethyldisiloxane in the presence of isopropyl alcohol. The resulting hydrogels were hydrophobic and readily transferred to organic solvents allowing their isolation. The surface area and porosity of the xerogel were controlled by varying the pH, time and temperature used to aggregate the hydrogel prior to treatment. The treated xerogels were evaluated as reinforcing fillers in silicone rubber formulations. When the bases were crosslinked with peroxides, silicone elastomers with acceptable mechanical properties were obtained. The relationship between the surface area, porosity and the type and degree of surface treatment of the xerogel, and its reinforcing ability was studied. In general, the mechanical properties of the elastomer increased as the filler structure increased; however, xerogels with higher surface areas were more difficult to incorporate and gave higher plasticity bases.
Preparations, Structures, and Properties of Polysiloxane-Silica Composites Prepared from a Variety of Hydrolyzable Precursors
Authors: Breiner J. M. , Mark J. E. , Beaucage G.
Published: April 2011

Poly(dimethylsiloxane) (PDMS) networks were prepared by tetrafunctionally endlinking hydroxyl-terminated chains with tetraethoxysilane (TEOS). The resulting networks were filled in-situ by hydrolysis-condensation reactions that were either acid or base catalyzed reactions on some novel precursors. These precursors included star-shaped molecules, rings, linear comb-like chains, and pre-hydrolyzed products of silanes such as TEOS. Both monomethoxy and trimethoxy groups were used as hydrolyzable groups on these molecules. The structures of the resulting composites were examined by small-angle X-ray scattering, and their mechanical properties were determined using equilibrium stress-strain measurements in elongation. Novel precursors with monomethoxy functionalities did not generate stable particulates, but those with trimethoxy functionalities did, with some improvements in mechanical properties. Partially-hydrolyzed TEOS provided the best reinforcement of these PDMS elastomers.
Effect of Pb/Ti Ratio on the Particle Size of Hydrothermal PbTiO3 Powders
Authors: Peterson C. R. , Slamovich E. B.
Published: April 2011

The influence of Pb/Ti ratio on the particle size of hydrothermally derived lead titanate (PbTiO3) powders was investigated. Phase pure PbTiO3 powder was synthesized by reacting nanocrystalline TiC2 powder in a 1 m KOH solution for 15 h at 200°C with Pb/Ti ratios of 1 and 5. Faceted platelet particles with a low aspect ratio were formed in solutions with Pb/Ti ratios of 1 and 5. The observed particle size of PbTiO3 was 200 nm and larger when Pb/Ti = 1, while 50 - 100 nm sized particles formed when Pb/Ti = 5. In support of TEM observations, the BET specific surface area data increased from 4.4 m2/g to 7.3 m2/g as the Pb/Ti ratio was increased from I to 5. PbTiO3 particle size was controlled by either inhibiting or promoting dissolution-precipitation. Dissolution-precipitation in a high pH solution was inhibited by maintaining an excess of Pb ions in solution and it was promoted when input concentrations of Pb and Ti were equivalent.
Production Methods for Metallic Foams
Authors: Banhart J. , Baumeister J.
Published: April 2011

The possibilities for making metallic foams or similar porous metal structures are reviewed. The various processes are classified according to the state of the starting metal - liquid, powdered, ionised. Liquid metal can be foamed directly by injecting gas, gas-releasing foaming agents or by producing supersaturated metal-gas solutions. Indirect methods include investment casting and usage of filler materials. Metal powders can also be used as starting materials for metallic foams: mixtures of such powders with foaming agents are compacted to foamable precursor materials that can be foamed in a second step. Instead of foaming agents inert gas can be directly entrapped in the precursor. Metal foams can also be made from metal powder slurries or by using polymer/powder mixtures. Finally, galvanic electro-deposition also allows to make highly porous metallic structures with open pores.
Elastic Properties of Low Density Core (LDC) Ti-6Al-4V Sandwich Cores
Authors: Queheillalt D. T. , Wadley H. N. G. , Schwartz D. S.
Published: April 2011

Lightweight, structurally efficient low density core (LDC) sandwich structures can be produced by entrapping argon gas within a finely dispersed distribution of pores in a microstructure and using a high temperature anneal to cause pore growth by gas expansion. This results in a porous microstructure with a relative density as low as ∼0.70. Laser ultrasonic methods have been used to measure the longitudinal and shear wave velocities and hence the elastic properties of LDC Ti-6Al-4V cores prior to, and after gas expansion treatments of up to 48 hr at 920°C. The data was compared with several analytical models for predicting the volume fraction of porosity dependent elastic properties of porous materials.
Characterization of Porous Gasar Aluminum
Authors: Bonenberger R. J. , Kee A. J. , Everett R. K. , Matic P.
Published: April 2011

Experimental and numerical analyses were performed on porous aluminum samples to evaluate microstructure and mechanical properties. Experiments consisted of tensile tests on dog-bone specimens containing 9 to 17% porosity, which were instrumented with axial and transverse extensometers. Properties measured included Young's modulus, Poisson's ratio, proportional limit, 0.2% offset yield strength, and ultimate tensile strength. Results indicated that Young's modulus and all strengths decreased with increasing porosity, but Poisson's ratio remained constant with porosity. For the numerical simulations, 3-D, mesoscale, multilayer models were constructed to evaluate the effects of pore morphology and interactions on material properties. The models allowed systematic spatial positioning of the pore within the cell and the ability to form solid zones. Pore arrangement, the effect of constraint, and gradients on the stress state were investigated. By using different combinations of hex cells as building blocks, several complicated microstructural arrangements were simulated.
Compressive, Tensile and Shear Testing of Melt-Foamed Aluminium
Authors: Von Hagen H. , Bleck W.
Published: April 2011

For construction purposes it is utterly important to get detailed information on the possible influence of the foam thickness on the mechanical properties and on the deformation behaviour of metallic foams. The effect of compressive, tensile and shear loads on aluminium foam samples has been examined with the testing methods for sandwich material as described in German and ASTM-standards. The aim is to provide more data on these mechanical properties varying the sample density and thickness. Regarding the results the most reliable material parameters as well as steps towards a relationship between the different strength parameters can be obtained.
Effects of Thermomechanical Processing on the Resulting Mechanical Properties of 6101 Aluminum Foam
Authors: Margevicius R. W. , Stanek P. W. , Jacobson L. A.
Published: April 2011

High porosity aluminum was fabricated in a number of ways. The starting material was a cast 6101 aluminum that had a relative density of 9.8%. The cast aluminum block was compressed by uniaxial, biaxial, and triaxial densification. Uniaxial compression was done at room temperature and 200°C. Biaxial compression was achieved by unidirectional rolling at room temperature and 200°C. Triaxial compression was done by cold isostatic pressing at 3.4, 6.7, and 34 MPa (0.5, 1.0, and 5.0 ksi). Metallography and mechanical test specimens were machined from the processed bars. The mechanical properties showed that the relative yield strength depended both on relative density and processing temperature.
Laser Ultrasonic Instrumentation for Accurate Temperature Measurement of Silicon Wafers in Rapid Thermal Processing Systems
Authors: Klimek Dan , Anthonyt Brian , Abbate Agostino , Kotidis Petros
Published: April 2011

Results are presented that demonstrate the use of laser ultrasonic methods to determine the temperature of silicon wafers under conditions consistent with applications in the RTP industry. The results show that it is possible to measure the temperature of Si(100) wafers to an accuracy approaching ± 1°C (1σ) even with wafer thickness variation over a range of 2 to 3 percent.
Cathodoluminescence Studies of Si-Sio2 Interfaces Prepared by Plasma-Assisted Oxidation and Subjected to Post-Oxidation Rapid Thermal Annealing
Authors: Schafer J. , Young A. P. , Brillson L. J. , Niimi H. , Lucovsky G.
Published: April 2011

We have used low energy cathodolumrdinescence spectroscopy (CLS) to characterize defects at ultrathin (50 Å) silicon dioxide films, prepared on Si substrates by low-temperature plasma deposition. Variable-depth excitation with different electron injection energies provided a clear distinction between deep levels localized within the films versus at their interfaces. Defect bands are evident at 0.8 eV and 1.9 eV, characteristic of an amorphous, silicon-rich local bonding environment. Closer to the film surface, CLS reveals a defect at 2.7 eV indicative of oxygen vacancies in stoichiometric SiO2. The effect of hydrogenation at 400°C, rapid thermal annealing at 900°C, and especially the combination of both processing steps is shown to reduce the density of these defects dramatically.
Optimization of Ti and Co Self-Aligned Silicide RTP for 0.10 μm Cmos
Authors: Kittl J. A. , Hong Q. Z. , Yang H. , Yu N. , Rodder M. , Apte P. P. , Shiau W. T. , Chao C. P. , Breedijk T. , Pas M. F.
Published: April 2011

As CMOS technologies are scaled to 0.10 μm and beyond, self-aligned silicide (salicide) processes find difficult challenges. As junction depths and linewidths are scaled, achieving both low sheet resistance and low contact resistance maintaining low diode leakage becomes increasingly difficult. In this paper we present studies of Ti and Co salicide processes implemented into a 0.10 μm CMOS technology. We show that both for Ti and Co, the optimization of RTP parameters plays a crucial roll in achieving a successful implementation. For Co salicide, optimization of RTP conditions results in elimination of shallow junction leakage (its main scaling problem). Two-step RTP and one-step RTP Ti salicide processes are compared, showing the advantages of one-step RTP. The RTP process windows for low resistance narrow gates (the main scaling issue for Ti salicide) are analyzed. Processes with pre-amorphization, with Mo doping and with a combination of both are compared. An optimal process using Mo and preamorphization implants and one-step RTP is shown to result in excellent device characteristics and low resistance to 0.06 μm gates.
Interfacial Stability and Surface Morphology in Layer-By-Layer Semiconductor Heteroepitaxy Luis
Authors: Zepeda-Ruiz A. , Maroudas Dimitrios , Weinberg W. Henry
Published: April 2011

A theoretical analysis based on continuum elasticity theory and atomistic simulations is presented of the interfacial stability with respect to misfit dislocation formation and of the film surface morphology during layer-by-layer growth semiconductor heteroepitaxy. The strain in the coherently strained films, the energetics of a transition from a coherent to a semicoherent interface consisting of misfit dislocation arrays or networks, and the morphological details of the film surface profile are calculated for InAs/GaAs(110) and InAs/GaAs(111)A. The analysis is presented for the general case of heteroepitaxy on a finite-thickness compliant substrate. The results are discussed in the context of recent experimental data.
Epitaxial Growth and Magnetism
Authors: Dreysse H. , Freyss M. , Stoeffler D.
Published: April 2011

Growth phenomena and magnetism of metallic films are not easy to describe at the same level of precision. A small variation of distances can drastically modify the magnetic properties of thin metallic films. In this contribution different aspects encountered in the growth of thin magnetic metallic films are addressed. Within an itinerant magnetism scheme, the main difficulty arises from the number of possible magnetic arrangements induced by the competition between nearest-neighbors Ferromagnetic and Antiferromagnetic couplings. However we show that the description of the electronic and magnetic structure at T = 0 K by well-established band structure frameworks provides useful and precise information on the growth of a transition metal on another. Due to the large amount of experimental data available, the Fe/Cr system is taken as an example. The influence of steps at the interface is discussed and the possibility of magnetic domains is shown. A simple model of growth taking into account variable interdiffusion rate and layer-by-layer quality is given. These simulations are used to explain experimental results where interdiffusion at the interface is very common.
Simulation of the Growth of Heterostructures
Authors: Harding J.H. , Harker A.H.
Published: April 2011

The production and morphology of hetero-structures presents problems at a variety of length-scales. A common problem is the production and accommodation of stresses in the film due to mis-match. We shall first discuss examples of atomistic nucleation and growth at interfaces and the use of atomistic simulations to obtain parameters for rate-theory models of cluster and film growth. We shall then consider the effect of stress on growing films. In strained-layer semi-conductor systems, for example, the growth of small islands gives rise to stress distributions which differ strongly from those in continuous layers. Interesting strain effects are also observed in ceramics. We will discuss the relationship between stress and the growth and morphology of films, where effective medium models may be used to derive effective bulk properties for films with imperfections such as porosity and cracks.
Optical Fiber Interconnect Subjected to a Not-Very-Small Ends Off-Set: Effect of the Reactive Tension
Authors: Suhir E.
Published: April 2011

We examine the mechanical response of an optical fiber interconnect clamped (by epoxy bonding or soldering) at the ends and then subjected to a not-very-small lateral ends off-set. The term “not-very-small” is used here to indicate that the off-set is small enough to apply the elementary (linear) beam theory, but, at the same time, is large enough, so that the effect of the reactive tension has to be accounted for. The obtained results can assist a reliability engineer to make, if necessary, the appropriate changes in the photonic package design.
Optical Fiber Strength and Its Relationship to Dynamic Mechanical Properties of Fiber Coatings by Direct Measurements on Fibers
Authors: Gebizlioglu O. S. , Kurkjian C. R.
Published: April 2011

While the telecommunications optical fiber technology is in its third decade of growth, and fibers that are aging-resistant and fatigue-resistant are highly desirable, basic physico-chemical aspects of fiber aging and mechanical strength degradation are not well understood. A key difficulty to understanding fiber strength degradation has been the unavailability of tools for direct assessments of the condition of fiber coatings on aged fibers. In this presentation, we report on our studies of the effects of DI-water aging on two experimental high n-value (fatigue-resistant) fibers and their coatings. We have found that the coatings of these high n value fibers are highly resistant to DI-water aging.
Time- and Temperature-Dependent Material Behavior and its Impact on Low-Temperature Performance of Fiber Optic Cables
Authors: Gebizlioglu Osman S.
Published: April 2011

A series of service-affecting field failures in cold weather (−40°C to 0°C) initially and in more moderate conditions (up to 15° C) recently have raised concerns about the temperaturedependent transmission performance of loose tube fiber optic cables. The first field failures occurred in 1550-nm aerial transmission lines while more recent failures have affected 1310-nm operations. Field analyses and laboratory temperature-cycling measurements of the affected cables established that the transmission loss resulted from fiber microbending due to random fiber contacts with the buffer tube walls caused by the axial shrinkage of the buffer tubes relative to the cable central member. High resolution thermal expansion/contraction measurements on commonly used PBT (Polybutylene Terephthalate) and PP (Polypropylene) buffer tubes indicated that the total axial shrinkage consists of two components: irreversible shrinkage due to the relaxation of processing-induced stresses and reversible thermal contraction/expansion. The magnitude of both components depends strongly on the buffer tube material and the processing conditions used to manufacture buffer tubes. In this report, we review our work to date in developing field installation and cable design solutions, present a comparison of two buffer tube materials, identify key materials issues that determine buffer tube dimensional stability, and discuss the implications of these issues on the field installation and cable design solutions that we have developed to minimize the risk of low-temperature transmission loss in loose tube cables.
Reliability Assessment of Optical Fibers and Fiber Gratings
Authors: Kannan Sriraman , Lemaire Paul
Published: April 2011

The topic of reliability of UV-induced fiber gratings is reviewed. Approaches to assess and predict changes in optical properties of fiber gratings due to thermal decay of refractive index modulation are presented and compared. The mastercurve/demarcation energy diagram approach is shown to be a powerful and general method for the purpose. The process of thermal stabilization to obtain gratings with superior stability is delineated. It is shown that the mastercurve approach could be used to analyze other reliability problems such as in predicting hydrogen-induced losses in fibers.
InGaN/GaN/AlGaN-Based Leds and Laser Diodes
Authors: Nakamura S. , Senoh M. , Nagahama S. , Iwasa N. , Matushita T. , Mukai T.
Published: April 2011

InGaN quantum-well-structure blue LEDs were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The output power of both LEDs was as high as 6 mW at a current of 20 mA. The LED on sapphire had a considerable amount of leakage current in comparison with that on ELOG. These results indicate that In composition fluctuation is not caused by threading dislocations (TDs), free carriers are captured by radiative recombination centers before they are captured by nonradiative recombination centers in InGaN, and that the dislocations form the leakage current pathway in InGaN. Red LED with an emission peak wavelength of 650 nm was fabricated by increasing the In composition and thickness of InGaN well layer. When the laser diodes (LD) was formed on the GaN layer above the SiO2 mask region, the threshold current density was as low as 3 kAcm-2. When the LD was formed on the window region, the threshold current density was as high as 6 to 9 kAcm-2. There is a possibility that a leakage current due to a large number of TDs caused the high threshold current density on the window region. InGaN multi-quantum-well (MQW) structure LDs grown on the ELOG substrate showed an output power as high as 420 mW under RT-CW operation. The longest lifetime of 9,800 hours at a constant output power of 2 mW was achieved. The InGaN MQW LDs were fabricated on a GaN substrate. The fundamental transverse mode was observed up to an output power of 80 mW.
GaN Homoepitaxy for Device Applications
Authors: Kamp M. , Kirchner C. , Schwegler V. , Pelzmann A. , Ebeling K.J. , Leszczynski M. , Grzegory I. , Suski T. , Porowski S.
Published: April 2011

Epitaxial growth on GaN single bulk crystals sets new standards in GaN material quality. The outstanding properties provide new insights into fundamental material parameters (e.g. lattice constants, exciton binding energies, etc.) being not accessible by heteroepitaxial growth on sapphire or SiC. With MOVPE and MBE we realized unstrained GaN layers with dislocation densities about six orders of magnitude lower than in heteroepitaxy. Those layers revealed an exceptional optical quality as determined by a reduction of the photoluminescence linewidth from 5 to 0.1 meV and a reduced XRD rocking curve width from 400 to 20 arcsec.

Only recently, progress in surface preparation allowed morphologies of the layers suitable for device applications. We report on InGaN/GaN MQW structures as well as the first GaN pn- and InGaN/GaN double heterostructure LEDs on GaN single bulk crystals. Those LEDs are twice as bright as their counterparts grown on sapphire. In addition they reveal an improved high power characteristics, which is attributed to an enhanced crystal quality and an increased p-doping. Time resolved electroluminescence measurements proof that band/band recombination is the dominant emission mechanism for the InGaN/GaN LEDs.
Electron Beam Induced Impurity Electro-Migration in Unintentionally Doped GaN
Authors: Toth M. , Fleischer K. , Phillips M. R.
Published: April 2011

Electron beam induced electromigration of ON+ and H+ impurities in unintentionally n-doped GaN was investigated using cathodoluminescence (CL) kinetics profiling, CL imaging of regions pre-irradiated with a stationary electron beam, and wavelength dispersive x-ray spectrometry (WDS). The presented results (i) illustrate induced impurity diffusion in wide bandgap semiconductors, (ii) provide experimental evidence for the (VGa-ON)2- model of yellow luminescence in GaN with low Si content (ii) confirm the roles of 0 in frequently reported bound exciton and donor-acceptor pair emissions and (iv) suggest the involvement of ON+ and hydrogenated gallium vacancies in a blue emission in autodoped GaN.
Molecular Beam Epitaxy of High Quality InGaN Alloys Using Ammonia: Optical and Structural Properties
Authors: Grandjean Nicolas , Massies Jean , Leroux Mathieu , Laügt Marguerite , Vennéguès Philippe , Dalmasso Stéphane , Ruterana Pierre , Hirsch Lionel , Barrière Serge
Published: April 2011

The growth of InGaN layers was carried out by molecular beam epitaxy (MBE). The nitrogen precursor was ammonia. The optical and structural properties of the InGaN layers have been investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD) and photoluminescence (PL). For optimized growth conditions, the PL spectrum of InGaN (x=0.1) alloy is narrow (FWHM ≤ 50 meV) and the Stokes shift measured by PL excitation is weak (<50 meV), i.e. near band edge transitions are observed. Under these conditions, flat surfaces can be obtained, and InGaN/GaN quantum wells (QWs) with sharp interfaces can be grown. On the other hand, when growth conditions depart from a narrow optimum window, the structural quality of the samples strongly degrade, whereas the luminescence spectra are dominated by deep levels, exhibiting a strong Stokes shift. MBE grown light emitting diodes (LEDs) using InGaN/GaN QWs have been fabricated. Their electroluminescence (EL) peaks at 440 nm at 300K.
Computational Materials Science, an Increasingly Reliable Engineering Tool: Anomalous Nitride Band Structures and Device Consequences
Authors: Sher A. , Schilfgaarde M. van , Berding M. A. , Krishnamurthy S. , Chen A.-B.
Published: April 2011

Computational materials science has evolved in recent years into a reliable theory capable of predicting not only idealized materials and device performance properties, but also those that apply to practical engineering developments. The codes run on workstations and even now are fast enough to be useful design tools. A review will be presented of the current status of this rapidly advancing field. Examples of the accuracy of the codes are displayed by comparing the predicted atomic volumes, and cohesive and excess energies of several materials with experiment. As a further demonstration of the methods, the band structures of AIN, GaN, and InN in wurtzite and zinc blende structures will be presented. There are anomalies in the conduction and valence bands of these materials. Some consequences on light emitting and power devices made from these materials will be examined.
Spectroscopy of Proton Implanted GaN
Authors: Weinstein M.G. , Stavola M. , Song C.Y. , Bozdog C. , Przbylinska H. , Watkins G.D. , Pearton S.J. , Wilson R.G
Published: April 2011

Vibrational spectroscopy, photoluminescence, and optically detected electron paramagnetic resonance (ODEPR) have been used to characterize the defects produced in undoped and Si-doped GaN by the implantation of hydrogen. Several new vibrational bands were found near 3100 cm-1 in GaN that had been implanted with protons. These frequencies are close to those predicted for VGa-Hn complexes, leading to the tentative assignment of the new lines to VGa defects decorated with different numbers of H atoms. The proton implantation also produces an infrared PL band centered at 0.95 eV and the ODEPR spectrum labeled LEI, both of which were seen previously for electron-irradiated GaN.
Embrittlement of FE-CR-AL-ALLOYS
Authors: Lange J. H. , Brede M. , Fischer B. , Spindler S. , Wagner H. , Wittmann R. , Gerthsen D. , Broska A. , Wolff J.
Published: April 2011

The mechanical behavior of Fe-Cr-Al-alloys was investigated at different temperatures and after several heat-treatments in order to determine critical conditions for the ductility of the material. It was found that a significant embrittlement takes place during deformation at higher temperatures around 400 °C as well as after heat-treatments at temperatures above 1000 °C in combination with very high or very low cooling rates. Possible reasons for this behavior are discussed with respect to the results of transmission electron microscopy (TEM), Auger spectroscopy (AES), positron annihilation spectroscopy (PAS) and measurements of the electrical resistivity.
Effect of Crack Geometry on Dislocation Nucleation and Cleavage Thresholds
Authors: Fischer L.L. , Beltz G.E.
Published: April 2011

A continuum model based upon the Peierls-Nabarro description of a dislocation ahead of a crack is used to evaluate the critical mode I loading for dislocation nucleation at the tip of a finite, pre-blunted crack. A similar approach is used to evaluate the critical mode I loading for atomic decohesion. Results are presented for various crack tip root radii (a measure of bluntness), for several crack lengths. It is shown that increasing the crack length increases the critical energy release rate for both material behaviors. Increasing the bluntness of a crack tip always increases the required loading for atomic decohesion but nucleation thresholds are initially decreased by very small increases in crack tip bluntness. Nucleation thresholds are later increased after reaching significant crack tip blunting. Implications for ductile versus brittle competition are discussed by comparing the ongoing competition between these two different material behaviors.
Transitions of Shear Resistance in a Single-Asperity Contact
Authors: Hurtado J. A. , Kim K.-S.
Published: April 2011

The shear force required to emit circular dislocation loops from the edge of a circular adhesive-contact zone is calculated analytically as a function of contact-zone radii. The emission condition is based on the balance of the configurational force and the Peierls force on a dislocation loop initiated at the edge of the adhesive contact zone. The analysis suggests that there is a transition, for a nanometer-scale single-asperity contact, from concurrent (mobile- dislocation-free) slip to single-dislocation-assisted (SDA) slip. The nanometer-scale friction stress (shear force required for slip/contact area), which experimentally is observed independent of normal loading and contact-zone size, is believed to be the stress required for concurrent slip. The analysis also predicts a second transition from SDA slip to multiple-dislocation-cooperated (MDC) slip at the scale of tens of micrometers in contact size. The friction stress at this large length scale has also been observed experimentally to be independent of normal loading and contact size; however, the friction stress at the nanometer scale is about 30 times that at the scale of tens of micrometers. The analysis is consistent with these experimental observations.
Characterization and Oxidation Kinetics of Reactively Sputtered Ti1−xAlxN Film
Authors: Ishizuka Yoshiki , Kim Dong Joo , Streiffer Stephen K. , Kingon Angus I.
Published: April 2011

We report on the use of Ti1−xAlxN as an electrically conductive barrier layer from the viewpoint of its oxidation kinetics and electrical properties. Auger electron spectroscopy depth profile analysis revealed the improvement of oxidation resistance with Al incorporation. At 650 °C, an oxygen diffusion coefficient and an activation energy of Ti0.47AI0.53N were determined to be 5.85×10−1 Å 2/sec and 2.51 eV respectively. Compared with TiN, this corresponds to an oxide gowth rate reduction of about two orders of magnitude. An Al-rich oxide layer, which gew near the Ti1−XAlxN surface, is believed to act as a passivation layer to oxidation. Furthermore, current-voltage characteristics showed that the oxidation resistant Ti1−xAlxN minimized the increase of electrical resistance after heat treatment in an oxidizing atmosphere. These results suggest that Ti1−xAlxN is an attractive candidate for an electrically conductive barrier layer for advanced memory device applications.
Influence of the substrate temperature on the structure of SrBi2Ta2O9 thin films obtained by laser ablation
Authors: Díaz J. A. , Cruz M. P. , Contreras O. E. , Siqueiros J. M. , Portelles J.
Published: April 2011

A systematic study is presented of the resulting SBT films deposited by PLD at substrate temperatures from 300 to 600°C. The characteristics of the film as-deposited are determined. Special attention is focused on the compositional and structural properties. XRD, SEM, and TEM analyses are reported.
Effects of the Purity of Metalorganic Sources on the Electrical Properties of Pb(ZrTi)O3 Thin Films by MOCVD
Authors: Shimizu M. , Yoshida M. , Fujisawa H. , Niu H.
Published: April 2011

Effects of the purity of metalorganic Pb,Zr and Ti precursors (Pb(C2H5)4, Zr(O-tC4H9)4 and Ti(O-iC3 H 7)4) on the electrical properties of Pb(ZrTi)O3 (PZT) thin films prepared by MOCVD were investigated. Generally, PZT thin films prepared using the high purity Pb source precursor had a tendency to show better current densities, breakdown electric fields and switching fatigue characteristics than those of PZT films prepared using the low purity precursor. On the other hand, distinct purity effects of Zr and Ti source precursors were not observed. These experimental results suggest that some types of impurities play important roles as donors and acceptors and influence ionic movement and space charge. At this stage, it is not well understood which impurities contained in precursors play important roles and what is the difference in the impurity effects between Pb, and Zr and Ti precursors.
Pulsed Laser Deposition of Piezoelectric Films for Micro-Fluidic Applications
Authors: Kim W.J. , Rife J.C. , Horwitz J.S. , Auyeung R.C.Y. , Chrisey D.B. , Bell M.I. , Smith R.W.
Published: April 2011

Abtract

Thick films of piezoelectric materials have been grown by pulsed laser deposition (PLD) for use in the development of a programmable micro-fluidic controller. ZnO and BaTiO3 (BTO) films were deposited onto various substrates, including Au/Cr coated Si, Pt/Ti coated Si, and Au/Pd coated glass microchannel plates, at substrate temperatures from room temperature to 800 °C in a background pressure of O2 from 3 to 350 mTorr. ZnO films (∼5 µm thick) were single phase and (001) oriented. BTO films, 33 µm thick, on Pt/Ti/Si were single phase and polycrystalline. To fabricate piezoelectric acoustic transducer, an array of 2 × 4 gold electrodes was deposited onto the thick BTO films through a shadow mask by PLD. The transducers were attached to a simple fluidic circuit with a 1.6 × 1.6 mm cross section and used to generate a flow velocity of 1 mm/s at an operating frequency of 50 MHz.
Thermal Expansion and Glass Transition Behaviour of Thin Polymer Films with and without a Free Surface Via Neutron Reflectometry
Authors: Pochan D. J. , Lin E. K. , Satija S. , Cheng S. Z. D. , Wu Wen-Li
Published: April 2011

The thermal expansion of thin deuterated polystyrene (dPS) films supported on energetically repulsive, fluorinated polyimide (PI) substrates (PI/dPS bilayer) was measured via neutron reflectometry as a function of initial dPS film thickness. Film thickness was measured before and after capping with a top layer of the same repulsive, high glass transition polyimide that comprised the substrate layer (PI/dPS/PI trilayer) in an attempt to observe any effects of the dPS free surface in the bilayer geometry. Bulk thermal expansion behavior, characterized by a discontinuous change in coefficient of thermal expansion (CTE) at the glass transition (Tg), is observed in films with thickness > 70 rim. For thicknesses between 70 nm and 40 nm a transition is seen from bulk behavior in bilayer films to glassy thermal behavior in the trilayer films persisting up to 20 °C above the bulk Tg. In films with thickness < 40 nm the bulk glassy CTE persists well above the bulk Tg for both bilayer and trilayer films
Thermodynamics and Kinetics in Model Light Harvesting Dendrimers
Authors: Bar-Haim Arie , Klafter Joseph
Published: April 2011

Thermodynamic and kinetic properties of model dendrimers are investigated. We show that for ideal dendrimers, with a superimposed energy funnel descending from the periphery to the center, one should be able to control the preferred location of the excitation by monitoring the temperature relative to the energy funnel. This opens the possibility for a controlled drive of photochemical processes in these supermolecules. The mean first passage time (MFPT) of excitations to reach the center of a dendrimer is calculated. A minimum in the MFPT as a function of temperature is predicted.
About Computations of Hele-Shaw Flow of Non-Newtonian Fluids
Authors: Kondic L. , Fast P. , Shelley M. J.
Published: April 2011

The flow of a fluid confined between two solid plates (Hele-Shaw cell) is of considerable interest in a variety of applications. Further interest in two phase flow in this geometry stems from the close analogy between the dynamics of fluid-fluid interface and the propagation of the solidification front. While the flow of Newtonian fluids is rather well understood, it is much more complicated to compute flows of non-Newtonian fluids. We find that the dense-branching morphology of Newtonian liquids may be replaced by dendritic fingers with stable tips and sidebranches, and discuss resulting length scales.
Large Area Deposition of Cadmium Sulfide by Chemical Bath Deposition for Photovoltaic Applications
Authors: Boyle David S. , O'brien Paul
Published: April 2011

There is considerable interest in the deposition of compound semiconductors by methods which involve relatively low capital expense and are technically undemanding on the experimentalist. One process to meet these criteria is Chemical Bath Deposition (CBD). Such processing methods are particularly appropriate for the production of devices for which large areas and low cost are essential, such as the BP Solar Ltd “Apollo” cells based on CdS:CdTe heterojunctions.

The electrical and optical properties of these devices have been investigated with respect to impurity profiles of 16-O, 34-S, 35-Cl and 12-C in the CdTe and CdS:CdTe interface. Device characteristics (e.g. Voc and Rs) have been correlated with SIMS data. The distribution of the carbon contaminant appears to influence the chloride-promoted recrystallisation of CdTe. XPS analysis of CdS layers appears to indicate that the annealing process induces the formation of a chloride-rich surface layer, which may promote the n- to p- type thermal conversion of CdTe.
Carbonization and/or Nitridation of Titanium and Zirconium for Increasing Melting Temperature
Authors: Nunogaki M. , Susuki Y. , Kitahama K. , Nakata Y , Hori F , Oshima R. , Emura S.
Published: April 2011

Samples of Ti and Zr metals have been carbonized or nitrided at high temperature by means of reactive plasma processing. Thickness and hardness of modified layers increased with the processing temperature and time in an experimental range below 1500°C for less 5h. The maximum hardness of TiC-layer modified at 1300°C for 3h was about 5000Hv(kg/mm2) and the maximum thickness of ZrC-layer formed at 1400°C for 5h reached about 100μm. A TiC-layer was analyzed with EPMA, XRD, EXAFS and PAS(Positron Annihilation Spectroscopy). It was confirmed that the sub-surface layer of Ti metal was the mixture of TiC ceramics and Ti metal, and that the thickness of TiC with NaCI type structure was very large.
Metal Alloy Propellants Produced from Lunar Resources
Authors: Hepp Aloysius F. , Linne Diane L. , Landis Geoffrey A.
Published: April 2011

The ultimate success of a permanent lunar base will depend upon the use of available resources. Two important resources available on the moon are oxygen and metals. We examine issues, including lunar resources, processing, power, and engine performance, surrounding the use of lunar resources for metal/oxygen engines, including the performance of metal alloys as rocket fuels. Results of this analysis have uncovered several promising candidates including alloys of Al-Ca, Al-Mg, Al-Si, Ca-Mg, and Ca-Si.