bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design and Growth of Band-GAP Graded a-SiGe:H Solar Cells
Authors: Vasanth K. , Payne A. , Crone B. , Sherman S. , Jakubowski M. , Wagner S. 
Published: April 2011

ABSTRACTThe i-layers of the middle and bottom cells in stable triple-junction amorphous silicon solar cells are composed of a-SiGe:H alloys which are graded in composition to enhance performance. We compare modeling and experimental results for three i-layer band gap grading schemes to determine the optimal profile. We find a good correlation between model trends and measured device parameters for all grading schemes. This is encouraging for the use of the model in predictive device design. We find that the highest white and red light performance do not necessarily have the same cell parameter set. Modeling and experiment indicate that thin cells without band gap profile and with suitably designed p/i and n/i buffer layers, have the best red light performance.
Analysis of Non-Uniform Creation of Light-Induced Defects in Schottky Barrier Solar Cell Structures
Authors: Liu Hongyue , Malone C. T. , Fortmaiiii C. M. , Wronski C. R. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon (a-Si:H) TCO/n+/i/Ni Schottky barrier solar cells were degraded with illuminations of white and red light through both sides of the structure. Because the forward dark I-V's are sensitive to the distribution and any spatial variation of defects in the i-layer, these measurements were used to characterize the degraded cell structures. These characteristics were analyzed using a charged defect distribution of gap states consisting of D+, D°, and D states derived from corresponding film analysis. It was found that the non-uniformities of light induced defects created in the i-layer can be represented by two regions of different defect densities. The relative densities depend on the direction of illumination and their ratio even with white light is about a factor of four. This non-uniformity is expected to be less for p-i-n cells which have higher built-in potential and hence electric fields.
Thin Film Transistors with Layered a-Si:H Structure
Authors: Kuo Yue 
Published: April 2011

ABSTRACTThin film transistors TFTs with the layered a-Si:H structure are presented and discussed. Compared with the conventional single layer a-Si:H TFT, transistor characteristics of this new structure can be superior or inferior, depending on the deposition condition and number of the bulk (non-interface) a-Si:H layers. The mechanism influencing transistor characteristics is discussed. Changes of these TFTs' characteristics are not significant, e.g., the mobility varies within 20%. More data are being collected to verify the statistical significance of this kind of TFT.
Very low off Current Behavior in high Performance a-Si:H TFT
Authors: Yoon Jung-Kee , Choi Woong-Sik , Jang Yong-Ho , Seo Seong-Mo 
Published: April 2011

ABSTRACTThe off currents in high performance a-Si:H TFT's were measured below 10−12 A. The Ioff-Vgs behavior is similar to that of a poly-Si TFT, in which the current increases rapidly with negative gate bias under a large drain bias while it stays almost constant under a small drain voltage. It seems the thermally-assisted tunneling via localized states occurs near the drain region as in the case of poly-Si TFT, although the current level is quite different. The off current change after negative bias stress at room temperature can be explained by the defect creation, but defects can be reduced by negative stress at 180 °C according to the defect pool model.
New Bias-Controlled Three-Color Detectors using Stacked a-SiC:H/a-Si:H Heterostructures
Authors: Topič Marko , Smole Franc , Groznik Aleš , Furlan Jože 
Published: April 2011

ABSTRACTA novel family of three-terminal three-color (blue, green, red) detectors based on stacked a-SiC:H/a-Si:H heterostructures is presented: TCO/PIN/TCO/PINIP/TCO/metal and TCO/PINIP/TCO/PIN/TCO/metal structure. The analysis of stacked photodetectors and the optimization of their geometrical dimensions is performed using the adopted ASPIN simulation program. Both structures are mutually compared with regard to calculated current-voltage characteristics and spectral responsivity. They both exhibit linear photocurrent/generation-rate relationship for all three colors at peak wavelengths 430, 530, 630 nm, applying ±1 V or more. This linearity allows that all three colors can be detected with high rejection ratio using simple system electronics.
Metastable Defect Formation by Hydrogen Relocation and Rebonding
Authors: Li Qiming , Biswas R. 
Published: April 2011

ABSTRACTMolecular dynamics with the tight-binding approach are utilized to examine the fundamental process of dangling bond creation via the rebonding of H from Si-H bonds to weak Si-Si bonds. The defect formation energy is found to strongly correlate with the bond-length of the weak Si-Si bond, indicating that the distribution of weak Si-Si bonds controls the total defect density. Rate equations for thermally generated and light-induced defects are developed and utilized to calculate the equilibrium and saturated defect density. The results agree well with experimental data.
Dependence of Sheet Hole Concentrations on Growth Kinetics of a Carbon Doped Electron Beam Heated Graphite Source in GaAs and Al0.3GaD0.7As Films Grown by Solid Source MBE
Authors: Sato D. L. , Szalkowski F. J. , Lee H. P. 
Published: April 2011

AbstractA series of carbon delta- and uniformly- doped GaAs and Al0.3Ga0.7As films have been grown by solid source Molecular Beam Epitaxy using an electron-beam heated graphite rod as the dopant source. In contrast to heated filament carbon sources, this electron-beam source produces atomic carbon C1, rather than C3 as the predominant species. The purpose of these experiments was to compare measured sheet carrier concentration of delta-doped GaAs and Al0.3Ga0.7As films under fixed growth conditions and with similar carbon beam fluxes using this electron-beam source. The films were characterized by Hall-effect measurements. The Al0.3Ga0.7As films have consistently higher hole sheet carrier concentrations than GaAs films with similar carbon fluxes. Delta-doped Al0.3Ga0.7 As sheet carrier concentrations of up to 2.2×1013 cm−2 were measured, and thin uniformly-doped Al0.3Ga0.7 As carrier densities were measured up to 5.7×1020 cm−3. The uniformly doped Al0.3Ga0.7As films appear to have higher atomic carbon activation than this delta-doped Al0.3Ga0.7As films. These results can be possibly explained in terms of several concurrent processes involving C-C pairing, stronger Al-C bonding, and dopant surface segregation taking place on the growth surface of the delta-doped layer. Photoluminescence intensity measurements of uniformly-doped GaAs shows degradation at hole concentrations greater then 1018 cm−3 and bandgap contraction at hole densities greater than mid 1018 cm−3.
Photodiffractive Characterization of Growth-Defects in GaAs
Authors: Jarasiunas K. , Sudzius M. , Kaniava A. , Vaitkus J. 
Published: April 2011

AbstractThe transient grating technique has been developed over the years and several reviews have been written concerning the subject [1,2]. The present paper will focus on its advantages for studies of main native defect in semiconducting GaAs crystals, namely, of EL2, which plays a crucial role in semi-insulating properties and optical absorption below band-gap, photorefractivity, metastability, etc. We will consider the role of EL2 in optical nonlinearities and its contribution to carrier transport in subnanosecond time domain. Nonlinear character of TG technique allows to get deeper insight into spatial distribution of growth defects (EL2 and dislocations) in the wafers and perform their nondestructive monitoring. Different experimental techniques, as DFWM in nano- and picosecond time domain, light selfdiffraction, and set of differently grown GaAs crystals enabled us to show applicability of this technique for basic research and nondestructive determination of parameters, defect distribution, reveal fast transients of optical nonlinearities. The photorefractive nonlinearity at 300K is shown being dependent on dislocation density due to local strain fields around charged dislocations. Moreover, transient quenching of EL2 by short laser pulses and enhancement of low-temperature photorefractive nonlinearity is demonstrated.
Crystallographic Defect Related Degradation in High Density Memory Devices
Authors: Kim S.S. , Wijaranakula W. 
Published: April 2011

AbstractCrystallographic defect related degradation in high density memory devices was investigated. The results indicate that the refresh time degradation and bit failure mechanism are directly related to the crystal originated defects generated during Czochralski crystal growth. Defects associated with vacancy aggregations are found to have a detrimental effect on the overall performance of memory devices. Other defects, such as oxide polyhedral precipitates, contribute to a high number of cumulative fail bits, particularly in the bottom section of the crystal.
Analysis and Control of the Performance-Limiting Defects in HEM-Grown Silicon for Solar Cells
Authors: Khattak Chandra P. , Schmid Frederick , Cudzinovic Michael , Symko Martha , Sopori Bhushan L. 
Published: April 2011

AbstractMulticrystalline silicon ingots of 55 cm × 55 cm cross section, 100 kg have been grown by the Heat Exchanger Method (HEM). Controlled growth features have been used to produce large grain size, vertically oriented grain boundaries, large areas of twins with low defect density and rejection of impurities to the top of the ingot. Ambient control has reduced C, N, and O concentration and minimized precipitates with no detectable metallic impurities. High performance solar cells have ben fabricated, and further improvements can be achieved by minimizing dislocation tangles and impurities in localized regions.
Resolving Degradation Mechanism in Carbon and Beryllium Doped HBT’s Using Pulsed Mode Current Stress
Authors: Chou Y. C. , Li G.P. , Wu C.S. , Chu Peter , Pao C.K. , Cisco T.C. 
Published: April 2011

AbstractThe reliability of high performance carbon and beryllium-doped heterojunction bipolar transistors (HBT’s) is investigated using a pulsed mode current stress. After the current stress, the collector current reduction (measured at a fixed Vbe) and the inverted collector current ratio change (measured at two different reverse Vbe biases) are used as measures of HBT degradation due to dopant acceptors migration. For carbon and beryllium doped HBT’s, degradation was found to be only significant beyond a threshold current density (Jth), showing that the carbon doped devices have a higher Jth than that of the Be-doped HBT's. Beyond the Jth, the device degradation is insensitive to the stress current density but depends on the total stress charge. As a result, the device degradation mechanisms of electric field assisted dopant and carrier recombination enhanced dopant migration can be distinguished under pulsed mode current stress.
Improved Performance of MESFET Devices with L.T.GaAs Buffer Layers
Authors: Lagadas M. , Hatzopoulos Z. , Karadima F. , Konstantinidis G. , Kornilios N. , Papavasiliou C. , Christou A. 
Published: April 2011

AbstractWe have investigated the electrical properties of n-GaAs epilayers grown by MBE on the top of L.T.GaAs .The Hall mobility and the channel depth of the epilayer decreases as the growth temperature of the buffer decreases. The degradation of the electrical properties is attributed to the outdiffusion of precipitates and point defects from the L.T. buffer layer. The use of intermediate layers (GaAs grown at 400°C-600°C and GaAs/AlxGa1-xAs (x=0.5, 1) superlattices ) between L.T. buffer and n-GaAs active layers in MESFET devices improves the Hall mobility of the channel, the gm and fT performance of the devices.This improvement has been attributed to the AlGaAs layer which hinders the defects outdiffusion.
Scanning Tunneling Microscopy Studies of GaAs1-xPx Single Crystals
Authors: Liu X. , Weber E. R. , Ogletree D. F. , Salmeron M. , Slupinski T. 
Published: April 2011

AbstractWe report cross-sectional scanning tunneling microscopy studies of GaAsP single crystals grown by the Liquid Encapsulated Czochralski technique. We show that the two group-V elements can be clearly distinguished, which is attributed to the difference in energies of surface dangling bond states of As and P. Our atomic scale imaging results show alloy composition in agreement with spectroscopic studies. They also provide valuable information about atomic scale alloy fluctuations and clustering effects.
Atomic Structure of the Interfaces Between Silicon Directly Bonded Wafers
Authors: Benamara M , Rocher A , Laporte A , Sarrabayrouse G , Lescouzères L , PeyreLavigne A , Fnaiech M , Claverie A 
Published: April 2011

AbstractThe so-called Direct Wafer Bonding (DWB) technique opens new possibilities for the electronic industry but still suffers from the poor knowledge we have of the microstructure of these interfaces and hence of their electrical activity. In this work, we have extensively used Transmission Electron Microscopy techniques in plan-view and cross-section to identify the structure of the interfaces found between two bonded silicon wafers. The general structure of these interfaces is that of a perfect grain boundary and evidently depends on the misorientation between the two bonded wafers. A twist component in the range 0>θ>13˚ creates a square network of pure screw dislocation whereas an unavoidable tilt component (<0.5˚) is compensated by a periodic array of 60˚ dislocation lines perpendicular to the tilt direction. Therefore, the regularity of these networks can be disrupted by the presence of steps (of up to several nanometers) in the interface plane. Silicon oxide precipitates are seen heterogeneously distributed on the interface with preferential nucleation sites on the dislocations.
Theoretical Prediction and Experimental Study of Mechanical Properties for Random and Magnetically Aligned Single-Walled Carbon Nanotube/Epoxy Composites
Authors: Wang Ben , Shankar Ravi , Liang Zhiyong , Wang Zhi , Zhang Chuck , Kramer Leslie 
Published: April 2011

ABSTRACTSingle-walled carbon nanotubes (SWNTs) have exceptional mechanical and functional properties. Many researchers consider SWNTs as the most promising reinforcement for realizing the optimal structural and multifunctional potential of the next generation of high performance nanocomposites. However, due to poor dispersion, weak interfacial bonding and deficient tube orientation, current nanotube-based nanocomposites fail to realize their anticipated properties. A new approach was developed by the authors to use preformed nanotube tube networks (called buckypapers) and a resin infiltration method for producing bulk polymeric nanocomposites with controlled nanostructure and high tube loading. Desired tube alignment in nanocomposites can be achieved by using magnetically aligned carbon nanotube buckypapers, in which SWNTs will tend to align along the direction of applied magnetic field. The mechanical properties of the resultant nanocomposites have been tested. The storage modulus of the magnetically aligned nanocomposites is as high as 47 GPa, which is one of the highest reported values of nanotube-reinforced composites.In this research, we investigated the influences of tube dispersion, loading and orientation on the mechanical properties of SWNT-reinforced composites. Random and aligned discontinuous reinforcement models of composites were applied to predict the tensile moduli of both individually dispersed SWNT-based and SWNT rope-based nanocomposites. The nanostructural parameters used in the calculation models were determined based on our experimental observations. Comparisons between theoretical estimates and experimental results have shown that the formation of SWNT ropes in the composites has a significant influence on the mechanical properties. The experimental results of the both random and aligned SWNT rope composites are in good agreement with the theoretical predictions.
Defects and Magnetic Properties: The Cr/Fe(001) Interfaces
Authors: Stoeffler D. , Vega A. , Dreyssé H. , Demangeat C. 
Published: April 2011

ABSTRACTWe report self-consistent band-structure calculations for the magnetism of Cr overlayers adsorbed on Fe(001) in order to study the role played by imperfect Fe-Cr interfaces, at the microscopic and macroscopic scales, on the total magnetisation. The surprisingly large reduction of the total magnetisation (≈ - 5 μB/interfacial atom) recently observed in Cr/Fe(001) through in situ magnetometer measurements is shown to be reproduced only when an interchange of one Cr and Fe monolayer at the interface after deposition of the second Cr monolayer occurs.
Nanosecond Structural Transformation of Magnetic thin Films: PtMnSb, Structure and Magnetic Properties
Authors: Kubota Yukiko , Marinero Ernesto E. 
Published: April 2011

ABSTRACTWe report on the phase transformation of amorphous PtMnSb thin films induced by laser annealing in the nanosecond time regime. Structural and magnetic transformations are investigated by TEM, XRD, AFM and in-situ MOKE and VSM. We have established that a minimum laser fluence is required to crystallize the amorphous films and thus, to induce magnetic activity. The transformation kinetics vs number of irradiation pulses reveals that the magnetically active C1b phase is formed via an intermediate phase, namely, tetragonal-PtMn. We have also established that the thin film crystallization induced by the nanosecond laser annealing proceeds via nucleation rather than grain growth. Measurement of the lattice parameter of the C1b-PtMnSb produced by the laser quenching (LQ) indicates an essentially unstrained structure with a =6.17 Å vs a =6.201 Å reported for the bulk. Nevertheless, we observe the generation of large surface undulations upon laser annealing and suggest that this is the mechanism for stress relaxation concomitant with the large volumetric changes involved in the phase transformation. In addition, we observe decrements in saturation moments and Curie temperatures which are attributed to the nanocrystalline nature of the LQ specimens.
Effects of Interface Intermixing on the Magnetoresistance of Spin Valves with Uncoupled Co-Layers
Authors: Willekens M.M.H. , Rijks TH.G.S.M. , Swagten H.J.M. , Jonge W.J.M. De 
Published: April 2011

ABSTRACTWe have studied the effect of an artificially intermixed region grown at the interfaces of Co/Cu spin valves with uncoupled layers. Two different structures are used: exchange-biased spin valves and engineered spin valves in which two layers are antiferromagnetically coupled and a third layer, on top of this system, is not coupled to the other two. It is shown that structural effects, induced by variation of the deposition parameters and by the intermixing can play an important role. Since the present study uses sputtered layers an intrinsic initial intermixing of 4-5Å is already present. For both types of spin valves Gp, ΔG and ΔR/R all show a gradual decrease when the nominal thickness of the total intermixed region is enlarged from 0 to 36Å. Also when the initial degree of intermixing is decreased by sputtering at higher Arpressure, Gp, ΔG and ΔR/R still show a gradual decrease as a function of intermixed layer thickness. Combined with the fact that there is no difference between an intermixed region of thickness t at one Co/Cu interface or intermixed regions of thickness t/2 at two interfaces, this indicates that the electron scattering in the intermixed region is predominantly spin independent, although this region preserves a magnetic moment.
197Au MÖssbauer Study of Au/Fe, Au/Co and Au/Ni Magnetic Multilayers
Authors: Nasu Saburo , Kobayashi Yasuhiro 
Published: April 2011

ABSTRACT197Au Mössbauer measurements have been performed for Au/Fe, Au/Co and Au/Ni magnetic multilayers. 197Au Mössbauer spectra observed from multilayers consist of at least 4 components having different magnitude of hyperfine fields and isomer shift values those depend on the local environments of the Au probe-atoms in multilayers. Rather large electron spin polarization at Au atoms has been observed in the interface with adjacent ferromagnetic layers, but nearly no magnetic hyperfine field has been observed to the interior of Au layer. It implies that the largest hyperfine field observed is not due to the conduction-electron polarization but induced by the hybridization in the interface with ferromagnetic layer.
Fourier Transform Infrared Spectroscopy of Polymer-Metal Interface Reactions
Authors: Cumpston B. H. , Lu J. P. , Willis B. G. , Jensen K. F. 
Published: April 2011

ABSTRACTApplications of Fourier transform infrared (FTIR) spectroscopy for probing polymer-metal interfaces are described with examples of polyimide (PI)-metal systems relevant to electronics packaging and poly(phenylene vinylene) (PPV) derivatives used in electroluminescent devices. Emphasis is placed on the detection and interpretation of interfacial reactions that influence performance characteristics (e.g., adhesion, stability, and light emission) of polymer-metal structures. In situ infrared reflection absorption spectroscopy (IRRAS) is used to explore the formation of PI-on-metal interfaces, the hydrolytic stability of such interfaces, and the reactivity of PPV systems when exposed to ultraviolet light and oxygen. Differences between polymer-on-metal and metal-onpolymer interfaces are discussed. Models of the infrared optical processes in the thin film composites are used to distinguish between chemical and optical effects. The FTIR observations are supported by additional spectroscopic characterizations, specifically ex situ X-ray photoelectron spectroscopy (XPS).
The Role of Coupling Agents in Composite Durability
Authors: Macturk K. S. , Schutte C. L. , Schultheisz C. R. , Hunston D. L. , Tarlov M. J. 
Published: April 2011

ABSTRACTWe investigated the role of coupling agents with respect to the relative durability of glass fiber/epoxy matrix composites exposed to water, which degrades both glass fibers and the fiber-matrix interface. Interface chemistry was tailored by coating fibers with mixtures of different coupling agents. Single-fiber fragmentation test results showed little decrease in the strengths of the interface and a slight decrease in fiber strengths upon exposure to water. XPS results showed expected variations in surface composition. Contact angle measurements demonstrated variations in surface hydrophobicity as coupling agent mixtures were changed.
Composition-Structure-Properties Relationship and Durability of Modified Organosilicate Polymeric Composite
Authors: Tchouppina Svetlana V. , Krasil'nikova Larisa N. 
Published: April 2011

ABSTRACTThe present work was aimed at the development of new organosilicate polymeric composite, based on polydimethylphenylsiloxane/polyurethane (PDMPS/PU) miscible blend, filled with silicates and metal oxides. Considerable improvement of mechanical and corrosion-protective properties due to introduction of polyurethane has been observed. Coatings with sufficient thermostability (up to 300°C) have been obtained in the case of 20% polyurethane content, related to amount of binders. The effects coating heat treatment temperature and curing conditions on adhesion of metal/composite interface have been studied. Surface energy characteristics of this coating have been obtained and were correlated with its microstructure, determined from Scanning Electron X-ray Microprobe Analyses. Recently developed composite appeared to show increased durability in atmosphere operation conditions.