Defect Density Level Research Articles

Defect density associated with constituent particles in AA2024‐T3 and its role in corrosion

Electron backscatter diffraction (EBSD) and scanning electron microscopy were combined to study the effect of residual defect density on corrosion initiation in aluminium alloy AA2024‐T3. EBSD was used to determine the level of misorientation (MO), from pixel to pixel, within individual grains. The MO can be determined with respect to either the average orientation angle of the grain or with respect to the average orientation angle of the surrounding pixels (in this instance, a matrix of 7 × 7 surrounding pixels has been applied). Herein, the MO, determined using the surrounding pixels, was used as the means for the assessing the level of defect density within a grain. It was found that there was a noteworthy, but not definitive, correlation of MO with corrosion initiation after 1 min exposure to 0.1 M NaCl solution. Additionally, the S and θ‐phase particles were also identified using EBSD, displaying a range of MO and therefore defect density. Copyright © 2015 John Wiley & Sons, Ltd.

Defect spectroscopy of single ZnO microwires

The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 × 1018 cm−3. This combination of techniques allows us to study the band gap values and defects states inside the gap in single ZnO microwires and opens the possibility to be used as a defect spectroscopy method.

Thermal conductivity of defective graphene

In this Letter, the thermal conductivity of defective graphene is investigated by using non-equilibrium molecular dynamics simulations. It is found that various defects including single vacancy, double vacancy and Stone–Wales defects can greatly reduce the thermal conductivity of graphene. The amount of reduction depends strongly on the density and type of defects at small density level. However, at higher defect density level, the thermal conductivity of defective graphene decreases slowly with increasing defect density and shows marginal dependence on the defect type. The thermal conductivity is found to become less sensitive to temperature with increasing defect density.

Mechanical stress in silicon oxides grown on hydrogen implanted Si

The work presents results on stress characterization of 10 nm silicon oxides thermally grown on Si hydrogenated at different conditions, namely RF plasma at different substrate temperatures and hydrogen plasma immersion implantation (PIII) at energy 2 keV and different fluences. From electroreflectance technique (ER) and spectral ellipsometry (SE) spectra the characteristic energy bands of direct electron transitions in Si are elaborated. The stress in dependence of hydrogenation conditions is considered and related to the shifts of the direct energy gaps. The stress values are evaluated from the Raman shifts around 520 cm-1 gained by micro-Raman spectroscopy (RS). The correlated data from the ER, SE and RS allow hydrogenation conditions using shallow implantation of H+ ions to be defined at which low strain and defect density level can be grown (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Defects in Cu(In,Ga)Se2 Chalcopyrite Semiconductors: A Comparative Study of Material Properties, Defect States, and Photovoltaic Performance

AbstractUnderstanding defects in Cu(In,Ga)(Se,S)2 (CIGS), especially correlating changes in the film formation process with differences in material properties, photovoltaic (PV) device performance, and defect levels extracted from admittance spectroscopy, is a critical but challenging undertaking due to the complex nature of this polycrystalline compound semiconductor. Here we present a systematic comparative study wherein varying defect density levels in CIGS films were intentionally induced by growing CIGS grains using different selenium activity levels. Material characterization results by techniques including X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, secondary ion mass spectrometry, X‐ray photoelectron spectroscopy, and medium energy ion scattering indicate that this process variation, although not significantly affecting CIGS grain structure, crystal orientation, or bulk composition, leads to enhanced formation of a defective chalcopyrite layer with high density of indium or gallium at copper antisite defects ((In, Ga)Cu) near the CIGS surface, for CIGS films grown with insufficient selenium supply. This defective layer or the film growth conditions associated with it is further linked with observed current‐voltage characteristics, including rollover and crossover behavior, and a defect state at around 110 meV (generally denoted as the N1 defect) commonly observed in admittance spectroscopy. The impact of the (In, Ga)Cu defects on device PV performance is also established.

Preferential Biofunctionalization of Carbon Nanotubes Grown by Microwave Plasma-Enhanced CVD

Multiwalled carbon nanotubes (CNTs) were grown by microwave plasma chemical vapor deposition using dendrimer-templated Fe nanoparticles as a catalyst. Variation of the dc bias voltage and the calcination temperature of the dendrimer-templated Fe2O3 catalyst yielded a matrix of CNT arrays. Samples were immobilized with glucose oxidase, which were used for amperometric cyclic voltammetry experiments. Spectroscopic and electron microscopic characterizations indicate that enzyme adsorption per unit CNT area is higher for samples with lower quality, suggesting that CNTs with higher levels of defect densities are desirable for biosensing applications.

Quality-driven optimized resource allocation

The assurance of a good software product quality necessitates a managed software process. Periodic product evaluation (inspection and testing) should be executed during the development process in order to simultaneously guarantee the timeliness and quality aspects of the development workflow. A faithful prediction of the efforts needed forms the basis of a project management (PM) in order to perform a proper human resource allocation to the different development and QA activities. However, even robust resource demand and quality estimation tools, like COCOMO II and COQUALMO do not cover the timeliness point of view sufficiently due to their static nature. Correspondingly, continuous quality monitoring and quality driven supervisory control of the development process became vital aspects in PM. A well-established complementary approach uses the Weibull model to describe the dynamics of the development and QA process by a mathematical model based on the observations gained during the development process. Supervisory PM control has to concentrate development and QA resources to eliminate quality bottlenecks, as different parts (modules) of the product under development may reveal different defect density levels. Nevertheless, traditional heuristic quality management is unable to perform optimal resource allocation in the case of complex target programs. This paper presents a model-based quality-driven optimized resource allocation method. It combines the COQUALMO model as early quality predictor and empirical knowledge formulated by a Weibull model gained by the continuous monitoring of the QA process flow. An exact mathematical optimization technique is used for human resource, like tester allocation.

Electron transport in implant isolation GaAs layers

We report results of ac electrical characterisation of diode structures with Hg electrodes and an implant isolation layer formed on a n +GaAs substrate. The C– f and G– f characteristics at varying bias voltage between 0 and 10 V at room temperature were examined. The frequency of 50 mV measuring signal was changed from 100 Hz to 10 MHz. The implant isolation layers were performed by ion implantation of oxygen with 100 keV followed by 250 keV process on well conducting commercial GaAs substrate. Ion doses ranging from 10 12 to 5×10 13 cm −2 were used. The high frequency C– V characteristics showed that all tested implant isolation layers were fully depleted beginning from zero bias voltage. The G– f characteristics showed that ac conductance increases as a function of frequency and approximately follows ω s dependence with s=0.6–0.9. These results are consistently interpreted as the result of the transport of injected carriers through the implant isolation layer via a hopping mechanism involving defects. Only in the samples with low level of defect density (low ion dose of 10 12 cm −2) for low frequency from 100 Hz to 5 kHz the high level conductance does not depend on frequency. This can be interpreted as the result of the transport of injected carriers through the extended states in conduction band.

Yield optimization of modular and redundant multimegabit RAMs: a study of effectiveness of coding versus static redundancy using the center-satellite model

To determine the optimal redundancy organization for yield enhancement, redundant and modular memories are analyzed using the center-satellite model. The model suggests that the degree of redundancy for a memory module be determined according to its distance from the periphery of the wafer since the defect density increases as the periphery is neared. Analytical expressions are formulated for the yield of memory modules with extra rows and/or extra columns, coding, and coding with extra rows. Results from the analysis suggest that, for high levels of defect densities, coding can be more effective than simple extra rows and columns. For high levels of defect densities, coding with extra rows is shown to offer even better yield. For low levels of defect densities, though, just extra rows and columns may be sufficient for a high yield. An optimal amount of redundancy can be found to achieve the highest possible yield using the model that considers precise cluster distributions on the wafer, defects in a cluster, and the radial variation of these defects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Converting a bulk radiation-hardened BiCMOS technology into a dielectrically-isolated process

A radiation-hardened dielectrically isolated BiCMOS process has been developed by retrofitting dielectric isolation to an existing radiation-hardened JI (junction-isolated) process. The process is fabricated on a bonded-wafer silicon-on-insulator (SOI) substrate and employs deep trenches for lateral device isolation. The isolation technique employed is similar to that used on advanced commercial complementary-bipolar processes. Trench/substrate induced defects are sensitive to the device layout and process flow. Optimization of the trench and posttrench processing and the device layouts has reduced the defect densities to acceptable levels. The defect density levels obtained are consistent with the economic manufacture of VLSI circuits. The dose-rate performance of the process has been improved without compromising the total-dose hardness. >

Structure and Carrier-Transport in a-Si:H, a-Si(Ge): H Films Prepared by Chemical Annealing

AbstractThe stability and opto-electric properties of a-Si:H films fabricated by “chemical annealing (CA)” with excited states of He (He*) were systematically investigated. The films made by the CA mode showed a high photoconductivity due to a low level of defect density, 2×1015cm-3, and improvement in the stability against light soaking. A marked improvement was also found in the hole-transport in films fabricated by the CA. The structural relaxation on the growing surface was also enhanced by addition of a small amount of Ge.

Dislocations and Flux Pinning inYBa 2 Cu 3 O 7-δ

Bulk YBa(2)Cu(3)O(7-delta) superconductors, under certain processing conditions such as melt texturing, exhibit a very high dislocation density of 10(9) to 10(10) per square centimeter. In addition, the density of low-angle grain boundaries in such samples can be significantly increased (to less than 700-nanometer spacing) through a dispersion of submicrometer-sized Y(2)BaCuO(5) inclusions. These defect densities are comparable to those in high critical current thin films as revealed through scanning tunneling microscopy, and yet the critical current densities in the bulk materials (at 77 kelvin and a field of 1 tesla for example) remain at a 10(4) amperes per square centimeter level, about two orders of magnitude lower than in thin films. The results imply that these defect density levels are not significant enough to explain the difference in flux pinning strength between the thin film and bulk materials. The observation of spiral-like growth of the superconductor phase in bulk Y-Ba-Cu-O is also reported.

Process-induced defects in VLSI

Shrinking device dimensions enhance the susceptibility of the devices to defects in the electrically active regions of the silicon substrate and the gate oxide. Typical harmful defects are discussed which may occur in micron and submicron silicon technology if processes are not optimized. Ion implantation is involved in the formation of most of those defects. Since economic mass production of devices in VLSI (very-large-scale integration) requires overall defect density levels below 1 cm −2, strategies and remedies for reducing defect densities are a major task. Some recently developed techniques for the characterisation and monitoring of defects and metal contamination are described

Polymeric optical disk recording media

Abstract High-speed, instantaneous optical recording by use of a laser is finally emerging from the laboratory as a powerful new technology for information storage. The technique offers the capability for low-cost, high-capacity data storage with rapid. random-access retrieval. Materials that have been evaluated for laser marking vary from thin metal films (particularly tellurium [Te] and its alloys) to organiclpolymeric-based systems. The challenge to find appropriate materials is a significant one — high marking sensitivity at an appropriate wavelength coupled with long-term stability of the recording medium and the recorded information. The medium must support several other important performance considerations. The signal-to-noise ratio (SNR) of recorded information should be high to facilitate data retrieval, and the defect density level should be extremely low to minimize errors. It is desirable for the medium to be read immediately (microseconds) after the marking event (direct read after write [DRAW]). and this eliminates materials requiring postimage proc- essing or slow image development. The DRAW capability is particularly important in pro- viding relief from the stringent reliability demands (< 1 error in 1013 bits) since data signals can be verified during the record cycle and immediately corrected in some preselected segment o f the disk surface.