Several Types Of Defects Research Articles

Inspection Of Recombination Active Defects For Sige And Solar Cells

AbstractMapping Low Angle Light Scattering method (MLALS) is proposed to study defect structure in materials used for solar cell production. Several types of defects are observed in Czochralski Si1−xGex (0.022<x<0.047) single crystals. Recombination activity of these defects is investigated. The possibility of contactless visualisation of grain boundary recombination in polysilicon is also demonstrated.

SiO2 gate insulator defects, spatial distributions, densities, types, and sizes

Standard IC processes, as well as those involving the use of ionizing radiation, such as x-ray lithography etc., result in the generation of bulk defects, and interface states in the gate insulator, or underlying substrate, respectively, of insulated gate field effect transistors. Bulk defects are believed to be present as positively and negatively charged electron and hole traps, respectively, as well as neutral hole and “large” and “small” neutral electron traps. This paper provides a perspective of the current state of knowledge about the spatial distributions of large bulk defects, their areal densities, sizes, possible interrelationships among them, and the special cases of defects created by ion implanted silicon and oxygen, where knock-on effects have been simulated. It appears that bulk defects may all have their origin in neutral hole traps, (so-called E′ centers) and that when the insulator thickness is decreased to about 6-7 nm, defects are either no longer present, or, more likely, are incapable of trapping charge at room temperature because trapped carriers can either tunnel to one of the interfaces, or be annihilated by a reverse process. It appears possible also that the precursor of the several types of defects only forms at a “grown” silicon-silicon oxide interface. In theory, this would make it possible to grow defect free insulators by a combination of deposition and oxidation processes.

Corrosion behaviour of aluminium alloy machining defects and quality of subsequently formed anodised oxide coatings

Abstract Several types of defect have been reproduced on machined surfaces of aluminium alloy 7010, and their corrosion response in saline solutions has been studied. The manner in which this corrosion influenced the quality of subsequently formed anodised coatings was also examined. It was found that chip buildup on the tool face could impart an extreme form of surface disturbance that was not necessarily revealed even by microscopic examination of the as machined surface. Such damaged areas, when subjected to a corrodent, promoted what appeared to be a rapid cathodic reaction, with the immediate formation of a film that effectively thickened in discrete steps owing to the burrowing action of other advancing films. As the film thickened active metal attack occurred beneath it, first by general tunnelling through the machining flow zone, then by advancing in an intergranular manner into the undisturbed microstructure. The characteristic insoluble particles present appeared to playa completely separate rol...

Observation of defects and growth orientations of YBa 2Cu 3O x thin films with YSZ buffer layers on Si

We have investigated defects and in-plate orientations of YBa 2Cu 3O x thin films prepared by pulsed laser deposition (PLD) with YSZ as a buffer layer. The films showed c-axis oriented growth with the transition temperature T co up to 87 K. Several types of defects including thermally induced cracks, grain boundaries and outgrowths were observed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The grain boundary provided a favorable path for crack propagation. The outgrowths nucleated on the YSZ surface grew with stoichiometric composition. According to X-ray diffraction (XRD) and HRTEM studies the YSZ buffer layer grew with the orientation relationship, YSZ〈110〉//Si〈110〉 and YSZ(001)//Si(001) up to the YBCO/YSZ interface. The superconducting YBCO films on top grew mainly with YBCO〈100〉//Si〈110〉 and YBCO(001)//Si(001), with some minor portions of YBCO〈110〉//Si〈110〉 and YBCO(001)//Si(001).

Cathodoluminescence and computer graphics in materials science

AbstractThe combination of cathodoluminescence (CL) in scanning electron microscopy (SEM) with computer graphics is proposed for studying semiconductors and dielectric materials. Spatial distribution of several types of defects that occurred naturally and by design in crystals, can be sorted out and visualized in CL mapping and in three‐dimensional images reconstructed in scanning cathodoluminescence microscopy. The possibilities of this method are illustrated on magnesium oxide single crystals indented with a Vickers diamond pyramid.

Structural model of CO dissociation on Pd particles

In order to modelize the CO dissociation observed on palladium particles, by means of Static Secondary Ion Mass Spectrometry, theoretical investigations were performed on small Pd clusters by using a local approximation of the density functional theory. Several types of defects were studied concerning their ability to dissociate the CO molecule.

Influence of orientation on the low-cycle fatigue of MAR-M200 single crystals at 650 °C. I. Fatigue life behaviour: Chieragatti, R. and Remy, L. Mater. Sci. Eng. A July 1991 A141, (1), 1–9

Cast low carbon CA-6NM (13%Cr-4%Ni) martensitic stainless steel has been used for hydraulic turbine runners manufacturing since the 60's owing to its high strength, toughness, corrosion, and cavitation-erosion resistance. These castings contain several types of defects which may have detrimental effects on the performance of the produced parts. Several aspects of the casting defects in these steels have not been specifically studied in detail. It is common in industry to evaluate the integrity of cast components by nondestructive testing such as X-ray radiography before putting them in operation. However, tortuous and complex geometry of macro-shrinkage porosities makes them difficult to be characterized precisely only by 2D radiographic results. In the present study, the relation between radiography mapping and actual macro-defect morphologies has been studied by the “salami” cross sectioning method in order to document the real shape and morphology of defects. Furthermore, metallographic characterization of cast microstructure in CA-6NM stainless steels has also been performed using several techniques to document both chemical composition and microstructure around macro-defects. Briefly stated, the main purpose of the investigation described herein is to study several severity levels of macro-defects in cast martensitic stainless steels and investigate some characteristics of real defects which can impact on the fatigue properties of cast parts at microstructural level.

Theoretical studies of defect-initiated particle emission from GaP(110) surfaces: Basis for a new technique of generating perfect surfaces

We have calculated the energy needed to eject P atoms from several types of defects on the GaP (110) surface as well as from the perfect surface. It is found that most types of defects have a Ga or P atom bonded less strongly than those on the perfect surface. In view of the result of calculation, and of recent experimental observation that less strongly bonded atoms are ejected by irradiation with laser pulses of lower fluences, we suggest a new method of producing perfect surfaces using laser irradiation to eliminate steps and adatoms and deposition to eliminate vacancies.

Structural defects and ‘‘hot spot’’ formation in a crystalline solid under rapid compression. I. Vacancy clusters and slip bands

Molecular dynamics have been employed in an investigation of the mechanisms of heating of ‘‘hot spots’’ in a model of a crystalline solid. Several types of defects—vacancy clusters of various sizes and geometries in two and three dimensions, and slip bands, grain boundaries, and dislocations in two dimensions have been investigated under rapid and two-stage compression at different temperatures. The results showed that on a molecular scale there were two mechanisms of heating. The first was simply due to the Maxwellian distribution of the kinetic energy, i.e., when energy was added to a system, by heating or by mechanical work, some molecules would be ‘‘hotter’’ than others and would remain hot for a time if the energy exchange among the various degrees of freedom was inefficient. The second mechanism involved the structural relaxation around defects in the solid under load. This process released some potential energy of the defect structure and converted it to the kinetic energy of the atoms around the defects, causing local hot spots. The amount of heating was related to the energy of defect motion during relaxation. The relaxation process, moreover, could propagate to other parts of the structure, so that the hot spot heating could extend to a considerably larger region than the immediate neighborhood of the original defects. These results from the simple model were found to be consistent with experiments. The present report examines the mechanisms of heating associated with vacancy clusters and slip bands. Hot spot heating due to grain boundaries and dislocations under load will be discussed in a subsequent report.

Coercivity of domain-wall motion in thin films of amorphous rare-earth–transition-metal alloys

Computer simulations of a two-dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare-earth–transition-metal alloys with application to erasable optical data-storage systems. Simulated dipoles follow the dynamic equation of Landau, Lifshitz, and Gilbert under the influence of an effective magnetic field arising from local anisotropy, near-neighbor exchange, classical dipole-dipole interactions, and externally applied fields. By introducing several types of defects and inhomogeneities in the lattice, we show that the motion of domain walls can be hampered in various ways and to varying degrees.

Scanning tunneling microscopy of defects induced by carbon bombardment on graphite surfaces

HOPG graphite samples are bombarded at room temperature with a 20 keV 12C + ion beam and the surface topography is investigated by scanning tunneling microscopy (STM) for increasing doses. Lattice deformations and point defects are observed on the nanometer scale and several types of defects can be identified. The surface topography modifications appearing on the atomic scale are analyzed and theoretical damage calculations are done in order to associate the surface features after bombardment with the generation of the defects due to the ionic impact and subsequent cascade development. The experiments reported here show that the number of visible defects is not linearly dependent on the dose. Most of the defects observed by STM seem to result from interstitial migrations and lattice rearrangements following disorder generation by the cascade. It is also reported that the “atomic” resolution of the STM is lost when the graphite is supposed amorphous.

Derivation of the Defect Size Distribution Function of the Monofilament in Case of the Coexistence of Several Types of Fracture Origins and an Application to Carbon Fibers

The defect size distribution of the monofilament in which several types of defects coexist, was theoretically derived using the competing risk theory and the fracture location theory. The defect size distribution indicated a similar form of the multimodal Weibull distribution. This was because the defect size had the one-to-one correspondence to the fracture stress. To apply this theory in practice, we conducted tensile tests of PAN-based carbon fibers. Observed defect sizes of PAN-based carbon fibers coincided with the theoretical distribution as a first approximation.

Defects in SiO 2 in buried-oxide structures formed by O + implantation

EPR measurements have been made on (100) n type silicon wafers implanted with 200 keV 16O + ions in the dose range (0.5–1.4) × 10 18 O + cm −2 and at implantation temperatures, T i, in the range 250–600°C. Several types of defect are observed including E' 1 centres. For a dose of 1.4 × 10 18 O cm −2 the E' 1 concentration is found to increase from 1.5 × 10 14 to 2.3 × 10 14 cm −2 as T i increases from 250 to 600°C. Measurements on lower dose samples indicate that E' 1 defects are present in SiO 2 precipitates as well as in the buried SiO 2 layer. The E' 1 EPR signal only starts to decrease for annealing temperatures ⪸ 450 ° C.

Light emission as a solar cell analysis technique

A new method for testing gallium arsenide solar cells by examining the light emitted when the solar cell is forward biased is presented. Examination of the emitted light reveals the presence and location of several types of defects. The effect of shunt defects on the emitted light is investigated. Other types of solar cell defects are also discussed.

The oxygen defect perovskite Sr 2Mn 2O 5: HREM study

Sr 2Mn 2O 5 was investigated by high-resolution electron microscopy (HREM). Numerous crystals are characterized by a regular contrast, corresponding to the tunnel structure Sr 2Mn 2O 5 which can be described as an ordered oxygen-defect perovskite ( a = a P √2, b = 2 a P √2, and c ⋍ a P ). Several types of defects were observed and interpreted in terms of different orderings of oxygen vacancies: Sr 2Mn 2O 5-type domains with antiphase boundaries (APB), Sr 2Mn 2O 5-type domains with perovskite domains, new ordered domains ( a ⋍ a P √2 and b ⋍ 4a P √2 ), and stacking faults.

Radiation damage in neutron irradiated boron carbide

In view of the fact that there is no information on the microstructure of specimens of boron carbide containing up to 60% B 10 isotope and irradiated at a temperature of 350-370 C, the authors undertook a detailed study of the radiation-induced defects in such material. The microstructure of unexposed boron carbide is characterized by the presence of pores originating during the technological process, dislocations, and twins. Irradiation of B/sub 4/C leads to the formation of defects measuring 3-20 nm and exhibiting a contrast that is characteristic of dislocation loops or two-dimensional second-phase precipitates and spherical pores measuring 1-4 nm in diameter. A specific microstructural feature of irradiated boron carbide is the formation of 30 nm wide zones that are free from pores and other radiation-induced defects near the gain boundaries. The obtained results indicate that irradiation of boron carbide in the 350-370 C range leads to the formation of several types of defects that can be detected by their image contrast under different conditions of photographing.

Effect of defect structure on the electrical conduction mechanism in metallic thin films

Thin metal films can be deposited in a number of different ways. As a result several types of defects or impurities are frozen in the film. In most practical cases films exhibit grain boundaries which play a decisive role in transport properties. This paper reviews the advances that have been made during the last five years in the field of theoretical description of electronic scattering at grain boundaries. Analytical expressions for the transport parameters (such as resistivity, temperature coefficient of resistivity and thermopower) of columnar, monocrystalline and polycrystalline films are derived. Care has been taken to give linearized equations for the transport phenomena. Methods for extracting grain parameters are outlined. Special attention is focused on correlated size effects. Imperfection or impurity effects on the film resistivity and thermopower are considered. Methods for determining the energetic parametersU andV and the componentS 1 of the thermopower associated with imperfections are proposed. Special emphasis is placed on procedures for identifying imperfections by simultaneous study of the restructuration processes induced by thermal ageing and of the changes in transport parameters on ageing.

Effect of defect structure on the electrical conduction mechanism in metallic thin films

Thin metal films can be deposited in a number of different ways. As a result several types of defects or impurities are frozen in the film. In most practical cases films exhibit grain boundaries which play a decisive role in transport properties. This paper reviews the advances that have been made during the last five years in the field of theoretical description of electronic scattering at grain boundaries.

Analysis of surface structural defects by low energy electron diffraction

The characterization of surface structural defects by low energy electron diffraction is discussed. The identification of crystal mosaic structure, random strain, antiphase domains and steps is emphasized, and it is shown that they produce characteristic effects in the angular distribution of intensity in diffracted beams. Analytical models are summarized. They are also applicable to other surface-sensitive diffraction techniques such as reflection high energy electron diffraction and grazing angle X-ray diffraction. The quantitative analysis of these several types of defects is illustrated by measurements on the surface of an epitaxially grown Ag(111) film and on a sputter-etched and annealed GaAs(110) surface.

Dynamic observation of defect annealing in CdTe at lattice resolution

Atomic-level events in the semiconductor material CdTe have been documented directly with real-time video recording, using a high resolution transmission electron microscope equipped with an image pick-up and display system. Among the various solid-state reactions observed were dislocation motion by slip, dislocation climb by diffusion and the annealing of several types of defects.