Papers by Keyword: Defect

Abstract: The aim of the present work is to study the structural properties of 3C-SiC which is grown on (0001) 6H-SiC and on (100) 3C-SiC (Hoya) seeds using the Continuous Feed Physical Vapor Transport (CF-PVT) method. Transmission Electron Microscopy (TEM) observations confirm that the overgrown layer is of the 3C-SiC polytype. In the case of the 6H-SiC substrate, microtwins (MTs), stacking faults (SFs) and dislocations (D) are observed at the substrate-overgrown interface with most of the dislocations annihilating within the first few µm from the interface. In the case of 3C-SiC crystals grown on 3C seeds, repeated SFs are formed locally and also coherent (111) twins of 3C-SiC are frequently observed near the surface. The SF density is reduced at the uppermost part of the grown material.

Abstract: Results on bulk growth of SiC crystals along rhombohedral [01-1n] directions are presented. 6H- and 4H-crystals were grown on rhombohedral planes, which make angles of about 45o with the (0001) plane. Etching features on three differently oriented planes cut from characteristic crystals were compared. Utmost care was concentrated on defect development in the case of non-conventional growth orientation using the seed cut from a “standard” (0001) crystal, containing a typical (standard for [0001] growth) set of crystal defects. We clearly distinguished between a transient layer adjacent to the seed and the main crystal body grown at latter stages. The defect selection and/or transformation in the transient layer appeared strongly depending on the SiC polytype and growth direction. This study brings directly the information on stability of particular defects in the chosen crystal orientation and allows us to distinguish between defects characteristic for [0001] and rhombohedral growth.

Abstract: Recent advances in PVT c-axis growth process have shown a path for eliminating micropipes in 4HN-SiC, leading to the demonstration of zero micropipe density 100 mm 4HN-SiC wafers. Combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes. Crystal growth studies for 3-inch material with similar processes have demonstrated a 1c screw dislocation median density of 175 cm-2, compared to typical densities of 2x103 to 4x103 cm-2 in current production wafers. These values were obtained through optical scanning analyzer methods and verified by x-ray topography.

Abstract: To get a better understanding of oxidation behavior of Ni-base alloys in PWR primary water, a numerical model for oxide scale growth has been developed. The final aim of the model is to estimate the effects of possible changes of experimental conditions. Hence, our model has not been restricted by the classical hypothesis of quasi-steady state and can consider transient stages. The model calculates the chemical species concentration profiles, but also the vacancy concentration profiles evolution in the oxide and in the metal as a function of time. It treats the elimination of the possible supersaturated vacancies formed at the metal/oxide interface by introducing a dislocation density at the interface and in the metal bulk. This latter density can be related to the cold-working state. Its effect on the vacancy profile evolution is studied in the case of a pure metal. Eventually an extension of the present model to the oxidation of Ni-base alloys is discussed regarding a recent vacancy diffusion model adjusted on Ni-base alloys.

Abstract: The dielectric constant values of a set of synthetic alpha alumina samples doped with Cr and Be were determined using parallel plate method. The voltage frequency was selected at 1 MHz. When Cr was doped to the sample, the dielectric constant was increased due to the increase in polarizations of the sample, whereas the Be-doped one showed the decrease in dielectric constant cf. the undoped synthetic alpha alumina (reference sample). Experiments on doping alpha alumina with both elements showed increasing in dielectric constant compared to the undoped reference sample, i.e., Cr has more influence to the dielectric constant value. Dielectric constants of a set of natural sapphires were also measured and compared to those obtained from the synthetic ones. The results of both natural and synthetic samples varied in the same direction. It suggests, however, that the geological origins of the samples are needed to be considered. This is due to the differences in physico-chemical conditions of their formations that would have influenced partitioning of trace elements as well as evolving of defects in natural samples. Increasing of the R1 and R2 photoluminescence wavelengths and decreasing of refractive indices of the doped samples cf. those of the reference sample were obtained from the experiments.

Abstract: The total leakage current in silicon p-n junction diodes compatible with 0.8 µm CMOS technology is investigated. The generation lifetime is a key parameter for the leakage current, which can be obtained from the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics. As will be shown, the electrically active defect from ion implantation process generated in p-n junction can be extracted from the generation current density.

Abstract: This chapter serves as an introduction to the chapters on III-nitrides in this book. It gives a brief review of the development of relevant III-nitride materials for light emitters since the late 1960´s, when single crystalline GaN layers grown on sapphire were first demonstrated. The first wave of scientific work died out in the late 1970´s, since low-ohmic p-GaN could not be made at the time. After another 10 years several important breakthroughs were made, using the technology of metal organic vapor phase epitaxy (MOVPE). Smooth thin epilayers could be made, and ways to dope the materials n-type as well as p-type were invented. In the period 1986-1997 high brightness violet and blue double heterostructure (DH) LEDs, narrow quantum well (QW) LEDs, and QW based violet laser diodes with a long operating lifetime of 10000 hours were demonstrated, mainly by Japanese groups. Since then the development efforts have spread worldwide, and a large spectrum of novel applications based on nitride emitters are already in practical use. Perhaps the most important one is the future possibility of using nitride LEDs for general lighting purposes.

Abstract: The effects of thixoforming defects on the stress-strain curves of aluminum structural part were quantitatively investigated. The A357-MHD billet was thixoformed to manufacture a shock tower part of a small electric vehicle. All tensile specimens were machined from only a shock tower product to minimize the effects of different processing conditions. Tensile tests were performed under the almost same conditions. The fraction of solid and liquid phase, the sizes and area fractions of defects in the specimens were measured and analyzed by an image analyzing program using OM and SEM micrograph. The fracture strain values of the stress-strain curves were greatly affected by amount of defects. However, the analyses with defects existed in the area of gauge length did not show a clear explanation about the relation with the fracture strain values. The measurements of defects in the fractured surface represented more plausible results about the correlation of forming defects and fracture strains.

Abstract: The specific features of the dynamics of oxygen ions in Ме2O · SiO2 (Ме = Li, Na, K, Cs) and Na2O·ZnO·P2O5 melts at а temperature of 2000 K were investigated bу the molecular dynamics method. It is demonstrated that, as in the systems studied earlier, the formation of defect complexes is а necessary condition fог an oxygen diffusion event to bе successful. The scenarios of generating defect соmplexes аrе described, and the lifetimes of these complexes are calculated. The structure of the defect complexes is determined. It is shown that two-membered rings, free and threefold-coordinated oxygen ions сап also bе involved in the formation of defect complexes.