Literatura científica selecionada sobre o tema "Basal stacking faults"

A review is presented of Synchrotron White Beam X-ray Topography (SWBXT) studies of stacking faults observed in PVT-Grown 4H-SiC crystals. A detailed analysis of various interesting phenomena were performed and one such observation is the deflection of threading dislocations with Burgers vector c/c+a onto the basal plane and associated stacking faults. Based on the model involving macrostep overgrowth of surface outcrops of threading dislocations, SWBXT image contrast studies of these stacking faults on different reflections and comparison with calculated phase shits for postulated fault vectors, has revealed faults to be of basically four types: (a) Frank faults; (b) Shockley faults; (c) Combined Shockley + Frank faults with fault vector s+c/2; (d) Combined Shockley + Frank faults with fault vector s+c/4.

The formation of basal plane stacking faults in highly nitrogen-doped 4H-SiC crystals was theoretically investigated. A novel theoretical model based on the so-called quantum well action (QWA) mechanism was proposed; the model considers several factors, which were overlooked in a previously proposed model, and explains well the annealing-induced formation of double layer Shockley-type stacking faults in highly nitrogen-doped 4H-SiC crystals. We further revised the model to consider the carrier distribution in the depletion regions adjacent to the stacking fault and were successful in explaining the shrinkage of stacking faults during annealing at even higher temperatures.

Defects recognition in GaN epilayers was performed using HRTEM and LACBED images. Edge type dislocations, basal plane and prismatic stacking faults were determined from HRTEM analysis. Stacking mismatch boundaries on zigzag steps were found and examined using LACBED patterns in bright and dark field. For stacking faults Bragg lines split into a main and a subsidiary line. The fault plane and displacement vector can be identified from trace analysis performed on LACBED patterns.

The deformation of sapphire at low temperatures and high strain rates produces basal twins and dislocation activity in various slip planes which appear as distinctive shear bands, where the dislocations line up in a row (figure 1). The most common shear band is in the basal plane (the lower band in figures 1a through 1c) and is made up of partial dislocations of the type 1/3<1010>(0001). These dislocations are all associated with the same stacking fault and the sum of three of these faults returns the structure to perfect stacking. The faults can be distinguished in bright field in the (1014) reflections (figure 1b) and clearly, in the lower band, the stacking fault disappears when three dislocations have traversed.

The stacking fault formation in highly nitrogen-doped n+ 4H-SiC single crystal substrates during high temperature treatment has been investigated in terms of the surface preparation conditions of substrates. Substrates with a relatively large surface roughness showed a resistivity increase after annealing at 1100°C, which was confirmed to be caused by the formation and expansion of double Shockley-type basal plane stacking faults in the substrates. The occurrence of the stacking faults largely depended on the surface preparation conditions of the substrates, which indicates that the primary nucleation sites of stacking faults exist in the near-surface regions of substrates. In this regard, mechano-chemically polished (MCP) substrates with a minimum surface roughness (< 0.3 nm) exhibited no resistivity increase and very few stacking faults after annealing even when the nitrogen concentration of the substrates exceeded 1×1019 cm-3.

A rapid nondestructive defect assessment and quantification method based on X-ray diffraction and three-dimensional reciprocal-space mapping has been established. A fast read-out two-dimensional detector with a high dynamic range of 20 bits, in combination with a powerful data analysis software package, is set up to provide fast feedback to crystal growers with the goal of supporting the development of reduced defect density GaN growth techniques. This would contribute strongly to the improvement of the crystal quality of epitaxial structures and therefore of optoelectronic properties. The method of normalized three-dimensional reciprocal-space mapping is found to be a reliable tool which shows clearly the influence of the parameters of the metal–organic vapour phase epitaxial and hydride vapour phase epitaxial (HVPE) growth methods on the extent of the diffuse scattering streak. This method enables determination of the basal stacking faults and an exploration of the presence of other types of defect such as partial dislocations and prismatic stacking faults. Three-dimensional reciprocal-space mapping is specifically used in the manuscript to determine basal stacking faults quantitatively and to discuss the presence of partial dislocations. This newly developed method has been applied to semipolar GaN structures grown on patterned sapphire substrates (PSSs). The fitting of the diffuse scattering intensity profiles along the stacking fault streaks with simulations based on a Monte Carlo approach has delivered an accurate determination of the basal plane stacking fault density. Three-dimensional reciprocal-space mapping is shown to be a method sensitive to the influence of crystallographic surface orientation on basal stacking fault densities during investigation of semipolar (11{\overline 2}2) GaN grown on anr-plane (1{\overline 1}02) PSS and semipolar (10{\overline 1}1) GaN grown on ann-plane (11{\overline 2}3) PSS. Moreover, the influence of HVPE overgrowth at reduced temperature on the quality of semipolar (11{\overline 2}2) GaN has been studied.

Three-dimensional reciprocal space mapping of semipolar (11{\overline 2}2) GaN grown on stripe-patternedr-plane (1{\overline 1}02) sapphire substrates is found to be a powerful and crucial method for the analysis of diffuse scattering originating from stacking faults that are diffracting in a noncoplanar geometry. Additionally, by measuring three-dimensional reciprocal space maps (3D-RSMs) of several reflections, the transmission electron microscopy visibility criteria could be confirmed. Furthermore, similar to cathodoluminescence, the 3D-RSM method could be used in future as a reliable tool to distinguish clearly between the diffuse scattering signals coming from prismatic and from basal plane stacking faults and from partial dislocations in semipolar (11{\overline 2}2) GaN. The fitting of the diffuse scattering intensity profile along the stacking fault streaks with a simulation based on the Monte Carlo approach has delivered an accurate determination of the basal plane stacking fault density. A reduction of the stacking fault density due to the intercalation of an SiN interlayer in the GaN layer deposited on the sidewall of the pre-patterned sapphire substrate has led to an improvement of the optoelectronic properties, influenced by the crystal quality, as has been demonstrated by a locally resolved cathodoluminescence investigation.

With wide band gap, high thermal conductivity, and high breakdown field, silicon carbide, typically 4H-SiC, has steadily become the material of choice for next generation high-power electronic devices[1]. However, the presence of defects especially dislocations and stacking faults (SFs), such as threading screw dislocations (TSDs), threading edge dislocations (TEDs), threading mixed dislocations (TMDs), basal plane dislocations (BPDs), Frank dislocations, Shockley SFs and Frank SFs, are hindering the widespread application of 4H-SiC device due to their harmful effects on the reliability of high-performance SiC power devices[2]. In particular, SFs are particularly deleterious as they degrade the blocking and on-state conduction performance and/or reliability of devices[3]. A recent approach to lowering defect densities is to closely examine the early-stages of crystal growth when many defects are nucleated. Recently, we have reported on the expansion of Shockley stacking faults in the facet region during the early growth stage[4]. Continuing these early-stage studies, we seek to better understand the effects of various growth parameters on resulting defect structures, especially stacking fault formations. Multiple short duration growths have been carried out under varying conditions of nucleation temperature, thermal gradients, and N incorporation. In this study, three types of Frank type or Frank+Shockley stacking faults are observed distributed across the growth surface: Type A, stacking faults bounded by 2 opposite sign Frank type dislocations; Type B, stacking faults bounded by a pair of same sign Frank-type dislocations. As higher partial pressures of N2 are deployed, the occurrence of the Type B stacking fault is found to be suppressed (Figure 1); Type C, stacking faults regions shown as “carrot” defects on the as-grown surface of crystal (Figure 2). The formation mechanisms of these stacking fault formation will be suggested. The implications of these observations to achieve better control of the PVT growth process and resultant defect reduction will be discussed. Figure 1

SiC BJTs show instability in the I-V characteristics after as little as 15 minutes of operation. The current gain reduces, the on-resistance in saturation increases, and the slope of the output characteristics in the active region increases. This degradation in the I-V characteristics continues with many hours of operation. It is speculated that this phenomenon is caused by the growth of stacking faults from certain basal plane dislocations within the base layer of the SiC BJT. Stacking fault growth within the base layer is observed by light emission imaging. The energy for this expansion of the stacking fault comes from the electron-hole recombination in the forward biased base-emitter junction. This results in reduction of the effective minority carrier lifetime, increasing the electron-hole recombination in the base in the immediate vicinity of the stacking fault, leading to a reduction in the current gain. It should be noted that this explanation is only a suggestion with no conclusive proof at this stage.

In this work a deep investigation of the dislocation on 4H-SiC substrate has been shown. The dislocation intersecting the surface were enhanced by KOH etching at 500 deg. C. performed on whole 6 inches substrate. A comparison between basal plane dislocations and threading screw dislocations in the substrate with the defects in the epitaxial layer (mainly stacking faults and carrots) was performed. The comparison between shows a correlation between basal plane dislocations density and stacking faults density maps.

Le silicium et le germanium, qui cristallisent dans la structure cubique du diamant (notée 3C), ont été les piliers de l'industrie électronique grâce à leurs propriétés intrinsèques. Néanmoins, l'ingénierie des phases cristallines métastables a émergé comme une méthode puissante pour ajuster les structures de bande électronique, ouvrant la voie à de nouvelles fonctionnalités tout en maintenant une compatibilité chimique. Notamment, le Ge dans la phase hexagonale 2H présente un gap direct de 0,38 eV. L'alliage SixGe(1-x)-2H présente une émission lumineuse intense avec une longueur d'onde modulable entre 1,8 µm et 3,5 µm, selon la concentration en silicium (40 % à 0 %). Ces propriétés positionnent SixGe(1-x)-2H comme un « matériau miracle» parmi les semi-conducteurs du groupe IV, avec des applications prometteuses dans l'émission lumineuse dans le moyen infrarouge et la détection sur des plateformes en silicium.Malgré les progrès récents, la synthèse de volumes importants de Ge-2H de haute qualité reste un défi. Jusqu'à présent, Le Ge-2H a été synthétisé sous forme de nanodomaines issus de transformations de phase induites par cisaillement, de nanofils cœur/enveloppe et de nanobranches. Ces approches limitent les volumes actifs et la fabrication évolutive de dispositifs. La synthèse de couches planaires de SixGe(1-x)-2H de haute qualité, avec un dopage contrôlé, est essentielle pour permettre une intégration optimale.Cette thèse vise à ouvrir la voie à la synthèse de couches planes de Ge hexagonal en utilisant l'épitaxie en phase vapeur sous ultra-haut vide (UHV-VPE) sur des substrats hexagonaux plan-m du groupe II-VI, tels que CdS-2H et ZnS-4H. Les travaux incluent le développement de techniques de préparation de surface pour les composés II-VI et des études détaillées sur la formation de structures hexagonales dans des matériaux tels que GaAs-4H, ZnS-2H via MOCVD, et le Ge dans les phases hexagonales 2H et 4H.Une étape préliminaire cruciale a consisté à préparer les surfaces des substrats, car leur qualité impacte directement celle des couches épitaxiées. La préparation des surfaces a inclus un polissage mecano-chimique avec une solution de Br2-MeOH pour éliminer les contaminants de surface. Les défis liés aux propriétés thermiques des substrats CdS-2H et ZnS-4H ont été abordés, notamment la désorption des composés II-VI et la formation de « negative whiskers » au-dessus de 500°C.La croissance épitaxiale par UHV-VPE a posé des contraintes de sélectivité sur les substrats II-VI, ce qui a conduit à explorer des configurations alternatives de croissance, telles que l'utilisation de couches buffer. Cette thèse présente la première synthèse d'une couche de GaAs dans la structure hexagonale 4H par épitaxie sur un substrat ZnS-4H plan-m, ainsi qu'une première caractérisation des défauts d'empilement basal dans cette couche. La faisabilité de la synthèse de Ge sur GaAs-4H a également été étudiée. Une part importante du travail a été consacrée à la croissance sur les substrats CdS-2H, démontrant la première couche de Ge avec des régions nanométriques de Ge-2H, offrant une preuve de concept pour la réplication de structures Ge-2H sur des surfaces II-VI sur plan-m. L'optimisation du processus a conduit au développement de couches tampons ZnS-2H sur CdS-2H via MOCVD. Une étude approfondie a montré que la température de croissance impacte fortement la qualité cristalline des substrats CdS. Les couches de ZnS cultivées à 360°C ont révélé une structure hexagonale pure avec une orientation épitaxiale optimale. La relaxation des contraintes s'est produite via des dislocations de réseau à l'interface, en raison des désaccords de maille de 7,63 % et 6,83 % le long des axes a et c, formant des défauts d'empilement basal et prismatique sur les plans {112 ̅0}. Enfin, pour appuyer notre étude, cette thèse présente des preuves démontrant la synthèse d'une couche de Ge avec une phase hexagonale partielle
Silicon and Germanium crystallizing in the cubic diamond (denoted 3C) structure, have been the cornerstone of the electronic industry due to their inherent properties. However, metastable crystal phase engineering has emerged as a powerful method for tuning electronic band structures and conduction properties, enabling new functionalities while maintaining chemical compatibility. Notably, Germanium within the hexagonal 2H phase exhibits a direct bandgap of 0.38 eV. The alloy SixGe(1-x)-2H demonstrates strong light emission with a tunable wavelength ranging from 1.8 µm to 3.5 µm, depending on silicon concentration (40% to 0%). These properties position SixGe(1-x)-2H as a "holy grail material" among group IV semiconductors, with promising applications in mid-infrared light emission (e.g., LEDs and lasers) and detection on silicon platform.Despite recent progress, synthesizing large volumes of high-quality Ge-2H remains a challenge. Until now, Ge-2H has been limited to nanostructures, including nanodomains formed by shear-induced phase transformation, core/shell nanowires, and nanobranches. These approaches restrict active volumes, hindering basic property investigation and scalable device manufacturing. Achieving high-quality planar crystals with controlled doping is essential for advancing SixGe(1-x)-2H integration.This thesis aims to pioneer the synthesis of planar layers of hexagonal Ge using Ultra High Vacuum - Vapor Phase Epitaxy (UHV-VPE) on hexagonal m-plane II-VI substrates such as CdS-2H and ZnS-4H. The work includes developing surface preparation techniques for II-VI compounds and conducting detailed studies on hexagonal structure formation in materials such as GaAs-4H, ZnS-2H (grown via Metal-Organic Chemical Vapor Deposition, MOCVD), and Ge in both 2H and 4H hexagonal phases.A crucial preliminary step involved preparing substrate surfaces, as their quality directly impacts the crystalline quality of the epitaxial layers. Surface preparation included chemical-mechanical polishing with a Br2-MeOH solution to remove surface contaminants, confirmed through XPS analysis. Challenges related to the thermal properties of CdS-2H and ZnS-4H substrates were addressed, including desorption of II-VI compounds and the formation of negative whiskers above 500°C.Epitaxial growth by UHV-VPE posed selectivity constraints on II-VI substrates, prompting the exploration of alternative growth configurations, such as using buffer template layers. This thesis presents the first synthesis of a GaAs layer in the 4H hexagonal structure grown by epitaxy on ZnS-4H m-plane substrate, along with a first characterization of basal stacking faults (BSFs) in this layer. The feasibility of synthesizing Ge on GaAs-4H was also investigated. A significant part of the work was dedicated to growth on the CdS-2H substrates, demonstrating the first Ge layer with nanoscale regions of Ge-2H epitaxy, providing proof of concept for structure replication of Ge-2H on II-VI m-plane surfaces. However, amorphous and highly defective regions were also observed. Process optimization led to the development of ZnS-2H template layers on CdS-2H using MOCVD, circumventing constraints of direct growth on CdS. A thorough investigation of growth regimes revealed a strong impact of growth temperature on the CdS substrate surface, significantly influencing crystalline quality. m-plane ZnS layers grown at 360°C exhibited a pure hexagonal structure with excellent epitaxial orientation relative to CdS-WZ substrates. Strain relaxation occurred through misfit dislocations at the interface due to lattice mismatches of 7.63% and 6.83% along the a- and c-axes, forming basal and prismatic stacking faults on {11-20} planes. Finally, as further proof of concept, the thesis presents evidence supporting the synthesis of a Ge layer with a partial hexagonal phase

ABSTRACT Franciscan subduction complex rocks of Mount Diablo form an 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to &lt;1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.