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The objective of this work is to study defect occurrence and appearance in thick sublimation epitaxial layers grown on top of LPE layers with different thickness and substrates with reduced micropipe density. Data from growth on C-terminated surfaces are also presented. The results were analyzed with the aid of optical microscopy, SEM images, HRXRD and synchrotron white beam X-ray topography. A pronounced effect of the LPE (buffer) layer surface roughness on formation of dislocations and micropipes is observed in the sublimation epitaxy layers. While with increasing the thickness of the buffer layer the efficiency of the micropipe reduction increases, the structure quality of the top sublimation epilayer degrades. LPE layers with a thickness of 0.1 μm appear to be the best compromise.

To reduce the defect density inherent in conventional heteroepitaxial growth of SiC on Si, selective epitaxy followed by lateral epitaxial growth was performed in a conventional atmospheric pressure chemical vapor deposition (APCVD) system. The source gas was primarily hexamethyldisilane (HMDS). Hydrogen was used as the carrier gas and small amounts of hydrogen chloride (HCl) were added to improve the selectivity. Si(001) wafers, with an oxide layer (∼ 700 nm thick) as a mask, were used as substrates. The grown films were analyzed using optical microscopy and scanning electron microscopy (SEM). In earlier work, we had demonstrated the problems associated with the application of this technique – viz., oxide degradation and high growth temperature. Using HMDS, the growth temperature has been considerably reduced allowing the continued use of an oxide mask. Selective growth was demonstrated in films grown at 1250° and below.

The status of SiC vapor growth technique (PVT) is reviewed and related innovative aspects are introduced. Problems of the preparation of SiC crystals with uniform electronic properties are addressed, especially the growth of semiinsulating SiC. An overview about the performance of numerical modeling is given as tool for the optimization of the PVT process. Development activities in the field of liquid phase processing for the preparation of SiC bulk crystals and micropipe healing are presented. Finally recent results on the present understanding of filamentary void formation/elimination (micropipes, macrodefects) are summarized.

A layer of porous SiC was fabricated by surface anodization of commercial 4H and 6H-SiC (0001)Si face off-axis wafers. A 8.5 μm 4H–SiC epilayer was grown on porous SiC (PSC) substrates using atmospheric pressure CVD. TEM investigation on cross-sectional specimens of the CVD epitaxial layers revealed that the presence of pores in the substrate does not lead to the formation of any micropipe in the epitaxial layer. The investigation also failed to detect a more than usual dislocation density on the basal plane of the epitaxial layer. Based upon the results of various analytical techniques applied to the CVD deposit we propose that the density of screw dislocations in the epitaxial layer is less than 5–104 cm−3. It should be noted that the density of similar types of dislocations in the initial substrate as determined by the TEM was ∼106 cm−3, so this preliminary investigation indicates that the epitaxial layer grown on PSC may have a reduction in dislocation density of more than an order of magnitude over those grown on conventional SiC substrates that are not porous. Synchrotron white beam x-ray topography (SWBXT) was performed on these layers. Comparison between the dislocation density on the porous and standard epitaxial layers proved to be very similar using this technique.

SiC is an important wide bandgap semiconductor material for high temperature and high power electronic device applications. Purity improvements in the growth environment has resulted in a two-fold benefit during growth: (a) minimized inconsistencies in the background doping resulting in high resistivity (>5000 ohm-cm) wafer yield increase from 10–15% to 70-85%, and (b) decrease in micropipe formation. Growth parameters play an important role in determining the perfection and properties of the SiC crystals, and are extremely critical in the growth of large diameter crystals. Several aspects of growth are vital in obtaining highly perfect, large diameter crystals, such as: (i) optimized furnace design, (ii) high purity growth environment, and (iii) carefully controlled growth conditions. Although significant reduction in micropipe density has been achieved by improvements in the growth process, more stringent device requirements mandate further reduction in the defect density. In-depth understanding of the mechanisms of micropipe formation is essential in order to devise approaches to eliminate them. Experiments have been performed to understand the role of growth conditions and ambient purity on crystal perfection by intentionally introducing arrays of impurity sites on one half of the growth surface. Results clearly suggest that presence of impurities or second phase inclusions during start or during growth can result in the nucleation of micropipes. Insights obtained from these studies were instrumental in the growth of ultra-low micropipe density (less than 2 micropipes cm−2 ) in 1.5 inch diameter boules.

Research now shows that interaction with silicon carbide substrate leads to the opening of a semiconductor gap in epitaxial graphene. This is an important first step towards bandgap engineering in this two-dimensional crystal, and its incorporation in electronic devices.

Micro/nanopipes are linear defects along the c-axis of hexagonal polytypes of SiC and GaN that are currently the focus of much attention. It has been shown that these defects can be very detrimental to the electronic properties of devices manufactured from, at least, 6H-SiC. In this paper, the origin of these defects is discussed in terms of Frank's theory [1] that dislocations will have a hollow core when their Burgers vector is large. Two fundamental issues about such dislocations are addressed: their formation along the c-axis of the crystal, and their stability despite their large Burgers vectors [2]. The proposed model is based on the mosaic structure of sublimation-grown 6H- or 4H-SiC, and VPE-grown 2H-GaN on sapphire substrates. The presence of unit c-axis screw dislocations is attributed to the accommodation of low-angle twist boundaries in the mosaic structure. The formation of superscrew dislocations with large Burgers vector, which empty their cores to reduce the excessive strain energy there, is shown to be the result of 3c screw dislocations in the axis of triple junctions which “getter” the neighboring unit dislocations and simultaneously increase their diameter. The predictions of the model are compared with available data in the literature, and suggestions are made for the decrease of nano/micropipe density.

The defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vectors > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per cm 2, nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has been previously shown that diodes containing elementary screw dislocations exhibit a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and concentrated microplasmic breakdown current filaments when measured under DC testing conditions. This paper details the impact of elementary screw dislocations on the experimentally observed reverse-breakdown pulse-failure characteristics of low-voltage (< 250 V) small-area (< 5 × 10-4 cm2) 4H-SiC p+n diodes. The presence of elementary screw dislocations did not significantly affect the failure properties of these diodes when subjected to non-adiabatic breakdown-bias pulsewidths ranging from 0.1 μs to 20 μs in duration. Diodes with and without elementary screw dislocations exhibited positive temperature coefficient of breakdown voltage and high junction failure power densities well above the failure power densities exhibited by highly reliable silicon power rectifiers. This preliminary result, based on measurements from one wafer of SiC diodes, suggests that highly reliable low-voltage SiC rectifiers may be attainable despite the presence of elementary screw dislocations.

The production of large diameter, high quality boules of SiC is essential to realize the full potential of this important semiconductor material. The objective of this paper is to provide a state-of-the-art analysis of the key directions for SiC bulk growth research, as well as presenting our most recent empirical results. Based on an analytical review of current knowledge, the following topics concerning growth of large 6H and 4H-SiC bulk crystals are discussed: 1) thermodynamics of the vapor phase including the efficiency of crystal growth, 2) kinetics of growth including mass transport in the boundary layer and 3) defect formation processes including thermoelastic stress. In addition, results of growth modeling are summarized and direction for further work suggested. Results on growth of semi-insulating and 50–75 mm diameter 4H-SiC wafers are presented. A discussion on micropipes, which are currently the most harmful defect in SiC wafers is presented. Although several mechanisms, or combinations of mechanisms, cause micropipes in SiC boules grown by the seeded sublimation method, we have reduced micropipe densities by orders of magnitude over the last few years. This continual reduction and the production of wafers with micropipe densities of less than 1 cm-2 (with >1 cm2 areas void of micropipes), indicate that micropipes will be reduced to a level that makes high current devices viable and that they may soon be totally eliminated.

The characteristics of SiC high-power devices are currently limited by the small area of the devices, which is usually less than 1 sq. mm. In order to increase device area, defect density in SiC epitaxial structures must be reduced. In this paper, we describe properties of silicon carbide epitaxial layers grown on 4H-SiC wafers with reduced micropipe density. These layers were grown by the vacuum sublimation method. Large area Schottky barriers (up to 8 mm2) were fabricated on SiC epitaxial layers and characterized.

The as-grown surfaces of 6H SiC seed crystals grown by the Lely method have been characterized by visible light microscopy and atomic force microscopy. The surfaces were then used to seed the sublimation growth of SiC at 2300°C, in 650 torr of Ar, with a gradient of 8 °C/cm. Repeated observations of the seed surface structure after predetermined intervals in the growth reactor demonstrated that transport starts at less than 2160 °C and that voids are nucleated by heterogeneous material on the original seed surface. Near these voids, the concentration of unit screw dislocations is increased and these defects migrate during growth. Screw dislocations of opposite sign act as step sources and build mesa structures around the heterogeneous material. After only 10 min at the growth temperature, micropipe/super screw dislocation complexes form in the centers of the mesas, possibly by the migration of unit dislocations to the voids.

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = Ic with no hollow core) in densities on the order of thousands per cm2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p+n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p+n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

In this paper we demonstrate the growth of thick SiC epitaxial layers (≥100 μm) of good structural quality at a high growth rate (>100 μm/hr) by controlling the vapor dynamics during conventional physical vapor transport (PVT) process. We propose that our PVT technique be used to ‘repair’ or ‘heal’ commercially available substrates dominated by micropipes, by ‘filling up’ the micropipes through crystal growth inside the micropipe. Extensive experiments performed on thick SiC epitaxial layers grown on Lely substrates indicate that the thick epitaxial layers are of single polytype of high structural quality, with a single peak X-ray rocking curve of less than 12 arcsecs FWHM.

Peculiarities of quantitative hard x-ray phase contrast imaging of micropipes in SiC are discussed. The micropipe is assumed as a hollow cylinder with an elliptical cross section. The major and minor diameters can be restored using the least square fitting procedure by comparing the experimental data, i.e. the profile across the micropipe axis, with those calculated based on phase contrast theory. It is shown that one projection image gives an information which does not allow a complete determination of the elliptical cross section, if an orientation of micropipe is not known. Another problem is a weak accuracy in estimating the diameters, partly because of using pink synchrotron radiation, which is necessary because a monochromatic beam intensity is not sufficient to reveal the weak contrast from a very small object. The general problems of accuracy in estimating the two diameters using the least square procedure are discussed. Two experimental examples are considered to demonstrate small as well as modest accuracies in estimating the diameters.

The growth surface of a 6H-SiC boule, grown by physical vapor transport, was examined using scanning force microscopy. The dimensions of surface/micropipe intersections and screw dislocation Burgers vectors have been determined from topographic data. All micropipes are positioned along the lines of super screw dislocations with a Burgers vectors of at least 4 times the c-axis repeat distance (15.2 Å). Perfect c-axis screw dislocations with Burgers vectors of only 15.2 Å are stable and do not have open cores. Measurements show that micropipe core radii, determined indirectly from the width of the craters formed at the surface/micropipe intersections, increase with the square of the dislocation Burgers vector.

A new technique for investigation of the electrical effects of micropipes in single-crystal 6H-SiC is presented. The setup allows the application of a parallel or normal electric field to MSM (metal-semiconductor-metal) test structures and the visualization of light emission sites in the test gap, including light activity underneath the metal contact. A special transparent metal [indium-tin-oxide(ITO)] was chosen for the metallic contacts. A map of micropipe locations was initially obtained at zero applied field using a laser scattering method. The initial map is compared with that of light emissions at different applied fields.Several tests on undoped and vanadium-doped (compensated) SiC, using NiCr/Au or ITO contacts, indicated the rapid activation of micropipes at relatively low fields in vertical MSM devices. A good match between the laser imaging map of micropipes at zero field and the map of field-induced light emission sites indicates that micropipes are the main current paths in vertical devices, carrying a large current density, and leading to light emissions and partial or total bulk breakdown of the test device.

Micropipes, the hollow cores of superscrew dislocations that lie along the c-direction in SiC single crystals, are quite deleterious to the performance of semiconductor devices. In the x-ray topography of longitudinal-cut samples of these crystals, topographs in the reflection (006) show dislocation image contrast associated with the superscrew dislocations lying along the c-axis of the crystal, which is also the direction of the dislocations' Burgers vectors. In the (110) reflection, whose g-vector is perpendicular to the c-axis and the dislocations' Burgers vector, there is also an image of the superscrew dislocation formed, albeit weaker than the corresponding image in the (006) reflection. This dislocation image is thought to represent stress components of the superscrew dislocation in directions perpendicular to the c-axis.In order to investigate the origin of these stress components, steps have been carried out to determine whether the dislocation image is anisotropic in all possible reflections where g={110}. To achieve this we have excised a hexagonal prism-shaped sample from a 6H-SiC wafer, 100μm wide, polished along the six {100} crystallographic faces, such that a single micropipe ran along the axis of the sample. This enabled x-ray topographs to be taken through each of these {100} faces

In this paper, we describe a simple and novel fabrication process to produce three-dimensional freestanding metal micropipes. This process is based on conventional micromachining and electroless nickel plating inside a microfluidic channel of structured and stacked silicon substrates. The nickel micropipe resists an etching with KOH, which facilitates to fabricate freestanding, functional micropipes. The in-channel electroless plating achieves a continuous and homogeneous deposition of nickel and shows an accurate coating of small microstructures down to 20 µm. Furthermore, the deposited nickel layers possess a high tensile strength for bonding (>200–300 N mm−2), are chemically inert against fluorine gas and withstand pressures up to 6 bar. Thermal measurements have shown that released micropipes show better heat flux densities than embedded micropipes with 86% at a cooling flow rate of 16 ml h−1. Hence, released micropipes feature accurate control of the temperature in the micropipe via a variance of the cooling fluid flow rate.

The availability of high-quality silicon carbide (SiC) single crystals with large diameter is a key issue in the development of the full potential of SiC-based device technology. The formation and suppression of misoriented grains (MGs) in the marginal area of as-grown 6H-SiC single crystals are mainly discussed in this paper. The polytype of the MGs is identified to be mainly 6H-SiC by Raman spectroscopy and XRD. Results of modulation growth, in which different stages are decorated with nitrogen, reveal that the growth rate of MG is higher than that of the matrix. Owing to the MG orientation deviating from [0001], no micropipe has been observed in the etched MG samples. At the same time, there exist many thermal decomposition cavities (TDCs) at the initial growth stage, which indicates that the MG may result from a TDC. Based on this possible formation process, a method viasputtering carbon film on C-terminated (0001) 6H-SiC surface for eliminating TDCs is proposed, which may be helpful to suppress formation of MGs, hence to effectively grow SiC crystals with high quality and large diameter by moderate controls of critical growth conditions in the PVT technique.

We have studied the structural change of defects caused by annealing Al-implanted SiC crystals at 1600 °C using channeling Rutherford backscattering spectrometry (RBS) and synchrotron white beam x-ray topography. Comparison of the RBS spectra before and after annealing showed damage recovery, i.e. a drastic decrease in interstitial atoms. X-ray topography revealed that the size of the white elliptical contrast in micropipe images was decreased by annealing. This result suggested that excess interstitial atoms near the micropipes flowed into their internal walls, and consequently, shrinkage of their hollow cores occurred during annealing.

Cubic silicon carbide is a widegap semiconductor whose chemical and physical properties make it applicable for fabrication of electronic devices operating in extreme environments: high temperature, radiation etc. In recent years considerable progress has been achieved in fabrication of semiconductor devices in 3C-SiC. However, the problem of producing good-quality and low-cost substrates of large enough dimensions is still unsolved. CVD- growth of large-area 3C-SiC on other materials, e.g. silicon[l–5], has become extensively used. With a 20% lattice mismatch between the 3C-SiC layer and the Si substrate the growth of good-quality epitaxial layers presents considerable technological difficulties.

A process for fabricating a high-precision micronozzle with irregular inner shapes (at its end) and high aspect ratio (at its main part) was developed. Micronozzles 3 mm long with slit-type openings of 100*10 mu m, triangular openings of 50 mu m, and circular openings of 6 mu m were successfully obtained. By using a WEDG (wire electrodischarge grinding) polishing technology, a core with a smooth mirrorlike surface was prepared, improving the precision and inner surface quality of the micronozzles produced. The core preparation process with WEDG and WECG can be carried out using common low-conductivity water. This makes the fabricating process simple and effective. Stainless steel was suitable as the core material for WECG operation. A micropipe with an inner diameter of 50 mu m and aspect ratio of 40 was successfully manufactured without using parting film. >

Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption by an elliptic pore nucleated at the boundary of a foreign polytype inclusion. It is shown that depending on the inclusion distortion, the pore can either be a separate micropipe, or grow up to a certain length, or occupy the whole facet of the inclusion.

The influence of structural defects on carrier lifetime in 4H-SiC epilayers has been studied using high spatial resolution optically detected lifetime measurements. Full wafers mappings with 200 μm spatial resolution revealed the carrier lifetime variations that can be associated with structural defects replicated from the substrate and variations in the epitaxial growth conditions due to the susceptor design. High resolution mappings over smaller regions with lateral step size down to 20 μm, revealed local carrier lifetime reductions associated with different structural defects in the epitaxial layers. Identified defects that influence the carrier lifetime are the carrot defects and different types of in-grown stacking faults. Also clusters of threading screw dislocations in the epilayer probably originating from the dissociation of micropipe in the substrate are found to effectively reduce the carrier lifetime. Furthermore, optically detected lifetime mapping has been demonstrated as a nondestructive te...

Momentum and heat transfer rates, as well as entropy generation have been numerically investigated for fully developed, forced convection, laminar flow in a micro-pipe. Compressible and variable fluid property continuity, Navier-Stokes and energy equations are solved for various Reynolds number, constant heat flux and surface roughness cases; entropy generation is discussed in conjunction with the velocity and temperature profiles, boundary layer parameters and heat transfer-frictional characteristics of the pipe flow. Simulations concentrated on the impact of wall roughness based viscous dissipation on the heat transfer behaviour and so occurring heating/cooling activity and the resulting overall and radial entropy generation.

The effects of patterned surface modification on 3D vortex flow generation in a micro capillary tube under a very low Reynolds number have been investigated. Microfabrication technology was successfully employed to pattern surface charges on the inner surfaces of a round capillary tube, which form non-uniform zeta potentials. This technique extends the heterogeneous surfaces from a flat surface to a curved surface. 3D vortices are visualized and measured at the vicinity of tube walls when an electric field is applied across the surfaces utilizing micro resolution PIV. It demonstrated that 3D vortices can also be generated by the patterned surface charges with the same polarity patches. Experimental results have been compared with numerical simulations using CFD-ACE+.

We reveal a correlated reduction in the cross sections of two neighboring micropipes (MPs) in the crystal growth of silicon carbide using computer simulation of phase contrast images. The correlated reduction is explained by the exchange of full-core dislocations in a contact-free reaction between two parallel MPs. We develop a theoretical model that describes the energetics of this process.

Phase contrast images of dislocation micropipe in SiC crystal are experimentally studied at various distances from the sample using synchrotron white beam. Computer simulation of these images enabled us to understand the peculiarities of image formation and measure the diameter of the micropipe. The phase contrast imaging of micropipes without monochromator is explained by the absorption of x rays in a thick (490μm) SiC crystal, effectively forming a high brilliance radiation spectrum with a pronounced maximum at 16keV.

The closing of micropipes during sublimation epitaxy has been studied. Shallow trenches are formed along the direction of the step-flow growth in the vicinity of closed micropipes. The trenches are related to a serious disturbance of the flowing steps and the formation of stacking faults in the (0001) basal plane as well as in the (11¯00) plane. A micropipe closes when the speed of the growth steps is higher than the spiral growth around the micropipe. This mechanism is related to a bending of the micropipe along the trench and the progressive emission of elementary screw dislocations along the trench. The morphology of the disturbed steps at the trenches and the related defects have been studied by transmission electron microscopy and atomic force microscopy. Supporting evidences are presented with optical micrographs from etched epilayers. Image forces, which are developed by the growth steps, stabilize the bending of the micropipes. The limitation of the bending is also discussed.

We have investigated crystal defects in the epitaxial layer on nitrogen-doped Czochralski-grown silicon (CZ-Si) substrate. It was found that two types of crystal defects are generated in the epitaxial layer on the nitrogen-doped CZ-Si substrate. One is revealed to be a stacking fault and the other is a perfect dislocation pair. The origin of these defects is a rod like void and a dislocation loop in the nitrogen-doped CZ-Si substrate. We discuss the formation mechanism of the crystal defect in the epitaxial layer caused by the grown-in defect.

n-Type 6H-SiC bulk crystals were etched by an electrochemical method using an aqueous KOH solution as an electrolyte. After etching using a 50 wt % KOH solution at room temperature, etched samples showed etch pits which are always pairs of a crescent (or a circle shaped pit and a triangle-shaped pit. The paired pits align in the radial direction from the wafer center and the triangle pit is in the water perimeter side with its base facing the perimeter From comparison with optical microscope observation and also with molten KOH etching, it was found that the origin of the electrochemically formed etch pits is not only micropipe but also some other kind of defects. which is most probably screw dislocation.

In this study, the effect of micropipe dissociation via 4H-SiC vapor phase epitaxy on the electrical properties of the epilayer was investigated. Ni/4H-SiC Schottky barrier diodes (SBDs) were fabricated on a 21-µm-thick epilayer, and their reverse blocking characteristics were examined. Some micropipes dissociated into closed core screw dislocations during epitaxial growth and some of them propagated into the epilayer. The SBDs that included a propagated micropipe showed poor reverse blocking performance, as reported previously, while the breakdown voltages were below -400 V. On the other hand, the SBDs that included a dissociated micropipe withstood breakdown up to -1000 V, where the leakage current density was 10-2 to 10-6 A/cm2. This demonstrated that a great improvement of the electrical properties could be achieved by the structural transformation of micropipes into closed core screw dislocations.

In this paper, we studied the structural transformation of screw dislocations through gas-phase 4H-SiC epitaxial growth. We confirmed based on the numbers and features of etch pits on a surface after KOH treatment that some micropipes were closed in the epitaxial layer, and were divided into several elementary screw dislocations. We discuss the magnitude of Burgers vectors of micropipes in 4H-SiC substrates in relation to the number of elementary screw dislocations generated by micropipe closing. A depth analysis further revealed that most micropipe closings took place in the initial stage of epitaxial growth.

The etching effect using molten KOH of micropipes and dislocations in silicon carbide single crystals is investigated. Most of the etch pits become hexagonal due to an anisotropic etching behavior. Micropipes are interconnected with dislocations, and this observation is discussed in relation to the growth process. The hexagonal pattern of micropipes is revealed by rapid etching provided by a large undersaturation. Etching from a melt gives a disintegration of the SiC crystal at the micropipe via spiral dissolution as a consequence of etching near equilibrium conditions. The Si- and C-faces are attacked by molten KOH preferentially and isotropically, respectively. The size of the micropipes with increasing etching time is studied for both the Si- and C-faces. The temperature dependence of the etch rate follows an Arrhenius dependence with an apparent activation energy of about 12-15 kcal/mol derived from measuring the etch rate and weight loss.

Materials research on diamond and SiC as it pertains to microelectronics and optoelectronics has recently increased. A small number of commercial products have resulted. However, additional studies must be conducted to achieve the full potential of these materials. Future directions for research to overcome these problems are described.

The conditions appropriate for direct structure imaging of silicon carbide polytypes in the high-resolution electron microscope have been investigated. Weak-phase-object calculations confirm that a resolution of better than 2.5 A is necessary before polytypic stacking sequences can be identified directly. Furthermore, resolutions closely approaching 1 A are required to resolve projected pairs of Si-C atoms, and considerably better than 1 A is necessary to differentiate between the two species. Extensive multi-slice calculations, based on both current and projected electron-optical characteristics, show that polytype stacking should be recognizable at 500 kV up to thicknesses of 45-75 A, but not at 100 kV, except possibly at the 'reversed' Scherzer defocus position with extremely coherent illumination. The occurrence of Fourier images complicates recognition of the correct objective-lens defocus particularly for thin crystals of the 3C polytype. In thicker-crystal regions (≥ 100 A), where linear image contributions are small, mutual interference between diffracted beams results generally in polytype images of apparently improved resolution and, at specific thickness and defocus values, leads to images of 3C resembling the 'atom-pair' configuration. The latter are then explained by consideration of the image amplitude and intensity spectra. Finally, the problems of recovering specimen structure from crystals of intermediate thickness, as well as some of the factors affecting any quantitative experimental studies, are briefly discussed.

As a result of investigation performed, the possibility of producing silicon carbide single-crystalline ingots grown from seeds in the 1800 to 2600°C range has been established. Silicon carbide single crystal growth in vacuum has been shown to be very promising at low temperatures.

Silicon carbide is a material with potential for the fabrication of composites and coatings in sensitive organs of space vectors and vessels. We have examined the effect of a laser shot on a silicon carbide coating deposited on graphite substrate. Micro-Raman spectroscopy was revealed to be a very suitable tool for the study of the structure evolution, physically as well as chemically. We have shown that silicon carbide completely disappeared while silicon was formed. The study of laser shots onto samples placed under controlled atmospheres, containing variable pressures of oxygen and nitrogen, allows a mechanism of carbon departure to be deduced. The formation of silicon dimers, trimers and tetramers in silicon carbide matrix, was also seen dependending on the laser power reaching the target. These species have specific spectral characteristics which are shown to be quite different from that of bulk silicon.

Single crystal silicon has been grown epitaxially on a number of single crystal oxide substrates by chemical vapor deposition techniques. Such growth has been obtained in large area single crystal form on α-alumina, spinel, and beryllia. The distinct orientation relationships between the silicon deposits and a multiplicity of crystallographic planes of the various insulating substrates are indicated. Compatible with the earlier observed growths of single crystal tungsten on α-alumina, a model which assumes a fit between the silicon and the metal ion sites in the oxide substrate can account for all the epitaxial geometries. A concept of multiple fits in the metal-oxide system in terms of integral lattice parameter values as a guide in substrate selection is suggested. Representative electronic properties of the films and model fabricated devices, as well as a measure of their consequence in microelectronics, are given.

Epitaxial silicon films deposited on foreign substrates by conventional chemical deposition techniques always exhibited structural imperfections due to the lattice mismatch or the occurrence of more than one epitaxial orientation. To improve the structural perfection of these films, a moving deposition-zone technique was used to control the nucleation and growth of silicon films on hexagonal silicon carbide substrates. This technique was found to be capable of promoting the growth of silicon films of a {110} orientation with considerably increased crystal size.