Showing papers on "Silicon carbide published in 1981"

Light emitting diodes with high external quantum efficiency

Abstract: A light emitting diode is disclosed that emits light in the blue portion of the visible spectrum with high external quantum efficiency. The diode comprises a single crystal silicon carbide substrate having a first conductivity type, a first epitaxial layer of silicon carbide on the substrate and having the same conductivity type as the substrate, and a second epitaxial layer of silicon carbide on the first epitaxial layer and having the opposite conductivity type from the first layer. The first and second epitaxial layers forming a p-n junction, and the diode includes ohmic contacts for applying a potential difference across the p-n junction. The second epitaxial layer has side walls and a top surface that forms the top surface of the diode, and the second epitaxial layer has a thickness sufficient to increase the solid angle at which light emitted by the junction will radiate externally from the side walls, but less than the thickness at which internal absorption in said second layer would substantially reduce the light emitted from said top surface of the diode.

Stoichiometric disturbances in ion implanted compound semiconductors

Abstract: Disturbances in the stoichiometry of compound semiconductors which result from ion implantation are calculated using a Boltzmann transport equation approach. Results for 50‐keV boron, 150‐keV silicon, and 400‐keV selenium implanted into silicon carbide, indium phosphide, and gallium arsenide are presented. Possible complications in the annealing of such implants are discussed.

Fabrication and characterization of SiC-AIN alloys

Abstract: SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silica, aluminium chloride and starch. The resulting single-phase SiC-AIN powder was hot-pressed without additives to a high density. The dense bodies had a fine-grained uniform microstructure. The Young's elastic modulus, microhardness, fracture toughness, thermal expansion and thermal conductivity were measured as functions of composition. The creep behaviour of the SiC-AIN alloy was compared with that of silicon carbide.

Silicon Carbide Reinforced Aluminum—A Formable Composite

Abstract: This paper describes a class of composites fabricated from inexpensive constituents, silicon carbide made from rice hulls and aluminum, which can be processed by conventional metal working techniques. Aluminum/silicon carbide composites can be extruded, rolled, forged, and pressed into engineering shapes. The mechanical properties of these composites as a function of silicon carbide loading fraction and aluminum matrix in a variety of shapes are presented.

Branched polycarbosilanes and their use in the production of silicon carbide

Abstract: Silicon carbide can be produced by the pyrolysis of branched polycarbosilanes which in turn are produced directly from selected monomer systems.

Composite mirror and method of construction

Abstract: A preferred embodiment of a composite mirror comprises (1) a substrate of carbon-carbon, (2) intermediate layers of silicon carbide, silicon dioxide, (3) optically polished layers of metals and/or suitable glass (ultralow-expansion or modified fused-silica glass) and (4) an optical coating of high reflectivity. The resulting mirror exhibits desired features including high optical quality and a low coefficient of thermal expansion; such mirrors being well suited to high thermal flux applications. Methods of producing the composite mirror are described.

Thermal Etching and Grain‐Boundary Grooving Silicon Ceramics

Abstract: Polished polycrystalline specimens of Si, Sic, and Si3N4 were heated to high temperatures and the rate of thermal etching was measured. Grain-boundary grooving occurred on silicon by surface diffusion, with a surface-diffusion coefficient given by Silicon carbide surfaces became extremely rough and very little grain-boundary grooving occurred. Silicon nitride decomposed in an N2-H2, atmosphere with an activation energy of 757 kJ/mol, which was very near the activation energy calculated from thermochemical data. The surfaces became fairly rough but grain-boundary grooves formed by an evaporation processsimilar to that for decomposition.

The 6H→ 3C“Reverse” Transformation in Silicon Carbide Compacts

Abstract: It is shown that an α→β transformation can be induced in reaction-bonded silicon carbide by high-temperature annealing in high nitrogen pressures. The transformation is the reverse of that commonly observed during high-temperature processing of SiC compacts and is accompanied by the formation of substantial amorphous grain-boundary films, suggesting a possible liquid-phase transformation mechanism.

Sintered high density boron carbide

Abstract: High density, sintered refractory articles composed of: 60 to 98% by weight of boron carbide and 2 to 40% by weight of silicon carbide, and 0 to 10% by weight of aluminum. As a result of the composition, products with densities in excess of 94% of theoretical can be produced by cold pressing followed by a pressureless heat treatment.

Dense sintered silicon carbide ceramic

Abstract: A dense sintered silicon carbide ceramic has high strength and a flexural strength of at least 25 kg/mm 2 at room temperature and 1400° C. which is obtained by molding a mixture of an aluminum oxide source at a ratio of 0.5 to 35 wt. % as Al 2 O 3 and silicon carbide at a substantial residual portion followed by a pressureless sintering.

Method for manufacture of silicon nitride

Abstract: Silicon carbide of improved quality is obtained by using a liquid silicic acid or modified liquid silicic acid as a silicic substance and carbon in a powdered form, a precursor of carbon in a powdered form, or a precursor of carbon in the form of a solution as a carbonaceous substance, and thermally treating these raw materials in a non-oxidative atmosphere. The silicon carbide thus produced is finely divided and in high-purity and suitable for use as raw material for the production of high-strength sintered articles.

Reflectance of silicon carbide in the vacuum ultraviolet

Abstract: Silicon carbide may be an ideal mirror material for synchrotron radiation applications. Measurement of reflectance at 45 degrees angle of incidence, with two orientations of the reflector about the optic axis, allowed direct comparison of the reflectivities of various polycrystalline forms of silicon carbide with that of gold. Scanning electron microscopy revealed the surface characteristics of the silicon carbide samples.

Boron Redistribution in Sintered α‐SiC During Thermal Oxidation

Abstract: The redistribution of the boron impurity in sintered α-SiC during thermal oxidation was investigated over the temperature range 1200· to 1400,°C using sputter-induced photon spectrometry (SIPS). The process was modeled with the Stanford University Processing Engineering Models Program (SUPREM) which permitted the estimation of diffusivities of boron in the growing oxide and the substrate. The process is characterized by segregation of the boron in the oxide near the interface and a corresponding depletion of boron in the substrate. The apparent diffusivities in the oxide were about three orders of magnitude higher than the published values for boron in pure SiO2, presumably because the film is much less pure than pure SiO2. The apparent diffusivities of the boron in the polycrystalline silicon carbide were almost five orders of magnitude higher than the published values for boron in single-crystal silicon carbide. The diffusivities in the silicon carbide represent boron transport via the grain boundaries which were partially oxidized during the thermal treatment.

Proton magnetic resonance spectra of plasma‐deposited inorganic thin films

Abstract: Proton magnetic resonance data are presented for the hydrogen alloys of plasma-deposited amorphous boron, carbon, silicon carbide, and silicon nitride. Linewidth and lineshape analysis leads to the conclusion that hydrogen nuclei are clustered in a-Si/C:H, a-C:H, and a-Si/C:H. Both a-Si/C:H and a-C:H data show that the hydrogen exists in two phases. Modeling of line- widths in a-Si/C:H indicates that the two phases are heavily hydrogenated carbon clusters imbedded in a weakly hydrogenated a-Si lattice. Finally, evidence is presented for the presence of motionally narrowed hydrogen spectra in a-Si/N:H, a-B:H, and a-C:H. It is suggested that the hydrogen nuclei giving rise to these spectra are associated with disorder modes.

Concurrent Flaw Populations in SiC

Abstract: Concurrent surface and edge flaw populations were identified on fracture surfaces of as-machined specimens of sintered silicon carbide. The overall strength distribution and the individual concurrent distributions were estimated using Weibull statistics. Design implications of using a single flaw population and the difficulties associated with rigorously separating the concurrent distributions are discussed.

Method of producing composite ceramic articles

Abstract: In accord with the present invention, a composite ceramic article may be produced by joining separate components of ceramic materials with a cement or brazing compound of finely-divided metal borides, such as Mo 2 B 5 , MoB 2 , TiB 2 , GeB 2 , ZrB 2 , SmB 6 , NbB 2 , HfB, VB 2 , WB 2 or TaB 2 . A particularly useful metal boride for use with silicon carbide is Mo 2 B 5 . If the metal carbide parts or components to be joined are sintered, the metal boride cement is selected to have a melting point within 150° C., but less than the sintering temperature of the metal carbide. If the metal carbide parts or components to be joined are unsintered, or an unsintered component is to be joined to a sintered component, the metal boride cement is selected to have a melting point slightly higher than the sintering temperature of the metal carbide components to be joined.

Reactive Ion-Beam Etching of Silicon Carbide

Abstract: A reactive ion-beam etching technique using freon gas is developed for microfabrication in SiC. The enhancement of the etching rate of SiC is apparent by admixing O2 gas in CF4 gas. The etching rate of SiC for CF4+O2 (40%) gas is about 2 times larger than that for Ar gas. This technique appears to be very useful for producing various devices of SiC.

Fission-product SiC reaction in HTGR fuel

Abstract: The primary barrier to release of fission product from any of the fuel types into the primary circuit of the HTGR are the coatings on the fuel particles. Both pyrolytic carbon and silicon carbide coatings are very effective in retaining fission gases under normal operating conditions. One of the possible performance limitations which has been observed in irradiation tests of TRISO fuel is chemical interaction of the SiC layer with fission products. This reaction reduces the thickness of the SiC layer in TRISO particles and can lead to release of fission products from the particles if the SiC layer is completely penetrated. The experimental section of this report describes the results of work at General Atomic concerning the reaction of fission products with silicon carbide. The discussion section describes data obtained by various laboratories and includes (1) a description of the fission products which have been found to react with SiC; (2) a description of the kinetics of silicon carbide thinning caused by fission product reaction during out-of-pile thermal gradient heating and the application of these kinetics to in-pile irradiation; and (3) a comparison of silicon carbide thinning in LEU and HEU fuels.

Method of manufacturing a semiconductor device using silicon carbide mask

Abstract: A method of manufacturing a semiconductor device which comprises the step of applying a silicon carbide film having a prescribed perforated pattern as a masking film selectively to etch a silicon dioxide film or diffuse an impurity into a substrate.

Epitaxial crystal fabrication of SiC:AlN

Abstract: Crystals of silicon carbide and aluminum nitride, substrates containing same, and the fabrication thereof.

Estimation of Fracture Toughness by Intrinsic Flaw Fractography for Sintered Alpha Silicon Carbide

Abstract: An attempt to apply three-dimensional flaw models to characterize fracture origins in sintered alpha silicon carbide is made. Some general improvements in the intrinsic flaw fractography results are obtained by using three-dimensional void models instead of two-dimensional crack models.

A new degradation phenomenon in blue light emitting silicon carbide diodes

Abstract: In 6H-SiC blue emitting diodes prepared by sawing epitaxial wafers the development of greenish striations in the luminescing layer is observed together with a decrease in external quantum efficiency. It is proposed that this degradation is due to the development of numerous stacking faults leading to an intermediate (cubic?) state of lower band gap than the 6H modification.