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Abstract In this work, Cu-P-SiC composite coatings were deposited via electroless plating with the addition of sodium hypophoshite (Na[H.sub.2]P[O.sub.2]) as a reducing agent. The coating compositions deposited were determined by [...]

The scattering of stellar orbits by galactic molecular clouds is studied in hope of explaining isotopic peculiarities of presolar grains from Asymptotic Giant Branch (AGB) stars. Silicon isotopic anomalies found in the mainstream Silicon Carbide (SiC) grains are observed to have heavy isotopes enriched. To explain the isotopic heaviness I propose that AGB stars that formed in the interior region of the galaxy, with metallicity higher than solar, change their orbits during close encounters with molecular clouds. The AGB stars give up their SiC grains in winds deposited in the solar neighborhood prior to the birth of the Sun. I model the dynamics by superposing on a standard axisymmetric galactic potential the discrete potentials of thousands of molecular clouds moving in constant circular orbits. Gravity assist occurs when a star scattered into a crossing orbit by one cloud experiences forward scattering from a second cloud. Key words: Silicon carbide, AGB stars, gravity assist, INTRODUCTION Many studies (e.g., 5 and 14) have shown that the mainstream presolar Silicon Carbide (SiC) grains extracted from meteorites formed in asymptotic giant branch stars. Ion probe studies show [...]

The performance of bias stress induced breakdown voltage (BV) slump measurements on DMOSFETs is discussed. Findings reveal that the BV slumped after the DMOSFET was bias stressed at 1200 V for 2 hours at 175 degree Celsius.

Semi-insulating silicon carbide (SiC) is an attractive material for application as high voltage, photoconductive semiconductor switches (PCSS) due to its large bandgap, high critical electric field strength, high electron saturation velocity and high thermal conductivity. The critical field strength of 300 MV/m for 6H-SiC makes it particularly attractive for compact, high voltage, fast switching applications. To realize the benefits of the high bulk electric field strength of SiC and diffuse switch current, carriers must be excited throughout the bulk of the photo switch. Photoconducting switches with opposing electrodes were fabricated on 'a' plane, vanadium compensated, semi-insulating, 6H-SiC substrates. The PCSS devices were switched by optically exciting deep extrinsic levels lying within the 6H-SiC bandgap. The SiC photoswitches were tested up to a bias voltage of 11000 V with a corresponding peak current of 150 A. The 6H-SiC substrates withstood average electric fields up to 27 MV/m. Minimum PCCS dynamic resistances of 2 and 10 [ohms] were obtained with 13 mJ optical pulses at 532 and 1064 nm wavelengths, respectively. Index Terms--Photoconducting devices, photoconductivity, light triggered switches, semiconductor switches, silicon carbide.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2005.06.004 Byline: Irina Vishnevetsky, Michael Epstein, Rami Ben-Zvi, Rahamim Rubin Keywords: Solar reactor; Non-windowed; Crucible; Silicon carbide; Thermal stress Abstract: This paper describes a solar reactor in which a ceramic crucible replaces the window. The crucible is made of SiC and combines two functions: heating surface and sealing partition of the reaction volume. The reactor is irradiated from top using a beam down optics. The main design issues are the sealing of the reactor and the thermal stresses created in the crucible. Careful design of the temperature profile subsequent with stress analyses, especially on the crucible, which is exposed directly to the concentrated solar radiation, and the material of construction can solve mechanical failures of the crucible. The modeling validity was verified experimentally for different operating conditions, both without reaction and with the endothermic carboreduction of ZnO. Author Affiliation: Solar Research Facilities Unit, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel Article History: Received 3 November 2004; Revised 7 June 2005; Accepted 8 June 2005

A physical analytic model is developed for behavior of electron transport, and for the output current-voltage (I-V) characteristics in 4H-SiC metal-semiconductor field-effect transistors (MESFETS). The resulting I-V characteristics are in excellent agreement with experimental data.

Suppression of edge break down in silicon carbide (SiC) avalanche photodiodes (APDs) by employing a 10-degree sidewall bevel angle has been reported. These devices have exhibited low dark currents, at the onset of avalanche gain.

In this paper, we present recent results on an SiC MESFET and we describe two of the main limitation mechanisms encountered: the self-heating and the trapping effects. Results on recent MESFET devices processed by THALES Research and Technology (TRT), Colombes, France, show that the trapping effects has been solved by using epitaxial layers on a higher purity 4H-SiC semi-insulating substrate sample made with a new technique by Okmetic, Vantaa, Finland. The association of two chips in the same case showed that the main limitation mechanism for power density originates from self-heating effects, which could be solved by optimizing the chip layout. 37.8-W output power at 500 MHz, 1.78-W/mm power density, and 35-dB third-order intermodulation-distortion ratio are the best obtained performances. An experimental analysis of trapping and self-heating effects on large-periphery SiC MESFETs is proposed in this paper. Index Terms--MESFET, self-heating, silicon carbide (SiC), trapping.

In this paper, physical models for vertical 4H-silicon carbide (4H-SiC) Schottky diodes are used to develop a design method, where a maximum cutoff frequency for a given punch-through is achieved. The models presented are also used to extract microwave simulator computer-aided design (CAD) models for the devices. A device process was developed and Schottky diodes were fabricated in-house. Characterization of the devices was performed and compared to the theoretical models with good agreement. A demonstrator singly balanced diode mixer was simulated using the developed models. The mixer was fabricated using the in-house developed diodes, and measurements on the mixer show good agreement with the CAD simulations. A conversion loss of 5.2 dB was achieved at 850 MHz, and an excellent II[P.sub.3] of 31 dBm at 850-MHz RF was measured, at 30-dBm [P.sub.LO]. These results verify the enhanced properties of the SiC Schottky diode compared to other nonwide bandgap diodes. Index Terms--Device modeling, microwave mixers, Schottky barrier diode (SBD), silicon carbide (SIC).

This paper presents the fabrication and characterization of silicon carbide (SIC) Schottky-barrier mixer diodes of 25- and 50-/[micro]m diameter on a conducting 4H--SiC wafer. The single-balanced mixer circuits with a diode in each arm (two diodes total) were tested at 200 MHz (VHF) and 1.5 GHz [global positioning system (GPS)]. The experiments show that the conversion loss/input third-order intercept point (IP3) are 8.0 dB/+25 dBm and 7.5 dB/+22 dBm at these frequencies, respectively. The measured second-order intercept point (IP2) over the VHF frequency band is +38 dBm. The above conversion-loss values are about the same as that of commercially available single-balanced mixers with silicon Schottky-barrier diodes. However, to achieve a comparable input IP3 performance with Si Schottky-barrier diodes, a more complex mixer design involving double-balanced mixers with two diodes in each arm of a quad (eight diodes total) is required. Applications include RF-based navigational instruments on board commercial/general aviation aircraft and GPSs. Index Terms--Global positioning system (GPS), intermodulation distortion (IMD), mixers, Schottky diodes, silicon carbide (4H-SiC), VHF circuits.

The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures., Presolar grains (1) are identified by the presence of elements with anomalous isotopic compositions that are distinct from the average solar mixture in a manner that cannot be produced by [...]

Results demonstrate temperature dependence of the piezoreflectnce of an iron-containing silicon carbon nitride crystalline film. Data reveal that the impurity to band and direct band-to band transition energies are influenced by temperature.

The growth characteristics of beta-silicon carbide are examined using Raman scattering, transmission electron microscope, Fourier transform infrared absorption and x-ray diffraction. Test samples were grown on Si (100) substrates and deposited on tilted and nontilted substrates. It was observed that single crystalline materials grow at 800 degrees centigrade. In addition, an avalanche mechanism was also seen.

An experiment is conducted to evaluate the mechanical properties and the Si-C bonding of amorphous silicon carbide thin films using the pulsed laser deposition method. Tests results show that the increase in deposition temperature results to an improvement in the elastic modulus and the hardness of the films. In addition, the rise in temperature also results to an increase in Si-C bond density.

Ultrahigh-vacuum study to investigate the mechanism of diamond thin film nucleation shows that hydrogen ions change the silicon carbide surface and near-surface layers to form sp(super 2) and sp(super 3)-carbon motifs. Highly textured and oriented diamond thin films are formed using this nucleation process. The elimination rate of silicon is more than that of carbon, which is responsible for the occurrence of C-C species. Hydrogen ion interactions with silicon carbide thin films were studied using Auger electron microscopy.

Analysis of instabilities in p-type 6H-silicon carbide metal-oxide semiconductor capacitors yields interface states and oxide traps in the capacitance voltage deformation and hysteresis curves. Mobile charge concentrations are detected in the oxide layer. Deep levels present during inversion layer formation, promote minority-carrier production.

Extended form of damage mechanics analysis of Ladeveze and coworkers helps examine damage mechanics of two-dimensional woven SiC/SiC ceramic matrix composites. Prediction of damage development process using four-node quadrilateral elements demonstrates the efficiency of the theory. Association of finite element method and damage form the basis of flexural analysis.

Chemical-vapor-deposited silicon carbide mirrors were exposed to bombardment by 8-km/s oxygen atoms that simulated the effects of exposure in low Earth orbit for periods up to 7.5 yr. The reflectances of four mirrors were measured before and after exposure at five wavelengths (58.4, 73.6, 104.8, 121.6, and 161 nm) and at 11 angles of incidence from 5 degrees to 80 degrees. The oxygen exposure reduced the normal-incidence reflectances by factors of 1.5-4.5 in the wavelength rate of 58.4-121.6 nm but had no effect on the visual appearance. The optical constants and the thicknesses of the thin surface layers present on the SiC substrates were determined from the reflectance measurements. This analysis indicated that before exposure the surface layers were composed of SiOx (where x is approximately 1.5) with thicknesses of 0.8-1.8 nm. After exposure to 8-km/s oxygen atoms, the surface layers were composed of SiOx with thicknesses of 3.5-4.5 nm. There were no systematic differences between the measured reflectances after simulated space exposures of 1.5, 4.5, and 7.5 years. This implied that most of the growth in thickness of the SiOx layers occurred early in the exposure and stabilized at thicknesses of 3.5-4.5 nm. The optical results were consistent with x-ray photoelectron spectroscopy of the four mirrors after oxygen exposure.

Photoemission spectroscopy of cubic SiC(100) surface indicates that the rubidium (Rb) monolayer increases oxidation and induces selective high silicon oxidation phase development. Desorption of Rb by thermal annealing results in the development of an Si oxide layer without carbon atoms on the oxide surface. Rb causes a fourfold increase in oxygen intake.

Hydrothermal treatment at 300-800 degrees centigrade is used to coat silicon carbide with carbon films of nanometer to micrometer thickness. Carbon films provide high strength and toughness to ceramic mixture composites. Hydrothermal treatment is less expensive than the conventional chemical vapor deposition technique.

Byline: Robert F. Davis The extreme thermal and electronic properties of diamond and of silicon carbide provide multiplicative combinations of attributes which lead to the highest figures of merit for any semiconductor materials for possible use in high-power, high-speed, high- temperature and high-frequency applications. The deposition of monocrystalline diamond. at or below 1 atm total pressure and at a temperature T < 1273 K has been achieved on diamond substrates; the deposited film has been polycrystalline on all other substrates but the achievement is no less significant. For electronic applications, heteroepitaxy of single-crystal films of diamond, an understanding of mechanisms of nucleation and growth methods of impurity introduction and activation, and further device development must be achieved. By contrast, all of these problems have already been solved for silicon carbide, including the operation of a MOSFET at 923 K - the highest operating temperature ever reported for a field-effect device. However, considerable research remains to be done regarding the development of large silicon carbide substrates of ohmic and rectifying contacts, of new types of devices, and of low temperature techniques for the deposition of insulating layers. Fugitive donor and acceptor species in unintentionally doped samples must also be identified and controlled.