Narrow Results

A series of density functional theory calculations was performed to understand the bonding and interaction of hydrogen adsorption on two-dimensional (2D) silicon carbide (SiC). The converged energy results pointed out that the H atom can sufficiently bond to 2D SiC at the top sites (atop Si and C), of which the most stable adsorption site is T_Si. The vibrational properties, along with the zero-point energy, were incorporated into the energy calculations to further understand the phonon effect of the adsorbed H. Most of the 2D SiC structure deformations caused by the H atoms were found at the adsorbent atom along the vertical axis. For the first time, five SiC defect formations, including the quadrilateral-octagon linear defect (8-4), the silicon interstitial defect, the divacancy (4-10-4) defect, the divacancy (8-4-4-8) defect, and the divacancy (4-8-8-4) defect, were investigated. The linear defect (8-4) has the lowest formation energy and is most likely to form. This study could be an interesting step toward future applications of hydrogen energy.

Results obtained in recent studies of deep centers in 6H-, 4H- and 3C-SiC are analyzed. The ionization energies and capture cross sections of centers formed by doping of SiC with different types of impurities or by irradiation, as well as the corresponding parameters of intrinsic defects, are presented. The involvement of these centers in radiative and nonradiative recombination is examined. Analysis of published data shows that a strong influence is exerted by intrinsic defects in the SiC crystal lattice both on the formation of deep centers and on the properties of the epitaxial layers themselves, such as their doping level and polytype homogeneity.

Experimental studies were carried out to validate the effects of dielectric cores in microwave assisted freeze drying. Silica gel was prepared as a porous material using the hydrolysis process, and quartz glass and sintered silicon carbide (SiC) were selected as the dielectric materials, respectively. The microwave input power varied from 91.4 to 96.5 Watts at a frequency of 2,450 MHz. Results show that using the dielectric material with a large loss factor can significantly enhance ordinary microwave freeze drying. At the input power of 91.4 Watts, the drying time with the sintered silicon carbide core was 160.8 min, 43.6% shorter than 285.1 min obtained with the quartz glass core. When the input power was 96.5 Watts, the drying time was reduced from 266.2 to 115.6 min with the enhancement being 56.6%. Analysis of energy utilization shows that the dielectric material with a larger loss factor can result in the higher energy efficiency.

Silicon carbide (SiC) offers significant advantages for microwave high power devises due to its unique electrical and thermal properties. This review presents a summary of the current position in the development of silicon carbide diodes operating at microwave frequencies: varactors, Schottky barrier mixer diodes, p-i-n and IMPATT diodes. Simplified theory of device operation is given for each kind of microwave diodes to derive the figures of merit, to estimate the potential silicon carbide performance for fabrication of these diodes and to compare SiC with conventional semiconductors. These analyses are followed by description of diode design, fabrication and measured characteristics.

The following sections are included:

• Introduction

• Turn-on process in the thyristors

• Steady-state current-voltage characteristics

• Turn-off performances

• Frequency properties

• Critical charge

• Acknowledgments

• References

Dense aluminum-lithium alloy reinforced with up to 20 vol.% SiC_p was prepared from powder mixture using spark plasma sintering process (SPS process). The process, originally developed by Sumitomo Coal Mining Co., has been found to be highly effective for the sintering of ceramic, metallic, and composite materials. Aluminum A 8090 was mixed with silicon carbide particles (SiC_p) by mechanical milling before sintered at 723 K under a pressure of 125 MPa for up to 10 minutes. Relative density of the sintered composite reinforced with 10 vol.% SiC_p was found to exceed 99% of the theoretical value. The Young modulus, yield stress, and ultimate tensile stress of the composite were 91 GPa, 256 MPa, and 332 MPa, respectively, which are, approximately, of the same values as those conventionally hot-isostatic press processed. The elongation of the composite was also found to be higher than that of the conventional one. The microstructure of the sintered composite was observed using both optical and scanning electron microscope. In the region away from the contact surface with the mould wall, the matrix powder was compressed along the vertical direction and elongated in the horizontal direction normal to the applied pressure. At the surface where the specimen was in contact with the mould and punch, the friction force controlled the deformation and thus the shape of the sintered powder. In this paper, the influences of reinforcement volume fractions, sintering temperatures, holding time, and applied pressure are also discussed.

The U. S. Army Research Laboratory (ARL) is investigating compact, energy-dense electronic components to realize high-power, vehicle-mounted survivability and lethality systems. These applications require switching components that are low in weight and volume, exhibit reliable performance, and are easy to integrate into the vehicles' systems. The devices reported here are 4 mm × 4 mm silicon carbide GTOs rated for 3000 V blocking. These devices were packaged at ARL for high pulse current capability, high voltage protection, and minimum package inductance. The GTOs were switched in a 1-ms half-sine, single-pulse discharge circuit to determine reliable peak current and recovery time (or T_q). The GTOs were repeatedly switched over 300 A peak (3.3 A/cm² and an action of 60 A²s) with a recovery time of 20 µs. The switches were also evaluated for dV/dt immunity up to an instantaneous slope of 3 kV/ µs.

Power semiconductor devices are important for numerous applications with power conversion being an important one. Wide energy gap semiconductors SiC and GaN have properties that make them attractive for such applications. Among these properties are high thermal conductivity, high breakdown electric field, wide energy gap, low intrinsic carrier concentration, high thermal stability, high saturation velocity and chemical inertness. These lead to low on-resistance, high breakdown voltage, high frequencies, small volume, and small passive inductors and capacitors. These desirable properties are offset by the higher material costs and higher defect densities. Although wide energy gap devices have been in development for many years, only recently have they become available commercially. Their main competition is silicon power devices with breakdown voltages up to 8000 V and very high surge current capacity. However, silicon power devices are approaching their material limits and wide energy gap devices are beginning to have an impact in the power electronics space. SiC has the advantage of substrates with diameters approaching 150 mm and the ability to grow thermal SiO₂. GaN has the heterojunction advantage, but no viable substrate technology. In fact, a large portion of SiC production is used for GaN substrates. GaN material development has also benefited significantly from the development of optical devices, e.g., light-emitting diodes and lasers.

Silicon carbide composite ceramic filtration membrane materials were prepared by air spray technology. In this process, using some organic solvents such as glycerol, ethanol, etc to fabricate a stable, excellent dispersibility inorganic silicon carbide slurry. Using air spray technology and coating the filter membrane. According to some heat treatments that sintering temperature from1350℃ to1450℃ for 3h, we can prepare a well-distributed, jumbo size SiC ceramic composite filtration membrane. The effects of particle size of SiC, sintering temperature, different ceramic binders on SiC filtration membrane were investigated. Meanwhile, the reaction bonding characteristics, phase composition, flexural strength as well as microstructure of SiC composite ceramics filtration membrane were also investigated. It is demonstrated that 22.8μm silicon carbide sintered at 1450℃ will obtain a better performance. With particle size increases, silicon carbide porous ceramic surface oxide layer thinner prepared at the same temperature. When 15wt% ceramic binder was added, a flexural strength of 36.6MPa was achieved at an open porosity of 35.3%. Al(OH)₃ used as a ceramic binder is very suitable due to its outstanding connectivity and better uniformity.

SiC/cordierite composite porous ceramics were fabricated by an in situ reaction bonding technique using SiC, A1₂O₃, MgO, and graphite as starting materials. C was burned out to produce pores. The surface of SiC was oxidized to SiO₂ at high temperature. With further increasing the temperature, SiO₂ reacted with A1₂O₃ and MgO to form cordierite. The reaction bonding characteristics, phase composition, mechanical strength, and microstructure of porous SiC ceramics were investigated.