Silicon carbide

Silicon carbide (SiC), also known as carborundum /kɑːrbəˈrʌndəm/, is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has been mass-produced since 1893 for use as an abrasive. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. Electronic applications of silicon carbide such as light-emitting diodes (LEDs) and detectors in early radios were first demonstrated around 1907. SiC is used in semiconductor electronics devices that operate at high temperatures or high voltages, or both. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.

Silicon carbide
Sample of silicon carbide as a boule
Names
Preferred IUPAC name
Silicon carbide
Other names
Carborundum
Moissanite
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.006.357
EC Number
  • 206-991-8
13642
MeSH Silicon+carbide
RTECS number
  • VW0450000
Properties
CSi
Molar mass 40.096 g·mol−1
Appearance Yellow to green to bluish-black, iridescent crystals[1]
Density 3.16 g·cm−3 (hex.)[2]
Melting point 2,830 °C (5,130 °F; 3,100 K)[2] (decomposes)
Solubility Insoluble in water, soluble in molten alkalis and molten iron[3]
Electron mobility ~900 cm2/V·s (all polytypes)
−12.8·10−6 cm3/mol[4]
2.55 (infrared; all polytypes)[5]
Hazards
Not listed
NFPA 704
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
REL (Recommended)
TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
IDLH (Immediate danger)
N.D.[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

History

Early experiments

Non-systematic, less-recognized and often unverified syntheses of silicon carbide include:

  • J. J. Berzelius's reduction of potassium fluorosilicate by potassium (1810)
  • César-Mansuète Despretz's passing an electric current through a carbon rod embedded in sand (1849)
  • Robert Sydney Marsden's dissolution of silica in molten silver in a graphite crucible (1881)
  • Paul Schuetzenberger's heating of a mixture of silicon and silica in a graphite crucible (1881)
  • Albert Colson's heating of silicon under a stream of ethylene (1882).[6]

Wide-scale production

SiC LED historic
A replication of H. J. Round's LED experiments

Wide-scale production is credited to Edward Goodrich Acheson in 1890.[7] Acheson was attempting to prepare artificial diamonds when he heated a mixture of clay (aluminium silicate) and powdered coke (carbon) in an iron bowl. He called the blue crystals that formed carborundum, believing it to be a new compound of carbon and aluminium, similar to corundum. In 1893, Ferdinand Henri Moissan discovered the very rare naturally occurring SiC mineral while examining rock samples found in the Canyon Diablo meteorite in Arizona. The mineral was named moissanite in his honor. Moissan also synthesized SiC by several routes, including dissolution of carbon in molten silicon, melting a mixture of calcium carbide and silica, and by reducing silica with carbon in an electric furnace.

Acheson patented the method for making silicon carbide powder on February 28, 1893.[8] Acheson also developed the electric batch furnace by which SiC is still made today and formed the Carborundum Company to manufacture bulk SiC, initially for use as an abrasive.[9] In 1900 the company settled with the Electric Smelting and Aluminum Company when a judge's decision gave "priority broadly" to its founders "for reducing ores and other substances by the incandescent method".[10] It is said that Acheson was trying to dissolve carbon in molten corundum (alumina) and discovered the presence of hard, blue-black crystals which he believed to be a compound of carbon and corundum: hence carborundum. It may be that he named the material "carborundum" by analogy to corundum, which is another very hard substance (9 on the Mohs scale).

The first use of SiC was as an abrasive. This was followed by electronic applications. In the beginning of the 20th century, silicon carbide was used as a detector in the first radios.[11] In 1907 Henry Joseph Round produced the first LED by applying a voltage to a SiC crystal and observing yellow, green and orange emission at the cathode. Those experiments were later repeated by O. V. Losev in the Soviet Union in 1923.[12]

Natural occurrence

Moissanite-USGS-20-1001d-14x-
Moissanite single crystal (≈1 mm in size)

Naturally occurring moissanite is found in only minute quantities in certain types of meteorite and in corundum deposits and kimberlite. Virtually all the silicon carbide sold in the world, including moissanite jewels, is synthetic. Natural moissanite was first found in 1893 as a small component of the Canyon Diablo meteorite in Arizona by Dr. Ferdinand Henri Moissan, after whom the material was named in 1905.[13] Moissan's discovery of naturally occurring SiC was initially disputed because his sample may have been contaminated by silicon carbide saw blades that were already on the market at that time.[14]

While rare on Earth, silicon carbide is remarkably common in space. It is a common form of stardust found around carbon-rich stars, and examples of this stardust have been found in pristine condition in primitive (unaltered) meteorites. The silicon carbide found in space and in meteorites is almost exclusively the beta-polymorph. Analysis of SiC grains found in the Murchison meteorite, a carbonaceous chondrite meteorite, has revealed anomalous isotopic ratios of carbon and silicon, indicating that these grains originated outside the solar system.[15]

Production

SiC crystals
Synthetic SiC crystals ~3 mm in diameter

Because natural moissanite is extremely scarce, most silicon carbide is synthetic. Silicon carbide is used as an abrasive, as well as a semiconductor and diamond simulant of gem quality. The simplest process to manufacture silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F). Fine SiO2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material.[16] The silica fume, which is a byproduct of producing silicon metal and ferrosilicon alloys, can also be converted to SiC by heating with graphite at 1,500 °C (2,730 °F).[17]

The material formed in the Acheson furnace varies in purity, according to its distance from the graphite resistor heat source. Colorless, pale yellow and green crystals have the highest purity and are found closest to the resistor. The color changes to blue and black at greater distance from the resistor, and these darker crystals are less pure. Nitrogen and aluminium are common impurities, and they affect the electrical conductivity of SiC.[18]

Lely SiC Crystal
Synthetic SiC Lely crystals

Pure silicon carbide can be made by the Lely process,[19] in which SiC powder is sublimed into high-temperature species of silicon, carbon, silicon dicarbide (SiC2), and disilicon carbide (Si2C) in an argon gas ambient at 2500 °C and redeposited into flake-like single crystals,[20] sized up to 2×2 cm, at a slightly colder substrate. This process yields high-quality single crystals, mostly of 6H-SiC phase (because of high growth temperature).

A modified Lely process involving induction heating in graphite crucibles yields even larger single crystals of 4 inches (10 cm) in diameter, having a section 81 times larger compared to the conventional Lely process.[21]

Cubic SiC is usually grown by the more expensive process of chemical vapor deposition (CVD).[18][22] Homoepitaxial and heteroepitaxial SiC layers can be grown employing both gas and liquid phase approaches.[23]

To form complex shaped SiC, preceramic polymers can be used as precursors which form the ceramic product through pyrolysis at temperatures in the range 1000° - 1100 °C [24]. Precursor materials to obtain silicon carbide in such a manner include polycarbosilanes, poly(methylsilyne) and polysilazanes [25]. Silicon carbide materials obtained through the pyrolysis of preceramic polymers are known as polymer derived ceramics or PDCs. Pyrolysis of preceramic polymers is most often conducted under an inert atmosphere at relatively low temperatures. Relative to the CVD process, the pyrolysis method is advantageous because the polymer can be formed into various shapes prior to thermalization into the ceramic.[26][27][28][29]

Structure and properties

Structure of major SiC polytypes.
SiC3Cstructure
SiC4Hstructure
SiC6Hstructure
(β)3C-SiC 4H-SiC (α)6H-SiC

Silicon carbide exists in about 250 crystalline forms.[30] Through the inert atmosphere pyrolysis of preceramic polymers, silicon carbide in a glassy amorphous form is also produced. [31] The polymorphism of SiC is characterized by a large family of similar crystalline structures called polytypes. They are variations of the same chemical compound that are identical in two dimensions and differ in the third. Thus, they can be viewed as layers stacked in a certain sequence.[32]

Alpha silicon carbide (α-SiC) is the most commonly encountered polymorph, and is formed at temperatures greater than 1700 °C and has a hexagonal crystal structure (similar to Wurtzite). The beta modification (β-SiC), with a zinc blende crystal structure (similar to diamond), is formed at temperatures below 1700 °C.[33] Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for heterogeneous catalysts, owing to its higher surface area compared to the alpha form.

Properties of major SiC polytypes[5][26]
Polytype 3C (β) 4H 6H (α)
Crystal structure Zinc blende (cubic) Hexagonal Hexagonal
Space group T2d-F43m C46v-P63mc C46v-P63mc
Pearson symbol cF8 hP8 hP12
Lattice constants (Å) 4.3596 3.0730; 10.053 3.0810; 15.12
Density (g/cm3) 3.21 3.21 3.21
Bandgap (eV) 2.36 3.23 3.05
Bulk modulus (GPa) 250 220 220
Thermal conductivity (W m−1K−1)

@ 300K (see [34] for temp. dependence)

360 370 490

Pure SiC is colorless. The brown to black color of the industrial product results from iron impurities. The rainbow-like luster of the crystals is caused by a passivation layer of silicon dioxide that forms on the surface.

The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for bearings and furnace parts. Silicon carbide does not melt at any known temperature. It is also highly inert chemically. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices.[35] SiC also has a very low coefficient of thermal expansion (4.0 × 10−6/K) and experiences no phase transitions that would cause discontinuities in thermal expansion.[18]

Electrical conductivity

Silicon carbide is a semiconductor, which can be doped n-type by nitrogen or phosphorus and p-type by beryllium, boron, aluminium, or gallium.[5] Metallic conductivity has been achieved by heavy doping with boron, aluminium or nitrogen.

Superconductivity has been detected in 3C-SiC:Al, 3C-SiC:B and 6H-SiC:B at the same temperature of 1.5 K.[33][36] A crucial difference is however observed for the magnetic field behavior between aluminium and boron doping: SiC:Al is type-II, same as Si:B. On the contrary, SiC:B is type-I. In attempt to explain this difference, it was noted that Si sites are more important than carbon sites for superconductivity in SiC. Whereas boron substitutes carbon in SiC, Al substitutes Si sites. Therefore, Al and B "see" different environments that might explain different properties of SiC:Al and SiC:B.[37]

Uses

Abrasive and cutting tools

Ultra-thin separated (Carborundum) disk
Cutting disks made of SiC

In the arts, silicon carbide is a popular abrasive in modern lapidary due to the durability and low cost of the material. In manufacturing, it is used for its hardness in abrasive machining processes such as grinding, honing, water-jet cutting and sandblasting. Particles of silicon carbide are laminated to paper to create sandpapers and the grip tape on skateboards.[38]

In 1982 an exceptionally strong composite of aluminium oxide and silicon carbide whiskers was discovered. Development of this laboratory-produced composite to a commercial product took only three years. In 1985, the first commercial cutting tools made from this alumina and silicon carbide whisker-reinforced composite were introduced into the market.[39]

Structural material

Soldier Plate Carrier System (SPCS)
Silicon carbide is used for trauma plates of ballistic vests

In the 1980s and 1990s, silicon carbide was studied in several research programs for high-temperature gas turbines in Europe, Japan and the United States. The components were intended to replace nickel superalloy turbine blades or nozzle vanes.[40] However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture toughness.[41]

Like other hard ceramics (namely alumina and boron carbide), silicon carbide is used in composite armor (e.g. Chobham armor), and in ceramic plates in bulletproof vests. Dragon Skin, which was produced by Pinnacle Armor, used disks of silicon carbide.[42]

Silicon carbide is used as a support and shelving material in high temperature kilns such as for firing ceramics, glass fusing, or glass casting. SiC kiln shelves are considerably lighter and more durable than traditional alumina shelves.[43]

In December 2015, infusion of silicon carbide nano-particles in molten magnesium was mentioned as a way to produce a new strong and plastic alloy suitable for use in aeronautics, aerospace, automobile and micro-electronics.[44]

Automobile parts

PCCB Brake Carrera GT
The Porsche Carrera GT's carbon-ceramic (silicon carbide) disk brake

Silicon-infiltrated carbon-carbon composite is used for high performance "ceramic" brake disks, as they are able to withstand extreme temperatures. The silicon reacts with the graphite in the carbon-carbon composite to become carbon-fiber-reinforced silicon carbide (C/SiC). These brake disks are used on some road-going sports cars, supercars, as well as other performance cars including the Porsche Carrera GT, the Bugatti Veyron, the Chevrolet Corvette ZR1, the McLaren P1,[45] Bentley, Ferrari, Lamborghini and some specific high-performance Audi cars. Silicon carbide is also used in a sintered form for diesel particulate filters.[46] It's also used as an oil additive to reduce friction, emissions, and harmonics.[47][48]

Foundry crucibles

SiC is used in crucibles for holding melting metal in small and large foundry applications.[49][50]

Electric systems

The earliest electrical application of SiC was in lightning arresters in electric power systems. These devices must exhibit high resistance until the voltage across them reaches a certain threshold VT at which point their resistance must drop to a lower level and maintain this level until the applied voltage drops below VT.[51]

It was recognized early on that SiC had such a voltage-dependent resistance, and so columns of SiC pellets were connected between high-voltage power lines and the earth. When a lightning strike to the line raises the line voltage sufficiently, the SiC column will conduct, allowing strike current to pass harmlessly to the earth instead of along the power line. The SiC columns proved to conduct significantly at normal power-line operating voltages and thus had to be placed in series with a spark gap. This spark gap is ionized and rendered conductive when lightning raises the voltage of the power line conductor, thus effectively connecting the SiC column between the power conductor and the earth. Spark gaps used in lightning arresters are unreliable, either failing to strike an arc when needed or failing to turn off afterwards, in the latter case due to material failure or contamination by dust or salt. Usage of SiC columns was originally intended to eliminate the need for the spark gap in lightning arresters. Gapped SiC arresters were used for lightning-protection and sold under the GE and Westinghouse brand names, among others. The gapped SiC arrester has been largely displaced by no-gap varistors that use columns of zinc oxide pellets.[52]

Electronic circuit elements

Uv-LED
Ultraviolet LED

Silicon carbide was the first commercially important semiconductor material. A crystal radio "carborundum" (synthetic silicon carbide) detector diode was patented by Henry Harrison Chase Dunwoody in 1906. It found much early use in shipboard receivers.

Power electronic devices

Silicon carbide is a semiconductor in research and early mass production providing advantages for fast, high-temperature and/or high-voltage devices. The first devices available were Schottky diodes, followed by junction-gate FETs and MOSFETs for high-power switching. Bipolar transistors and thyristors are currently developed.[35] A major problem for SiC commercialization has been the elimination of defects: edge dislocations, screw dislocations (both hollow and closed core), triangular defects and basal plane dislocations.[53] As a result, devices made of SiC crystals initially displayed poor reverse blocking performance though researchers have been tentatively finding solutions to improve the breakdown performance.[54] Apart from crystal quality, problems with the interface of SiC with silicon dioxide have hampered the development of SiC-based power MOSFETs and insulated-gate bipolar transistors. Although the mechanism is still unclear, nitriding has dramatically reduced the defects causing the interface problems.[55] In 2008, the first commercial JFETs rated at 1200 V were introduced to the market,[56] followed in 2011 by the first commercial MOSFETs rated at 1200 V. Beside SiC switches and SiC Schottky diodes (also Schottky barrier diode, SBD) in the popular TO-247 and TO-220 packages, companies started even earlier to implement the bare chips into their power electronic modules. SiC SBD diodes found wide market spread being used in PFC circuits and IGBT power modules.[57] Conferences such as the International Conference on Integrated Power Electronics Systems (CIPS) report regularly about the technological progress of SiC power devices. Major challenges for fully unleashing the capabilities of SiC power devices are:

  • Gate drive: SiC devices often require gate drive voltage levels that are different from their silicon counterparts and may be even unsymmetric, for example, +20 V and −5 V.[58]
  • Packaging: SiC chips may have a higher power density than silicon power devices and are able to handle higher temperatures exceeding the silicon limit of 150 °C. New die attach technologies such as sintering are required to efficiently get the heat out of the devices and ensure a reliable interconnection.[59]

LEDs

The phenomenon of electroluminescence was discovered in 1907 using silicon carbide and the first commercial LEDs were based on SiC. Yellow LEDs made from 3C-SiC were manufactured in the Soviet Union in the 1970s[60] and blue LEDs (6H-SiC) worldwide in the 1980s.[61] The production was soon stopped because gallium nitride showed 10–100 times brighter emission. This difference in efficiency is due to the unfavorable indirect bandgap of SiC, whereas GaN has a direct bandgap which favors light emission. However, SiC is still one of the important LED components – it is a popular substrate for growing GaN devices, and it also serves as a heat spreader in high-power LEDs.[61]

Astronomy

The low thermal expansion coefficient, high hardness, rigidity and thermal conductivity make silicon carbide a desirable mirror material for astronomical telescopes. The growth technology (chemical vapor deposition) has been scaled up to produce disks of polycrystalline silicon carbide up to 3.5 m (11 ft) in diameter, and several telescopes like the Herschel Space Telescope are already equipped with SiC optics,[62][63] as well the Gaia space observatory spacecraft subsystems are mounted on a rigid silicon carbide frame, which provides a stable structure that will not expand or contract due to heat.

Thin filament pyrometry

SiCpyrometer
Test flame and glowing SiC fibers. The flame is about 7 cm (2.8 in) tall.

Silicon carbide fibers are used to measure gas temperatures in an optical technique called thin filament pyrometry. It involves the placement of a thin filament in a hot gas stream. Radiative emissions from the filament can be correlated with filament temperature. Filaments are SiC fibers with a diameter of 15 micrometers, about one fifth that of a human hair. Because the fibers are so thin, they do little to disturb the flame and their temperature remains close to that of the local gas. Temperatures of about 800–2500 K can be measured.[64][65]

Heating elements

References to silicon carbide heating elements exist from the early 20th century when they were produced by Acheson's Carborundum Co. in the U.S. and EKL in Berlin. Silicon carbide offered increased operating temperatures compared with metallic heaters. Silicon carbide elements are used today in the melting of glass and non-ferrous metal, heat treatment of metals, float glass production, production of ceramics and electronics components, igniters in pilot lights for gas heaters, etc.[66]

Nuclear fuel particles and cladding

Silicon carbide is an important material in TRISO-coated fuel particles, the type of nuclear fuel found in high temperature gas cooled reactors such as the Pebble Bed Reactor. A layer of silicon carbide gives coated fuel particles structural support and is the main diffusion barrier to the release of fission products.[67]

Silicon carbide composite material has been investigated for use as a replacement for Zircaloy cladding in light water reactors. One of the reasons for this investigation is that, Zircaloy experiences hydrogen embrittlement as a consequence of the corrosion reaction with water. This produces a reduction in fracture toughness with increasing volumetric fraction of radial hydrides. This phenomenon increases drastically with increasing temperature to the detriment of the material.[68] Silicon carbide cladding does not experience this same mechanical degradation, but instead retains strength properties with increasing temperature. The composite consists of SiC fibers wrapped around a SiC inner layer and surrounded by an SiC outer layer.[69] Problems have been reported with the ability to join the pieces of the SiC composite.[70]

Jewelry

Moissanite ring natural light
A moissanite engagement ring

As a gemstone used in jewelry, silicon carbide is called "synthetic moissanite" or just "moissanite" after the mineral name. Moissanite is similar to diamond in several important respects: it is transparent and hard (9–9.5 on the Mohs scale, compared to 10 for diamond), with a refractive index between 2.65 and 2.69 (compared to 2.42 for diamond). Moissanite is somewhat harder than common cubic zirconia. Unlike diamond, moissanite can be strongly birefringent. For this reason, moissanite jewels are cut along the optic axis of the crystal to minimize birefringent effects. It is lighter (density 3.21 g/cm3 vs. 3.53 g/cm3), and much more resistant to heat than diamond. This results in a stone of higher luster, sharper facets, and good resilience. Loose moissanite stones may be placed directly into wax ring moulds for lost-wax casting, as can diamond,[71] as moissanite remains undamaged by temperatures up to 1,800 °C (3,270 °F). Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its thermal conductivity is closer to diamond than any other substitute. Many thermal diamond-testing devices cannot distinguish moissanite from diamond, but the gem is distinct in its birefringence and a very slight green or yellow fluorescence under ultraviolet light. Some moissanite stones also have curved, string-like inclusions, which diamonds never have.[72]

Steel production

Silicon carbide chunk
Piece of silicon carbide used in steel making

Silicon carbide, dissolved in a basic oxygen furnace used for making steel, acts as a fuel. The additional energy liberated allows the furnace to process more scrap with the same charge of hot metal. It can also be used to raise tap temperatures and adjust the carbon and silicon content. Silicon carbide is cheaper than a combination of ferrosilicon and carbon, produces cleaner steel and lower emissions due to low levels of trace elements, has a low gas content, and does not lower the temperature of steel.[73]

Catalyst support

The natural resistance to oxidation exhibited by silicon carbide, as well as the discovery of new ways to synthesize the cubic β-SiC form, with its larger surface area, has led to significant interest in its use as a heterogeneous catalyst support. This form has already been employed as a catalyst support for the oxidation of hydrocarbons, such as n-butane, to maleic anhydride.[74][75]

Carborundum printmaking

Silicon carbide is used in carborundum printmaking – a collagraph printmaking technique. Carborundum grit is applied in a paste to the surface of an aluminium plate. When the paste is dry, ink is applied and trapped in its granular surface, then wiped from the bare areas of the plate. The ink plate is then printed onto paper in a rolling-bed press used for intaglio printmaking. The result is a print of painted marks embossed into the paper.[76]

Graphene production

Silicon carbide can be used in the production of graphene because of its chemical properties that promote the epitaxial production of graphene on the surface of SiC nanostructures.

When it comes to its production, silicon is used primarily as a substrate to grow the graphene. But there are actually several methods that can be used to grow the graphene on the silicon carbide. The confinement controlled sublimation (CCS) growth method consists of a SiC chip that is heated under vacuum with graphite. Then the vacuum is released very gradually to control the growth of graphene. This method yields the highest quality graphene layers. But other methods have been reported to yield the same product as well.

Another way of growing graphene would be thermally decomposing SiC at a high temperature within a vacuum.[77] But this method turns out to yield graphene layers that contain smaller grains within the layers.[78] So there have been efforts to improve the quality and yield of graphene. One such method is to perform ex situ graphitization of silicon terminated SiC in an atmosphere consisting of argon. This method has proved to yield layers of graphene with larger domain sizes than the layer that would be attainable via other methods. This new method can be very viable to make higher quality graphene for a multitude of technological applications.

When it comes to understanding how or when to use these methods of graphene production, most of them mainly produce or grow this graphene on the SiC within a growth enabling environment. It is utilized most often at rather higher temperatures (such as 1300˚C) because of SiC thermal properties.[79] However, there have been certain procedures that have been performed and studied that could potentially yield methods that use lower temperatures to help manufacture graphene. More specifically this different approach to graphene growth has been observed to produce graphene within a temperature environment of around 750˚C. This method entails the combination of certain methods like chemical vapor deposition (CVD) and surface segregation. And when it comes to the substrate, the procedure would consist of coating a SiC substrate with thin films of a transition metal. And after the rapid heat treating of this substance, the carbon atoms would then become more abundant at the surface interface of the transition metal film which would then yield graphene. And this process was found to yield graphene layers that were more continuous throughout the substrate surface.[80]

Quantum physics

Silicon carbide can host point defects in the crystal lattice which are known as color centers. These defects can produce single photons on demand and thus serve as a platform for single-photon source. Such a device is a fundamental resource for many emerging applications of quantum information science. If one pumps a color center via an external optical source or electrical current, the color center will be brought to the excited state and then relax with the emission of one photon.[81][82]

One well known point defect in silicon carbide is the divacancy which has a similar electronic structure as the nitrogen-vacancy center in diamond. In 4H-SiC, the divacancy has four different configurations which correspond to four zero-phonon lines (ZPL). These ZPL values are written using the notation VSi-VC and the unit eV: hh(1.095), kk(1.096), kh(1.119), and hk(1.150).[83]

See also

References

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External links

Acheson process

The Acheson process was invented by Edward Goodrich Acheson to synthesize silicon carbide (SiC) and graphite.

AlSiC

AlSiC, pronounced "alsick", is a metal matrix composite consisting of aluminium matrix with silicon carbide particles. It has high thermal conductivity (180–200 W/m K), and its thermal expansion can be adjusted to match other materials, e.g. silicon and gallium arsenide chips and various ceramics. It is chiefly used in microelectronics as substrate for power semiconductor devices and high density multi-chip modules, where it aids with removal of waste heat.

Several variants exist:

AlSiC-9, containing 37 vol.% of A 356.2 aluminium alloy and 63 vol.% silicon carbide. Its thermal conductivity is 190–200 W/m K. Its thermal expansion roughly matches gallium arsenide, silicon, indium phosphide, alumina, aluminium nitride, silicon nitride, and Direct Bonded Copper aluminium nitride. It is also compatible with some low temperature co-fired ceramics, e.g. Ferro A6M and A6S, Heraeus CT 2000, and Kyocera GL560. Its density at 25 °C is 3.01 g/cm3.

AlSiC-10, containing 45 vol.% of A 356.2 aluminium alloy and 55 vol.% silicon carbide. Its thermal conductivity is 190–200 W/m K. Its thermal expansion roughly matches e.g. printed circuit boards, FR-4, and Duroid. Its density at 25 °C is 2.96 g/cm3.

AlSiC-12, containing 63 vol.% of A 356.2 aluminium alloy and 37 vol.% silicon carbide. Its thermal conductivity is 170–180 W/m K. It is compatible with generally the same materials as AlSiC-10. Its density at 25 °C is 2.89 g/cm3.AlSiC composites are suitable replacements for copper-molybdenum (CuMo) and copper-tungsten (CuW) alloys; they have about 1/3 the weight of copper, 1/5 of CuMo, and 1/6 of CuW, making them suitable for weight-sensitive applications; they are also stronger and stiffer than copper. They are stiff, lightweight, and strong. They can be used as heatsinks, substrates for power electronics (e.g. IGBTs and high-power LEDs), heat spreaders, housings for electronics, and lids for chips, e.g. microprocessors and ASICs. Metal and ceramic inserts and channels for a coolant can be integrated into the parts during manufacture. AlSiC composites can be produced relatively inexpensively (USD 2-4/lb in large series); the dedicated tooling however causes large up-front expenses, making AlSiC more suitable for mature designs. Heat pipes can be embedded into AlSiC, raising effective heat conductivity to 500–800 W/m K.AlSiC parts are typically manufactured by near net shape approach, by creating a SiC preform by metal injection molding of an SiC-binder slurry, fired to remove the binder, then infiltrated under pressure with molten aluminium. Parts can be made with sufficiently low tolerances to not require further machining. The material is fully dense, without voids, and is hermetic. High stiffness and low density appears making larger parts with thin wall, and manufacturing large fins for heat dissipation. AlSiC can be plated with nickel and nickel-gold, or by other metals by thermal spraying. Ceramic and metal insets can be inserted into the preform before aluminium infiltration, resulting in a hermetic seal. AlSiC can be also prepared by mechanical alloying. When lower degree of SiC content is used, parts can be stamped from AlSiC sheets.

The aluminium matrix contains high amount of dislocations, responsible for the strength of the material. The dislocations are introduced during cooling by the SiC particles, due to their different thermal expansion coefficient.A similar material is Dymalloy, with copper-silver alloy instead of aluminium and diamond instead of silicon carbide. Other materials are copper reinforced with carbon fiber, diamond-reinforced aluminium, reinforced carbon-carbon, and pyrolytic graphite.

Aluminium carbide

Aluminum carbide, chemical formula Al4C3, is a carbide of aluminum. It has the appearance of pale yellow to brown crystals. It is stable up to 1400 °C. It decomposes in water with the production of methane.

Beveled glass

Beveled glass is usually made by taking thick glass and creating an angled surface cut (bevel) around the entire periphery. Bevels act as prisms in sunlight creating an interesting color diffraction which both highlights the glass work and provides a spectrum of colors which would ordinarily be absent in clear float glass.

Beveled glass can be obtained as clusters which are arranged to create a specific design. These can vary from simple three or four piece designs, often used in top lights (commonly known as transoms) of windows and conservatories, to more complex combinations of many pieces, suitable for larger panels such as doors and side screens (known in the door industry as sidelites).

Beveled glass has also been used with clear and colored textured glass to create designs. Textured glass is typically 1/8" thick and has a distinct visible texture. Beveled glass is typical made from 1/4" float plate glass but thicknesses up to 1/2" have been used for larger windows. The width of the bevel also can vary depending on the desired effect. The combination of beveled glass is juxtaposed to the textured glass creating dramatic visual effects.

Modern beveled glass is machine made. The automation of this traditionally hand made craft was facilitated by the development of plastic based metal deburring wheels which provided adequate smoothing of the ground glass face without the difficulties involved with traditional aluminum oxide and natural sandstone smoothing stones. The best natural smoothing stones came from a quarry in Newcastle, England and would be round wheels with a central hole several feet in diameter and 8" thick. The stone's quality was dictated by the consistency of the sandstone, as any imperfection would scratch the glass being smoothed. These large stones would smooth the rough scratches created by the grinding process. The type of grinding and smoothing equipment depended upon whether one was creating straight line, outside or inside curved bevels. Outside curves and straight lines are ground on a flat rotating platter covered in a thin slurry of silicon carbide and water. Inside curves were ground on a silicon carbide grinding wheel of appropriate grit with water running on the wheel. Smoothing the ground face was done using the Newcastle stone for outside curves and straight line bevels and a cone shaped polishing wheel of relatively fine grit aluminum oxide. Despite the advantages of the plastic smoothing wheels, the crispness of the bevel edge is superior on the stone smoothed traditionally beveled pieces and can distinguish hand made beveled glass. The final step was polishing the beveled face using a felt covered wheel with a slurry of water and optical polishing powder. It was not uncommon to have pieces with a combination of outside and inside curve as well as straight line bevels. The objective was to have an even bevel width, even edge thickness with no facets in the bevel face and a crisp bevel edge. In the early 1900s in USA it was not uncommon to see beveled oval door glass 5' in length with 2" wide bevels on 3/8" thick plate glass. Creating such bevels required two craftsmen working as a team.

Carbide

In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by the chemical bonds type as follows: (i) salt-like, (ii) covalent compounds, (iii) interstitial compounds, and (iv) "intermediate" transition metal carbides. Examples include calcium carbide (CaC2), silicon carbide (SiC), tungsten carbide (WC; often called, simply, carbide when referring to machine tooling), and cementite (Fe3C), each used in key industrial applications. The naming of ionic carbides is not systematic.

Cree Inc.

Cree, Inc. is an American manufacturer and marketer of lighting-class LEDs, lighting products and products for power and radio frequency (RF) applications. Most of its products are based on silicon carbide (SiC), a mineral compound which early Cree researchers successfully synthesized in a laboratory.

Diesel particulate filter

A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.

Fiber

Fiber (or fibre in British English, see spelling differences; from the Latin fibra) is a natural or synthetic substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene.

Synthetic fibers can often be produced very cheaply and in large amounts compared to natural fibers, but for clothing natural fibers can give some benefits, such as comfort, over their synthetic counterparts.

Lely method

The Lely method or Lely process is a crystal growth technology used for producing silicon carbide crystals for the semi-conductor industry. The patent for this process was filed in the Netherlands in 1954 and in the United States in 1955 by Jan Anthony Lely of Philips Electronics. The patent was subsequently granted on 30 September 1958, and was refined by D.R. Hamilton et al. in 1960, and by V.P. Novikov and V.I. Ionov in 1968.

Moissanite

Moissanite () is naturally occurring silicon carbide and its various crystalline polymorphs. It has the chemical formula SiC and is a rare mineral, discovered by the French chemist Henri Moissan in 1893. Silicon carbide is useful for commercial and industrial applications due to its hardness, optical properties and thermal conductivity.

Nikasil

Nikasil is a trademarked electrodeposited lipophilic nickel matrix silicon carbide coating for engine components, mainly piston engine cylinder liners.

Polymorphs of silicon carbide

Many compound materials exhibit polymorphism, that is they can exist in different structures called polymorphs. Silicon carbide (SiC) is unique in this regard as more than 250 polymorphs of silicon carbide had been identified by 2006, with some of them having a lattice constant as long as 301.5 nm, about one thousand times the usual SiC lattice spacings.The polymorphs of SiC include various amorphous phases observed in thin films and fibers, as well as a large family of similar crystalline structures called polytypes. They are variations of the same chemical compound that are identical in two dimensions and differ in the third. Thus, they can be viewed as layers stacked in a certain sequence. The atoms of those layers can be arranged in three configurations, A, B or C, to achieve closest packing. The stacking sequence of those configurations defines the crystal structure, where the unit cell is the shortest periodically repeated sequence of the stacking sequence. This description is not unique to SiC, but also applies to other binary tetrahedral materials, such as zinc oxide and cadmium sulfide.

Polysilane

Polysilanes are organosilicon compounds with the formula (R2Si)n. They are relatives of traditional organic polymers but their backbones are composed of silicon atoms. They exhibit distinctive optical and electrical properties. They are mainly used industrially as precursors to silicon carbide.

Reaction bonded silicon carbide

Reaction bonded silicon carbide, also known as siliconized silicon carbide or SiSiC, is a type of silicon carbide that is manufactured by a chemical reaction between porous carbon or graphite with molten silicon. Due to the left over traces of silicon, reaction bonded silicon carbide is often referred to as siliconized silicon carbide, or its abbreviation SiSiC.

If pure silicon carbide is produced by sintering of silicon carbide powder, it usually contains traces of chemicals called sintering aids, which are added to support the sintering process by allowing lower sintering temperatures. This type of silicon carbide is often referred to as sintered silicon carbide, or abbreviated to SSiC.

The silicon carbide powder is gained from silicon carbide produced as described in the article silicon carbide.

Sandpaper

Sandpaper and glasspaper are names used for a type of coated abrasive that consists of sheets of paper or cloth with abrasive material glued to one face.

Despite the use of the names neither sand nor glass are now used in the manufacture of these products as they have been replaced by other abrasives such as aluminium oxide or silicon carbide. Sandpaper is produced in a range of grit sizes and is used to remove material from surfaces, either to make them smoother (for example, in painting and wood finishing), to remove a layer of material (such as old paint), or sometimes to make the surface rougher (for example, as a preparation for gluing). It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper".

The grit size of sandpaper is usually stated as a number that is inversely related to the particle size. A small number such as 20 or 40 indicates a coarse grit, while a large number such as 1500 indicates a fine grit.

Schottky diode

The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

When sufficient forward voltage is applied, a current flows in the forward direction. A silicon diode has a typical forward voltage of 600–700 mV, while the Schottky's forward voltage is 150–450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency.

Silica fume

Silica fume, also known as microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The main field of application is as pozzolanic material for high performance concrete.

It is sometimes confused with fumed silica (also known as pyrogenic silica, CAS number 112945-52-5). However, the production process, particle characteristics and fields of application of fumed silica are all different from those of silica fume.

Silicon carbide fibers

Silicon carbide fibers fibers range from 5–150 micrometres in diameter and composed primarily of silicon carbide molecules. Depending on manufacturing process, they may have some excess silicon or carbon, or have a small amount of oxygen. Relative to organic fibers and some ceramic fibers, silicon carbide fibers have high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. (refs) These properties have made silicon carbide fiber the choice for hot section components in the next generation of gas turbines, e.g. the LEAP engine from GE (General Electric).There are several manufacturing approaches to making silicon carbide fibers. The one with the longest historical experience, invented in 1975 and called the Yajima process, uses a pre-ceramic liquid polymer that is injected through a spinneret to produce solidified green (unfired) fibers that go through a series of processing steps, including significant time in high temperature furnaces to convert the polymer to the desired SiC chemistry. These fibers are typically smaller than 20 microns in diameter and supplied as twisted tows containing 300+ fibers. Several companies employ some variation of this technique, including Nippon Carbon (Japan), Ube Industries (Japan), and the NGS consortium (USA).

A second approach utilizes chemical vapor deposition (CVD) to form silicon carbide on a central core of a dissimilar material as the core traverses a high temperature reactor. Developed by Textron (now Specialty Materials Inc located in Massachusetts) over 40 years ago, the silicon carbide deposit resulting from the gas-phase CVD reaction builds up on a carbon core with a columnar microstructure. The fiber, sold as the SCS product family, is relatively large in diameter, measuring from approximately 80 to 140 microns.Laser-driven CVD (LCVD) is a related approach using multiple laser beams as the energy source to incite the gas phase reaction, with the significant difference that the fibers are grown as-formed and not on any core structure,,. The LCVD fibers are fabricated in a parallel array as each laser beam corresponds to a deposited fiber, with growth rates ranging from 100 microns to over 1 millimeter per second and fiber diameters ranging from 20 to 80 microns. Free Form Fibers, based in upstate New York, has developed the LCVD technology for the past 10 years.

Titanium silicon carbide

Titanium silicon carbide, chemical formula Ti3SiC2, is a material with both metallic and ceramic properties. It is one of the MAX phases.

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