Silicon

Daisy

Apr. 09, 2024

Silicon

Silicon (pronounced /ˈsɪlɪkən/ or /ˈsɪlɪkɒn/, Latin: silicium) is the chemical element that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. As the eighth most common element in the universe by mass, silicon occasionally occurs as the pure free element in nature, but is more widely distributed in dusts, planetoids and planets as various forms of silicon dioxide or silicate. On Earth, silicon is the second most abundant element (after oxygen) in the crust, making up 25.7% of the crust by mass.

Silicon has many industrial uses. Elemental silicon is the principal component of most semiconductor devices, most importantly integrated circuits or microchips. Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than almost all other material combinations.

In the form of silica and silicates, silicon forms useful glasses, cements, and ceramics. It is also a component of silicones, a class-name for various synthetic plastic substances made of silicon, oxygen, carbon and hydrogen, often confused with silicon itself.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatoms.

Notable characteristics

The outer electron orbitals (half filled subshell holding up to eight electrons) have the same structure as in carbon and the two elements are very similar chemically. Even though it is a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) do not affect it. Having four bonding electrons however gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.

Both silicon and carbon are semiconductors, readily either donating or sharing their four outer electrons allowing many different forms of chemical bonding. Pure silicon has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.

In its crystalline form, pure silicon has a gray color and a metallic luster. It is similar to glass in that it is rather strong, very brittle, and prone to chipping.

Occurrence

Measured by mass, silicon makes up 25.7% of the Earth's crust and is the second most abundant element on Earth, after oxygen. Pure silicon crystals are only occasionally found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as silica), and silicate.

Silica occurs in minerals consisting of (practically) pure silicon dioxide in different crystalline forms. Sand, amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal are some of the forms in which silicon dioxide appears. (They are known as "lithogenic", as opposed to "biogenic", silicas.)

Silicon also occurs as silicates (various minerals containing silicon, oxygen and one or another metal), for example feldspar. These minerals occur in clay, sand and various types of rock such as granite and sandstone. Asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.

Silicon is a principal component of aerolites, which are a class of meteoroids, and also is a component of tektites, which are a natural form of glass.

See also Category:Silicate minerals

Isotopes

Main article: isotopes of silicon

Silicon has numerous known isotopes, with mass numbers ranging from 22 to 44. 28Si (the most abundant isotope, at 92.23%), 29Si (4.67%), and 30Si (3.1%) are stable; 32Si is a radioactive isotope produced by argon decay. Its half-life has been determined to be approximately 170 years (0.21 MeV), and it decays by beta - emission to 32P (which has a 14.28 day half-life [5]) and then to 32S.

Compounds

For examples of silicon compounds see silicate, silane (SiH4), silicic acid (H4SiO4), silicon carbide (SiC), silicon dioxide (SiO2), silicon tetrachloride (SiCl4), silicon tetrafluoride (SiF4), and trichlorosilane (HSiCl3).

See also Category:Silicon compounds

Applications

As the second most abundant element in the earth's crust, silicon is vital to the construction industry as a principal constituent of natural stone, glass, concrete and cement. Silicon's greatest impact on the modern world's economy and lifestyle has resulted from its use as the substrate in the manufacture of discrete electronic devices such as power transistors, and in the development of integrated circuits such as computer chips.

Alloys

The largest application of pure silicon (metallurgical grade silicon) is in aluminium-silicon alloys, often called "light alloys", to produce cast parts, mainly for automotive industry. (This represents about 55% of the world consumption of pure silicon.)
Steel and cast iron: Silicon is an important constituent of some steels, and it is used in the production process of cast iron. It is introduced as ferrosilicon or silicocalcium alloys.

In electronic applications

Pure silicon is also used to produce ultra-pure silicon for electronic and photovoltaic applications:
- Semiconductor: Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers. Such control is necessary for transistors, solar cells, microprocessors, semiconductor detectors and other semiconductor devices which are used in electronics and other high-tech applications.
- Photonics: Silicon can be used as a continuous wave Raman laser to produce coherent light. (Though it is ineffective as a light source.)
- LCDs and solar cells: Hydrogenated amorphous silicon is widely used in the production of low-cost, large-area electronics in applications such as LCDs. It has also shown promise for large-area, low-cost thin-film solar cells.

Silicones

The second largest application of silicon (about 40% of world consumption) is as a raw material in the production of silicones, compounds containing silicon-oxygen and silicon-carbon bonds that have the capability to acting as bonding intermediates between glass and organic compounds, and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are used in waterproofing treatments, moulding compounds and mould-release agents, mechanical seals, high temperature greases and waxes, caulking compounds and even in applications as diverse as breast implants and explosives and pyrotechnics [1] .

Construction: Silicon dioxide or silica in the form of sand and clay is an important ingredient of concrete and brick and is also used to produce Portland cement.
Pottery/Enamel is a refractory material used in high-temperature material production and its silicates are used in making enamels and pottery.
Glass: Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and with many different physical properties. Silica is used as a base material to make window glass, containers, insulators, and many other useful objects.
Abrasives: Silicon carbide is one of the most important abrasives.
Silly Putty was originally made by adding boric acid to silicone oil. Now name-brand Silly Putty also contains significant amounts of elemental silicon. (Silicon binds to the silicone and allows the material to bounce 20% higher.)
[citation needed]

See also Category:Silicon compounds

Production

Silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal, in an electric arc furnace using carbon electrodes. At temperatures over 1900 °C, the carbon reduces the silica to silicon according to the chemical equation

SiO2 + C → Si + CO2.

SiO2 + 2C → Si + 2CO.

Liquid silicon collects in the bottom of the furnace, and is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated, as explained by this equation:

2 SiC + SiO2 → 3 Si + 2 CO.

In 2005, metallurgical grade silicon cost about $ 0.77 per pound ($1.70/kg).[6]

Purification

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Historically, a number of methods have been used to produce high-purity silicon.

Physical methods

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity is desired.

Chemical methods

Today, silicon is purified by converting it to a silicon compound that can be more easily purified than in its original state, and then converting that silicon element back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity silicon.

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon according to the chemical equation

SiCl4 + 2 Zn → Si + 2 ZnCl2.

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process.

In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them according to chemical reactions like

2 HSiCl3 → Si + 2 HCl + SiCl4.

Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than 10−9.

In 2006 REC announced construction of a plant based on fluidized bed technology using silane [2].

3SiCl4 + Si + 2H2 → 4HSiCl3

4HSiCl3 → 3SiCl4 + SiH4

SiH4 → Si + 2H2

Crystallization

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. However, silicon single-crystals grown by the Czochralski method contain impurities since the crucible which contains the melt dissolves. For certain electronic devices, particularly those required for high power applications, silicon grown by the Czochralski method is not pure enough. For these applications, float-zone silicon (FZ-Si) can be used instead. It is worth mentioning though, in contrast with CZ-Si method in which the seed is dipped into the silicon melt and the growing crystal is pulled upward, the thin seed crystal in the FZ-Si method sustains the growing crystal as well as the polysilicon rod from the bottom. As a result, it is difficult to grow large size crystals using the float-zone method. Today, all the dislocation-free silicon crystals used in semiconductor industry with diameter 300mm or larger are grown by the Czochralski method with purity level significantly improved.

Different forms of silicon

One can notice the color change in silicon nanopowder. This is caused by the quantum effects which occur in particles of nanometric dimensions. See also Potential well, Quantum dot, and Nanoparticle.

Silicon-based life

See also: Alternative biochemistry

Since silicon is similar to carbon, particularly in its valency, some people have proposed the possibility of silicon-based life. One main detraction for silicon-based life is that unlike carbon, silicon does not have the tendency to form double and triple bonds.

Although there are no known forms of life that rely entirely on silicon-based chemistry, there are some that rely on silicon minerals for specific functions. Some bacteria and other forms of life, such as the protozoa radiolaria, have silicon dioxide skeletons, and the sea urchin has spines made of silicon dioxide. These forms of silicon dioxide are known as biogenic silica. Silicate bacteria use silicates in their metabolism.

Life as we know it could not have developed based on a silicon biochemistry. The main reason for this fact is that life on Earth depends on the carbon cycle: autotrophic entities use carbon dioxide to synthesize organic compounds with carbon, which is then used as food by heterotrophic entities, which produce energy and carbon dioxide from these compounds. If carbon was to be replaced with silicon, there would be a need for a silicon cycle. However, silicon dioxide precipitates in aqueous systems, and cannot be transported among living beings by common biological means.

As such, another solvent would be necessary to sustain silicon-based life forms; it would be difficult (if not impossible) to find another common compound with the unusual properties of water which make it an ideal solvent for carbon-based life. Larger silicon compounds analogous to common hydrocarbon chains (silanes) are also generally unstable owing to the larger atomic radius of silicon and the correspondingly weaker silicon-silicon bond; silanes decompose readily and often violently in the presence of oxygen making them unsuitable for an oxidizing atmosphere such as our own. Silicon also does not readily participate in pi-bonding (the second and third bonds in triple bonds and double bonds are pi-bonds) as its p-orbital electrons experience greater shielding and are less able to take on the necessary geometry. Furthermore, although some silicon rings (cyclosilanes) analogous to common the cycloalkanes formed by carbon have been synthesized, these are largely unknown. Their synthesis suffers from the difficulties inherent in producing any silane compound, whereas carbon will readily form five-, six-, and seven-membered rings by a variety of pathways (the Diels-Alder reaction is one naturally-occurring example), even in the presence of oxygen. Silicon's inability to readily form long silane chains, multiple bonds, and rings severely limits the diversity of compounds that can be synthesized from it. Under known conditions, silicon chemistry simply cannot begin to approach the diversity of organic chemistry, a crucial factor in carbon's role in biology.

However, silicon-based life could be construed as being life which exists under a computational substrate. This concept is yet to be explored in mainstream technology but receives ample coverage by sci-fi authors.

A. G. Cairns-Smith has proposed that the first living organisms to exist were forms of clay minerals—which were probably based around the silicon atom.

History

Silicon was first identified by Antoine Lavoisier in 1787 (as a component of the Latin silex, or silicis (meaning what were more generally termed "the flints" or "Hard Rocks" during the Early Modern era where nowadays as we would say "silica" or "silicates"), and was later mistaken by Humphry Davy in 1800 for a compound. In 1811 Gay-Lussac and Thénard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. It was first discovered as an element by Berzelius in 1823. In 1824, Berzelius prepared amorphous silicon using approximately the same method as Lussac. Berzelius also purified the product by repeatedly washing it.

Because silicon is an important element in semiconductors and high-tech devices, the high-tech region of Silicon Valley, California is named after this element.

References

^ [1], E.-C. Koch, D. Clement, Special Materials in Pyrotechnics: VI. Silicon - An Old Fuel with New Perspectives
^ http://hugin.info/136555/R/1115224/203491.pdf REC presentation to investors accessed 8 July 2007

Los Alamos National Laboratory: Silicon
Elastic Waves in Solids II, Eugène Dieulesaint, Daniel Royer (Springer) 2000 (ISBN 3-540-65931-5) (speed of sound)

What are Polycrystalline Silicon Wafers?

Polycrystalline Silicon, or Multicrystalline Silicon, also called Polysilicon or poly-Si, is a highly purified, polycrystalline form of silicon used as the feedstock in solar PV and electronics industries. Polysilicon, a high-purity form of silicon, is a critical raw material in the supply chain for solar photovoltaics (PVs).

There are four basic types of polycrystalline silicon wafers: single crystalline, multicrystalline, and amorphous. Amorphous material is used in solar cells. Single crystal silicon is the most commonly used type of silicon, as it produces the most efficient solar cells. While monocrystalline silicon can be sliced into small squares, it has a more complex structure. As such, polycrystalline silicon wafers are more efficient than monocrystalline silicon.

Wire-sawing block-cast silicon ingots make polycrystalline silicon wafers into thin slices. They are lightly p-type doped, which results in an array of small, round cells. The n-type dopants are applied to the front surface, forming a p-n junction below the surface. The crystalline silicon is then annealed at high temperatures to make it suitable for solar cells.

In the photovoltaic industry, polycrystalline silicon is the feedstock for conventional solar cells. In 2006, over half of the world's polysilicon was used by PV manufacturers. However, the feedstock shortage in 2007 hampered the solar industry. In 2008, there were only twelve factories that were capable of producing solar-grade polysilicon. Monocrystalline silicon, on the other hand, is more expensive than polycrystalline silicon, and it undergoes additional recrystallization by the Czochralski method.

Single-crystal silicon (monocrystalline) is the most common type of silicon. Single-crystal silicon has no grain boundaries and a homogeneous structure. Large single crystals are rare and difficult to produce in the laboratory. Amorphous silicon, on the other hand, is amorphous. It lacks order on the atomic level. It has a random structure and is highly conductive when formed.

Single-crystal silicon wafers are more expensive and difficult to process. But these polycrystalline silicon wafers can be fabricated into a variety of shapes and sizes. They can be used as gate electrode material for MOS devices. And because they have a very high electrical conductivity, they are an important part of photovoltaic technology. But what are Polycrystalline Silicon Wafers? You'll be pleasantly surprised to find that they are both inexpensive and versatile.

Monocrystalline silicon is the most common type of silicon. It is a single-crystal material. In nature, it is a homogenous, single-crystalline material with no grain boundaries. In the lab, it's extremely difficult to make single-crystal silicon. The amorphous form is highly disordered and has no structure at all. As a result, it is hard to produce.

The main difference between monocrystalline and polycrystalline silicon is in the amount of silicon. For example, Poly-Si is made of small grains of monocrystalline silicon. It is highly uniform and is cheaper than monocrystalline silicon. It is a very important component of solar cells. It is used in most electronic devices in the world, including solar panels, semiconductors, and transistors. When the latter are used, they are nearly identical to those made with monocrystalline silicon.

Polycrystalline silicon wafers are made of small grains of monocrystalline silicon. Monocrystalline silicon wafers are used in photovoltaic cells, while polycrystalline silicon is used for solar energy. Metallurgical silicon is fine for making metal alloys, but it is not graded for use in electrical components. It is used for a wide range of purposes, including high-tech gadgets, and can be reused.

Polycrystalline silicon wafers are the most common form of solar PV materials. They are the most popular type of solar PV material and are crucial to the manufacturing process. It can be used in a variety of different applications, and it has many uses. Its purity makes it an important component of photovoltaic technology. It can be found in a variety of applications. It is also used in other forms, such as solar modules.

What are Advantages do Polycrystalline Silicon Have?

The main advantage of Polycrystalline Silicon is its lower cost. Compared to Monocrystalline Silicon, Polycrystalline Silicon is easier to produce and is significantly less expensive. In addition, its durability is comparable to that of a monocrystalline module. Despite the disadvantages, Polycrystalline Solar Cells are a low-cost way to create a solar photovoltaic system. The low price of Polycrystalline Silicon could make solar power more affordable for those who do not have access to monocrystalline silicon cells.

One of the most important advantages of Polycrystalline Silicon is its high purity. It is the cheapest source of silicon on the market, which is why it is the most common and widely used. It is also the most popular material for solar PV due to its low cost. It is essential for photovoltaic cells, and it is an important part of photovoltaic technology. You can find polycrystalline Silicon in many different applications, from LED lights to solar panels.

The demand for Polycrystalline Silicon soared to an all-time high in the past two decades. Since 1995, semiconductor demand has doubled from 13,600 MT to 28,000 MT, and the demand for solar PV modules has tripled every 2.7 years. Today, the demand for Polycrystalline Silicon has risen to 420,000 MT. In 20 years, demand for Polycrystalline Silicon will reach the equivalent of 28,000 MT of copper.

Polycrystalline Silicon is an important material for solar panels because it can be manufactured in near-pure form. Its high purity makes it ideal for solar panels, as it can produce nearly the same amount of energy as pure single crystal silicon. Its use in this industry is far-reaching and has become vital to the global economy. For example, it is used in microwaves, radios, and watches. It is also found in all electronic devices, from small components to the controls of automobiles.

Polycrystalline Silicon is used in the manufacturing of semiconductors. It can be used as a gate electrode material in MOS devices. Metal silicides can increase the electrical conductivity of polysilicon. It can also be used as a conductor and resistor. It can also be used as an ohmic contact in shallow junctions. Its electrical conductivity is higher than single crystal silicon, but it is more expensive.

In the photovoltaic industry, Polycrystalline Silicon is the primary feedstock in conventional solar cells. It is used for the manufacturing of conventional solar cells. In 2006, over half of the polysilicon in the world was consumed by PV manufacturers. During the year 2008, the shortage of the chemical material crippled the solar industry. It is much more expensive and less efficient than monocrystalline silicon. It is also more difficult to obtain.

The rate of polysilicon deposition increases with temperature. As a result, the activation energy of polysilicon is 1.7 eV. As a result, the rate of polysilicon deposition is faster than the unreacted silane at the surface. The higher the temperature, the higher the rate of polysilicon deposition. As a result, the price of the chemical compound fell drastically in the past several years.

Single-crystal silicon, also known as monocrystalline, is the most common type of Silicon. Its homogeneous structure can be recognized by its external colouring. The material is a continuous crystal with no grain boundaries. Large single-crystals are very rare in nature and are extremely difficult to produce in the laboratory. In contrast, amorphous structures are highly disordered and have little order. Further, their atomic-scale structure is not uniform and lacks order.

While the production of polycrystalline silicon has risen dramatically in recent years, China has recently tripled its production output from 2008 levels. By 2012, China's total output is projected to reach around three hundred thousand tons. In fact, the earth's crust is made up of 26 percent of siliceous minerals containing silicon. In the past, the Earth has had limited amounts of polycrystalline silicon, but it's now a popular alternative for a wide range of applications.

Polysilicon Applications

Among its many applications in the semiconductor industry, polysilicon is a popular gate electrode material for MOS devices. By adding a metal silicide or a metal layer over the polysilicon gate, it increases its electrical conductivity. In addition to its gate electrode function, polysilicon is also a good resistor and ohmic contact in shallow junctions. The doping process can increase or decrease its electrical conductivity according to the application and the required resistance or conductivity.

While the underlying chemical reactions for the polysilicon deposition process are relatively straightforward, the overall chemistry is complex. The reaction rate of polysilicon is often governed by the concentration of reactants and the rate at which the gas flows. In contrast, a process involving the introduction of dopants can alter the grain size and orientation of the deposited polysilicon. In addition to its efficiency, the deposition process is very cost-efficient and produces high-quality materials.

Typical properties of polysilicon are its crystalline structure. This means that it is composed of silicon grains, or crystals. The grains typically contain millions of atoms and are arranged in a periodic structure. Unlike amorphous silicon, which is not a solid, amorphous silicon has no discernible periodic structure. It can be created by adding hydrogen or by hydrodegenation. Depending on the application, amorphous silicon is easily deposited on a large surface.

When the polysilicon undergoes oxidation, it becomes a crystal. The oxidation process occurs because phosphorus is dissolved in the silicon. This is a necessary step to make the polysilicon semiconductor. However, it is important to note that the growth of polysilicon is regulated by a variety of factors. One of these factors is the degree of amorphousness. Amorphous polysilicon will have more crystalline than amorphous silicon.

The process of removing polysilicon crystals requires a high temperature. The process requires a vacuum chamber for the process to be successful. During the oxidation process, abrasives are incorporated in a special chemical called abrasive. The additives in these processes improve the surface quality of polysilicon by increasing their adhesion strength. This is a critical step for making silicon semiconductors.

What is The Size of the Polysilicon Market

The polysilicon industry has become increasingly consolidated in recent years. The top five companies in the industry will account for 73% of global production in 2020, up from 60% in 2008. This has led to a decline in local producers and an increase in polysilicon imports. Sino-American companies are the largest producer of polysilicon in the world. They are also the biggest consumers of polysilicon in the world. So, if you're looking for a high-quality product at a low price, a higher price is the answer.

The process of doping polysilicon involves using heavily-doped glass on an undoped silicon wafer. The dopants are then dissolved in the glass, which is heated to 900 or more. This process makes the polysilicon layer annealed at a high temperature. Aside from the high temperature required in the process, it also allows for the incorporation of other substances, such as boronium.

The most common method for obtaining polysilicon is through low pressure chemical vapor deposition. Unlike other types of materials, Poly-Si is inexpensive and can be obtained at relatively low levels. Some Poly-Si uses include diffusion and electrical isolation. For other applications, the polysilicon is doped after the deposition process to enhance its performance. This process is a great choice if you're looking for a highly uniform layer of polysilicon.

In addition to its benefits, polysilicon has many applications in electronics. It boosts the performance of solar cells and semiconductors. It is also used as a base material for crystalline silicon solar cells. Whether you need a small or large quantity, polysilicon will provide you with the right material for your application. The benefits of polysilicon are endless. The material can be used for a variety of different applications, and is a great alternative to conventional crystalline silicon.

Polysilicon is an excellent material for flexible screens. It can be deposited on a variety of plastic substrates. The use of epitaxial growth tools is another technique. In contrast to PECVD, sputter deposition is a relatively new technique used to deposit a-Si without melting it. The resulting film can be removed with XeF2 gas. Regardless of the method of deposition, polysilicon is an ideal material for electronics.

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