Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. It belongs to group 14 of the periodic table and is commonly classified as a metalloid. Elemental silicon is a solid with a blue-grey metallic appearance and is an important semiconductor. In nature, it occurs predominantly in oxygen-containing compounds rather than as the free element. (periodic-table.rsc.org)

Atomic and physical properties

A neutral silicon atom contains 14 electrons, with the electron configuration [Ne] 3s² 3p². Its four outer-shell electrons account for its capacity to form four bonds. Selected properties of the ordinary crystalline material are listed below. (periodic-table.rsc.org)

The atomic-weight interval reflects natural variation in isotopic composition; the other values describe specified forms and conditions rather than every possible silicon sample. (periodic-table.rsc.org)

In the diamond-cubic structure, each atom has four nearest neighbours arranged tetrahedrally. This extended covalent bonding network is the structural basis of crystalline silicon. Its lattice spacing and atomic density can be measured accurately, making high-quality silicon crystals useful in precision measurement. (ioffe.ru)

Natural silicon has three stable isotopes: silicon-28, silicon-29, and silicon-30. Representative abundances are approximately 92.22%, 4.69%, and 3.09%, respectively. All have 14 protons but differ in their numbers of neutrons. (pml.nist.gov)

Occurrence and important compounds

Silicon constitutes about 28% of Earth’s crust by mass, making it the second most abundant crustal element after oxygen. Its principal natural forms are silicon dioxide and silicate minerals. Silicon dioxide, also called silica, has the formula SiO₂; quartz is its most common natural crystalline form. Silicate minerals include feldspars and micas and are major constituents of many rocks. (periodic-table.rsc.org)

Three similar-looking terms denote different substances:

• Silicon is the chemical element, or the elemental material.
• Silica is silicon dioxide, a compound of silicon and oxygen.
• Silicones are a family of silicon–oxygen polymers with attached organic groups, used in oils, elastomers, and sealants.

Silica and silicate materials are important in glass, ceramics, cement, and construction; silicones are chemically and functionally distinct from both elemental silicon and mineral silica. (periodic-table.rsc.org)

Silicon carbide, SiC, is another important silicon compound. It is used as an abrasive and is itself a semiconductor. Its electronic properties differ substantially from those of elemental silicon: for example, the 4H crystal form has a room-temperature band gap of about 3.23 eV, considerably wider than silicon’s. (periodic-table.rsc.org)

Semiconductor behaviour

Silicon’s electronic behaviour follows from its electronic band structure. An electron must acquire sufficient energy to cross the band gap from the valence band into the conduction band, leaving an electron hole behind. Electrons and holes can then carry electric current. The gap decreases with increasing temperature, while the intrinsic carrier concentration rises strongly. (ioffe.ru)

Electrical properties can be adjusted by doping—introducing controlled quantities of impurities. Donors such as phosphorus provide n-type material, in which electrons are the majority carriers; acceptors such as boron provide p-type material, in which holes are the majority carriers. The arrangement of differently doped regions is central to silicon electronic devices. (periodic-table.rsc.org)

Silicon has an indirect band gap: its valence-band maximum and conduction-band minimum occur at different crystal momenta. Consequently, transitions near the gap generally involve lattice vibrations as well as light. This makes ordinary silicon a comparatively inefficient light emitter, although it remains an effective absorber for photovoltaic devices. (ioffe.ru)

A particularly useful feature of silicon technology is its compatibility with insulating silicon dioxide. Traditional metal–oxide–semiconductor field-effect transistors use an oxide-based dielectric between the gate and semiconductor; the gate voltage controls conduction through the silicon channel. Silicon-on-insulator devices and three-dimensional transistor structures use different geometries to improve isolation or electrostatic control. (tsapps.nist.gov)

Production and material forms

Industrial production begins by reducing silica with carbon in an electric furnace. The resulting material requires further purification for electronic applications. High-purity silicon can be obtained through purified volatile precursors such as trichlorosilane, followed by deposition and recrystallization. Ordinary industrial silicon and semiconductor-grade silicon therefore differ chiefly in impurity control and subsequent processing. (periodic-table.rsc.org)

For crystalline photovoltaic manufacture, purified silicon is melted and grown into ingots. Single-crystal ingots can be pulled from the melt and then sliced into thin wafers using diamond-wire saws. The wafers undergo further processing to create electrically active regions, surface coatings, and contacts. (energy.gov)

Silicon used in devices takes several material forms:

• Monocrystalline silicon has a continuous crystal lattice and is widely used in wafer-based devices.
• Polycrystalline silicon contains multiple crystalline grains.
• Amorphous silicon lacks long-range crystalline order and is used in thin-film photovoltaic devices.

These forms are not interchangeable: crystal structure, defects, and manufacturing methods affect charge transport and device performance. (energy.gov)

Applications and limitations

High-purity silicon supports the manufacture of transistors and integrated circuits. Doping, insulating layers, and device geometry allow the same base material to perform different electrical functions. Silicon’s role in electronics depends on this controllability, not on high electrical conductivity alone. (periodic-table.rsc.org)

Silicon is also the most widely used semiconductor absorber in solar cells. Absorbed light generates charge carriers that the device collects as electrical current. Crystalline photovoltaic modules combine processed cells with electrical interconnections, protective glass and polymer layers, and supporting frames. Conversion performance depends on absorption, carrier collection, surface treatment, and losses within the device. (energy.gov)

Outside electronics, silicon is used in aluminium–silicon alloys and ferrosilicon, including metallurgical applications such as steel deoxidation. These uses do not require the exceptional purity demanded by semiconductor devices. (periodic-table.rsc.org)

Isotopically enriched silicon is investigated for quantum computing. Silicon-28 has zero nuclear spin, whereas silicon-29 has spin ½. Reducing silicon-29 content can lessen interactions that disturb spin-based qubits, although isotopic enrichment is distinct from removing chemical impurities. (nist.gov)

History

The name derives from the Latin silex or silicis, referring to flint. Jöns Jacob Berzelius is generally credited with isolating and characterizing silicon in 1824. Henri Sainte-Claire Deville prepared crystalline silicon in 1854. These developments distinguished the element from its long-familiar mineral compounds. (pubchem.ncbi.nlm.nih.gov)

Biological occurrence and occupational hazards

Silicon has a biological role in organisms that form silica structures. Diatoms, for example, require silicon to build their opaline shells and take it up from water in the form of dissolved silicic acid, Si(OH)₄. Their uptake can also alter the isotopic composition of dissolved silicon. (pubchem.ncbi.nlm.nih.gov)

The best-established occupational hazard associated with silicon-containing materials is inhalation of respirable crystalline silica, rather than exposure to silicon as an element. Cutting, grinding, or drilling silica-bearing stone and construction materials can produce particles small enough to reach deep into the lungs. Such exposure can cause silicosis and is associated with other serious diseases, including lung cancer. These risks depend on the compound, particle size, and exposure conditions; they cannot be inferred from the presence of silicon alone. (cdc.gov)

References

1. Silicon - Element information, properties and uses | Periodic Tableperiodic-table.rsc.org
2. Redefining the Molenist.gov
3. Atomic Weights and Isotopic Compositions for Siliconpml.nist.gov
4. Silicon | Si (Element) - PubChempubchem.ncbi.nlm.nih.gov
5. Crystalline Silicon Photovoltaics Researchenergy.gov
6. Solar Photovoltaic Cell Basicsenergy.gov
7. Review article on silicon transistors and emerging technologiestsapps.nist.gov
8. Enriched Silicon and Devices for Quantum Informationnist.gov
9. WebElements Periodic Table » Silicon » historical informationwinter.group.shef.ac.uk