Silicon is a discreet chemical element, but it is omnipresent and essential to our daily lives. Found in the Earth’s crust in the form of silica or silicates, it is a component of rocks, sand and glass, as well as the most advanced electronic components. Its importance in key sectors such as electronics, solar energy, construction and healthcare is often overlooked by the public. Yet without it, there would be no mobile phones, computers or solar panels. Thanks to its exceptional semiconductor properties, it has enabled the development of microelectronics and, with it, the digital age. This text offers a scientific and technological journey through the many facets of silicon, from its cosmic origins to its cutting-edge applications.

1. Silicon, a discrete but omnipresent element

Among the chemical elements found in nature, silicon occupies a discreet yet central place in the history of science and modern industry (Figure 1). Discovered in its elemental form in 1824 by Swedish chemist Jöns Jacob Berzelius, silicon (chemical symbol Si) is now recognised not only for its abundance, but also for its fundamental role in fields as diverse as electronics, energy, construction and even biology.

Silicon, along with oxygen, is the basic element of clay and most rocks, in the form of silicates or silica (SiO₂). In its pure elemental state, silicon is very rarely found in nature. Traces have been identified in certain meteorites or mineral inclusions, but these remain exceptional.

However, thanks to scientific advances in the 19^th and 20^th centuries, researchers have developed sophisticated purification methods to obtain ultra-pure silicon, which is essential for the manufacture of semiconductors. This material has become the backbone of information technology development, to such an extent that Silicon Valley near San Francisco, the cradle of digital innovation, owes its name to this element. Beyond electronic components, silicon is used in MEMS sensors, miniature electromechanical systems that integrate sensors and actuators on a chip. These sensors are used in airbags, smartphones and medical devices, among other applications.

But silicon’s importance isn’t limited to the world of electronics. In the construction industry, silica has been used since ancient times in the manufacture of cement, glass and ceramics. In the health sector, silicones, which are silicon-based polymers, are used in medical devices, prosthetics and cosmetics. In biology, although silicon is not an essential element for all organisms, certain species, such as diatoms and some plants such as horsetails, use this element to strengthen their cell structures.

Ultimately, silicon is much more than just a chemical element: it has become a pillar of scientific and economic progress, a vector of modernity and a symbol of human innovation. Understanding its nature, applications, challenges and prospects is therefore essential to grasping the dynamics of the contemporary world and anticipating the future transformations of our technological societies.

2. The use of silicon, a long story

2.1 Early uses

Silicon is omnipresent in nature. In the form of silicon dioxide (SiO₂) or silicates, it makes up nearly 28% of the Earth’s crust, making it the second most abundant element after oxygen.

The use of flint is at the heart of the primitive history of humanity. The name silicon derives from the Latin silex or silicis, meaning ‘flint’ or ‘hard stone’. Clay has also been used since the dawn of humanity (see Clay: a natural and surprising nanomaterial). Its transformation into terracotta and ceramics dates back at least 20,000 years. The Egyptians and Romans already made glass from sand (mainly silicon dioxide) by heating it with soda and lime at a temperature of around 1,000°C (see Glass: a material for eternity).

2.2 The isolation of silicon

In 1824, Swedish chemist Jöns Jacob Berzelius succeeded in isolating pure silicon for the first time. He heated potassium fluorosilicate (K₂SiF₆) with metallic potassium, producing brown amorphous silicon. His work was fundamental to the further development of inorganic chemistry.

However, crystalline silicon, which is the form we use for semiconductors, was not produced until much later. The production of pure, structured silicon crystals relies on the advances in metallurgy and chemistry of the 20^th century.

2.3 Industrial advances

Throughout the 19^th and early 20^th centuries, silicon was mainly used in the manufacture of steel and certain alloys, improving their strength and durability.

It was in the first half of the 20^th century that researchers began to explore its unique electrical properties. In the 1940s, the development of the first transistor used germanium (another semiconductor) because it was easier to purify. However, scientists soon realised that silicon, due to its abundance and better thermal properties, was a more promising choice. Its good thermal conductivity allows heat to be dissipated, and its low expansion limits mechanical stress.

2.4 The electronic revolution

The real turning point for silicon came in the 1950s thanks to the work of William Shockley and his colleagues, who invented the transistor. Texas Instruments and Fairchild Semiconductor were among the first companies to produce silicon-based transistors.

In 1958, Jack Kilby developed the first integrated circuit, ushering in the era of microprocessors. Silicon then became established as the basic material for microelectronics, thanks to techniques such as epitaxial growthProcess which consists of producing a single crystal, a periodic stack of atoms or molecules, by aligning it with a pre-existing single crystal substrate. Molecular beam epitaxy is used to manufacture single-crystal semiconductor layers on a silicon wafer. The technique involves projecting a vapour produced by vacuum evaporation onto the substrate. Under appropriate gas flow and temperature conditions, the atoms gradually deposit on the single crystal substrate and align themselves with the periodic pattern of the silicon atoms, forming a crystalline layer that mirrors the substrate. and photolithographySet of operations used to etch a substrate by reproducing an image, a technique used in the manufacture of electronic integrated circuits. In the first step, a light-sensitive resin (photoresin) is deposited as a thin film on the surface of a substrate, such as a silicon wafer. It is then exposed to light by projecting a mask made up of opaque and transparent areas, designed according to the pattern to be reproduced. The irradiated resin is sensitive to dissolution by a solvent, or conversely made resistant (depending on the type of resin chosen), which allows circuits to be etched in the image of the projected mask.. These techniques produce crystals by evaporating thin layers onto the silicon substrate under vacuum, combined with selective chemical etching to draw circuits.

Silicon was particularly well suited to these industrial processes: it could be transformed into monocrystals of exceptional purity using the Czochralski method (see section 5), enabling the production of silicon wafers (Figure 2) that were perfectly suited to the semiconductor industry.

2.5 Silicon today

Today, almost all microprocessors, electronic chips and solar panels are made from silicon. Its electronic properties, in particular the ease with which its conductivity can be modified by doping (adding impurities such as boron or phosphorus), make it an irreplaceable material for manufacturing diodes, transistors, photovoltaic cells and integrated circuits.

In industry, silicon is used in many alloys, particularly aluminium-silicon alloys used in the automotive and aerospace industries for their lightness and strength. In chemistry, it is the basis for the manufacture of silicones, flexible and resistant synthetic polymers used in cosmetics, medical devices, waterproofing and construction.

Finally, in materials science and fundamental research, silicon is a model for understanding crystal structures, electronic interactions and the behaviour of materials at the nanometre scale. At this scale, quantum mechanical effects come into play, opening up the possibility of developing quantum computers [1] based on completely new principles.

The versatility of silicon, combined with its natural abundance, makes it one of the most strategic elements of the current technological era.

3. The origin and natural abundance of silicon

Silicon is one of the most fundamental elements in the universe, both in terms of its abundance and its role in the composition of rocky planets such as Earth. Its cosmic origin, abundance in the Earth’s crust and multiple natural forms make it a central player in planetary chemistry and geology.

3.1 Cosmic origin

Silicon has its roots in the most spectacular nuclear processes in the universe: stellar fusion reactions. Inside massive stars, during the final stages of their lives, oxygen nuclei (8 protons) and carbon nuclei (6 protons) fuse under extreme temperatures and pressures to form silicon (14 protons). This phase often precedes the final collapse of the star in the form of a supernova.

During a supernova explosion, massive amounts of silicon, along with other heavy elements, are scattered into interstellar space. These materials enrich gas and dust nebulae, serving as raw material for the formation of new stars, planets and celestial bodies. Thus, all the silicon on Earth (like most elements) is literally a legacy of dead stars.

3.2 Abundance on Earth and the Universe

Silicon is the eighth most abundant element in the universe in terms of mass, after hydrogen, helium, oxygen, carbon, neon, iron and nitrogen. Its high nuclear stability and role in nucleosynthesis processes explain its cosmic abundance.

Silicon is therefore an essential element of all rocky planets. It is found in meteorites called chondrites, in combination with oxygen, magnesium and iron.

Silicon is therefore the second most abundant element in the Earth’s crust, in the form of silicate minerals. It accounts for 27.7% of its mass, just behind oxygen (46.6%). Deeper down, the Earth’s mantle is also composed mainly of silicates, particularly in the form of olivine and pyroxenes. The Earth’s core is a metal alloy based on iron. However, it may also contain silicon, but in much smaller proportions than in the upper layers.

It should be noted that despite its abundance on the surface, silicon is virtually absent from the Earth’s atmosphere. Its presence is almost exclusively limited to fine mineral dust in suspension. These mineral particles can have harmful effects on human respiratory health. This is the well-known case of asbestos, a form of fibrous silicate extracted from rocks.

3.3. Main mineral forms

In its natural state, silicon almost never exists in its free elemental form. It is mainly found in the form of silicon dioxide (SiO₂) and complex silicates. Its main mineral forms are:

• Quartz (SiO₂, Figure 3A): a very common mineral and the main component of sand and many rocks. There are several microcrystalline varieties, such as chalcedony, jasper and agate.
• Feldspar (e.g. orthoclase, albite, Figure 3B): silicates of aluminium, potassium, sodium or calcium.
• Micas, pyroxenes, amphiboles: other groups of silicate minerals found in igneous, metamorphic and sedimentary rocks.
• Igneous rocks such as granite (Figure 3C) are rich in quartz and feldspars.
• Sands, clays and other sediments are largely made up of quartz grains

In soils, silicon is a component of clay minerals, which are essential for soil fertility. Clay soils retain water and the minerals necessary for plant growth (however, an excess of clay can lead to harmful compaction).

3.4 Silicon cycle

Silicon participates in a natural biogeochemical cycle. In the oceans, certain microscopic algae, known as diatoms, build shells made of hydrated silica (See The Tara Oceans expedition explores the diversity of plankton). When these organisms die, their shells fall to the bottom of the ocean and contribute to silica-rich sediments, thus perpetuating the natural silicon cycle [2].

Although silicon is not as vital an element as carbon or nitrogen for terrestrial life forms, it plays an important role in certain biological structures. In addition to diatoms, plants such as grasses accumulate silicon in their tissues to strengthen their structure against attacks from herbivores and environmental stress [3]. Silicon is then returned to the soil and dissolved in rivers, contributing to the terrestrial silicon cycle [4].

4. The physical and chemical properties of silicon

The unique physical and chemical properties of silicon explain its importance in the electronics, photovoltaic and even construction industries. Let’s explore its fundamental characteristics.

4.1 The element silicon

Silicon is the chemical element with atomic number 14, meaning that its nucleus is composed of 14 protons, associated with 14 electrons in the neutral atom. The nucleus also contains neutrons, 14 in the dominant form, so that the mass number is 28, which is denoted ²⁸Si. The isotopes ²⁹S and ³⁰S, containing one or two additional neutrons, are also present in small proportions (5 and 3% respectively).

As in all atoms, the electrons are arranged in concentric layers. The first layer is complete with two electrons, as is the second layer with eight electrons. The remaining four electrons are located on an incomplete outer layer and can thus pair with those of neighbouring atoms to form four chemical bonds. The chemical properties are therefore similar to those of carbon, which also has four peripheral electrons (out of a total of six).

The crystalline form of pure silicon is therefore similar to that of diamond, with each atom forming four bonds with its neighbours in the form of a tetrahedron. These tetrahedrons stack to form a structure called a ‘face-centred cubic’ structure, shown in Figure 5.

In this pure crystal form, silicon has a density of 2.33 g/cm³, making it lighter than metals such as iron or copper, but denser than most organic materials. This is due to its intermediate atomic mass. The density of silicate rocks is also close to 2.5 g/cm³.

4.2 Thermal and electrical properties

Silicon melts at 1,414 °C and boils at 3,265 °C. It has good thermal conductivity: 150 W/m·K for monocrystalline silicon, which is almost half that of copper. This helps dissipate heat in electronic devices. Its thermal expansion is low, which is an advantage for applications requiring dimensional stability.

Pure silicon is bluish-grey and has a slightly shiny metallic appearance (Figure 6). In thin layers, it is partially transparent, particularly at certain infrared wavelengths, which is exploited in optoelectronic devices.

These optical properties are related to its electrical properties. Silicon is an intrinsic semiconductor. This means that in its pure state, it partially conducts electricity, especially when exposed to heat or light. Under the effect of thermal agitation, the outer electrons have a small probability of escaping and moving freely through the crystal, allowing electrical conduction. These electrons are said to ‘jump the band gap’. At a temperature of 300 degrees Kelvin (27 °C), this band gap is 1.12 eV (electron volts), which is the kinetic energy that an electron must have to overcome a potential difference of 1.12 volts.

This energy barrier is about ten times greater than the average energy of electrons associated with thermal agitation at normal temperatures, so the probability of spontaneous crossing is negligible. Conductivity therefore remains very low in pure silicon (one billion times lower than that of copper). However, the conductivity of silicon can be modified by doping, i.e. introducing impurities such as phosphorus or boron. The former introduces conduction electrons, which are negative charges (n-doping), while the latter absorbs electrons (p-doping). This makes it possible to produce a diode, which conducts electrons from the n-doped zone to the p-doped zone, but not in the opposite direction. In a transistor, this current is also controlled by a third electrode, which therefore acts as an electrical switch. This is the basis of all electronic and computer systems. In photovoltaic cells, the energy released is provided by light photons, which have an energy of approximately 2 eV for visible light. This is what enables the efficient conversion of light energy into electrical energy.

It should be noted that these electronic properties are very sensitive to the initial purity and quality of the crystal. When exposed to high doses of radiation (e.g. in satellites or nuclear reactors), silicon can develop defects in its crystal structure, altering its electronic properties. Intensive research is being conducted to understand and limit these effects.

4.3 Chemical reactivity

In its pure form, silicon is relatively inert at room temperature. It does not react with air or cold water. This is due to the formation of a thin layer of silicon oxide (SiO₂) on its surface, which protects the underlying material from further oxidation, a behaviour similar to the passivation of aluminium.

At temperatures above approximately 700°C, silicon reacts with oxygen to form silicon dioxide (SiO₂). Silicon also reacts with halogens (fluorine, chlorine, bromine, iodine) at moderate temperatures to form silicon halides such as SiCl₄, which are very useful in the chemical industry.

Silicon is resistant to most acids (even concentrated ones), with the exception of hydrofluoric acid (HF), which attacks the SiO₂ layer to form soluble complexes. Silicon reacts with concentrated hot strong bases (such as sodium hydroxide NaOH) to form soluble silicates and release hydrogen gas.

Silicon forms a wide range of compounds:

• Silicates: combinations of silicon, oxygen and metals such as aluminium, magnesium, calcium, sodium or potassium. These are the main constituents of rocks.
• Silicon carbide (SiC): extremely hard and resistant, used in abrasives and power semiconductors.
• Polysilanes: polymers containing Si-Si chains, with applications in advanced electronics. They are analogous to organic polymers, with silicon atoms playing the role of carbon.
• Silicones: polymers based on chains of Si-O-Si-O.

In summary, silicon is a material with a unique combination of physical properties (controllable semiconductivity, thermal stability, mechanical strength) and chemical properties (modulated reactivity, formation of protective oxides) that make it a pillar of modern industry. Its ability to adapt to different chemical and physical environments ensures that it has a bright future in many emerging applications.

5. The development of silicon, from silica to microprocessors

The production of silicon is a complex process that transforms a naturally abundant material, silica (silicon dioxide, SiO₂), into an ultra-pure material that is essential for modern electronics. Silica is very abundant as the main component of sand, but the industry extracts it from quartz mines for greater purity [5]. The process begins with the chemical reduction of silicon dioxide. In practice, silica is heated to a very high temperature (2,000 °C) in the presence of carbon (in the form of coke) in electric furnaces to obtain metallurgical silicon, according to the reaction SiO₂ + 2C → Si + 2CO.

This raw silicon, which is generally around 98–99% pure, is insufficient for electronic applications (see Figure 3). It is therefore purified using a method called the Siemens process: the silicon is first converted into gaseous trichlorosilane (HSiCl₃), which is then purified by fractional distillation. This purified gas is then decomposed by heating in a high-temperature reactor to redeposit extremely pure silicon (99.9999999% pure, or ‘9N’ purity). The silicon obtained in this way is amorphous or polycrystalline.

To obtain a single crystal, which is essential for electronic components, the Czochralski process is used, as shown in Figure 7: a crystal seed is immersed in molten silicon and slowly withdrawn while rotating, forming a long monocrystalline cylinder (ingot, Figure 8) called a ‘ball’. This ingot is then cut into thin slices, called wafers, which are a few millimetres thick (Figure 8). These wafers are then polished and treated to serve as substrates for integrated circuits (see Figure 7) [6].

During the manufacture of electronic devices, silicon is ‘doped’ by introducing elements such as phosphorus (n-type) or boron (p-type), which precisely adjusts its electrical conductivity.

The production of photovoltaic silicon follows similar steps, but tolerates slightly lower purity, with an emphasis on the production of multicrystalline silicon for cost reasons. Today, the industry is exploring alternative techniques such as directional casting or the manufacture of thin sheets directly from the molten bath to reduce material losses and improve energy efficiency. In short, silicon production represents the perfect combination of industrial chemistry, precision metallurgy and mastery of crystallographic processes.

6. Economic and environmental challenges

Silicon plays a crucial role in the global economy, both through its direct contribution to key industrial sectors and through the strategic dynamics it induces at the geopolitical level. As the main base material for the semiconductor industry, silicon fuels an extremely broad value chain that encompasses the design of electronic chips, the manufacture of integrated circuits (Figure 9), and their integration into everyday consumer products such as smartphones, computers, connected vehicles and medical equipment. This industry, which is worth several hundred billion euros, is at the heart of the digital economy and technological innovation. In 2019, global production reached 4 million tonnes, distributed according to flows specified in a BRGM report [7]. Electronic and photovoltaic applications account for less than half of this, with more traditional uses in metal alloys and silicone synthesis remaining dominant in terms of volume.

Most silicon is produced in China (over 60%), followed by Russia, the United States and Norway. Refining, particularly for electronic silicon (9N), is dominated by a few industrial players. Each stage, from mining to reduction, purification and crystallisation, has an environmental impact. The production of raw silicon requires 11 kWh/kg of energy, which is close to the energy required for aluminium production. However, approximately 150 kWh/kg of energy is required to achieve the purity required for electronic silicon [8], to which must be added the energy for conversion into monocrystalline ingots and cutting. The environmental impact of this energy consumption, particularly CO₂ emissions, depends greatly on the location of production.

Beyond energy resources, silicon extraction causes landscape degradation, fine dust and sometimes damage to local biodiversity. The purification of silicon, particularly to obtain electronic-grade or solar-grade silicon, requires very high temperatures (up to 2,000°C) and the use of chemical reagents (such as trichlorosilane or chlorine), which are sources of air and water pollution if emissions are not properly controlled. Cleaning wafers before processing requires large quantities of ultra-pure water, typically 20 litres/cm², but this water is returned to the environment without contamination (and even purified).

The main processing sites are in China (the world leader), the United States, Germany, Japan and, more recently, Vietnam and Malaysia. Another source of environmental impact is linked to the management of electronic waste, which contains large quantities of silicon. The recycling of components remains insufficient on a global scale, partly due to the complexity of dismantling printed circuit boards.

Finally, factories producing wafers or solar cells can generate chemical effluents (acids, solvents) if they are not properly treated. Thus, despite its beneficial uses (solar energy, digital technology), the silicon industry must rise to the challenge of reducing its ecological footprint by developing cleaner production processes and strengthening recycling capacities worldwide. Recycling remains low given the abundance of the resource, but it is progressing, particularly for solar panels.

Furthermore, the global energy transition is placing silicon at the heart of renewable energy development, particularly through photovoltaic panels (Figure 10), whose global market is experiencing exponential growth. This is generating massive investment in silicon extraction, purification and processing, particularly in countries such as China, the United States, Germany and France.

The economic opportunities for silicon also extend to the chemical industry, through silicones used in construction, healthcare, electronics and even agri-food. In addition, the explosion of artificial intelligence, 5G, data centres and quantum technologies is increasing our dependence on ever more powerful electronic components, of which silicon remains the fundamental element. As such, control over this strategic resource is becoming a major economic issue, determining not only the industrial competitiveness of nations, but also their technological sovereignty in an increasingly digitalised world.

7. The future and prospects for silicon

The future of silicon looks both promising and complex, at the crossroads of technological innovation, energy requirements and geopolitical challenges. Although its use is currently dominant in microelectronics and photovoltaic technologies, new prospects are emerging that are redefining the contours of its exploitation.

In the field of semiconductors, advances towards extreme miniaturisation of electronic components, with etching of less than 3 nanometres (millionths of a millimetre), continue to push the limits of silicon, even though alternative materials such as graphene, gallium nitride (GaN) and other so-called ‘wide bandgap’ semiconductors are beginning to be explored for improved performance. However, silicon remains indispensable thanks to its abundance, industrial maturity and well-established production ecosystem.

In the photovoltaic sector, growing global demand for clean electricity is driving rapid expansion of the solar market, where crystalline silicon-based cells maintain an efficiency and reliability that makes them difficult to compete with on a large scale. Ongoing research into tandem photovoltaic cells, combining silicon and perovskites, is paving the way for even higher efficiencies [9].

The rise of artificial intelligence (AI), cloud computing, embedded electronics in autonomous vehicles and space technologies is further increasing global dependence on silicon integrated circuits. However, this dependence is also putting pressure on supply chains, making the development of local silicon production and recycling industries a strategic priority.

Silicon remains at the heart of future technologies, with prospects for development marked by hybridisation with other materials, optimisation of manufacturing processes and a central role in the global ecological and digital transition.

In new technologies such as artificial intelligence, the computers of the future (quantum computers) and high-performance solar panels, scientists are further improving silicon, a widely used material, by changing its form to make it work even better.

In short, the history of silicon is the story of an ordinary material that has become a cornerstone of modern civilisation. Its ability to adapt to technological developments makes it a major player in contemporary industrial revolutions.

8. Messages to remember

• Silicon, along with oxygen, is the main component of most rocks and is therefore found in abundance in the Earth’s crust.
• Thanks to its exceptional properties, silicon is central to the digital revolution, enabling the manufacture of semiconductors, the backbone of our electronic and computer systems.
• It is also at the heart of the global energy transition, fuelling the development of photovoltaic technologies.
• Silicon is also used in many innovative products and materials, such as medical prostheses.
• Silicon is therefore a material that underpins the very foundations of the economy, industry and contemporary technological development.
• This increased dependence on silicon raises major geopolitical, environmental and economic issues, calling for reflection on its sustainable production, secure supply and recycling.
  

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  Notes & references

  Cover image. Adapted from the cover scheme of the webpage À la découverte du silicium, l’élément chimique de base des ordinateurs (in french). [Source © David Montavon, reproduced with the author’s permission]

[1] Quantique sur silicium, CEA Leti, Press release, 2021 (in french)

[2] Tréguer, P., Bowler, C., Moriceau, B. et al. (2018) Influence of diatom diversity on the ocean biological carbon pump. Nature Geosci. 11, 27–37. https://doi.org/10.1038/s41561-017-0028-x

[3] Phytoliths are various forms of silica concretions found in plants or plant remains, which may be fossilised.

[4]  Meunier J.-D.  (2003), Le rôle des plantes dans le transfert du silicium à la surface des continents. C. R. Geoscience 335,  1199-1206. (in french)

[5] Silicium, in the Elémentarium (in french, Universal reference system to which all types of physical and chemical behaviour of elements can be related.)

[6] Doctorate dissertation, Simon Ilas, Univ. Pierre et Marie Curie, https://theses.hal.science/tel-01020851v1 (in french)

[7] Chaîne de transformation et commerce du silicium métal, BRGM (in french)

[8] Le silicium : un élément chimique très abondant, un affinage stratégique, Minéral Info, The french portal for non energetic mineral ressources (in french)

[9] Green, M. A., Dunlop, E. D., Hohl‐Ebinger, J., Yoshita, M., Kopidakis, N., & Hao, X. (2024). Solar cell efficiency tables (version 63). Progress in Photovoltaics: Research and Applications, 32(1), 3–22 DOI: 10.1002/pip.3709.