![Monokristalines Silizium für die Waferherstellung](https://upload.wikimedia.org/wikipedia/commons/2/23/Monokristalines_Silizium_f%C3%BCr_die_Waferherstellung.jpg)
Monocrystalline silicon, more often called single-crystal silicon, in short mono c-Si or mono-Si, is the base material for
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
-based
discrete components and
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s used in virtually all modern electronic equipment. Mono-Si also serves as a
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
, light-absorbing material in the manufacture of
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s.
It consists of silicon in which the
crystal lattice
In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by
: \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...
of the entire solid is continuous, unbroken to its edges, and free of any
grain boundaries
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional crystallographic defect, defects in the crystal structure, and tend to decrease the ...
(i.e. a
single crystal
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...
). Mono-Si can be prepared as an
intrinsic semiconductor
An intrinsic (pure) semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the ...
that consists only of exceedingly pure silicon, or it can be
doped by the addition of other elements such as
boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
or
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
to make
p-type or
n-type silicon. Due to its
semiconducting
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
properties, single-crystal silicon is perhaps the most important technological material of the last few decades—the "silicon era", because its availability at an affordable cost has been essential for the development of the electronic devices on which the
present-day electronics and
IT revolution is based.
Monocrystalline silicon differs from other
allotropic
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: th ...
forms, such as non-crystalline
amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films onto ...
—used in
thin-film solar cell
A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially use ...
s—and
polycrystalline silicon
Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry.
Polysilicon is produ ...
, which consists of small crystals known as
crystallite
A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains.
Bacillite is a type of crystallite. It is rodlike with parallel longulites.
Stru ...
s.
Production
Monocrystalline
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...
silicon is generally created by one of several methods that involve melting high-purity, semiconductor-grade silicon (only a few parts per million of impurities) and the use of a
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
to initiate the formation of a continuous single crystal. This process is normally performed in an inert atmosphere, such as argon, and in an inert crucible, such as
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
, to avoid impurities that would affect the crystal uniformity.
The most common production technique is the
Czochralski method
The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platinum, silver, ...
, which dips a precisely oriented rod-mounted
seed crystal into the molten silicon. The rod is then slowly pulled upwards and rotated simultaneously, allowing the pulled material to solidify into a monocrystalline cylindrical ingot up to 2 meters in length and weighing several hundred kilograms. Magnetic fields may also be applied to control and suppress turbulent flow, further improving the uniformity of the crystallization. Other methods are
zone melting
Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molte ...
, which passes a polycrystalline silicon rod through a radiofrequency heating coil that creates a localized molten zone, from which a seed crystal ingot grows, and
Bridgman techniques, which move the crucible through a temperature gradient to cool it from the end of the container containing the seed. The solidified ingots are then sliced into thin
wafers
A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...
during a process called
wafering. After post-wafering processing, the wafers are ready for use in fabrication.
Compared to the casting of polycrystalline ingots, the production of monocrystalline silicon is very slow and expensive. However, the demand for mono-Si continues to rise due to the superior electronic properties—the lack of grain boundaries allows better charge carrier flow and prevents electron
recombination—allowing improved performance of integrated circuits and photovoltaics.
In electronics
The primary application of monocrystalline silicon is in the production of
discrete components and
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s. Ingots made by the Czochralski method are sliced into wafers about 0.75 mm thick and polished to obtain a regular, flat substrate, onto which
microelectronic
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-sc ...
devices are built through various
microfabrication
Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" ...
processes, such as
doping or
ion implantation
Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the physical, chemical, or electrical properties of the target. Ion implantation is used in semiconductor device fab ...
,
etching
Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types ...
,
deposition of various materials, and
photolithographic
In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...
patterning.
A single continuous crystal is critical for electronics, since grain boundaries,
impurities, and
crystallographic defect
A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell para ...
s can significantly impact the local electronic properties of the material, which in turn affects the functionality, performance, and reliability of
semiconductor device
A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...
s by interfering with their proper operation. For example, without crystalline perfection, it would be virtually impossible to build
very large-scale integration
Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) c ...
(VLSI) devices, in which billions of transistor-based circuits, all of which must function reliably, are combined into a single chip to form a microprocessor. As such, the electronics industry has invested heavily in facilities to produce large single crystals of silicon.
In solar cells
![Global photovoltaics market share by technology 1980-2021](https://upload.wikimedia.org/wikipedia/commons/1/1b/Global_photovoltaics_market_share_by_technology_1980-2021.svg)
Monocrystalline silicon is also used for high-performance
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
(PV) devices. Since there are less stringent demands on structural imperfections compared to microelectronics applications, lower-quality solar-grade silicon (Sog-Si) is often used for solar cells. Despite this, the monocrystalline-silicon photovoltaic industry has benefitted greatly from the development of faster mono-Si production methods for the electronics industry.
Market share
Being the second most common form of PV technology, monocrystalline silicon is ranked behind only its sister,
polycrystalline silicon
Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry.
Polysilicon is produ ...
. Due to the significantly higher production rate and steadily decreasing costs of poly-silicon, the market share of mono-Si has been decreasing: in 2013, monocrystalline solar cells had a market share of 36%, which translated into the production of 12.6 GW of photovoltaic capacity, but the market share had dropped below 25% by 2016. Despite the lowered market share, the equivalent mono-Si PV capacity produced in 2016 was 20.2 GW, indicating a significant increase in the overall production of photovoltaic technologies.
Efficiency
With a recorded single-junction cell lab efficiency of 26.7%, monocrystalline silicon has the highest confirmed conversion efficiency out of all commercial PV technologies, ahead of poly-Si (22.3%) and established
thin-film technologies, such as
CIGS cells (21.7%),
CdTe cells (21.0%), and
a-Si cells (10.2%).
Solar module
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
efficiencies for mono-Si—which are always lower than those of their corresponding cells—finally crossed the 20% mark for in 2012 and hit 24.4% in 2016. The high efficiency is largely attributable to the lack of recombination sites in the single crystal and better absorption of photons due to its black color, as compared to the characteristic blue hue of poly-silicon. Since they are more expensive than their polycrystalline counterparts, mono-Si cells are useful for applications where the main considerations are limitations on weight or available area.
Manufacturing
Besides the low production rate, there are also concerns over wasted material in the manufacturing process. Creating space-efficient solar panels requires cutting the circular wafers (a product of the cylindrical ingots formed through the Czochralski process) into octagonal cells that can be packed closely together. The leftover material is not used to create PV cells and is either discarded or recycled by going back to ingot production for melting. Furthermore, even though mono-Si cells can absorb the majority of photons within 20 μm of the incident surface, limitations on the ingot sawing process mean commercial wafer thickness are generally around 200 μm. However, advances in technology are expected to reduce wafer thicknesses to 140 μm by 2026.
Other manufacturing methods are being researched, such as direct wafer
epitaxial growth
Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited crystalline film is called an epit ...
, which involves growing gaseous layers on reusable silicon substrates. Newer processes may allow growth of square crystals that can then be processed into thinner wafers without compromising quality or efficiency, thereby eliminating the waste from traditional ingot sawing and cutting methods.
Appearance
File:Silicon-unit-cell-3D-balls.png, The crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...
of silicon forms a diamond cubic
The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the sem ...
File:ICC 2008 Poland Silicon Wafer 1 edit.png, VLSI
Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) c ...
devices fabricated by Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
on a monocrystalline silicon wafer
File:Monocrystalline solar panel.png, Solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
made of octagonal monocrystalline silicon cells
File:Comparison solar cell poly-Si vs mono-Si.png, Comparison of solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s: poly-Si (left) and mono-Si (right)
References
{{DEFAULTSORT:Monocrystalline Silicon
Silicon, Monocrystaline
Crystals
Silicon solar cells
Silicon forms