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Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
Silicon is a chemical element; it has 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 table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive.
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits.
A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature of chemistry.
The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). It lies within the p-block.
Silicon carbide (SiC), also known as carborundum, is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal 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. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.
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 epitaxial film or epitaxial layer. The relative orientation(s) of the epitaxial layer to the seed layer is defined in terms of the orientation of the crystal lattice of each material. For most epitaxial growths, the new layer is usually crystalline and each crystallographic domain of the overlayer must have a well-defined orientation relative to the substrate crystal structure. Epitaxy can involve single-crystal structures, although grain-to-grain epitaxy has been observed in granular films. For most technological applications, single domain epitaxy, which is the growth of an overlayer crystal with one well-defined orientation with respect to the substrate crystal, is preferred. Epitaxy can also play an important role while growing superlattice structures.
Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes have been discovered and researched, including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3‑periodic allotropes of carbon are known at the present time, according to the Samara Carbon Allotrope Database (SACADA).
In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor.
Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure. The name is derived from "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon contains numerous double bonds.
Covalent superconductors are superconducting materials where the atoms are linked by covalent bonds. The first such material was boron-doped synthetic diamond grown by the high-pressure high-temperature (HPHT) method. The discovery had no practical importance, but surprised most scientists as superconductivity had not been observed in covalent semiconductors, including diamond and silicon.
A network solid or covalent network solid is a chemical compound in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule. Formulas for network solids, like those for ionic compounds, are simple ratios of the component atoms represented by a formula unit.
Silicene is a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of graphene. Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is much stronger than in multilayered graphene; and the oxidized form of silicene, 2D silica, has a very different chemical structure from graphene oxide.
Graphyne is an allotrope of carbon. Its structure is one-atom-thick planar sheets of sp and sp2-bonded carbon atoms arranged in crystal lattice. It can be seen as a lattice of benzene rings connected by acetylene bonds. The material is called graphyne-n when benzene rings are connected by n sequential acetylene molecules, and graphdiyne for a particular case of n = 2.
Germanane is a single-layer crystal composed of germanium with one hydrogen bonded in the z-direction for each atom, in contrast to germanene which contains no hydrogen. In material science, great interest is shown in related single layered materials, such as graphene, composed of carbon, and silicene, composed of silicon. Such materials represent a new generation of semiconductors with potential applications in computer chips and solar cells. Germanane's structure is similar to graphane, and therefore graphene. Bulk germanium does not adopt this structure. Germanane has been produced in a two-step route starting with calcium germanide. From this material, the calcium is removed by de-intercalation with HCl to give a layered solid with the empirical formula GeH. The Ca sites in Zintl phase CaGe2 interchange with the H atoms in the HCl solution, which leaves GeH and CaCl2.
Silicynes are allotropes of silicon.
In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds.
Germanene is a material made up of a single layer of germanium atoms. The material is created in a process similar to that of silicene and graphene, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate. High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and materials science research.
Penta-graphene is a hypothetical carbon allotrope composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling. Penta-graphene was proposed in 2014 on the basis of analyses and simulations. Further calculations predicted that it is unstable in its pure form, but can be stabilized by hydrogenation. Due to its atomic configuration, penta-graphene has an unusually negative Poisson’s ratio and very high ideal strength believed to exceed that of a similar material, graphene.
Penta-silicene or pentasilicene denotes a silicon-based two-dimensional (2D) structure, a cousin of silicene, composed entirely of Si pentagons, in analogy with penta-graphene,a hypothetical variant of graphene. As of 2017 such a structure has only been obtained synthetically as one-dimensional nanoribbons (1D-NRs) grown on a silver (110) substrate. These nanoribbons adopt a highly ordered chiral arrangement in single- and/or double-strands. They were discovered in 2005 upon depositing Si onto the Ag(110) surface held at room temperature or at about 200 °C, and observed in Scanning Tunneling Microscopy. However, their unique atomic structure was unveiled only in 2016 through thorough density functional theory calculations and simulations of the STM images. It consists of alternating Si pentagons residing along a missing row formed at the silver surface during the growth process. In the Penta-silicene NRs each Si pentagonal moiety displays an envelope conformation whereby four atoms are coplanar and a fifth flap atom protrudes out of the surface. The pentagons, nevertheless, do not deviate much from regular ones. DNRs consist of two SNRs with the same handedness running in parallel along two missing rows separated by two Ag lattice constants.
References
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- ↑ "Silicon and Germanium". hyperphysics.phy-astr.gsu.edu. Retrieved 2021-06-07.
- ↑ Leandri, C.; Lay, G. Le; Aufray, B.; Girardeaux, C.; Avila, J.; Dávila, M.E.; Asensio, M.C.; Ottaviani, C.; Cricenti, A. (2005). "Self-aligned silicon quantum wires on Ag(110)". Surface Science. 574 (1): L9–L15. doi:10.1016/j.susc.2004.10.052.
- ↑ Sahaf, H.; Masson, L.; Léandri, C.; Aufray, B.; Le Lay, G.; Ronci, F. (2007-06-25). "Formation of a one-dimensional grating at the molecular scale by self-assembly of straight silicon nanowires". Applied Physics Letters. 90 (26): 263110. doi:10.1063/1.2752125. ISSN 0003-6951.
- 1 2 Irving, Michael (2021-06-07). "Scientists create strange new form of silicon". New Atlas. Retrieved 2021-06-07.
- 1 2 Shiell, Thomas B.; Zhu, Li; Cook, Brenton A.; Bradby, Jodie E.; McCulloch, Dougal G.; Strobel, Timothy A. (2021-05-25). "Bulk Crystalline $4H$-Silicon through a Metastable Allotropic Transition". Physical Review Letters. 126 (21): 215701. doi:10.1103/PhysRevLett.126.215701. hdl: 1885/293483 . PMID 34114875. S2CID 235404142.
- 1 2 3 "New type of silicon could find use in solar cells and LEDs". New Atlas. 2014-11-20. Retrieved 2021-06-07.
- ↑ Linghu, Jiajun; Shen, Lei; Yang, Ming; Xu, Shuyan; Feng, Yuan Ping (2017-07-27). "Si24: An Efficient Solar Cell Material". The Journal of Physical Chemistry C. 121 (29): 15574–15579. doi:10.1021/acs.jpcc.7b04032. ISSN 1932-7447.
- ↑ Phillip F. Schewe & Ben Stein (3 September 1998). "Silicyne, A New Form Of Silicon". Inside Science Research - Physics News Update. No. 388. American Institute of Physics. p. Story #3. Archived from the original on 6 August 2007. Retrieved 2013-10-12.
- ↑ Pei Yang (裴 洋) and Wu Hai-Bin (武海斌) (2013). "Optimized geometry and electronic structure of graphyne-like silicyne nanoribbons". Chinese Physics B. 22 (5): 057303. doi:10.1088/1674-1056/22/5/057303. S2CID 250784436.