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Epitaxy
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 superlatti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compound Semiconductor
Semiconductor materials are nominally small band gap insulators. The defining property of a semiconductor material is that it can be compromised by doping it with impurities that alter its electronic properties in a controllable way. Because of their application in the computer and photovoltaic industry—in devices such as transistors, lasers, and solar cells—the search for new semiconductor materials and the improvement of existing materials is an important field of study in materials science. Most commonly used semiconductor materials are crystalline inorganic solids. These materials are classified according to the periodic table groups of their constituent atoms. Different semiconductor materials differ in their properties. Thus, in comparison with silicon, compound semiconductors have both advantages and disadvantages. For example, gallium arsenide (GaAs) has six times higher electron mobility than silicon, which allows faster operation; wider band gap, which allows op ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gallium Nitride
Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic, high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without requiring nonlinear optical frequency-doubling. Its sensitivity to ionizing radiation is low (like other group III nitrides), making it a suitable material for solar cell arrays for satellites. Military and space applications could also benefit as devices have shown stability in high radiation environments. Because GaN transistors can operate at much higher temperatures and work at much higher voltages than gallium arsenide (GaAs) transistors, they make ideal power amplifiers at microwave frequencies. In addition, GaN offers promising characteris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gallium Arsenide
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a Zincblende (crystal structure), zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared light-emitting diodes, laser diodes, solar cells and optical windows. GaAs is often used as a substrate material for the epitaxial growth of other III-V semiconductors, including indium gallium arsenide, aluminum gallium arsenide and others. Preparation and chemistry In the compound, gallium has a +3 oxidation state. Gallium arsenide single crystals can be prepared by three industrial processes: * The vertical gradient freeze (VGF) process. * Crystal growth using a horizontal zone furnace in the Bridgman-Stockbarger technique, in which gallium and arsenic vapors react, and free molecules deposit on a seed crystal at the cooler end of the furnace. * Liquid encapsulated Czochralski process, Czoch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminium Gallium Indium Phosphide
Aluminium gallium indium phosphide (, also AlInGaP, InGaAlP, GaInP, etc.) is a semiconductor material that provides a platform for the development of novel multi-junction photovoltaics and optoelectronic devices, as it spans a direct bandgap from deep ultraviolet to infrared. AlGaInP is used in manufacture of light-emitting diodes of high-brightness red, orange, green, and yellow color, to form the heterostructure emitting light. It is also used to make diode lasers. Formation AlGaInP layer is often grown by heteroepitaxy on gallium arsenide or gallium phosphide in order to form a quantum well structure. Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material. This technology is often used to grow crystalline films of materials for which single crystals cannot 1D view. Another example of heteroepitaxy is gallium nitride (GaN) on sapphire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doping (semiconductors)
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. Small numbers of dopant atoms can change the ability of a semiconductor to conduct electricity. When on the order of one dopant atom is added per 100 million atoms, the doping is said to be ''low'' or ''light''. When many more dopant atoms are added, on the order of one per ten thousand atoms, the doping is referred to as ''high'' or ''heavy''. This is often shown as ''n+'' for n-type doping or ''p+'' for p-type doping. (''See the article on semiconductors for a more detailed description of the doping mechanism.'') A semiconductor doped to such high levels that it acts more like a conductor than a semiconductor is referred to as a degenerate semiconductor. A semiconductor can be considered i-type semiconductor if it has b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bipolar Junction Transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching. BJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. The superior predictability and performance of junction transistors quickly displaced the original point-contact transistor. Diffused transistors, along wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frank–Van Der Merwe Growth
Frank–Van der Merwe growth (or FM growth) is one of the three primary modes by which thin films grow epitaxially at a crystal surface or interface. It is also known as 'layer-by-layer growth'. It is considered an ideal growth model, requiring perfect lattice matching between the substrate and the layer growing on to it, and it is usually limited to homoepitaxy. For FM growth to occur, the atoms that are to be deposited should be more attracted to the substrate than to each other, which is in contrast to the layer-plus-island growth model. FM growth is the preferred growth model for producing smooth films. It was first described by South African physicist Jan van der Merwe and British physicist Frederick Charles Frank in a series of four papers based on Van der Merwe's PhD research between 1947 and 1949. See also * Epitaxy * Thin films * Molecular-beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Band-gap Engineering
Band-gap engineering is the process of controlling or altering the band gap of a material. This is typically done to semiconductors by controlling the composition of alloys, constructing layered materials with alternating compositions, or by inducing strain either epitaxially or topologically. A band gap is the range in a solid where no electron state can exist. The band gap of insulators is much larger than in semiconductors. Conductors or metals have a much smaller or nonexistent band gap than semiconductors since the valence and conduction bands overlap. Controlling the band gap allows for the creation of desirable electrical properties. Molecular-beam epitaxy (MBE) Molecular-beam epitaxy is a technique used to construct thin epitaxial films of materials ranging from oxides to semiconductors to metals. Different beams of atoms and molecules in an ultra-high vacuum environment are shot onto a nearly atomically clean crystal, creating a layering effect. This is a type of thin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adatom
An adatom is an atom that lies on a crystal surface, and can be thought of as the opposite of a surface vacancy. This term is used in surface chemistry and epitaxy, when describing single atoms lying on surfaces and surface roughness. The word is a portmanteau of "adsorbed atom". A single atom, a cluster of atoms, or a molecule or cluster of molecules may all be referred to by the general term " adparticle". This is often a thermodynamically unfavorable state. However, cases such as graphene may provide counter-examples. Adatom growth Adatom is short for adsorbed atom. When the atom arrives at a crystal surface, it is adsorbed by the periodic potential of the crystal, thus becoming an adatom. The minima of this potential form a network of adsorption sites on the surface. There are different types of adsorption sites. Each of these sites corresponds to a different structure of the surface. There are five different types of adsorption sites, which are: on a terrace, where t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Vapor Deposition
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. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon ( dioxide, carbide, nitride, oxynitride), carbon (fiber, nanofibers, nanotubes, diamond and graphene), fluorocarbons, filaments, tungsten, titanium nitride and various high-κ dielectrics. The term ''chemical vapour deposition'' was coined 1960 by ''John M. Blocher, Jr.'' who intended to differentiate ''chemic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stranski–Krastanov Growth
Stranski–Krastanov growth (SK growth, also Stransky–Krastanov or Stranski–Krastanow) is one of the three primary modes by which thin films grow epitaxially at a crystal surface or interface. Also known as 'layer-plus-island growth', the SK mode follows a two step process: initially, complete films of adsorbates, up to several monolayers thick, grow in a layer-by-layer fashion on a crystal substrate. Beyond a critical layer thickness, which depends on strain and the chemical potential of the deposited film, growth continues through the nucleation and coalescence of adsorbate 'islands'. This growth mechanism was first noted by Ivan Stranski and Lyubomir Krastanov in 1938. It wasn't until 1958 however, in a seminal work by Ernst Bauer published in ''Zeitschrift für Kristallographie'', that the SK, Volmer–Weber, and Frank–van der Merwe mechanisms were systematically classified as the primary thin-film growth processes. Since then, SK growth has been the subject of intense ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lattice Constant
A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has only one lattice constant, the distance between atoms, but in general lattices in three dimensions have six lattice constants: the lengths ''a'', ''b'', and ''c'' of the three cell edges meeting at a vertex, and the angles ''α'', ''β'', and ''γ'' between those edges. The crystal lattice parameters ''a'', ''b'', and ''c'' have the dimension of length. The three numbers represent the size of the unit cell, that is, the distance from a given atom to an identical atom in the same position and orientation in a neighboring cell (except for very simple crystal structures, this will not necessarily be disance to the nearest neighbor). Their SI unit is the meter, and they are traditionally specified in angstroms (Å); an angstrom being 0.1 nanome ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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