1.
Boule (crystal)
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A boule is a single crystal ingot produced by synthetic means. A boule of silicon is the material for most of the integrated circuits used today. In the semiconductor industry, boules can be made by a number of methods, such as the Bridgman technique and the Czochralski process, in the Czochralski process a seed crystal is required to create a larger crystal, or ingot. This seed crystal is dipped into the molten silicon and slowly extracted. The molten silicon grows on the crystal in a crystalline fashion. As the seed is extracted the silicon solidifies and eventually a large, the process is also used to create sapphires, which are used for substrates in the production of blue and white LEDs, optical windows in special applications and as the protective covers for watches
2.
Integrated circuit
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An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material, normally silicon. The ICs mass production capability, reliability and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of using discrete transistors. ICs are now used in all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other home appliances are now inextricable parts of the structure of modern societies, made possible by the small size. These advances, roughly following Moores law, allow a computer chip of 2016 to have millions of times the capacity, ICs have two main advantages over discrete circuits, cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography rather than being constructed one transistor at a time, furthermore, packaged ICs use much less material than discrete circuits. Performance is high because the ICs components switch quickly and consume little power because of their small size, the main disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This high initial cost means ICs are only practical when high production volumes are anticipated, Circuits meeting this definition can be constructed using many different technologies, including thin-film transistor, thick film technology, or hybrid integrated circuit. However, in general usage integrated circuit has come to refer to the single-piece circuit construction originally known as a integrated circuit. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent, an immediate commercial use of his patent has not been reported. The idea of the circuit was conceived by Geoffrey Dummer. Dummer presented the idea to the public at the Symposium on Progress in Quality Electronic Components in Washington and he gave many symposia publicly to propagate his ideas, and unsuccessfully attempted to build such a circuit in 1956. A precursor idea to the IC was to create small ceramic squares, Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which seemed very promising in 1957, was proposed to the US Army by Jack Kilby, however, as the project was gaining momentum, Kilby came up with a new, revolutionary design, the IC. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material … wherein all the components of the circuit are completely integrated. The first customer for the new invention was the US Air Force, Kilby won the 2000 Nobel Prize in Physics for his part in the invention of the integrated circuit. His work was named an IEEE Milestone in 2009, half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilbys had not. Noyces design was made of silicon, whereas Kilbys chip was made of germanium, Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation, a key concept behind the IC
3.
Photovoltaics
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A typical photovoltaic system employs solar panels, each comprising a number of solar cells, which generate electrical power. PV installations may be ground-mounted, rooftop mounted or wall mounted, the mount may be fixed, or use a solar tracker to follow the sun across the sky. Dust, clouds, and other things in the atmosphere also diminish the power output, another main issue is the concentration of the production in the hours corresponding to main insolation, which dont usually match the peaks in demand in human activity cycles. Unless current societal patterns of consumption and electrical networks mutually adjust to this scenario, electricity still need to be made up by other power sources, Photovoltaic systems have long been used in specialized applications, and standalone and grid-connected PV systems have been in use since the 1990s. They were first mass-produced in 2000, when German environmentalists and the Eurosolar organization got government funding for a ten thousand roof program, advances in technology and increased manufacturing scale have in any case reduced the cost, increased the reliability, and increased the efficiency of photovoltaic installations. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries, more than 100 countries now use solar PV. After hydro and wind powers, PV is the renewable energy source in terms of globally capacity. In 2014, worldwide installed PV capacity increased to 177 gigawatts, with current technology, photovoltaics recoups the energy needed to manufacture them in 1.5 years in Southern Europe and 2.5 years in Northern Europe. The term photo-voltaic has been in use in English since 1849, photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into a flow of electrons by the photovoltaic effect. Solar cells produce direct current electricity from sunlight which can be used to power equipment or to recharge a battery, the first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC, there is a smaller market for off-grid power for remote dwellings, boats, recreational vehicles, electric cars, roadside emergency telephones, remote sensing, and cathodic protection of pipelines. Photovoltaic power generation employs solar panels composed of a number of cells containing a photovoltaic material. Copper solar cables connect modules, arrays, and sub-fields, because of the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced considerably in recent years. Solar photovoltaic power generation has long seen as a clean energy technology which draws upon the planet’s most plentiful. Cells require protection from the environment and are usually packaged tightly in solar panels, Photovoltaic power capacity is measured as maximum power output under standardized test conditions in Wp. Solar photovoltaic array capacity factors are typically under 25%, which is lower than other industrial sources of electricity. For best performance, terrestrial PV systems aim to maximize the time they face the sun, Solar trackers achieve this by moving PV panels to follow the sun. The increase can be by as much as 20% in winter, static mounted systems can be optimized by analysis of the sun path
4.
Solar cell
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A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance. Solar cells are the blocks of photovoltaic modules, otherwise known as solar panels. Solar cells are described as being photovoltaic, irrespective of whether the source is sunlight or an artificial light and they are used as a photodetector, detecting light or other electromagnetic radiation near the visible range, or measuring light intensity. The operation of a cell requires three basic attributes, The absorption of light, generating either electron-hole pairs or excitons. The separation of carriers of opposite types. The separate extraction of those carriers to an external circuit, in contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A photoelectrolytic cell, on the hand, refers either to a type of photovoltaic cell. Assemblies of solar cells are used to make solar modules that generate power from sunlight. A solar array generates power using solar energy. Multiple solar cells in a group, all oriented in one plane. Photovoltaic modules often have a sheet of glass on the sun-facing side, Solar cells are usually connected in series and parallel circuits or series in modules, creating an additive voltage. Strings of series cells are usually handled independently and not connected in parallel, though as of 2014, individual power boxes are often supplied for each module, and are connected in parallel. Although modules can be interconnected to create an array with the desired peak DC voltage and loading current capacity, otherwise, shunt diodes can reduce shadowing power loss in arrays with series/parallel connected cells. The photovoltaic effect was demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the worlds first photovoltaic cell in his fathers laboratory, willoughby Smith first described the Effect of Light on Selenium during the passage of an Electric Current in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a layer of gold to form the junctions. In 1888 Russian physicist Aleksandr Stoletov built the first cell based on the photoelectric effect discovered by Heinrich Hertz in 1887
5.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
6.
Bravais lattice
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This discrete set of vectors must be closed under vector addition and subtraction. For any choice of position vector R, the lattice looks exactly the same, when the discrete points are atoms, ions, or polymer strings of solid matter, the Bravais lattice concept is used to formally define a crystalline arrangement and its frontiers. A crystal is made up of an arrangement of one or more atoms repeated at each lattice point. Consequently, the crystal looks the same when viewed from any equivalent lattice point, two Bravais lattices are often considered equivalent if they have isomorphic symmetry groups. In this sense, there are 14 possible Bravais lattices in three-dimensional space, the 14 possible symmetry groups of Bravais lattices are 14 of the 230 space groups. In two-dimensional space, there are 5 Bravais lattices, grouped into four crystal families, the unit cells are specified according to the relative lengths of the cell edges and the angle between them. The area of the cell can be calculated by evaluating the norm || a × b ||. The properties of the families are given below, In three-dimensional space. These are obtained by combining one of the six families with one of the centering types. For example, the monoclinic I lattice can be described by a monoclinic C lattice by different choice of crystal axes, similarly, all A- or B-centred lattices can be described either by a C- or P-centering. This reduces the number of combinations to 14 conventional Bravais lattices, the unit cells are specified according to the relative lengths of the cell edges and the angles between them. The volume of the cell can be calculated by evaluating the triple product a ·, where a, b. The properties of the families are given below, In four dimensions. Of these,23 are primitive and 41 are centered, ten Bravais lattices split into enantiomorphic pairs. Bravais, A. Mémoire sur les systèmes formés par les points distribués régulièrement sur un plan ou dans lespace, hahn, Theo, ed. International Tables for Crystallography, Volume A, Space Group Symmetry. Catalogue of Lattices Smith, Walter Fox
7.
Grain boundary
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A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and they are also important to many of the mechanisms of creep. It is convenient to categorize grain boundaries according to the extent of misorientation between the two grains, low-angle grain boundaries or subgrain boundaries are those with a misorientation less than about 15 degrees. Generally speaking they are composed of an array of dislocations and their properties, in contrast the properties of high-angle grain boundaries, whose misorientation is greater than about 11 degrees, are normally found to be independent of the misorientation. However, there are special boundaries at particular orientations whose interfacial energies are markedly lower than those of general HAGBs, the simplest boundary is that of a tilt boundary where the rotation axis is parallel to the boundary plane. This boundary can be conceived as forming from a single, contiguous crystallite or grain which is bent by some external force. As the grain is bent further, more and more dislocations must be introduced to accommodate the resulting in a growing wall of dislocations – a low-angle boundary. The grain can now be considered to have split into two sub-grains of related crystallography but notably different orientations, an alternative is a twist boundary where the misorientation occurs around an axis that is perpendicular to the boundary plane. This type of boundary incorporates two sets of screw dislocations, if the Burgers vectors of the dislocations are orthogonal, then the dislocations do not strongly interact and form a square network. In other cases, the dislocations may interact to form a more complex hexagonal structure and these concepts of tilt and twist boundaries represent somewhat idealized cases. The majority of boundaries are of a type, containing dislocations of different types and Burgers vectors. If the dislocations in the boundary remain isolated and distinct, the boundary can be considered to be low-angle, if deformation continues, the density of dislocations will increase and so reduce the spacing between neighboring dislocations. Eventually, the cores of the dislocations will begin to overlap, at this point the boundary can be considered to be high-angle and the original grain to have separated into two entirely separate grains. In comparison to LAGBs, high-angle boundaries are considerably more disordered, with areas of poor fit. Indeed, they were thought to be some form of amorphous or even liquid layer between the grains. It is now accepted that a boundary consists of units which depend on both the misorientation of the two grains and the plane of the interface. In coincident site lattice theory, the degree of fit between the structures of the two grains is described by the reciprocal of the ratio of coincidence sites to the number of sites
8.
Boron
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Boron is a chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is an element in the Solar system. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds and these are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a metalloid that is found in small amounts in meteoroids, industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist, amorphous boron is a powder, crystalline boron is silvery to black, extremely hard. The primary use of boron is as boron filaments with applications similar to carbon fibers in some high-strength materials. Boron is primarily used in chemical compounds, about half of all consumption globally, boron is used as an additive in glass fibers of boron-containing fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural, borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron compounds are used as fertilizers in agriculture and in sodium perborate bleaches, a small amount of boron is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study, natural boron is composed of two stable isotopes, one of which has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals, but are toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and several natural boron-containing organic antibiotics are known, small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron a necessary plant nutrient. Boron is involved in the metabolism of calcium in both plants and animals and it is considered an essential nutrient for humans, and boron deficiency is implicated in osteoporosis. The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy, in 1777, boric acid was recognized in the hot springs near Florence, Italy, and became known as sal sedativum, with primarily medical uses. The rare mineral is called sassolite, which is found at Sasso, Sasso was the main source of European borax from 1827 to 1872, when American sources replaced it. Boron compounds were relatively rarely used until the late 1800s when Francis Marion Smiths Pacific Coast Borax Company first popularized and produced them in volume at low cost
9.
Phosphorus
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Phosphorus is a chemical element with symbol P and atomic number 15. As an element, phosphorus exists in two major forms—white phosphorus and red phosphorus—but because it is reactive, phosphorus is never found as a free element on Earth. At 0. 099%, phosphorus is the most abundant pnictogen in the Earths crust, with few exceptions, minerals containing phosphorus are in the maximally oxidised state as inorganic phosphate rocks. The glow of phosphorus itself originates from oxidation of the white phosphorus — a process now termed chemiluminescence, together with nitrogen, arsenic, antimony, and bismuth, phosphorus is classified as a pnictogen. Phosphates are a component of DNA, RNA, ATP, and the phospholipids, demonstrating the link between phosphorus and life, elemental phosphorus was first isolated from human urine, and bone ash was an important early phosphate source. Phosphate mines contain fossils, especially marine fossils, because phosphate is present in the deposits of animal remains. Low phosphate levels are an important limit to growth in aquatic systems. The vast majority of compounds produced are consumed as fertilisers. Phosphate is needed to replace the phosphorus that plants remove from the soil, other applications include the role of organophosphorus compounds in detergents, pesticides, and nerve agents. Phosphorus exists as several forms that exhibit different properties. The two most common allotropes are white phosphorus and red phosphorus, from the perspective of applications and chemical literature, the most important form of elemental phosphorus is white phosphorus, often abbreviated as WP. It is a soft and waxy solid consists of tetrahedral P4 molecules. This P4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °C when it starts decomposing to P2 molecules, White phosphorus exists in two crystalline forms, α and β. At room temperature, the α-form is stable, which is common and it has cubic crystal structure and at 195.2 K, it transforms into β-form. These forms differ in terms of the orientations of the constituent P4 tetrahedra. White phosphorus is the least stable, the most reactive, the most volatile, the least dense, White phosphorus gradually changes to red phosphorus. This transformation is accelerated by light and heat, and samples of white phosphorus almost always some red phosphorus. For this reason, white phosphorus that is aged or otherwise impure is also called yellow phosphorus, when exposed to oxygen, white phosphorus glows in the dark with a very faint tinge of green and blue
10.
Extrinsic semiconductor
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An extrinsic semiconductor is one that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic semiconductor. Dominant carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type semiconductor, the electrical properties of extrinsic semiconductors make them essential components of many electronic devices. Semiconductor doping is the process changes a intrinsic semiconductor to an extrinsic semiconductor. During doping, impurity atoms are introduced to an intrinsic semiconductor, impurity atoms are atoms of a different element than the atoms of the intrinsic semiconductor. Impurity atoms act as donors or acceptors to the intrinsic semiconductor, changing the electron. Impurity atoms are classified as donor or acceptor atoms based on the effect they have on the intrinsic semiconductor, donor impurity atoms have more valence electrons than the atoms they replace in the intrinsic semiconductor lattice. Donor impurities donate their extra valence electrons to a conduction band. Excess electrons increase the electron concentration of the semiconductor, making it n-type. Acceptor impurity atoms have fewer electrons than the atoms they replace in the intrinsic semiconductor lattice. They accept electrons from the valence band. This provides excess holes to the intrinsic semiconductor, excess holes increase the hole carrier concentration of the semiconductor, creating a p-type semiconductor. Semiconductors and dopant atoms are defined by the column of the table in which they fall. The column definition of the semiconductor determines how many valence electrons its atoms have, group IV semiconductors use group V atoms as donors and group III atoms as acceptors. Group III-V semiconductors, the semiconductors, use group VI atoms as donors. Group III-V semiconductors can also use group IV atoms as donors or acceptors. When a group IV atom replaces the group III element in the semiconductor lattice, conversely, when a group IV atom replaces the group V element, the group IV atom acts as an acceptor. Group IV atoms can act as donors and acceptors, therefore, they are known as amphoteric impurities. N-type semiconductors have a larger electron concentration than hole concentration, the term n-type comes from the negative charge of the electron
11.
Semiconductor
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Semiconductors are crystalline or amorphous solids with distinct electrical characteristics. They are of high electrical resistance — higher than typical resistance materials and their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics. Semiconductor devices can display a range of properties such as passing current more easily in one direction than the other, showing variable resistance. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of carriers in a crystal lattice. Doping greatly increases the number of carriers within the crystal. When a doped semiconductor contains mostly free holes it is called p-type, the semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions, although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices. Elements near the so-called metalloid staircase, where the metalloids are located on the table, are usually used as semiconductors. Some of the properties of materials were observed throughout the mid 19th. The first practical application of semiconductors in electronics was the 1904 development of the Cats-whisker detector, developments in quantum physics in turn allowed the development of the transistor in 1947 and the integrated circuit in 1958. There are several developed techniques that allow semiconducting materials to behave like conducting materials and these modifications have two outcomes, n-type and p-type. These refer to the excess or shortage of electrons, respectively, an unbalanced number of electrons would cause a current to flow through the material. Heterojunctions Heterojunctions occur when two differently doped semiconducting materials are joined together, for example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials, the n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until equilibrium is reached by a process called recombination, a product of this process is charged ions, which result in an electric field. Excited Electrons A difference in electric potential on a material would cause it to leave thermal equilibrium. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion, whenever thermal equilibrium is disturbed in a semiconducting material, the amount of holes and electrons changes
12.
Electronics
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Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements, the science of electronics is also considered to be a branch of physics and electrical engineering. The ability of electronic devices to act as switches makes digital information processing possible, until 1950 this field was called radio technology because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes. Today, most electronic devices use semiconductor components to perform electron control and this article focuses on engineering aspects of electronics. Components are generally intended to be connected together, usually by being soldered to a circuit board. Components may be packaged singly, or in more complex groups as integrated circuits, some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active or passive, vacuum tubes were among the earliest electronic components. They were almost solely responsible for the revolution of the first half of the Twentieth Century. They took electronics from parlor tricks and gave us radio, television, phonographs, radar, long distance telephony and they played a leading role in the field of microwave and high power transmission as well as television receivers until the middle of the 1980s. Since that time, solid state devices have all but completely taken over, vacuum tubes are still used in some specialist applications such as high power RF amplifiers, cathode ray tubes, specialist audio equipment, guitar amplifiers and some microwave devices. The 608 contained more than 3,000 germanium transistors, thomas J. Watson Jr. ordered all future IBM products to use transistors in their design. From that time on transistors were almost exclusively used for computer logic, circuits and components can be divided into two groups, analog and digital. A particular device may consist of circuitry that has one or the other or a mix of the two types, most analog electronic appliances, such as radio receivers, are constructed from combinations of a few types of basic circuits. Analog circuits use a range of voltage or current as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a circuit can be defined as anything from a single component, analog circuits are sometimes called linear circuits although many non-linear effects are used in analog circuits such as mixers, modulators, etc. Good examples of analog circuits include vacuum tube and transistor amplifiers, one rarely finds modern circuits that are entirely analog. These days analog circuitry may use digital or even microprocessor techniques to improve performance and this type of circuit is usually called mixed signal rather than analog or digital. Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation, an example is the comparator which takes in a continuous range of voltage but only outputs one of two levels as in a digital circuit
13.
Information technology
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Information technology is the application of computers to store, study, retrieve, transmit, and manipulate data, or information, often in the context of a business or other enterprise. IT is considered a subset of information and communications technology, the term is commonly used as a synonym for computers and computer networks, but it also encompasses other information distribution technologies such as television and telephones. Several industries are associated with technology, including computer hardware, software, electronics, semiconductors, internet, telecom equipment. Leavitt and Thomas L. Whisler commented that the new technology not yet have a single established name. We shall call it information technology, based on the storage and processing technologies employed, it is possible to distinguish four distinct phases of IT development, pre-mechanical, mechanical, electromechanical, electronic. This article focuses on the most recent period, which began in about 1940, devices have been used to aid computation for thousands of years, probably initially in the form of a tally stick. Electronic computers, using either relays or valves, began to appear in the early 1940s, the electromechanical Zuse Z3, completed in 1941, was the worlds first programmable computer, and by modern standards one of the first machines that could be considered a complete computing machine. Colossus, developed during the Second World War to decrypt German messages was the first electronic digital computer, although it was programmable, it was not general-purpose, being designed to perform only a single task. It also lacked the ability to store its program in memory, programming was carried out using plugs, the first recognisably modern electronic digital stored-program computer was the Manchester Small-Scale Experimental Machine, which ran its first program on 21 June 1948. The development of transistors in the late 1940s at Bell Laboratories allowed a new generation of computers to be designed with reduced power consumption. The first commercially available stored-program computer, the Ferranti Mark I, by comparison the first transistorised computer, developed at the University of Manchester and operational by November 1953, consumed only 150 watts in its final version. Early electronic computers such as Colossus made use of punched tape, a strip of paper on which data was represented by a series of holes. IBM introduced the first hard drive in 1956, as a component of their 305 RAMAC computer system. Most digital data today is stored magnetically on hard disks. Until 2002 most information was stored on analog devices, but that year digital storage capacity exceeded analog for the first time. As of 2007 almost 94% of the data stored worldwide was held digitally, 52% on hard disks, 28% on optical devices and 11% on digital magnetic tape. It has been estimated that the capacity to store information on electronic devices grew from less than 3 exabytes in 1986 to 295 exabytes in 2007. Database management systems emerged in the 1960s to address the problem of storing and retrieving large amounts of data accurately and quickly, one of the earliest such systems was IBMs Information Management System, which is still widely deployed more than 50 years later
14.
Allotropic
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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 these elements. Allotropes are different structural modifications of an element, the atoms of the element are bonded together in a different manner, for example, the allotropes of carbon include diamond, graphite, graphene, and fullerenes. The term allotropy is used for only, not for compounds. The more general term, used for any material, is polymorphism. Allotropy refers only to different forms of an element within the same phase, for some elements, allotropes have different molecular formulae which can persist in different phases – for example, two allotropes of oxygen, can both exist in the solid, liquid and gaseous states. The concepts of allotropy was originally proposed in 1841 by the Swedish scientist Baron Jöns Jakob Berzelius, the term is derived from Greek άλλοτροπἱα, meaning variability, changeableness. After the acceptance of Avogadros hypothesis in 1860 it was understood that elements could exist as molecules. In the early 20th century it was recognized that other such as carbon were due to differences in crystal structure. Although many other chemists have repeated this advice, IUPAC and most chemistry texts still favour the usage of allotrope, allotropes are different structural forms of the same element and can exhibit quite different physical properties and chemical behaviours. The change between allotropic forms is triggered by the forces that affect other structures, i. e. pressure, light. Therefore, the stability of the particular allotropes depends on particular conditions.2 °C, as an example of allotropes having different chemical behaviour, ozone is a much stronger oxidizing agent than dioxygen. Typically, elements capable of variable coordination number and/or oxidation states tend to exhibit greater numbers of allotropic forms, another contributing factor is the ability of an element to catenate. Cerium, samarium, dysprosium and ytterbium have three allotropes, praseodymium, neodymium, gadolinium and terbium have two allotropes. Plutonium has six distinct solid allotropes under normal pressures and their densities vary within a ratio of some 4,3, which vastly complicates all kinds of work with the metal. A seventh plutonium allotrope exists at high pressures. The transuranium metals Np, Am, and Cm are also allotropic, promethium, americium, berkelium and californium have three allotropes each. Isomer Polymorphism Superdense carbon allotropes Chisholm, Hugh, ed. Allotropy
15.
Amorphous silicon
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Amorphous silicon is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCD displays. Used as semiconductor material for solar cells, or thin-film silicon solar cells, it is deposited in thin films onto a variety of flexible substrates, such as glass, metal. Amorphous silicon differs from other variations, such as monocrystalline silicon—a single crystal, and polycrystalline silicon. Silicon is a fourfold coordinated atom that is normally tetrahedrally bonded to four neighboring silicon atoms, in crystalline silicon this tetrahedral structure continues over a large range, thus forming a well-ordered crystal lattice. In amorphous silicon this long range order is not present, rather, the atoms form a continuous random network. Moreover, not all the atoms within amorphous silicon are fourfold coordinated, due to the disordered nature of the material some atoms have a dangling bond. Physically, these dangling bonds represent defects in the random network. The material can be passivated by hydrogen, which bonds to the dangling bonds, hydrogenated amorphous silicon has a sufficiently low amount of defects to be used within devices such as solar photovoltaic cells, particularly in the protocrystalline growth regime. However, hydrogenation is associated with light-induced degradation of the material, amorphous alloys of silicon and carbon are an interesting variant. Introduction of carbon atoms adds extra degrees of freedom for control of the properties of the material, the film could also be made transparent to visible light. Increasing concentrations of carbon in the alloy widen the gap between conduction and valence bands. This can potentially increase the efficiency of solar cells made with amorphous silicon carbide layers. On the other hand, the properties as a semiconductor, are adversely affected by the increasing content of carbon in the alloy. The density of amorphous Si has been calculated as 4. 90×1022 atom/cm3 at 300 K and this was done using thin strips of amorphous silicon. This density is 1. 8±0. 1% less dense than crystalline Si at 300 K, Silicon is one of the few elements that expands upon cooling and has a lower density as a solid than as a liquid. By introducing hydrogen during the fabrication of amorphous silicon, photoconductivity is significantly improved, hydrogenated amorphous silicon, a-Si, H, was first fabricated in 1969 by Chittick, Alexander and Sterling by deposition using a silane gas precursor. The resulting material showed a lower density and increased conductivity due to impurities. Interest in a-Si, H came when, LeComber and Spear discovered the ability for substitutional doping of a-Si, starting in the 1970s, a-Si, H was developed in solar cells by RCA by which steadily climbed in efficiency to about 13. 6% in 2015
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Thin-film solar cell
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A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are used in several technologies, including cadmium telluride, copper indium gallium diselenide. This allows thin film cells to be flexible, and lower in weight and it is used in building integrated photovoltaics and as semi-transparent, photovoltaic glazing material that can be laminated onto windows. Other commercial applications use rigid thin film solar panels in some of the worlds largest photovoltaic power stations, thin-film technology has always been cheaper but less efficient than conventional c-Si technology. However, it has improved over the years. The lab cell efficiency for CdTe and CIGS is now beyond 21 percent, outperforming multicrystalline silicon, thin film cells are well-known since the late 1970s, when solar calculators powered by a small strip of amorphous silicon appeared on the market. It is now available in very large used in sophisticated building-integrated installations. Thin-film technologies reduce the amount of material in a cell. Most sandwich active material between two panes of glass, since silicon solar panels only use one pane of glass, thin film panels are approximately twice as heavy as crystalline silicon panels, although they have a smaller ecological impact. The majority of panels have 2-3 percentage points lower conversion efficiencies than crystalline silicon. Cadmium telluride, copper indium selenide and amorphous silicon are three thin-film technologies often used for outdoor applications. Cadmium telluride is the predominant thin film technology, with about 5 percent of worldwide PV production, it accounts for more than half of the thin film market. The cells lab efficiency has increased significantly in recent years and is on a par with CIGS thin film. Also, CdTe has the lowest Energy payback time of all mass-produced PV technologies, a prominent manufacturer is the US-company First Solar based in Tempe, Arizona, that produces CdTe-panels with an efficiency of about 14 percent at a reported cost of $0.59 per watt. The usage of materials may also become a limiting factor to the industrial scalability of CdTe thin film technology. The rarity of tellurium—of which telluride is the anionic form—is comparable to that of platinum in the earths crust and contributes significantly to the modules cost. A copper indium gallium selenide solar cell or CIGS cell uses an absorber made of copper, indium, gallium, selenide, a prominent manufacturer of cylindrical CIGS-panels was the now-bankrupt company Solyndra in Fremont, California. Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering, in 2008, IBM and Tokyo Ohka Kogyo Co. Ltd. announced they had developed a new, non-vacuum, solution-based manufacturing process for CIGS cells and are aiming for efficiencies of 15% and beyond
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Polycrystalline silicon
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Polycrystalline silicon, also called polysilicon or poly-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produced from metallurgical grade silicon by a purification process. This process involves distillation of volatile compounds, and their decomposition into silicon at high temperatures. An emerging, alternative process of refinement uses a fluidized bed reactor, the photovoltaic industry also produces upgraded metallurgical-grade silicon, using metallurgical instead of chemical purification processes. When produced for the industry, polysilicon contains impurity levels of less than one part per billion. The products are then sliced into thin wafers and used for the production of solar cells, integrated circuits. Polysilicon consists of crystals, also known as crystallites, giving the material its typical metal flake effect. About 5 tons of polysilicon is required to manufacture 1 megawatt of conventional solar modules, Polysilicon is distinct from monocrystalline silicon and amorphous silicon. In single crystal silicon, also known as silicon, the crystalline framework is homogenous. The entire sample is one single, continuous and unbroken crystal as its structure contains no grain boundaries, large single crystals are rare in nature and can also be difficult to produce in the laboratory. In contrast, in a structure the order in atomic positions is limited to short range. Polycrystalline and paracrystalline phases are composed of a number of crystals or crystallites. Polycrystalline silicon is a material consisting of small silicon crystals. Polycrystalline cells can be recognized by a grain, a metal flake effect. Single crystal silicon is used to manufacture most Si-based microelectronic devices, polycrystalline silicon can be as much as 99. 9999% pure. Ultra-pure poly is used in the industry, starting from poly rods that are two to three meters in length. In microelectronic industry, poly is used both at the macro-scale and micro-scale level, single crystals are grown using the Czochralski process, float-zone and Bridgman techniques. At the component level, polysilicon has long used as the conducting gate material in MOSFET
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Crystallite
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A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. The orientation of crystallites can be random with no preferred direction, called random texture, or directed, possibly due to growth, fiber texture is an example of the latter. Crystallites are also referred to as grains, the areas where crystallite grains meet are known as grain boundaries. Polycrystalline or multicrystalline materials, or polycrystals are solids that are composed of many crystallites of varying size, most inorganic solids are polycrystalline, including all common metals, many ceramics, rocks and ice. The extent to which a solid is crystalline has important effects on its physical properties, sulfur, while usually polycrystalline, may also occur in other allotropic forms with completely different properties. Although crystallites are referred to as grains, powder grains are different, while the structure of a crystal is highly ordered and its lattice is continuous and unbroken. Amorphous materials, such as glass and many polymers, are non-crystalline, Polycrystalline structures and paracrystalline phases are in between these two extremes. Crystal size is measured from X-ray diffraction patterns and grain size by other experimental techniques like transmission electron microscopy. Solid objects that are enough to see and handle are rarely composed of a single crystal. Most materials are polycrystalline, they are made of a number of single crystals — crystallites — held together by thin layers of amorphous solid. The crystallite size can vary from a few nanometers to several millimeters, if the individual crystallites are oriented completely at random, a large enough volume of polycrystalline material will be approximately isotropic. This property helps the simplifying assumptions of continuum mechanics to apply to real-world solids, however, most manufactured materials have some alignment to their crystallites, resulting in texture that must be taken into account for accurate predictions of their behavior and characteristics. When the crystallites are mostly ordered with just some random spread of orientations, material fractures can be intergranular fracture or a transgranular fracture. There is an ambiguity with powder grains, a grain can be made of several crystallites. Thus, the size found by laser granulometry can be different from the grain size found by X-ray diffraction, by optical microscopy under polarised light. Coarse grained rocks are formed very slowly, while fine grained rocks are formed quickly, if a rock forms very quickly, such as the solidification of lava ejected from a volcano, there may be no crystals at all. Grain boundaries are interfaces where crystals of different orientations meet, a grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. The term crystallite boundary is sometimes, though rarely, used, grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary
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Seed crystal
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A seed crystal is a small piece of single crystal / polycrystal material from which a large crystal of the same material typically is to be grown. The theory behind this effect is thought to derive from the physical interaction that occurs between compounds in a supersaturated solution. In solution, liberated molecules are free to move about in random flow and this random flow permits for the possibility of two or more molecular compounds to interact. This interaction can potentiate intermolecular forces between the molecules and form a basis for a crystal lattice. The placement of a seed crystal into solution allows the process to expedite by eliminating the need for random molecular collision / interaction. By introducing an already pre-formed basis of the crystal to act upon. Often, this transition from solute in a solution to a crystal lattice will be referred to as nucleation. Seeding is therefore said to decrease the amount of time needed for nucleation to occur in a recrystallization process. Crystal structure Crystallization Laser heated pedestal growth Micro-pulling-down Single crystal Wafer
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Argon
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Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the table and is a noble gas. Argon is the third-most abundant gas in the Earths atmosphere, at 0. 934% and it is more than twice as abundant as water vapor,23 times as abundant as carbon dioxide, and more than 500 times as abundant as neon. Argon is the most abundant noble gas in Earths crust, comprising 0. 00015% of the crust, nearly all of the argon in Earths atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the Earths crust. In the universe, argon-36 is by far the most common argon isotope, the name argon is derived from the Greek word ἀργόν, neuter singular form of ἀργός meaning lazy or inactive, as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet in the atomic shell makes argon stable. Its triple point temperature of 83.8058 K is a fixed point in the International Temperature Scale of 1990. Argon is produced industrially by the distillation of liquid air. Argon is also used in incandescent, fluorescent lighting, and other gas-discharge tubes, Argon makes a distinctive blue-green gas laser. Argon is also used in fluorescent glow starters, Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas, Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature. Although argon is a gas, it can form some compounds under extreme conditions. Argon fluorohydride, a compound of argon with fluorine and hydrogen that is stable below 17 K, has been demonstrated. Although the neutral ground-state chemical compounds of argon are presently limited to HArF, ions, such as ArH+, and excited-state complexes, such as ArF, have been demonstrated. Theoretical calculation predicts several more argon compounds that should be stable but have not yet been synthesized, Argon was suspected to be a component of air by Henry Cavendish in 1785. Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water and they had determined that nitrogen produced from chemical compounds was 0. 5% lighter than nitrogen from the atmosphere. The difference was slight, but it was important enough to attract their attention for many months and they concluded that there was another gas in the air mixed in with the nitrogen. Argon was also encountered in 1882 through independent research of H. F. Newall, each observed new lines in the color spectrum of air that did not match known elements
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Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
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Czochralski process
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The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors, metals, salts and synthetic gemstones. The process is named after Polish scientist Jan Czochralski, who invented the method in 1915 while investigating the rates of metals. Other semiconductors, such as gallium arsenide, can also be grown by this method, monocrystalline silicon grown by the Czochralski process is often referred to as monocrystalline Czochralski silicon. It is the material in the production of integrated circuits used in computers, TVs, mobile phones and all types of electronic equipment. Monocrystalline silicon is used in large quantities by the photovoltaic industry for the production of conventional mono-Si solar cells. The almost perfect crystal structure yields the highest light-to-electricity conversion efficiency for silicon, high-purity, semiconductor-grade silicon is melted in a crucible at 1425 degrees Celsius, usually made of quartz. A precisely oriented rod-mounted seed crystal is dipped into the molten silicon, the seed crystals rod is slowly pulled upwards and rotated simultaneously. By precisely controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, occurrence of unwanted instabilities in the melt can be avoided by investigating and visualizing the temperature and velocity fields during the crystal growth process. This process is performed in an inert atmosphere, such as argon, in an inert chamber. Due to the efficiencies of common wafer specifications, the industry has used wafers with standardized dimensions. In the early days, the boules were smaller, only a few inches wide, with advanced technology, high-end device manufacturers use 200 mm and 300 mm diameter wafers. The width is controlled by control of the temperature, the speeds of rotation. The crystal ingots from which these wafers are sliced can be up to 2 metres in length, larger wafers allow improvements in manufacturing efficiency, as more chips can be fabricated on each wafer, so there has been a steady drive to increase silicon wafer sizes. The next step up,450 mm, is scheduled for introduction in 2018. Silicon wafers are typically about 0. 2–0.75 mm thick, the process begins when the chamber is heated to approximately 1500 degrees Celsius, melting the silicon. When the silicon is melted, a small seed crystal mounted on the end of a rotating shaft is slowly lowered until it just dips below the surface of the molten silicon. The shaft rotates counterclockwise and the crucible rotates clockwise, the rotating rod is then drawn upwards very slowly—about 25 mm per hour when making a crystal of ruby—allowing a roughly cylindrical boule to be formed. The boule can be one to two metres, depending on the amount of silicon in the crucible
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Wafer (electronics)
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Finally the individual microcircuits are separated and packaged. By 1960, silicon wafers were being manufactured in the U. S. by companies such as MEMC/SunEdison. In 1965, American engineers Eric O. Ernst, Donald J. Hurd, Wafers are formed of highly pure, nearly defect-free single crystalline material. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, an ingot of high purity mono crystalline semiconductor, such as silicon or germanium. The boule is then sliced with a saw and polished to form wafers. The size of wafers for photovoltaics is 100–200 mm square and the thickness is 200–300 μm, in the future,160 μm will be the standard. Electronics use wafer sizes from 100–450 mm diameter, Wafers are cleaned with weak acids to remove unwanted particles, or repair damage caused during the sawing process. When used for cells, the wafers are textured to create a rough surface to increase their efficiency. The generated PSG is removed from the edge of the wafer in the etching, silicon wafers are available in a variety of diameters from 25.4 mm to 300 mm. Semiconductor fabrication plants are defined by the diameter of wafers that they are tooled to produce, Wafers grown using materials other than silicon will have different thicknesses than a silicon wafer of the same diameter. Wafer thickness is determined by the strength of the material used. This was the cost basis for increasing wafer size, conversion to 300 mm wafers from 200 mm wafers began in earnest in 2000, and reduced the price per die about 30-40%. However, this was not without significant problems for the industry, there is considerable resistance to the 450 mm transition despite the possible productivity improvement, because of concern about insufficient return on investment. Higher cost semiconductor fabrication equipment for larger wafers increases the cost of 450 mm fabs, converting to larger 450 mm wafers would reduce price per die only for process operations such as etch where cost is related to wafer count, not wafer area. Cost for processes such as lithography is proportional to wafer area, nikon plans to deliver 450-mm lithography equipment in 2015, with volume production in 2017. In November 2013 ASML paused development of 450-mm lithography equipment, citing uncertain timing of chipmaker demand, the time-line for 450 mm has not been fixed. Mark Durcan, CEO of Micron Technology, said in February 2014 that he expects 450 mm adoption to be delayed indefinitely or discontinued, “I am not convinced that 450mm will ever happen but, to the extent that it does, it’s a long way out in the future
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Carrier generation and recombination
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In the solid-state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many semiconductor devices, such as photodiodes, LEDs. They are also critical to a analysis of p-n junction devices such as bipolar junction transistors. Like other solids, semiconductor materials have a band structure determined by the crystal properties of the material. The actual energy distribution among the electrons is described by the Fermi level, at absolute zero temperature, all of the electrons have energy below the Fermi level, but at non-zero temperatures the energy levels are filled following a Boltzmann distribution. In semiconductors the Fermi level lies in the middle of a band or band gap between two allowed bands called the valence band and the conduction band. The valence band, immediately below the band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is nearly completely empty. Because the valence band is so full, its electrons are not mobile. However, if an electron in the valence band acquires enough energy to reach the conduction band, furthermore, it will also leave behind an electron hole that can flow as current exactly like a physical charged particle. In a material at thermal equilibrium generation and recombination are balanced, the equilibrium carrier density that results from the balance of these interactions is predicted by thermodynamics. The resulting probability of occupation of states in each energy band is given by Fermi–Dirac statistics. Recombination and generation are happening in semiconductors, both optically and thermally, and their rates are in balance at equilibrium. The product of the electron and hole densities is a constant at equilibrium, when there is a surplus of carriers, the rate of recombination becomes greater than the rate of generation, driving the system back towards equilibrium. Likewise, when there is a deficit of carriers, the rate becomes greater than the recombination rate. As the electron moves from one band to another, the energy. The following models are used to describe generation and recombination, depending on which particles are involved in the process, the localized state can absorb differences in momentum between the carriers, and so this process is the dominant generation and recombination process in silicon and other indirect bandgap materials. It can also dominate in direct bandgap materials under conditions of very low carrier densities, the energy is exchanged in the form of lattice vibration, a phonon exchanging thermal energy with the material
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Semiconductor device fabrication
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Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications, the entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing, as devices became more integrated, cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, the workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination. Semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, including Europe, the Middle East and it is a global business today. The leading semiconductor manufacturers typically have facilities all over the world, intel, the worlds largest manufacturer, has facilities in Europe and Asia as well as the U. S. A typical wafer is made out of pure silicon that is grown into mono-crystalline cylindrical ingots up to 300 mm in diameter using the Czochralski process. These ingots are sliced into wafers about 0.75 mm thick and polished to obtain a very regular. In semiconductor device fabrication, the processing steps fall into four general categories, deposition, removal, patterning. Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer, available technologies include physical vapor deposition, chemical vapor deposition, electrochemical deposition, molecular beam epitaxy and more recently, atomic layer deposition among others. Removal is any process that removes material from the wafer, examples include etch processes, patterning is the shaping or altering of deposited materials, and is generally referred to as lithography. After etching or other processing, the remaining photoresist is removed by plasma ashing, modification of electrical properties has historically entailed doping transistor sources and drains. These doping processes are followed by annealing or, in advanced devices. Modification of electrical properties now also extends to the reduction of a dielectric constant in low-k insulators via exposure to ultraviolet light in UV processing. Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps, FEOL processing refers to the formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, in the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. One method involves introducing a straining step wherein a silicon variant such as silicon-germanium is deposited, once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility
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Microfabrication
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Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, flat-panel displays and solar cells are also using similar techniques. It is also giving rise to various kinds of interdisciplinary research, the major concepts and principles of microfabrication are microlithography, doping, thin films, etching, bonding, and polishing. This parallelism is present in various imprint, casting and moulding techniques which have successfully applied in the microregime. For example, injection moulding of DVDs involves fabrication of submicrometer-sized spots on the disc, Microfabrication is actually a collection of technologies which are utilized in making microdevices. Some of them have very old origins, not connected to manufacturing, polishing was borrowed from optics manufacturing, and many of the vacuum techniques come from 19th century physics research. Electroplating is also a 19th-century technique adapted to produce micrometre scale structures, to fabricate a microdevice, many processes must be performed, one after the other, many times repeatedly. These processes typically include depositing a film, patterning the film with the micro features. For example, in memory chip fabrication there are some 30 lithography steps,10 oxidation steps,20 etching steps,10 doping steps, the complexity of microfabrication processes can be described by their mask count. This is the number of different pattern layers that constitute the final device, modern microprocessors are made with 30 masks while a few masks suffice for a microfluidic device or a laser diode. Microfabrication resembles multiple exposure photography, with many patterns aligned to other to create the final structure. Microfabricated devices are not generally freestanding devices but are formed over or in a thicker support substrate. For electronic applications, semiconducting substrates such as silicon wafers can be used, for optical devices or flat panel displays, transparent substrates such as glass or quartz are common. The substrate enables easy handling of the device through the many fabrication steps. Often many individual devices are made together on one substrate and then singulated into separated devices toward the end of fabrication, microfabricated devices are typically constructed using one or more thin films. The purpose of these thin films depends on the type of device, electronic devices may have thin films which are conductors, insulators or semiconductors. Optical devices may have films which are reflective, transparent, light guiding or scattering, films may also have a chemical or mechanical purpose as well as for MEMS applications. These features are on the micrometer or nanometer scale and the technology is what defines microfabrication
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Ion implantation
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Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into a solid. This process is used to change the physical, chemical, or electrical properties of the solid, ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research. The ions alter the composition of the target, stopping in the target. They also cause chemical and physical changes in the target by transferring their energy and momentum to the electrons. This causes a change, in that the crystal structure of the target can be damaged or even destroyed by the energetic collision cascades. Because the ions have masses comparable to those of the target atoms, if the ion energy is sufficiently high to overcome the coulomb barrier, there can even be a small amount of nuclear transmutation. Thus ion implantation is a case of particle radiation. Each ion is typically a single atom or molecule, and thus the amount of material implanted in the target is the integral over time of the ion current. This amount is called the dose, the currents supplied by implanters are typically small, and thus the dose which can be implanted in a reasonable amount of time is small. Therefore, ion implantation finds application in cases where the amount of change required is small. Typical ion energies are in the range of 10 to 500 keV, energies in the range 1 to 10 keV can be used, but result in a penetration of only a few nanometers or less. Energies lower than this result in little damage to the target. Higher energies can also be used, accelerators capable of 5 MeV are common, however, there is often great structural damage to the target, and because the depth distribution is broad, the net composition change at any point in the target will be small. The average penetration depth is called the range of the ions, under typical circumstances ion ranges will be between 10 nanometers and 1 micrometer. Thus, ion implantation is especially useful in cases where the chemical or structural change is desired to be near the surface of the target, the loss of ion energy in the target is called stopping and can be simulated with the binary collision approximation method. Accelerator systems for ion implantation are generally classified into medium current, high current, high energy, all varieties of ion implantation beamline designs contain certain general groups of functional components. The first major segment of an ion beamline includes a device known as an ion source to generate the ion species, •The introduction of dopants in a semiconductor is the most common application of ion implantation. • Dopant ions such as boron, phosphorus or arsenic are generally created from a gas source, •These gases tend to be very hazardous
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Etching (microfabrication)
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Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is an important process module, and every wafer undergoes many etching steps before it is complete. For many etch steps, part of the wafer is protected from the etchant by a material which resists etching. In some cases, the material is a photoresist which has been patterned using photolithography. Other situations require a more durable mask, such as silicon nitride, if the etch is intended to make a cavity in a material, the depth of the cavity may be controlled approximately using the etching time and the known etch rate. More often, though, etching must entirely remove the top layer of a multilayer structure, the etching systems ability to do this depends on the ratio of etch rates in the two materials. Some etches undercut the masking layer and form cavities with sloping sidewalls, the distance of undercutting is called bias. Etchants with large bias are called isotropic, because they erode the substrate equally in all directions, Modern processes greatly prefer anisotropic etches, because they produce sharp, well-controlled features. The two fundamental types of etchants are liquid-phase and plasma-phase, each of these exists in several varieties. The first etching processes used liquid-phase etchants, the wafer can be immersed in a bath of etchant, which must be agitated to achieve good process control. For instance, buffered hydrofluoric acid is used commonly to etch silicon dioxide over a silicon substrate, different specialised etchants can be used to characterise the surface etched. Wet etchants are usually isotropic, which leads to large bias when etching thick films and they also require the disposal of large amounts of toxic waste. For these reasons, they are used in state-of-the-art processes. However, the developer used for photoresist resembles wet etching. As an alternative to immersion, single wafer machines use the Bernoulli principle to employ a gas to cushion and it can be done to either the front side or back side. The etch chemistry is dispensed on the top side when in the machine and this etch method is particularly effective just before backend processing, where wafers are normally very much thinner after wafer backgrinding, and very sensitive to thermal or mechanical stress. Etching a thin layer of even a few micrometres will remove microcracks produced during backgrinding resulting in the wafer having dramatically increased strength, some wet etchants etch crystalline materials at very different rates depending upon which crystal face is exposed. In single-crystal materials, this effect can allow very high anisotropy, the term crystallographic etching is synonymous with anisotropic etching along crystal planes
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Thin-film deposition
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A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. The controlled synthesis of materials as thin films is a step in many applications. A familiar example is the mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once used to produce mirrors. It is also being applied to pharmaceuticals, via thin-film drug delivery, a stack of thin films is called a multilayer. In addition to their applied interest, thin films play an important role in the development and study of materials with new, examples include multiferroic materials, and superlattices that allow the study of quantum confinement by creating two-dimensional electron states. The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a film of material onto a substrate or onto previously deposited layers. Thin is a term, but most deposition techniques control layer thickness within a few tens of nanometres. Molecular beam epitaxy and atomic layer deposition allow a single layer of atoms to be deposited at a time and it is useful in the manufacture of optics, electronics, packaging, and in contemporary art. Deposition techniques fall into two categories, depending on whether the process is primarily chemical or physical. Here, a fluid precursor undergoes a change at a solid surface. An everyday example is the formation of soot on an object when it is placed inside a flame. Chemical deposition is further categorized by the phase of the precursor, Plating relies on liquid precursors, some plating processes are driven entirely by reagents in the solution, but by far the most commercially important process is electroplating. It was not commonly used in processing for many years. Chemical solution deposition or chemical bath deposition uses a liquid precursor and this is a relatively inexpensive, simple thin film process that is able to produce stoichiometrically accurate crystalline phases. This technique is known as the sol-gel method because the sol gradually evolves towards the formation of a gel-like diphasic system. The speed at which the solution is spun and the viscosity of the sol determine the thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired, thermal treatment is often carried out in order to crystallize the amorphous spin coated film
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Photolithography
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Photolithography, also termed optical lithography or UV lithography, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical photoresist, or simply resist, on the substrate. A series of chemical treatments then engraves the exposure pattern into, or enables deposition of a new material in the desired pattern upon. For example, in integrated circuits, a modern CMOS wafer will go through the photolithographic cycle up to 50 times. This procedure is comparable to a high precision version of the used to make printed circuit boards. Subsequent stages in the process have more in common with etching than with lithographic printing and its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions. The root words photo, litho, and graphy all have Greek origins, with the light, stone. As suggested by the name compounded from them, photolithography is a method in which light plays an essential role. In the 1820s, Nicephore Niepce invented a process that used Bitumen of Judea. In 1954, Louis Plambeck Jr. developed the Dycryl polymeric letterpress plate, a single iteration of photolithography combines several steps in sequence. Modern cleanrooms use automated, robotic wafer track systems to coordinate the process, the procedure described here omits some advanced treatments, such as thinning agents or edge-bead removal. Other solutions made with trichloroethylene, acetone or methanol can also be used to clean, the wafer is initially heated to a temperature sufficient to drive off any moisture that may be present on the wafer surface,150 °C for ten minutes is sufficient. Wafers that have been in storage must be cleaned to remove contamination. A liquid or gaseous adhesion promoter, such as Bisamine, is applied to promote adhesion of the photoresist to the wafer. The surface layer of silicon dioxide on the wafer reacts with HMDS to form tri-methylated silicon-dioxide, in order to ensure the development of the image, it is best covered and placed over a hot plate and let it dry while stabilizing the temperature at 120 °C. The wafer is covered with photoresist by spin coating, a viscous, liquid solution of photoresist is dispensed onto the wafer, and the wafer is spun rapidly to produce a uniformly thick layer. The spin coating typically runs at 1200 to 4800 rpm for 30 to 60 seconds, the spin coating process results in a uniform thin layer, usually with uniformity of within 5 to 10 nanometres. Thus, the top layer of resist is quickly ejected from the edge while the bottom layer still creeps slowly radially along the wafer
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Crystallographic defect
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Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, however, the arrangement of atoms or molecules in most crystalline materials is not perfect. The regular patterns are interrupted by crystallographic defects, point defects are defects that occur only at or around a single lattice point. They are not extended in space in any dimension, strict limits for how small a point defect is are generally not defined explicitly. However, these defects typically involve at most a few extra or missing atoms, larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects, especially in ionic crystals, are called centers, for example a vacancy in many ionic solids is called a luminescence center and these dislocations permit ionic transport through crystals leading to electrochemical reactions. These are frequently specified using Kröger–Vink Notation, vacancy defects are lattice sites which would be occupied in a perfect crystal, but are vacant. If a neighboring atom moves to occupy the vacant site, the moves in the opposite direction to the site which used to be occupied by the moving atom. The stability of the crystal structure guarantees that the neighboring atoms will not simply collapse around the vacancy. In some materials, neighboring atoms actually move away from a vacancy, a vacancy is sometimes called a Schottky defect. Interstitial defects are atoms that occupy a site in the structure at which there is usually not an atom. They are generally high energy configurations, small atoms in some crystals can occupy interstices without high energy, such as hydrogen in palladium. A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair and this is caused when an ion moves into an interstitial site and creates a vacancy. Due to fundamental limitations of material purification methods, materials are never 100% pure, in the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site, the atom is not supposed to be anywhere in the crystal, and is thus an impurity. In some cases where the radius of the atom is substantially smaller than that of the atom it is replacing. These types of defects are often referred to as off-center ions. There are two different types of defects, Isovalent substitution and aliovalent substitution
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Very-large-scale integration
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Very-large-scale integration is the process of creating an integrated circuit by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed, the microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM, VLSI lets IC designers add all of these into one chip. The History of the dates to the mid-1920s when several inventors attempted devices that were intended to control current in solid-state diodes. Success came after World War II, when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication, scientists who had been diverted to radar development returned to solid-state device development. With the invention of transistors at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state devices, with the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits. As the complexity of circuits grew, problems arose, one problem was the size of the circuit. A complex circuit, like a computer, was dependent on speed, the Invention of the integrated circuit by Jack Kilby, Robert Noyce solved this problem by making all the components and the chip out of the same block of semiconductor material. The circuits could be smaller, and the manufacturing process could be automated. The first semiconductor chips held two transistors each, subsequent advances added more transistors, and as a consequence, more individual functions or systems were integrated over time. Now known retrospectively as small-scale integration, improvements in technique led to devices with hundreds of logic gates, further improvements led to large-scale integration, i. e. systems with at least a thousand logic gates. Current technology has moved far past this mark and todays microprocessors have many millions of gates, at one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration were used, but the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use, in 2008, billion-transistor processors became commercially available. This became more commonplace as semiconductor fabrication advanced from the then-current generation of 65 nm processes, certain high-performance logic blocks like the SRAM cell, are still designed by hand to ensure the highest efficiency. Structured VLSI design is a modular methodology originated by Carver Mead and this is obtained by repetitive arrangement of rectangular macro blocks which can be interconnected using wiring by abutment. An example is partitioning the layout of an adder into a row of equal bit slices cells, in complex designs this structuring may be achieved by hierarchical nesting
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Copper indium gallium selenide solar cells
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A copper indium gallium selenide solar cell is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a layer of copper, indium, gallium and selenide on glass or plastic backing, along with electrodes on the front. Because the material has an absorption coefficient and strongly absorbs sunlight. CIGS is one of three mainstream thin-film PV technologies, the two being cadmium telluride and amorphous silicon. Like these materials, CIGS layers are thin enough to be flexible, however, as all of these technologies normally use high-temperature deposition techniques, the best performance normally comes from cells deposited on glass. Even then the performance is compared to modern polysilicon-based panels. Advances in low-temperature deposition of CIGS cells have erased much of this performance difference, thin-film market share is stagnated at around 15 percent, leaving the rest of the PV market to conventional solar cells made of crystalline silicon. In 2013, the share of CIGS alone was about 2 percent. CIGS cells continue being developed, as they promise to reach silicon-like efficiencies, while maintaining their low costs, prominent manufacturers of CIGS photovoltaics were the now-bankrupt companies Nanosolar and Solyndra. Current market leader is the Japanese company Solar Frontier, producing solar modules free of any heavy metals such as cadmium or lead, CIGS is a I-III-VI2 compound semiconductor material composed of copper, indium, gallium, and selenium. The material is a solution of copper indium selenide and copper gallium selenide, with a chemical formula of CuInxGaSe2. It is a tetrahedrally bonded semiconductor, with the crystal structure. The bandgap varies continuously with x from about 1.0 eV to about 1.7 eV, CIGS has an exceptionally high absorption coefficient of more than 105/cm for 1.5 eV and higher energy photons. The most common structure for CIGS solar cells is shown in the diagram. However, many companies are looking at lighter and more flexible substrates such as polyimide or metal foils. A molybdenum metal layer is deposited which serves as the back contact, following molybdenum deposition a p-type CIGS absorber layer is grown by one of several unique methods. A thin n-type buffer layer is added on top of the absorber, the buffer is typically cadmium sulfide deposited via chemical bath deposition. The buffer is overlaid with a thin, intrinsic zinc oxide layer which is capped by a thicker, the Al doped ZnO serves as a transparent conducting oxide to collect and move electrons out of the cell while absorbing as little light as possible
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Cadmium telluride photovoltaics
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Cadmium telluride photovoltaics describes a photovoltaic technology that is based on the use of cadmium telluride, a thin semiconductor layer designed to absorb and convert sunlight into electricity. Cadmium telluride PV is the thin film technology with lower costs than conventional solar cells made of crystalline silicon in multi-kilowatt systems. On a lifecycle basis, CdTe PV has the smallest carbon footprint, lowest water use, cdTes energy payback time of less than a year allows for faster carbon reductions without short-term energy deficits. The usage of materials may also become a limiting factor to the industrial scalability of CdTe technology in the mid-term future. The abundance of tellurium—of which telluride is the anionic form—is comparable to that of platinum in the earths crust, CdTe photovoltaics are used in some of the worlds largest photovoltaic power stations, such as the Topaz Solar Farm. With a share of 5. 1% of worldwide PV production, a prominent manufacturer of CdTe thin film technology is the company First Solar, based in Tempe, Arizona. The dominant PV technology has always been based on silicon wafers. Thin films and concentrators were early attempts to lower costs, thin films are based on using thinner semiconductor layers to absorb and convert sunlight. Concentrators lower the number of panels by using lenses or mirrors to put more sunlight on each panel, the first thin film technology to be extensively developed was amorphous silicon. However, this suffers from low efficiencies and slow deposition rates. Instead, the PV market reached some 4 gigawatts in 2007 with crystalline silicon comprising almost 90% of sales, the same source estimated that about 3 gigawatts were installed in 2007. During this period cadmium telluride and copper indium diselenide or CIS-alloys remained under development, the latter is beginning to be produced in volumes of 1–30 megawatts per year due to very high, small-area cell efficiencies approaching 20% in the laboratory. CdTe cell efficiency is approaching 20% in the laboratory with a record of 19. 6% as of 2013. Research in CdTe dates back to the 1950s, because its band gap is almost a match to the distribution of photons in the solar spectrum in terms of conversion to electricity. A simple heterojunction design evolved in which p-type CdTe was matched with n-type cadmium sulfide, the cell was completed by adding top and bottom contacts. Early leaders in CdS/CdTe cell efficiencies were GE in the 1960s, and then Kodak, Monosolar, Matsushita, by 1981, Kodak used close spaced sublimation and made the first 10% cells and first multi-cell devices. Monosolar and AMETEK used electrodeposition, an early method. Matsushita started with screen printing but shifted in the 1990s to CSS, Cells of about 10% sunlight-to-electricity efficiency were produced by the early 1980s at Kodak, Matsushita, Monosolar and AMETEK
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Solar panel
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Solar panel refers to a panel designed to absorb the suns rays as a source of energy for generating electricity or heating. A photovoltaic module is a packaged, connect assembly of typically 6×10 photovoltaic solar cells, photovoltaic modules constitute the photovoltaic array of a photovoltaic system that generates and supplies solar electricity in commercial and residential applications. Each module is rated by its DC output power under standard test conditions, the efficiency of a module determines the area of a module given the same rated output – an 8% efficient 230 watt module will have twice the area of a 16% efficient 230 watt module. There are a few commercially available solar modules that exceed 22% efficiency, a single solar module can produce only a limited amount of power, most installations contain multiple modules. A photovoltaic system typically includes an array of photovoltaic modules, an inverter, a pack for storage, interconnection wiring. The most common application of solar panels is solar heating systems. The price of power has continued to fall so that in many countries it is cheaper than ordinary fossil fuel electricity from the grid. Photovoltaic modules use light energy from the Sun to generate electricity through the photovoltaic effect, the majority of modules use wafer-based crystalline silicon cells or thin-film cells. The structural member of a module can either be the top layer or the back layer, cells must also be protected from mechanical damage and moisture. Most modules are rigid, but semi-flexible ones are available, based on thin-film cells, the cells must be connected electrically in series, one to another. Externally, most of photovoltaic modules use MC4 connectors type to facilitate easy connections to the rest of the system. Modules electrical connections are made in series to achieve an output voltage and/or in parallel to provide a desired current capability. The conducting wires that take the current off the modules may contain silver, copper or other non-magnetic conductive transition metals, bypass diodes may be incorporated or used externally, in case of partial module shading, to maximize the output of module sections still illuminated. Some special solar PV modules include concentrators in which light is focused by lenses or mirrors onto smaller cells and this enables the use of cells with a high cost per unit area in a cost-effective way. Depending on construction, photovoltaic modules can produce electricity from a range of frequencies of light, hence, much of the incident sunlight energy is wasted by solar modules, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into different wavelength ranges and this has been projected to be capable of raising efficiency by 50%. Scientists from Spectrolab, a subsidiary of Boeing, have reported development of solar cells with an efficiency of more than 40%. Currently the best achieved sunlight conversion rate is around 21. 5% in new products typically lower than the efficiencies of their cells in isolation
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Multi-junction solar cell
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Multi-junction solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each materials p-n junction will produce current in response to different wavelengths of light. The use of multiple semiconducting materials allows the absorbance of a range of wavelengths. Traditional single-junction cells have a theoretical efficiency of 33. 16%. Theoretically, a number of junctions would have a limiting efficiency of 86. 8% under highly concentrated sunlight. Commercial examples of tandem cells are available at 30% under one-sun illumination. However, this efficiency is gained at the cost of increased complexity, to date, their higher price and higher price-to-performance ratio have limited their use to special roles, notably in aerospace where their high power-to-weight ratio is desirable. In terrestrial applications, these cells are emerging in concentrator photovoltaics. Tandem fabrication techniques have been used to improve the performance of existing designs and this approach has been used by several commercial vendors, but these products are currently limited to certain niche roles, like roofing materials. Traditional photovoltaic cells are composed of doped silicon with metallic contacts deposited on the top. The doping is normally applied to a layer on the top of the cell, producing a pn-junction with a particular bandgap energy. Photons that hit the top of the cell are either reflected or transmitted into the cell. Transmitted photons have the potential to give their energy hν to an electron if hν ≥ Eg, in the depletion region, the drift electric field Edrift accelerates both electrons and holes towards their respective n-doped and p-doped regions. The resulting current Ig is called the generated photocurrent, in the quasi-neutral region, the scattering electric field Escatt accelerates holes towards the p-doped region, which gives a scattering photocurrent Ipscatt. Consequently, due to the accumulation of charges, a potential V, the expression for this photocurrent is obtained by adding generation and scattering photocurrents, Iph = Ig + Inscatt + Ipscatt. The J-V characteristics of a cell under illumination are obtained by shifting the J-V characteristics of a diode in the dark downward by Iph. Since solar cells are designed to power and not absorb it. Hence, the point is located in the region where V>0 and Iph<0
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Epitaxial growth
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Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate. The overlayer is called a film or epitaxial layer. The term epitaxy comes from the Greek roots epi, meaning above and it can be translated as arranging upon. For most technological applications, it is desired that the material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure. Epitaxial films may be grown from gaseous or liquid precursors, because the substrate acts as a seed crystal, the deposited film may lock into one or more crystallographic orientations with respect to the substrate crystal. If the overlayer either forms a random orientation with respect to the substrate or does not form an ordered overlayer, if an epitaxial film is deposited on a substrate of the same composition, the process is called homoepitaxy, otherwise it is called heteroepitaxy. Homoepitaxy is a kind of epitaxy performed with only one material and this technology is used to grow a film which is more pure than the substrate and to fabricate layers having different doping levels. In academic literature, homoepitaxy is often abbreviated to homoepi, heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a crystalline film grows on a substrate or film of a different material. This technology is used to grow crystalline films of materials for which crystals cannot otherwise be obtained. Examples include silicon on sapphire, gallium nitride on sapphire, aluminium gallium indium phosphide on gallium arsenide or diamond or iridium. Heterotopotaxy is a similar to heteroepitaxy except that thin film growth is not limited to two-dimensional growth. Pendeo-epitaxy is a process in which the film is growing vertically and laterally at the same time. Epitaxy is used in nanotechnology and in semiconductor fabrication, indeed, epitaxy is the only affordable method of high quality crystal growth for many semiconductor materials. In surface science, epitaxy is used to create and study monolayer and multilayer films of adsorbed organic molecules on single crystalline surfaces, adsorbed molecules form ordered structures on atomically flat terraces of single crystalline surfaces and can directly be observed via scanning tunnelling microscopy. Molecular-beam and liquid-phase epitaxy are also used, mainly for compound semiconductors, solid-phase epitaxy is used primarily for crystal-damage healing. Growth rates above 2 micrometres per minute produce polycrystalline silicon, an additional etching reaction competes with the deposition reaction, SiCl4 + Si ↔ 2SiCl2 Silicon VPE may also use silane, dichlorosilane, and trichlorosilane source gases. VPE is sometimes classified by the chemistry of the gases, such as hydride VPE
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Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
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Diamond cubic
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The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. Diamond cubic is in the Fd3m space group, which follows the face-centered cubic Bravais lattice, the diamond lattice can be viewed as a pair of intersecting face-centered cubic lattices, with each separated by 1/4 of the width of the unit cell in each dimension. Many compound semiconductors such as gallium arsenide, β-silicon carbide, and indium antimonide adopt the analogous zincblende structure, zincblendes space group is F43m, but many of its structural properties are quite similar to the diamond structure. The atomic packing factor of the cubic structure is π√3/16 ≈0.34. Zincblende structures have higher packing factors than 0.34 depending on the sizes of their two component atoms. The first-, second-, third-, fourth- and fifth-nearest-neighbor distances in units of the lattice constant are √3/4, √2/2, √11/4,1 and √19/4. Mathematically, the points of the cubic structure can be given coordinates as a subset of a three-dimensional integer lattice by using a cubic unit cell four units across. With these coordinates, the points of the structure have coordinates satisfying the equations x = y = z, and x + y + z =0 or 1. There are eight points that satisfy these conditions, All of the points in the structure may be obtained by adding multiples of four to the x, y. Adjacent points in this structure are at distance √3 apart in the integer lattice and this structure may be scaled to a cubical unit cell that is some number a of units across by multiplying all coordinates by a/4. Alternatively, each point of the cubic structure may be given by four-dimensional integer coordinates whose sum is either zero or one. Two points are adjacent in the structure if and only if their four-dimensional coordinates differ by one in a single coordinate. The total difference in values between any two points gives the number of edges in the shortest path between them in the diamond structure. These four-dimensional coordinates may be transformed into three-dimensional coordinates by the formula →, because the diamond structure forms a distance-preserving subset of the four-dimensional integer lattice, it is a partial cube. Yet another coordinatization of the diamond cubic involves the removal of some of the edges from a grid graph. The diamond cubic is sometimes called the lattice but it is not, mathematically. However, it is still a highly symmetric structure, any incident pair of a vertex, moreover the diamond crystal as a network in space has a strong isotropic property. Another crystal with this property is the Laves graph, the compressive strength and hardness of diamond and various other materials, such as boron nitride, is attributed to the diamond cubic structure
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VLSI
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Very-large-scale integration is the process of creating an integrated circuit by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed, the microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM, VLSI lets IC designers add all of these into one chip. The History of the dates to the mid-1920s when several inventors attempted devices that were intended to control current in solid-state diodes. Success came after World War II, when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication, scientists who had been diverted to radar development returned to solid-state device development. With the invention of transistors at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state devices, with the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits. As the complexity of circuits grew, problems arose, one problem was the size of the circuit. A complex circuit, like a computer, was dependent on speed, the Invention of the integrated circuit by Jack Kilby, Robert Noyce solved this problem by making all the components and the chip out of the same block of semiconductor material. The circuits could be smaller, and the manufacturing process could be automated. The first semiconductor chips held two transistors each, subsequent advances added more transistors, and as a consequence, more individual functions or systems were integrated over time. Now known retrospectively as small-scale integration, improvements in technique led to devices with hundreds of logic gates, further improvements led to large-scale integration, i. e. systems with at least a thousand logic gates. Current technology has moved far past this mark and todays microprocessors have many millions of gates, at one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration were used, but the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use, in 2008, billion-transistor processors became commercially available. This became more commonplace as semiconductor fabrication advanced from the then-current generation of 65 nm processes, certain high-performance logic blocks like the SRAM cell, are still designed by hand to ensure the highest efficiency. Structured VLSI design is a modular methodology originated by Carver Mead and this is obtained by repetitive arrangement of rectangular macro blocks which can be interconnected using wiring by abutment. An example is partitioning the layout of an adder into a row of equal bit slices cells, in complex designs this structuring may be achieved by hierarchical nesting
41.
Intel
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Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California that was founded by Gordon Moore and Robert Noyce. It is the worlds largest and highest valued semiconductor chip makers based on revenue, and is the inventor of the x86 series of microprocessors, Intel supplies processors for computer system manufacturers such as Apple, Lenovo, HP, and Dell. Intel Corporation was founded on July 18,1968, by semiconductor pioneers Robert Noyce and Gordon Moore, the companys name was conceived as portmanteau of the words integrated and electronics. The fact that intel is the term for intelligence information made the name appropriate. Intel was a developer of SRAM and DRAM memory chips. Although Intel created the worlds first commercial microprocessor chip in 1971, during the 1990s, Intel invested heavily in new microprocessor designs fostering the rapid growth of the computer industry. The Open Source Technology Center at Intel hosts PowerTOP and LatencyTOP, and supports other projects such as Wayland, Intel Array Building Blocks, and Threading Building Blocks. Client Computing Group – 55% of 2016 revenues – produces hardware components used in desktop, data Center Group – 29% of 2016 revenues – produces hardware components used in server, network, and storage platforms. Internet of Things Group – 5% of 2016 revenues – offers platforms designed for retail, transportation, industrial, buildings, non-Volatile Memory Solutions Group – 4% of 2016 revenues – manufactures NAND flash memory products primarily used in solid-state drives. Intel Security Group – 4% of 2016 revenues – produces software, particularly security, programmable Solutions Group – 3% of 2016 revenues – manufactures programmable semiconductors. In 2016, Dell accounted for 15% of Intels total revenues, Lenovo accounted for 13% of total revenues, in the 1980s, Intel was among the top ten sellers of semiconductors in the world. In 1991, Intel became the biggest chip maker by revenue and has held the position ever since, other top semiconductor companies include TSMC, Advanced Micro Devices, Samsung, Texas Instruments, Toshiba and STMicroelectronics. Competitors in PC chip sets include Advanced Micro Devices, VIA Technologies, Silicon Integrated Systems, however, the cross-licensing agreement is canceled in the event of an AMD bankruptcy or takeover. Some smaller competitors such as VIA Technologies produce low-power x86 processors for small factor computers, however, the advent of such mobile computing devices, in particular, smartphones, has in recent years led to a decline in PC sales. Since over 95% of the worlds smartphones currently use processors designed by ARM Holdings, ARM is also planning to make inroads into the PC and server market. Intel has been involved in disputes regarding violation of antitrust laws. Intel was founded in Mountain View, California in 1968 by Gordon E. Moore, a chemist, and Robert Noyce, arthur Rock helped them find investors, while Max Palevsky was on the board from an early stage. Moore and Noyce had left Fairchild Semiconductor to found Intel, Rock was not an employee, but he was an investor and was chairman of the board
