Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, grayish-white metalloid in the carbon group, chemically similar to its group neighbours silicon and tin. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium reacts and forms complexes with oxygen in nature; because it appears in high concentration, germanium was discovered comparatively late in the history of chemistry. Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, called the element ekasilicon. Nearly two decades in 1886, Clemens Winkler found the new element along with silver and sulfur, in a rare mineral called argyrodite. Although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleev's predictions for a relative of silicon.
Winkler named the element after Germany. Today, germanium is mined from sphalerite, though germanium is recovered commercially from silver and copper ores. Elemental germanium is used as a semiconductor in various other electronic devices; the first decade of semiconductor electronics was based on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, light-emitting diodes. Germanium compounds are used for polymerization catalysts and have most found use in the production of nanowires; this element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry. Germanium is considered a technology-critical element. Germanium is not thought to be an essential element for any living organism; some complex organic germanium compounds are being investigated as possible pharmaceuticals, though none have yet proven successful. Similar to silicon and aluminium, natural germanium compounds tend to be insoluble in water and thus have little oral toxicity.
However, synthetic soluble germanium salts are nephrotoxic, synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins. In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family, located between silicon and tin; because of its position in his periodic table, Mendeleev called it ekasilicon, he estimated its atomic weight to be 70. In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content; the chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, a new element. Winkler found it similar to antimony, he considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon. Before Winkler published his results on the new element, he decided that he would name his element neptunium, since the recent discovery of planet Neptune in 1846 had been preceded by mathematical predictions of its existence.
However, the name "neptunium" had been given to another proposed chemical element. So instead, Winkler named the new element germanium in honor of his homeland. Argyrodite proved empirically to be Ag8GeS6; because this new element showed some similarities with the elements arsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that place on the periodic table. With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887, he determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride, while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element. Winkler was able to prepare several new compounds of germanium, including fluorides, sulfides and tetraethylgermane, the first organogermane; the physical data from those compounds—which corresponded well with Mendeleev's predictions—made the discovery an important confirmation of Mendeleev's idea of element periodicity.
Here is a comparison between the prediction and Winkler's data: Until the late 1930s, germanium was thought to be a poorly conducting metal. Germanium did not become economically significant until after 1945 when its properties as an electronic semiconductor were recognized. During World War II, small amounts of germanium were used in some special electronic devices diodes; the first major use was the point-contact Schottky diodes for radar pulse detection during the War. The first silicon-germanium alloys were obtained in 1955. Before 1945, only a few hundred kilograms of germanium were produced in smelters each year, but by the end of the 1950s, the annual worldwide production had reached 40 metric tons; the development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics. From 1950 through the early 1970s, this area provided an increasing market for germanium, but high-purity silicon began replacing germanium in transistors and rectifiers.
For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transist
A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals; because the controlled power can be higher than the controlling power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits; the transistor is the fundamental building block of modern electronic devices, is ubiquitous in modern electronic systems. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to construct a working device at that time; the first implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, William Shockley. The transistor revolutionized the field of electronics, paved the way for smaller and cheaper radios and computers, among other things.
The transistor is on the list of IEEE milestones in electronics, Bardeen and Shockley shared the 1956 Nobel Prize in Physics for their achievement. Most transistors are made from pure silicon or germanium, but certain other semiconductor materials can be used. A transistor may have only one kind of charge carrier, in a field effect transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Compared with the vacuum tube, transistors are smaller, require less power to operate. Certain vacuum tubes have advantages over transistors at high operating frequencies or high operating voltages. Many types of transistors are made to standardized specifications by multiple manufacturers; the thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, was a fragile device that consumed a substantial amount of power. In 1909 physicist William Eccles discovered the crystal diode oscillator. Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor in Canada in 1925, intended to be a solid-state replacement for the triode.
Lilienfeld filed identical patents in the United States in 1926 and 1928. However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any specific examples of a working prototype; because the production of high-quality semiconductor materials was still decades away, Lilienfeld's solid-state amplifier ideas would not have found practical use in the 1920s and 1930s if such a device had been built. In 1934, German inventor Oskar Heil patented a similar device in Europe. From November 17, 1947, to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in Murray Hill, New Jersey of the United States performed experiments and observed that when two gold point contacts were applied to a crystal of germanium, a signal was produced with the output power greater than the input. Solid State Physics Group leader William Shockley saw the potential in this, over the next few months worked to expand the knowledge of semiconductors; the term transistor was coined by John R. Pierce as a contraction of the term transresistance.
According to Lillian Hoddeson and Vicki Daitch, authors of a biography of John Bardeen, Shockley had proposed that Bell Labs' first patent for a transistor should be based on the field-effect and that he be named as the inventor. Having unearthed Lilienfeld’s patents that went into obscurity years earlier, lawyers at Bell Labs advised against Shockley's proposal because the idea of a field-effect transistor that used an electric field as a "grid" was not new. Instead, what Bardeen and Shockley invented in 1947 was the first point-contact transistor. In acknowledgement of this accomplishment, Shockley and Brattain were jointly awarded the 1956 Nobel Prize in Physics "for their researches on semiconductors and their discovery of the transistor effect". In 1948, the point-contact transistor was independently invented by German physicists Herbert Mataré and Heinrich Welker while working at the Compagnie des Freins et Signaux, a Westinghouse subsidiary located in Paris. Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II.
Using this knowledge, he began researching the phenomenon of "interference" in 1947. By June 1948, witnessing currents flowing through point-contacts, Mataré produced consistent results using samples of germanium produced by Welker, similar to what Bardeen and Brattain had accomplished earlier in December 1947. Realizing that Bell Labs' scientists had invented the transistor before them, the company rushed to get its "transistron" into production for amplified use in France's telephone network; the first bipolar junction transistors were invented by Bell Labs' William Shockley, which applied for patent on June 26, 1948. On April 12, 1950, Bell Labs chemists Gordon Teal and Morgan Sparks had produced a working bipolar NPN junction amplifying germanium transistor. Bell Labs had announced the discovery of this new "sandwich" transistor in a press release on July 4, 1951; the first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953, capable of operating up to 60 MHz.
These were made by etching depressions into an N-type germanium base from both sides with jets of Indium sulfate until it was a few ten-thousandths of an inch thick. Indium electroplated into the depressions formed the emitter; the first "prototype" pocket transistor radio was shown by I
Silicon-tin or SiSn, is in general a term used for an alloy of the form SiSnx. The molecular ratio of tin in silicon can vary based on the fabrication methods or doping conditions. In general, SiSn is known to be intrinsically semiconducting, small amounts of Sn doping in silicon can be used to create strain in the silicon lattice and alter the charge transport properties. Several theoretical works have shown SiSn to be semiconducting; these include DFT-based studies. The band structures obtained using these works show a change in band gap of silicon with the inclusion of tin into the silicon lattice. Thus, like SiGe, SiSn has a variable band gap that can be controlled using Sn concentration as a variable. In 2015, Hussain et al. experimentally verified the tuning of band gap associated with the diffusion of tin using homogenous, abrupt p-n junction diodes. SiSn can be obtained experimentally using several approaches. For small quantity of Sn in silicon, the Czochralski process is well known. Diffusion of tin into silicon has been tried extensively in the past.
Sn has the same valency and electronegativity as silicon and can be found in the diamond cubic crystal structure. Thus and tin meet three out of the four Hume-Rothery rules for solid state solubility; the one criterion, not met is that of difference in atomic size. The tin atom is bigger than the silicon atom; this reduces the solid state solubility of tin in silicon. The first Metal-Oxide-Semiconductor Field-Effect Transistor using SiSn as a channel material was shown in 2013; this study proved that SiSn can be used as semiconductor for MOSFET fabrication, that there may be certain applications where the use of SiSn instead of silicon may be more advantageous. In particular, the off current of SiSn transistors is much lower than that of silicon transistors. Thus, logic circuits based on SiSn MOSFETs consume lower static power compared to silicon based circuits; this is advantageous in battery operated devices, where the standby power has to be reduced for longer battery life. Si-Sn alloys have the lowest conductivity of all the bulk alloys among Si-Ge, Ge-Sn and Si-Ge-Sn, more than 2 times lower than Si-Ge which has extensively been studied, attributed to the larger difference in mass between the two constituents.
In addition, thin films offer an additional reduction in thermal conductivity, reaching around 1 W/mK in 20-nm-thick Si-Sn, Ge-Sn, ternary Si-Ge-Sn films, near the conductivity of amorphous SiO2. Group-IV alloys containing Sn have the potential for high-efficiency thermoelectric energy conversion. Silicon germanium Silicon carbide
In semiconductor manufacturing, the International Technology Roadmap for Semiconductors defines the 7 nanometer node as the technology node following the 10 nm node. Single transistor 7 nm scale devices were first produced in the early 2000s. While some claim that the node designation of "7 nm" has no physical meaning beyond marketing purposes, others point to transistor density as the real important number, represented by these designations; the 7 nm process offerings by Samsung and TSMC are the same as the 10 nm process offered by Intel, what matters beyond 10 nm is transistor density, not transistor size. As of September 2018, mass production of 7 nm devices has begun; the first mainstream 7 nm mobile processor intended for mass market use, the Apple A12 Bionic, was released at their September 2018 event. Although Huawei announced its own 7 nm processor before the Apple A12 Bionic, the Kirin 980 on August 31, 2018, the Apple A12 Bionic was released for public, mass market use to consumers before the Kirin 980.
Both chips are manufactured by TSMC. AMD is working on their "Rome" workstation processors, which are based on the 7 nanometer node and feature up to 64 cores. In July 2015, IBM announced that they had built the first functional transistors with 7 nm technology, using a silicon-germanium process. By early 2017, TSMC had produced 256 Mbit SRAM cells at their 7 nm process with a cell area of 0.027 mm2 with reasonable risk production yields. In April 2016, TSMC announced that 7 nm trial production would begin in the first half of 2017. In March 2017, TSMC announced 7 nm with EUV risk production starting by June 2018. TSMC's 7 nm production plans, as of early 2017, were to use DUV immersion lithography on this process node, transition from risk to commercial volume manufacturing from Q2 2017 to Q2 2018, their generation 7 nm production is planned to use EUV multiple patterning and to have an estimated transition from risk to volume manufacturing between 2018 and 2019. In September 2016, GlobalFoundries announced trial production in the second half of 2017 and risk production in early 2018, with test chips running.
In February 2017, Intel announced Fab 42 in Chandler, Arizona will produce microprocessors using 7 nm manufacturing process. The company has not published any expected values for feature lengths at this process node. In April 2018, TSMC announced volume production of 7 nm chips. In June 2018, the company announced mass production ramp up. In May 2018, Samsung announced production of 7 nm chips this year. ASML Holding NV is their main supplier of EUV lithography machines. In June 2018, AMD announced 7 nm Radeon Instinct GPUs launching in the second half of 2018. In August 2018, the company has confirmed the release of the GPUs. In August 2018, GlobalFoundries announced. On September 12, 2018, Apple announced their A12 Bionic chip used in iPhone XS and iPhone XR built using a 7 nm process; the A12 processor became the first 7 nm chip intended for mass market use. On October 30, 2018, Apple announced their A12X Bionic chip used in iPad Pro built using a 7 nm process, similar to the standard A12 chip.
The 7 nm foundry node is expected to utilize any of or a combination of the following patterning technologies: pitch splitting, self-aligned patterning, EUV lithography. Each of these technologies carries significant challenges in critical dimension control as well as pattern placement, all involving neighboring features. Pitch splitting involves splitting features that are too close together onto different masks, which are exposed successively, followed by litho-etch processing. Due to the use of different exposures, there is always the risk of overlay error between the two exposures, as well as different CDs resulting from the different exposures. Spacer patterning involves depositing a layer onto pre-patterned features etching back to form spacers on the sidewalls of those features, referred to as core features. After removing the core features, the spacers are used as an etch mask to define trenches in the underlying layer. While the spacer CD control is excellent, the trench CD may fall into one of two populations, due to the two possibilities of being located where a core feature was located or in the remaining gap.
This is known as'pitch walking'. Pitch = core CD + gap CD + 2 * spacer CD, but this does not guarantee core CD = gap CD. For FEOL features like gate or active area isolation, the trench CD is not as critical as the spacer-defined CD, in which case, spacer patterning is the preferred patterning approach; when self-aligned quadruple patterning is used, there is a second spacer, utilized, replacing the first one. In this case, the core CD is replaced by core CD - 2* 2nd spacer CD, the gap CD is replaced by gap CD - 2 * 2nd spacer CD. Thus, some feature dimensions are defined by the second spacer CD, while the remaining feature dimensions are defined by the core CD, core pitch, first and second spacer CD's; the core CD and core pitch are defined by conventional lithography, while the spacer CDs are independent of lithography. This is expected to have less variation than pitch splitting, where an additional exposure defines its own CD, both directly and through overlay. Spacer-defined lines require cutting.
The cut spots may shift at exposure, resulting in distorted line ends or intrusions into adjacent lines. EUV lithography is capable of resolving features below 20 nm in conventional lithography style. However, the 3D reflective nature of the EUV mask results in new anomalies in the imaging. One particular nuisance is the two-bar effect, where a pair of identical bar-shape
The metal-oxide-semiconductor field-effect transistor is a type of field-effect transistor, most fabricated by the controlled oxidation of silicon. It has an insulated gate; this ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. A metal-insulator-semiconductor field-effect transistor or MISFET is a term synonymous with MOSFET. Another synonym is IGFET for insulated-gate field-effect transistor; the basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925. The main advantage of a MOSFET is that it requires no input current to control the load current, when compared with bipolar transistors. In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity; the "metal" in the name MOSFET is sometimes a misnomer, because the gate material can be a layer of polysilicon.
"oxide" in the name can be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. The MOSFET is by far the most common transistor in digital circuits, as billions may be included in a memory chip or microprocessor. Since MOSFETs can be made with either p-type or n-type semiconductors, complementary pairs of MOS transistors can be used to make switching circuits with low power consumption, in the form of CMOS logic; the basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925. In 1959, Dawon Kahng and Martin M. Atalla at Bell Labs invented the metal-oxide-semiconductor field-effect transistor as an offshoot to the patented FET design. Operationally and structurally different from the bipolar junction transistor, the MOSFET was made by putting an insulating layer on the surface of the semiconductor and placing a metallic gate electrode on that, it used crystalline silicon for the semiconductor and a thermally oxidized layer of silicon dioxide for the insulator.
The silicon MOSFET did not generate localized electron traps at the interface between the silicon and its native oxide layer, thus was inherently free from the trapping and scattering of carriers that had impeded the performance of earlier field-effect transistors. The semiconductor of choice is silicon; some chip manufacturers, most notably IBM and Intel, have started using a chemical compound of silicon and germanium in MOSFET channels. Many semiconductors with better electrical properties than silicon, such as gallium arsenide, do not form good semiconductor-to-insulator interfaces, thus are not suitable for MOSFETs. Research continues on creating insulators with acceptable electrical characteristics on other semiconductor materials. To overcome the increase in power consumption due to gate current leakage, a high-κ dielectric is used instead of silicon dioxide for the gate insulator, while polysilicon is replaced by metal gates; the gate is separated from the channel by a thin insulating layer, traditionally of silicon dioxide and of silicon oxynitride.
Some companies have started to introduce a high-κ dielectric and metal gate combination in the 45 nanometer node. When a voltage is applied between the gate and body terminals, the electric field generated penetrates through the oxide and creates an inversion layer or channel at the semiconductor-insulator interface; the inversion layer provides a channel through which current can pass between source and drain terminals. Varying the voltage between the gate and body modulates the conductivity of this layer and thereby controls the current flow between drain and source; this is known as enhancement mode. The traditional metal-oxide-semiconductor structure is obtained by growing a layer of silicon dioxide on top of a silicon substrate and depositing a layer of metal or polycrystalline silicon; as the silicon dioxide is a dielectric material, its structure is equivalent to a planar capacitor, with one of the electrodes replaced by a semiconductor. When a voltage is applied across a MOS structure, it modifies the distribution of charges in the semiconductor.
If we consider a p-type semiconductor, a positive voltage, V GB, from gate to body creates a depletion layer by forcing the positively charged holes away from the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, negatively charged acceptor ions. If V GB is high enough, a high concentration of negative charge carriers forms in an inversion layer located in a thin layer next to the interface between the semiconductor and the insulator. Conventionally, the gate voltage at which the volume density of electrons in the inversion layer is the same as the volume density of holes in the body is called the threshold voltage; when the voltage between transistor gate and source exceeds the threshold voltage, the difference is known as overdrive voltage. This structure with p-type body is the basis of the n-type MOSFET, which requires the addition of n-type source and drain regions; the MOS capacitor structure is the heart of the MOSFET. Let's consider a MOS capacitor.
If a positive voltage is applied at
International Business Machines Corporation is an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the Computing-Tabulating-Recording Company and was renamed "International Business Machines" in 1924. IBM produces and sells computer hardware and software, provides hosting and consulting services in areas ranging from mainframe computers to nanotechnology. IBM is a major research organization, holding the record for most U. S. patents generated by a business for 26 consecutive years. Inventions by IBM include the automated teller machine, the floppy disk, the hard disk drive, the magnetic stripe card, the relational database, the SQL programming language, the UPC barcode, dynamic random-access memory; the IBM mainframe, exemplified by the System/360, was the dominant computing platform during the 1960s and 1970s. IBM has continually shifted business operations by focusing on higher-value, more profitable markets.
This includes spinning off printer manufacturer Lexmark in 1991 and the sale of personal computer and x86-based server businesses to Lenovo, acquiring companies such as PwC Consulting, SPSS, The Weather Company, Red Hat. In 2014, IBM announced that it would go "fabless", continuing to design semiconductors, but offloading manufacturing to GlobalFoundries. Nicknamed Big Blue, IBM is one of 30 companies included in the Dow Jones Industrial Average and one of the world's largest employers, with over 380,000 employees, known as "IBMers". At least 70% of IBMers are based outside the United States, the country with the largest number of IBMers is India. IBM employees have been awarded five Nobel Prizes, six Turing Awards, ten National Medals of Technology and five National Medals of Science. In the 1880s, technologies emerged that would form the core of International Business Machines. Julius E. Pitrap patented the computing scale in 1885. On June 16, 1911, their four companies were amalgamated in New York State by Charles Ranlett Flint forming a fifth company, the Computing-Tabulating-Recording Company based in Endicott, New York.
The five companies had offices and plants in Endicott and Binghamton, New York. C.. They manufactured machinery for sale and lease, ranging from commercial scales and industrial time recorders and cheese slicers, to tabulators and punched cards. Thomas J. Watson, Sr. fired from the National Cash Register Company by John Henry Patterson, called on Flint and, in 1914, was offered a position at CTR. Watson joined CTR as General Manager 11 months was made President when court cases relating to his time at NCR were resolved. Having learned Patterson's pioneering business practices, Watson proceeded to put the stamp of NCR onto CTR's companies, he implemented sales conventions, "generous sales incentives, a focus on customer service, an insistence on well-groomed, dark-suited salesmen and had an evangelical fervor for instilling company pride and loyalty in every worker". His favorite slogan, "THINK", became a mantra for each company's employees. During Watson's first four years, revenues reached $9 million and the company's operations expanded to Europe, South America and Australia.
Watson never liked the clumsy hyphenated name "Computing-Tabulating-Recording Company" and on February 14, 1924 chose to replace it with the more expansive title "International Business Machines". By 1933 most of the subsidiaries had been merged into one company, IBM. In 1937, IBM's tabulating equipment enabled organizations to process unprecedented amounts of data, its clients including the U. S. Government, during its first effort to maintain the employment records for 26 million people pursuant to the Social Security Act, the tracking of persecuted groups by Hitler's Third Reich through the German subsidiary Dehomag. In 1949, Thomas Watson, Sr. created IBM World Trade Corporation, a subsidiary of IBM focused on foreign operations. In 1952, he stepped down after 40 years at the company helm, his son Thomas Watson, Jr. was named president. In 1956, the company demonstrated the first practical example of artificial intelligence when Arthur L. Samuel of IBM's Poughkeepsie, New York, laboratory programmed an IBM 704 not to play checkers but "learn" from its own experience.
In 1957, the FORTRAN scientific programming language was developed. In 1961, IBM developed the SABRE reservation system for American Airlines and introduced the successful Selectric typewriter. In 1963, IBM employees and computers helped. A year it moved its corporate headquarters from New York City to Armonk, New York; the latter half of the 1960s saw IBM continue its support of space exploration, participating in the 1965 Gemini flights, 1966 Saturn flights and 1969 lunar mission. On April 7, 1964, IBM announced the first computer system family, the IBM System/360, it spanned the complete range of commercial and scientific applications from large to small, allowing companies for the first time to upgrade to models with greater computing capability without having to rewrite their applications. It was followed by the IBM System/370 in 1970. Together the
Gallium arsenide is a compound of the elements gallium and arsenic. It is a III-V direct bandgap semiconductor with a zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared light-emitting diodes, laser diodes, solar cells and optical windows. GaAs is used as a substrate material for the epitaxial growth of other III-V semiconductors including indium gallium arsenide, aluminum gallium arsenide and others. In the compound, gallium has a +3 oxidation state. Gallium arsenide single crystals can be prepared by three industrial processes: The vertical gradient freeze process. Crystal growth using a horizontal zone furnace in the Bridgman-Stockbarger technique, in which gallium and arsenic vapors react, free molecules deposit on a seed crystal at the cooler end of the furnace. Liquid encapsulated Czochralski growth is used for producing high-purity single crystals that can exhibit semi-insulating characteristics.
Alternative methods for producing films of GaAs include: VPE reaction of gaseous gallium metal and arsenic trichloride: 2 Ga + 2 AsCl3 → 2 GaAs + 3 Cl2 MOCVD reaction of trimethylgallium and arsine: Ga3 + AsH3 → GaAs + 3 CH4 Molecular beam epitaxy of gallium and arsenic: 4 Ga + As4 → 4 GaAs or 2 Ga + As2 → 2 GaAsOxidation of GaAs occurs in air and degrades performance of the semiconductor. The surface can be passivated by depositing a cubic gallium sulfide layer using a tert-butyl gallium sulfide compound such as 7. If a GaAs boule is grown with excess arsenic present, it gets certain defects, in particular arsenic antisite defects; the electronic properties of these defects cause the Fermi level to be pinned to near the center of the bandgap, so that this GaAs crystal has low concentration of electrons and holes. This low carrier concentration is similar to an intrinsic crystal, but much easier to achieve in practice; these crystals are called reflecting their high resistivity of 107 -- 109 Ω · cm.
Wet etching of GaAs industrially uses an oxidizing agent such as hydrogen peroxide or bromine water, the same strategy has been described in a patent relating to processing scrap components containing GaAs where the Ga3+ is complexed with a hydroxamic acid, for example: GaAs + H2O2 + "HA" → "GaA" complex + H3AsO4 + 4 H2OThis reaction produces arsenic acid. GaAs can be used for various transistor types: MESFET HEMT JFET Heterojunction bipolar transistor The HBT can be used in integrated injection logic; the earliest GaAs logic gate used Buffered FET Logic. From ~1975 to 1995 the main logic families used were: Source-coupled FET logic fastest and most complex, Capacitor–diode FET logic Direct-coupled FET logic simplest and lowest power Some electronic properties of gallium arsenide are superior to those of silicon, it has a higher saturated electron velocity and higher electron mobility, allowing gallium arsenide transistors to function at frequencies in excess of 250 GHz. GaAs devices are insensitive to overheating, owing to their wider energy bandgap, they tend to create less noise in electronic circuits than silicon devices at high frequencies.
This is a result of lower resistive device parasitics. These superior properties are compelling reasons to use GaAs circuitry in mobile phones, satellite communications, microwave point-to-point links and higher frequency radar systems, it is used in the manufacture of Gunn diodes for the generation of microwaves. Another advantage of GaAs is that it has a direct band gap, which means that it can be used to absorb and emit light efficiently. Silicon has an indirect bandgap and so is poor at emitting light; as a wide direct band gap material with resulting resistance to radiation damage, GaAs is an excellent material for outer space electronics and optical windows in high power applications. Because of its wide bandgap, pure GaAs is resistive. Combined with a high dielectric constant, this property makes GaAs a good substrate for Integrated circuits and unlike Si provides natural isolation between devices and circuits; this has made it an ideal material for monolithic microwave integrated circuits, MMICs, where active and essential passive components can be produced on a single slice of GaAs.
One of the first GaAs microprocessors was developed in the early 1980s by the RCA corporation and was considered for the Star Wars program of the United States Department of Defense. These processors were several times faster and several orders of magnitude more radiation proof than silicon counterparts, but were more expensive. Other GaAs processors were implemented by the supercomputer vendors Cray Computer Corporation and Alliant in an attempt to stay ahead of the ever-improving CMOS microprocessor. Cray built one GaAs-based machine in the early 1990s, the Cray-3, but the effort was not adequately capitalized, the company filed for bankruptcy in 1995. Complex layered structures of gallium arsenide in combination with aluminium arsenide or the alloy AlxGa1−xAs can be grown using molecular beam epitaxy or using metalorganic vapor phase epitaxy; because GaAs and AlAs have the same lattice constant, the layers have little induced strain, which allows them to be g