An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. A common mnemonic is ACID for "anode current into device"; the direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow out the anode into the outside circuit. In a galvanic cell, the anode is the electrode. An anode is the wire or plate having excess positive charge. Anions will tend to move towards the anode; the terms anode and cathode are not defined by the voltage polarity of electrodes but the direction of current through the electrode. An anode is an electrode through which conventional current flows into the device from the external circuit, while a cathode is an electrode through which conventional current flows out of the device. If the current through the electrodes reverses direction, as occurs for example in a rechargeable battery when it is being charged, the naming of the electrodes as anode and cathode is reversed.
Conventional current depends not only on the direction the charge carriers move, but the carriers' electric charge. The currents outside the device are carried by electrons in a metal conductor. Since electrons have a negative charge, the direction of electron flow is opposite to the direction of conventional current. Electrons leave the device through the anode and enter the device through the cathode; the definition of anode and cathode is different for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow. These devices allow substantial current flow in one direction but negligible current in the other direction; therefore the electrodes are named based on the direction of this "forward" current. In a diode the anode is the terminal through which current enters and the cathode is the terminal through which current leaves, when the diode is forward biased; the names of the electrodes do not change in cases. In a vacuum tube only one electrode can emit electrons into the evacuated tube due to being heated by a filament, so electrons can only enter the device from the external circuit through the heated electrode.
Therefore this electrode is permanently named the cathode, the electrode through which the electrons exit the tube is named the anode. The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. In the following examples, the anode is negative in a device that provides power, positive in a device that consumes power: In a discharging battery or galvanic cell, the anode is the negative terminal because it is where conventional current flows into "the device"; this inward current is carried externally by electrons moving outwards, negative charge flowing in one direction being electrically equivalent to positive charge flowing in the opposite direction. In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator; the current through a recharging battery is opposite to the direction of current during discharge. In a diode, the anode is the positive terminal at the tail of the arrow symbol, where current flows into the device.
Note electrode naming for diodes is always based on the direction of the forward current for types such as Zener diodes or solar cells where the current of interest is the reverse current. In a cathode ray tube, the anode is the positive terminal where electrons flow out of the device, i.e. where positive electric current flows in. The word was coined in 1834 from the Greek ἄνοδος,'ascent', by William Whewell, consulted by Michael Faraday over some new names needed to complete a paper on the discovered process of electrolysis. In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the "decomposing body" in a direction "from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move", the anode is where the current enters the electrolyte, on the East side: "ano upwards, odos a way; the use of'East' to mean the'in' direction may appear contrived. As related in the first reference cited above, Faraday had used the more straightforward term "eisode".
His motivation for changing it to something meaning'the East electrode' was to make it immune to a possible change in the direction convention for current, whose exact nature was not known at the time. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant, he fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. This made the internal current East to West as mentioned, but in the event of a convention change it woul
A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known since it "straightens" the direction of current. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, stacks of copper and selenium oxide plates, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena to serve as a point-contact rectifier or "crystal detector". Rectifiers have many uses, but are found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power; as noted, detectors of radio signals serve as rectifiers.
In gas heating systems flame rectification is used to detect presence of a flame. Depending on the type of alternating current supply and the arrangement of the rectifier circuit, the output voltage may require additional smoothing to produce a uniform steady voltage. Many applications of rectifiers, such as power supplies for radio and computer equipment, require a steady constant DC voltage. In these applications the output of the rectifier is smoothed by an electronic filter, which may be a capacitor, choke, or set of capacitors and resistors followed by a voltage regulator to produce a steady voltage. More complex circuitry that performs the opposite function, converting DC to AC, is called an inverter. Before the development of silicon semiconductor rectifiers, vacuum tube thermionic diodes and copper oxide- or selenium-based metal rectifier stacks were used. With the introduction of semiconductor electronics, vacuum tube rectifiers became obsolete, except for some enthusiasts of vacuum tube audio equipment.
For power rectification from low to high current, semiconductor diodes of various types are used. Other devices that have control electrodes as well as acting as unidirectional current valves are used where more than simple rectification is required—e.g. Where variable output voltage is needed. High-power rectifiers, such as those used in high-voltage direct current power transmission, employ silicon semiconductor devices of various types; these are thyristors or other controlled switching solid-state switches, which function as diodes to pass current in only one direction. Rectifier circuits may be multi-phase. Most low power rectifiers for domestic equipment are single-phase, but three-phase rectification is important for industrial applications and for the transmission of energy as DC. In half-wave rectification of a single-phase supply, either the positive or negative half of the AC wave is passed, while the other half is blocked. Mathematically, it is a step function: passing positive corresponds to the ramp function being the identity on positive inputs, blocking negative corresponds to being zero on negative inputs.
Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply. Rectifiers yield a pulsating direct current; the no-load output DC voltage of an ideal half-wave rectifier for a sinusoidal input voltage is: V r m s = V p e a k 2 V d c = V p e a k π where: Vdc, Vav – the DC or average output voltage, the peak value of the phase input voltages, the root mean square value of output voltage. A full-wave rectifier converts the whole of the input waveform to one of constant polarity at its output. Mathematically, this corresponds to the absolute value function. Full-wave rectification converts both polarities of the input waveform to pulsating DC, yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source, are needed. Single semiconductor diodes, double diodes with common cathode or common anode, four-diode bridges, are manufactured as single components.
For single-phase AC, if the transformer is center-tapped two diodes back-to-back can form a full-wave rectifier. Twice as many turns are required on the transformer secondary to obtain the same output voltage than for a bridge rectifier, but the power rating is unchanged; the average and RMS no-load output voltages of an ideal single-phase full-wave rectifier are: V
William Bradford Shockley Jr. was an American physicist and inventor. Shockley was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain; the three scientists were jointly awarded the 1956 Nobel Prize in Physics for "their researches on semiconductors and their discovery of the transistor effect". Shockley's attempts to commercialize a new transistor design in the 1950s and 1960s led to California's "Silicon Valley" becoming a hotbed of electronics innovation. In his life, Shockley was a professor of electrical engineering at Stanford University and became a proponent of eugenics. Shockley was born in London, to American parents, raised in his family's hometown of Palo Alto, California from the age of three, his father, William Hillman Shockley, was a mining engineer who speculated in mines for a living and spoke eight languages. His mother, grew up in the American West, graduated from Stanford University and became the first female U. S. Deputy mining surveyor.
Shockley earned his Bachelor of Science degree from Caltech in 1932 and a PhD from MIT in 1936. The title of his doctoral thesis was Electronic Bands in Sodium Chloride, a topic suggested by his thesis advisor, John C. Slater. After receiving his doctorate, Shockley joined a research group headed by Clinton Davisson at Bell Labs in New Jersey; the next few years were productive for Shockley. He published a number of fundamental papers on solid state physics in Physical Review. In 1938, he got his first patent, "Electron Discharge Device", on electron multipliers; when World War II broke out, Shockley became involved in radar research at Bell Labs in Manhattan. In May 1942, he took leave from Bell Labs to become a research director at Columbia University's Anti-Submarine Warfare Operations Group; this involved devising methods for countering the tactics of submarines with improved convoying techniques, optimizing depth charge patterns, so on. This project required frequent trips to the Pentagon and Washington, where Shockley met many high-ranking officers and government officials.
In 1944, he organized a training program for B-29 bomber pilots to use new radar bomb sights. In late 1944 he took a three-month tour to bases around the world to assess the results. For this project, Secretary of War Robert Patterson awarded Shockley the Medal for Merit on October 17, 1946. In July 1945, the War Department asked Shockley to prepare a report on the question of probable casualties from an invasion of the Japanese mainland. Shockley concluded: If the study shows that the behavior of nations in all historical cases comparable to Japan's has in fact been invariably consistent with the behavior of the troops in battle it means that the Japanese dead and ineffectives at the time of the defeat will exceed the corresponding number for the Germans. In other words, we shall have to kill at least 5 to 10 million Japanese; this might cost us between 4 million casualties including 400,000 to 800,000 killed. This report influenced the decision of the United States to drop atomic bombs on Hiroshima and Nagasaki, which precipitated the unconditional surrender of Japan.
Shockley was the first physicist to propose a lognormal distribution to model the creation process for scientific research papers. Shortly after the war ended in 1945, Bell Labs formed a solid-state physics group, led by Shockley and chemist Stanley Morgan, which included John Bardeen, Walter Brattain, physicist Gerald Pearson, chemist Robert Gibney, electronics expert Hilbert Moore, several technicians, their assignment was to seek a solid-state alternative to fragile glass vacuum tube amplifiers. Its first attempts were based on Shockley's ideas about using an external electrical field on a semiconductor to affect its conductivity; these experiments failed every time in all sorts of materials. The group was at a standstill until Bardeen suggested a theory that invoked surface states that prevented the field from penetrating the semiconductor; the group changed its focus to study these surface states and they met daily to discuss the work. The rapport of the group was excellent, ideas were exchanged.
By the winter of 1946 they had enough results that Bardeen submitted a paper on the surface states to Physical Review. Brattain started experiments to study the surface states through observations made while shining a bright light on the semiconductor's surface; this led to several more papers, which estimated the density of the surface states to be more than enough to account for their failed experiments. The pace of the work picked up when they started to surround point contacts between the semiconductor and the conducting wires with electrolytes. Moore built a circuit, they began to get some evidence of power amplification when Pearson, acting on a suggestion by Shockley, put a voltage on a droplet of glycol borate placed across a P-N junction. Bell Labs' attorneys soon discovered Shockley's field effect principle had been anticipated and devices based on it patented in 1930 by Julius Lilienfeld, who filed his MESFET-like patent in Canada on October 22, 1925. Although the patent appeared "breakable" the patent attorneys based one of its four patent applications only on the Bardeen-Brattain point contact design.
Three others covered the electrolyte-based transistors with Bardeen and Brattain as the inventors. Shockley's name was not on any of these patent applications; this an
Solid-state electronics means semiconductor electronics. The term is used for devices in which semiconductor electronics which have no moving parts replace devices with moving parts, such as the solid-state relay in which transistor switches are used in place of a moving-arm electromechanical relay, or the solid-state drive a type of semiconductor memory used in computers to replace hard disk drives, which store data on a rotating disk; the term "solid state" became popular in the beginning of the semiconductor era in the 1960s to distinguish this new technology based on the transistor, in which the electronic action of devices occurred in a solid state, from previous electronic equipment that used vacuum tubes, in which the electronic action occurred in a gaseous state. A semiconductor device works by controlling an electric current consisting of electrons or holes moving within a solid crystalline piece of semiconducting material such as silicon, while the thermionic vacuum tubes it replaced worked by controlling current conducted by a gas of particles, electrons or ions, moving in a vacuum within a sealed tube.
Although the first solid state electronic device was the cat's whisker detector, a crude semiconductor diode invented around 1904, solid state electronics started with the invention of the transistor in 1947. Before that, all electronic equipment used vacuum tubes, because vacuum tubes were the only electronic components that could amplify, an essential capability in all electronics; the replacement of bulky, energy-wasting vacuum tubes by transistors in the 1960s and 1970s created a revolution not just in technology but in people's habits, making possible the first portable consumer electronics such as the transistor radio, cassette tape player, walkie-talkie and quartz watch, as well as the first practical computers and mobile phones. Today all electronics are solid-state except in some applications such as radio transmitters, in which vacuum tubes are still used, some power industrial control circuits which use electromechanical devices such as relays. Additional examples of solid state electronic devices are the microprocessor chip, LED lamp, solar cell, charge coupled device image sensor used in cameras, semiconductor laser.
Condensed matter physics Laser diode Materials science Semiconductor device Solar cell Solid-state physics
Reona Esaki known as Leo Esaki, is a Japanese physicist who shared the Nobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his work in electron tunneling in semiconductor materials which led to his invention of the Esaki diode, which exploited that phenomenon. This research was done, he has contributed in being a pioneer of the semiconductor superlattices. Esaki was born in Takaida-mura, Nakakawachi-gun, Osaka Prefecture and grew up in Kyoto, near by Kyoto Imperial University and Doshisha University, he first had American culture in Doshisha Junior High School. After graduating from the Third Higher School, he studied physics at Tokyo Imperial University, where he had attended Hideki Yukawa's course in nuclear theory in October 1944, he lived through the Bombing of Tokyo while he was at college. Esaki received his B. Sc. and Ph. D. in 1947 and 1959 from the University of Tokyo. From 1947 to 1960, Esaki joined Tokyo Tsushin Kogyo. Meanwhile, American physicists John Bardeen, Walter Brattain, William Shockley invented the transistor, which encouraged Esaki to change fields from vacuum tube to heavily-doped germanium and silicon research in Sony.
One year he recognized that when the PN junction width of germanium is thinned, the current-voltage characteristic is dominated by the influence of the tunnel effect and, as a result, he discovered that as the voltage is increased, the current decreases inversely, indicating negative resistance. This discovery was the first demonstration of solid tunneling effects in physics, it was the birth of new electronic devices in electronics called Esaki diode, he received a doctorate degree from UTokyo due to this breakthrough invention in 1959. In 1973, Esaki was awarded the Nobel Prize for research conducted around 1958 regarding electron tunneling in solids, he became the first Nobel laureate to receive the prize from the hands of the King Carl XVI Gustaf. Esaki moved to the United States in 1960 and joined the IBM T. J. Watson Research Center, where he became an IBM Fellow in 1967, he predicted that semiconductor superlattices will be formed to induce a differential negative-resistance effect via an artificially one-dimensional periodic structural changes in semiconductor crystals.
His unique "molecular beam epitaxy" thin-film crystal growth method can be regulated quite in ultrahigh vacuum. His first paper on the semiconductor superlattice was published in 1970. A 1987 comment by Esaki regarding the original paper notes: "The original version of the paper was rejected for publication by Physical Review on the referee's unimaginative assertion that it was'too speculative' and involved'no new physics.' However, this proposal was accepted by the Army Research Office..." In 1972, Esaki realized his concept of superlattices in III-V group semiconductors the concept influenced many fields like metals, magnetic materials. He was awarded the IEEE Medal of Honor "for contributions to and leadership in tunneling, semiconductor superlattices, quantum wells" in 1991 and the Japan Prize "for the creation and realization of the concept of man-made superlattice crystals which lead to generation of new materials with useful applications" in 1998. In 1994 Lindau Nobel Laureate Meetings, Esaki suggests a list of “five don’ts” which anyone in realizing his creative potential should follow.
Two months the chairman of the Nobel Committee for Physics Carl Nordling incorporated the rules in his own speech. Don’t allow yourself to be trapped by your past experiences. Don’t allow yourself to become overly attached to any one authority in your field – the great professor, perhaps. Don’t hold on to what you don’t need. Don’t avoid confrontation. Don’t forget your spirit of childhood curiosity. Esaki moved back to Japan in 1992, subsequently, he served as president of the University of Tsukuba and Shibaura Institute of Technology. Since 2006 he is the president of Yokohama College of Pharmacy. Esaki is the recipient of The International Center in New York's Award of Excellence, the Order of Culture and the Grand Cordon of the Order of the Rising Sun. In recognition of three Nobel laureates' contributions, the bronze statues of Shin'ichirō Tomonaga, Leo Esaki, Makoto Kobayashi were set up in the Central Park of Azuma 2 in Tsukuba City in 2015. After the death of Yoichiro Nambu on 2015, Esaki is the eldest Japanese Nobel laureate.
List of Japanese Nobel laureates List of Nobel laureates affiliated with the University of Tokyo Large scale integrated circuits technology: state of the art and prospects, proceedings of the NATO Advanced Study Institute on "Large Scale Integrated Circuits Technology: State of the Art and Prospects," Erice, July 15–27, 1981 / edited by Leo Esaki and Giovanni Soncini Highlights in condensed matter physics and future prospects / edited by Leo Esaki Leo Esaki – Biography. Retrieved August 5, 2003 from http://www.nobel.se/physics/laureates/1973/esaki-bio.html IBM record IEEE History Center – Leo Esaki. Retrieved July 19, 2011 from http://www.ieeeghn.org/wiki/index.php/Leo_Esaki Sony History – The Esaki Diode. Retrieved August 5, 2003 from https://web.archive.org/web/20030804052243/http://www.sony.net/Fun/SH/1-7/h5.html Freeview video'An Interview with Leo Esaki' by the Vega Science Trust
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
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