Gallium Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...

arsenide In chemistry, an arsenide is a compound of arsenic with a less electronegative element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many stoichiometries, and in this respect ars ...

(GaAs) is a

III-V Semiconductor materials are nominally small band gap insulators. The defining property of a semiconductor material is that it can be compromised by doping it with impurities that alter its electronic properties in a controllable way. Because of t ...

direct band gap In semiconductor physics, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characteriz ...

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

with a

zinc blende Sphalerite (sometimes spelled sphaelerite) is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Va ...

crystal structure. Gallium arsenide is used in the manufacture of devices such as

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

frequency

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

monolithic microwave integrated circuit Monolithic microwave integrated circuit, or MMIC (sometimes pronounced "mimic"), is a type of integrated circuit (IC) device that operates at microwave frequencies (300 MHz to 300 GHz). These devices typically perform functions such as ...

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...

laser diode file:Laser diode chip.jpg, The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a di ...

solar cells A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physics, physical and Chemical substance, chemical phenomenon. GaAs is often used as a substrate material for the epitaxial growth of other III-V semiconductors, including

indium gallium arsenide Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound) of indium arsenide (InAs) and gallium arsenide (GaAs). Indium and gallium are ( group III) elements of the periodic table whil ...

aluminum gallium arsenide Aluminium gallium arsenide (also gallium aluminium arsenide) ( Alx Ga1−x As) is a semiconductor material with very nearly the same lattice constant as GaAs, but a larger bandgap. The ''x'' in the formula above is a number between 0 and 1 - this ...

and others.

Preparation and chemistry

In the compound, gallium has a +3

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

. Gallium arsenide

single crystal In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...

s can be prepared by three industrial processes: * The vertical gradient freeze (VGF) process. * Crystal growth using a horizontal zone furnace in the Bridgman-Stockbarger technique, in which gallium and arsenic vapors react, and free molecules deposit on a seed crystal at the cooler end of the furnace. * Liquid encapsulated Czochralski (LEC) growth is used for producing high-purity single crystals that can exhibit semi-insulating characteristics (see below). Most GaAs wafers are produced using this process. Alternative methods for producing films of GaAs include: * VPE reaction of gaseous gallium metal and

arsenic trichloride Arsenic trichloride is an inorganic compound with the formula AsCl3, also known as arsenous chloride or butter of arsenic. This poisonous oil is colourless, although impure samples may appear yellow. It is an intermediate in the manufacture of o ...

: 2 Ga + 2 → 2 GaAs + 3 *

MOCVD Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...

reaction of

trimethylgallium Trimethylgallium, often abbreviated to TMG or TMGa, is the organogallium compound with the formula Ga(CH3)3. It is a colorless, pyrophoric liquid. Unlike trimethylaluminium, TMG adopts a monomeric structure. When examined in detail, the monomeric ...

and

arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in th ...

: + → GaAs + 3 *

Molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the devel ...

(MBE) of

gallium Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...

and

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

: 4 Ga + → 4 GaAs or 2 Ga + → 2 GaAs Oxidation of GaAs occurs in air, degrading performance of the semiconductor. The surface can be passivated by depositing a cubic

gallium(II) sulfide Gallium(II) sulfide, GaS, is a chemical compound of gallium and sulfur. The normal form of gallium(II) sulfide as made from the elements has a hexagonal layer structure containing Ga24+ units which have a Ga-Ga distance of 248pm. This layer struct ...

layer using a tert-butyl gallium sulfide compound such as (.

Semi-insulating crystals

In the presence of excess arsenic, GaAs

boules ''Boules'' () is a collective name for a wide range of games similar to bowls and bocce (In French: jeu or jeux, in Croatian: boćanje and in Italian: gioco or giochi) in which the objective is to throw or roll heavy balls (called in France, ...

grow with

crystallographic defect A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell para ...

s; specifically, arsenic antisite defects (an arsenic atom at a gallium atom site within the crystal lattice). The electronic properties of these defects (interacting with others) cause the

Fermi level The Fermi level of a solid-state body is the thermodynamic work required to add one electron to the body. It is a thermodynamic quantity usually denoted by ''µ'' or ''E''F for brevity. The Fermi level does not include the work required to remove ...

to be pinned to near the center of the band gap, so that this GaAs crystal has very low concentration of electrons and holes. This low carrier concentration is similar to an intrinsic (perfectly undoped) crystal, but much easier to achieve in practice. These crystals are called "semi-insulating", reflecting their high resistivity of 10⁷–10⁹ Ω·cm (which is quite high for a semiconductor, but still much lower than a true insulator like glass).McCluskey, Matthew D. and Haller, Eugene E. (2012) ''Dopants and Defects in Semiconductors'', pp. 41 and 66,

Etching

Wet etching of GaAs industrially uses an oxidizing agent such as

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...

water, and the same strategy has been described in a patent relating to processing scrap components containing GaAs where the is complexed with a

hydroxamic acid A hydroxamic acid is a class of organic compounds bearing the functional group RC(O)N(OH)R', with R and R' as organic residues and CO as a carbonyl group. They are amides (RC(O)NHR') wherein the NH center has an OH substitution. They are often us ...

("HA"), for example: :GaAs + + "HA" → "GaA" complex + + 4 This reaction produces

arsenic acid Arsenic acid or trihydrogen arsenate is the chemical compound with the formula . More descriptively written as , this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as ...

Electronics

GaAs digital logic

GaAs can be used for various transistor types: 'Clear search' to see pages *

Metal–semiconductor field-effect transistor A MESFET (metal–semiconductor field-effect transistor) is a field-effect transistor semiconductor device similar to a JFET with a Schottky barrier, Schottky (metal–semiconductor) junction instead of a p–n junction for a gate (transistor), gat ...

(MESFET) *

High-electron-mobility transistor A high-electron-mobility transistor (HEMT), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field-effect transistor incorporating a junction between two materials with different band gaps (i.e. a heterojunction) ...

(HEMT) *

Junction field-effect transistor The junction-gate field-effect transistor (JFET) is one of the simplest types of field-effect transistor. JFETs are three-terminal semiconductor devices that can be used as electronically controlled switches or resistors, or to build amplifiers ...

(JFET) *

Heterojunction bipolar transistor The heterojunction bipolar transistor (HBT) is a type of bipolar junction transistor (BJT) which uses differing semiconductor materials for the emitter and base regions, creating a heterojunction. The HBT improves on the BJT in that it can handle s ...

(HBT) *

Metal–oxide–semiconductor field-effect transistor The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

(MOSFET) The HBT can be used in

integrated injection logic Integrated injection logic (IIL, I2L, or I2L) is a class of digital circuits built with multiple collector bipolar junction transistors (BJT). When introduced it had speed comparable to TTL yet was almost as low power as CMOS, making it ideal fo ...

(I²L). The earliest GaAs logic gate used

Buffered FET Logic Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Buffering agent, the weak acid or base in a buffer solution * Lysis buffer, in cell biology * Metal ion buffer * ...

(BFL). From to 1995 the main logic families used were: * Source-coupled FET logic (SCFL) fastest and most complex, (used by TriQuint & Vitesse) * Capacitor–diode FET logic (CDFL) (used by Cray for

Cray-3 The Cray-3 was a vector supercomputer, Seymour Cray's designated successor to the Cray-2. The system was one of the first major applications of gallium arsenide (GaAs) semiconductors in computing, using hundreds of custom built ICs packed into ...

) *

Direct-coupled FET logic Direct coupled or Direct-coupled may refer to: * Direct-coupled amplifier * Direct-coupled transistor logic * Direct coupled (applied to an engine An engine or motor is a machine designed to convert one or more forms of energy into mechanica ...

(DCFL) simplest and lowest power (used by Vitesse for VLSI gate arrays)

Comparison with silicon for electronics

GaAs advantages

Some electronic properties of gallium arsenide are superior to those of

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

. It has a higher saturated electron velocity and higher

electron mobility In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobili ...

, allowing gallium arsenide transistors to function at frequencies in excess of 250 GHz. GaAs devices are relatively insensitive to overheating, owing to their wider energy band gap, and they also tend to create less

noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...

(disturbance in an electrical signal) in electronic circuits than silicon devices, especially at high frequencies. This is a result of higher carrier mobilities and lower resistive device parasitics. These superior properties are compelling reasons to use GaAs circuitry in

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

communications, microwave point-to-point links and higher frequency

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

systems. It is also used in the manufacture of

Gunn diode A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 19 ...

s for the generation of

s. Another advantage of GaAs is that it has a

, which means that it can be used to absorb and emit light efficiently. Silicon has an

indirect band gap In semiconductor physics, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characteriz ...

and so is relatively 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 band gap, pure GaAs is highly resistive. Combined with a high

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

, this property makes GaAs a very good substrate for

s and unlike Si provides natural isolation between devices and circuits. This has made it an ideal material for

s (MMICs), where active and essential passive components can readily be produced on a single slice of GaAs. One of the first GaAs

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

s was developed in the early 1980s by the

RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...

Corporation and was considered for the Star Wars program of the

United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secu ...

. These processors were several times faster and several orders of magnitude more radiation resistant than their silicon counterparts, but were more expensive. Other GaAs processors were implemented by the

supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second ( FLOPS) instead of million instructions ...

vendors

Cray Cray Inc., a subsidiary of Hewlett Packard Enterprise, is an American supercomputer manufacturer headquartered in Seattle, Washington. It also manufactures systems for data storage and analytics. Several Cray supercomputer systems are listed ...

Computer Corporation,

Convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytope ...

, and Alliant in an attempt to stay ahead of the ever-improving

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...

microprocessor. Cray eventually built one GaAs-based machine in the early 1990s, the

, but the effort was not adequately capitalized, and the company filed for bankruptcy in 1995. Complex layered structures of gallium arsenide in combination with

aluminium arsenide Aluminium arsenide () is a semiconductor material with almost the same lattice constant as gallium arsenide and aluminium gallium arsenide and wider band gap than gallium arsenide. (AlAs) can form a superlattice with gallium arsenide ( GaAs) which ...

(AlAs) or the alloy Al_xGa_1−xAs can be grown using

molecular-beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the develo ...

(MBE) or using metalorganic vapor-phase epitaxy (MOVPE). Because GaAs and AlAs have almost the same

lattice constant A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has o ...

, the layers have very little induced

strain Strain may refer to: Science and technology * Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes * Strain (chemistry), a chemical stress of a molecule * Strain (injury), an injury to a mu ...

, which allows them to be grown almost arbitrarily thick. This allows extremely high performance and high electron mobility

HEMT A high-electron-mobility transistor (HEMT), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field-effect transistor incorporating a junction between two materials with different band gaps (i.e. a heterojunction) ...

transistors and other

quantum well A quantum well is a potential well with only discrete energy values. The classic model used to demonstrate a quantum well is to confine particles, which were initially free to move in three dimensions, to two dimensions, by forcing them to occupy ...

devices. GaAs is used for monolithic radar power amplifiers (but

GaN The word Gan or the initials GAN may refer to: Places *Gan, a component of Hebrew placenames literally meaning "garden" China * Gan River (Jiangxi) * Gan River (Inner Mongolia), * Gan County, in Jiangxi province * Gansu, abbreviated ''Gā ...

can be less susceptible to heat damage).

Silicon advantages

Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process in the form of

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

minerals. The

economies of scale In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...

available to the silicon industry has also hindered the adoption of GaAs. In addition, a Si crystal has a very stable structure and can be grown to very large diameter boules and processed with very good yields. It is also a fairly good thermal conductor, thus enabling very dense packing of transistors that need to get rid of their heat of operation, all very desirable for design and manufacturing of very large ICs. Such good mechanical characteristics also make it a suitable material for the rapidly developing field of

nanoelectronics Nanoelectronics refers to the use of nanotechnology in electronic components. The term covers a diverse set of devices and materials, with the common characteristic that they are so small that inter-atomic interactions and quantum mechanical pr ...

. Naturally, a GaAs surface cannot withstand the high temperatures needed for diffusion; however a viable and actively pursued alternative as of the 1980s was ion implantation. The second major advantage of Si is the existence of a native oxide (

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

, SiO₂), which is used as an insulator. Silicon dioxide can be incorporated onto silicon circuits easily, and such layers are adherent to the underlying silicon. SiO₂ is not only a good insulator (with a

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

of 8.9 eV), but the Si-SiO₂ interface can be easily engineered to have excellent electrical properties, most importantly low density of interface states. GaAs does not have a native oxide, does not easily support a stable adherent insulating layer, and does not possess the dielectric strength or surface passivating qualities of the Si-SiO₂. Aluminum oxide (Al₂O₃) has been extensively studied as a possible gate oxide for GaAs (as well as

InGaAs Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound) of indium arsenide (InAs) and gallium arsenide (GaAs). Indium and gallium are ( group III) elements of the periodic table whil ...

). The third advantage of silicon is that it possesses a higher

hole A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...

mobility compared to GaAs (500 versus 400 cm²V⁻¹s⁻¹). This high mobility allows the fabrication of higher-speed P-channel

field-effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...

s, which are required for

logic. Because they lack a fast CMOS structure, GaAs circuits must use logic styles which have much higher power consumption; this has made GaAs logic circuits unable to compete with silicon logic circuits. For manufacturing solar cells, silicon has relatively low absorptivity for sunlight, meaning about 100 micrometers of Si is needed to absorb most sunlight. Such a layer is relatively robust and easy to handle. In contrast, the absorptivity of GaAs is so high that only a few micrometers of thickness are needed to absorb all of the light. Consequently, GaAs thin films must be supported on a substrate material.Single-Crystalline Thin Film
US Department of Energy Silicon is a pure element, avoiding the problems of stoichiometric imbalance and thermal unmixing of GaAs. Silicon has a nearly perfect lattice; impurity density is very low and allows very small structures to be built (down to

5 nm In semiconductor manufacturing, the International Roadmap for Devices and Systems defines the 5 nm process as the MOSFET technology node following the 7 nm node. In 2020, Samsung and TSMC entered volume production of 5 nm chips, ...

in commercial production as of 2020). In contrast, GaAs has a very high impurity density, which makes it difficult to build integrated circuits with small structures, so the 500 nm process is a common process for GaAs. Silicon has about three times the thermal conductivity of GaAs, with less risk of local overheating in high power devices.

Other applications

Transistor uses

Gallium arsenide (GaAs) transistors are used in the RF power amplifiers for cell phones and wireless communicating.

Solar cells and detectors

Gallium arsenide is an important semiconductor material for high-cost, high-efficiency

solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.

s and is used for single-crystalline

thin-film solar cell A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially use ...

s and for

multi-junction solar cells Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...

. The first known operational use of GaAs solar cells in space was for the

Venera 3 Venera 3 (russian: Венера-3 meaning ''Venus 3'') was a Venera program space probe that was built and launched by the Soviet Union to explore the surface of Venus. It was launched on 16 November 1965 at 04:19 UTC from Baikonur, Kazakhstan ...

mission, launched in 1965. The GaAs solar cells, manufactured by Kvant, were chosen because of their higher performance in high temperature environments. GaAs cells were then used for the Lunokhod rovers for the same reason. In 1970, the GaAs heterostructure solar cells were developed by the team led by

Zhores Alferov Zhores Ivanovich Alferov (russian: link=no, Жоре́с Ива́нович Алфёров, ; be, Жарэс Іва́навіч Алфёраў; 15 March 19301 March 2019) was a Soviet and Russian physicist and academic who contributed signific ...

in the

USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

, achieving much higher efficiencies. In the early 1980s, the efficiency of the best GaAs solar cells surpassed that of conventional,

crystalline silicon Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...

-based solar cells. In the 1990s, GaAs solar cells took over from silicon as the cell type most commonly used for

photovoltaic array A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and co ...

s for satellite applications. Later, dual- and triple-junction solar cells based on GaAs with

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

and

indium gallium phosphide Indium gallium phosphide (InGaP), also called gallium indium phosphide (GaInP), is a semiconductor composed of indium, gallium and phosphorus. It is used in high-power and high-frequency electronics because of its superior electron velocity with ...

layers were developed as the basis of a triple-junction solar cell, which held a record efficiency of over 32 % and can operate also with light as concentrated as 2,000 suns. This kind of solar cell powered the

Mars Exploration Rover NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...

Spirit Spirit or spirits may refer to: Liquor and other volatile liquids * Spirits, a.k.a. liquor, distilled alcoholic drinks * Spirit or tincture, an extract of plant or animal material dissolved in ethanol * Volatile (especially flammable) liquids, ...

and

Opportunity Opportunity may refer to: Places * Opportunity, Montana, an unincorporated community, United States * Opportunity, Nebraska, an unincorporated community, United States * Opportunity, Washington, a former census-designated place, United States * 3 ...

, which explored

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

' surface. Also many

solar car A solar car is a solar vehicle for use on public roads or race tracks. Solar vehicles are electric vehicles that use self-contained solar cells to power themselves fully or partially from sunlight. Solar vehicles typically contain a rechargeable b ...

s utilize GaAs in solar arrays, as did the Hubble Telescope. GaAs-based devices hold the world record for the highest-efficiency single-junction solar cell at 29.1% (as of 2019). This high efficiency is attributed to the extreme high quality GaAs epitaxial growth, surface passivation by the AlGaAs, and the promotion of photon recycling by the thin film design. GaAs-based

photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...

are also responsible for the highest efficiency (as of 2022) of conversion of light to electricity, as researchers from the

Fraunhofer Institute for Solar Energy Systems The Fraunhofer Institute for Solar Energy Systems ISE (or Fraunhofer ISE) is an institute of the Fraunhofer-Gesellschaft. Located in Freiburg, Germany, The Institute performs applied scientific and engineering research and development for all a ...

achieved a 68.9% efficiency when exposing a GaAs

thin film A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...

photovoltaic cell to monochromatic laser light with a wavelength of 858 nanometers. Today, multi-junction GaAs cells have the highest efficiencies of existing photovoltaic cells and trajectories show that this is likely to continue to be the case for the foreseeable future. In 2022,

Rocket Lab Rocket Lab is a public American aerospace manufacturer and launch service provider, with a New Zealand subsidiary. The company operates lightweight Electron orbital rockets, which provide dedicated launches for small satellites. Rocket Lab also ...

unveiled a solar cell with 33.3% efficiency based on inverted metamorphic multi-junction (IMM) technology. In IMM, the lattice-matched (same lattice parameters) materials are grown first, followed by mismatched materials. The top cell, GaInP, is grown first and lattice matched to the GaAs substrate, followed by a layer of either GaAs or GaInAs with a minimal mismatch, and the last layer has the greatest lattice mismatch. After growth, the cell is mounted to a secondary handle and the GaAs substrate is removed. A main advantage of the IMM process is that the inverted growth according to lattice mismatch allows a path to higher cell efficiency. Complex designs of Al_xGa_1−xAs-GaAs devices using

s can be sensitive to infrared radiation (

QWIP A Quantum Well Infrared Photodetector (QWIP) is an infrared photodetector, which uses electronic intersubband transitions in quantum wells to absorb photons. In order to be used for infrared detection, the parameters of the quantum wells in the qua ...

). GaAs diodes can be used for the detection of X-rays.

Future outlook of GaAs solar cells

Despite GaAs-based photovoltaics being the clear champions of efficiency for solar cells, they have relatively limited use in today's market. In both world electricity generation and world electricity generating capacity, solar electricity is growing faster than any other source of fuel (wind, hydro, biomass, and so on) for the last decade. However, GaAs solar cells have not currently been adopted for widespread solar electricity generation. This is largely due to the cost of GaAs solar cells - in space applications, high performance is required and the corresponding high cost of the existing GaAs technologies is accepted. For example, GaAs-based photovoltaics show the best resistance to gamma radiation and high temperature fluctuations, which are of great importance for spacecraft. But in comparison to other solar cells, III-V solar cells are two to three orders of magnitude more expensive than other technologies such as silicon-based solar cells. The primary sources of this cost are the

epitaxial growth Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited crystalline film is called an epit ...

costs and the substrate the cell is deposited on. GaAs solar cells are most commonly fabricated utilizing epitaxial growth techniques such as metal-organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). A significant reduction in costs for these methods would require improvements in tool costs, throughput, material costs, and manufacturing efficiency. Increasing the deposition rate could reduce costs, but this cost reduction would be limited by the fixed times in other parts of the process such as cooling and heating. The substrate used to grow these solar cells is usually germanium or gallium arsenide which are notably expensive materials. One of the main pathways to reduce substrate costs is to reuse the substrate. An early method proposed to accomplish this is epitaxial lift-off (ELO), but this method is time-consuming, somewhat dangerous (with its use of

hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...

), and requires multiple post-processing steps. However, other methods have been proposed that use phosphide-based materials and hydrochloric acid to achieve ELO with

surface passivation A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is t ...

and minimal post-

etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types ...

residues and allows for direct reuse of the GaAs substrate. There is also preliminary evidence that

spalling Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...

could be used to remove the substrate for reuse. An alternative path to reduce substrate cost is to use cheaper materials, although materials for this application are not currently commercially available or developed. Yet another consideration to lower GaAs solar cell costs could be

concentrator photovoltaics Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight onto ...

. Concentrators use lenses or parabolic mirrors to focus light onto a solar cell, and thus a smaller (and therefore less expensive) GaAs solar cell is needed to achieve the same results. Concentrator systems have the highest efficiency of existing photovoltaics. So, technologies such as concentrator photovoltaics and methods in development to lower epitaxial growth and substrate costs could lead to a reduction in the cost of GaAs solar cells and forge a path for use in terrestrial applications.

Light-emission devices

GaAs has been used to produce near-infrared laser diodes since 1962. It is often used in alloys with other semiconductor compounds for these applications. ''N''-type GaAs doped with silicon donor atoms (on Ga sites) and boron acceptor atoms (on As sites) responds to ionizing radiation by emitting scintillation photons. At cryogenic temperatures it is among the brightest scintillators known and is a promising candidate for detecting rare electronic excitations from interacting dark matter, due to the following six essential factors: # Silicon donor electrons in GaAs have a binding energy that is among the lowest of all known ''n''-type semiconductors. Free electrons above per cm³ are not “frozen out" and remain delocalized at cryogenic temperatures. # Boron and gallium are group III elements, so boron as an impurity primarily occupies the gallium site. However, a sufficient number occupy the arsenic site and act as acceptors that efficiently trap ionization event holes from the valence band. # After trapping an ionization event hole from the valence band, the boron acceptors can combine radiatively with delocalized donor electrons to produce photons 0.2 eV below the cryogenic band-gap energy (1.52 eV). This is an efficient radiative process that produces scintillation photons that are not absorbed by the GaAs crystal. # There is no afterglow, because metastable radiative centers are quickly annihilated by the delocalized electrons. This is evidenced by the lack of thermally induced luminescence. # ''N''-type GaAs has a high refractive index (~3.5) and the narrow-beam absorption coefficient is proportional to the free electron density and typically several per cm. One would expect that almost all of the scintillation photons should be trapped and absorbed in the crystal, but this is not the case. One explanation for the high luminosity is that the narrow-beam absorption is largely optical scattering that allows most of the photons to avoid total internal reflection trapping. # ''N''-type GaAs(Si,B) is commercially grown as 10 kg crystal ingots and sliced into thin wafers as substrates for electronic circuits. Boron oxide is used as an encapsulant to prevent the loss of arsenic during crystal growth, but also has the benefit of providing boron acceptors for scintillation.

Fiber optic temperature measurement

For this purpose an optical fiber tip of an optical fiber temperature sensor is equipped with a gallium arsenide crystal. Starting at a light wavelength of 850 nm GaAs becomes optically translucent. Since the spectral position of the band gap is temperature dependent, it shifts about 0.4 nm/K. The measurement device contains a light source and a device for the spectral detection of the band gap. With the changing of the band gap, (0.4 nm/K) an algorithm calculates the temperature (all 250 ms).A New Fiber Optical Thermometer and Its Application for Process Control in Strong Electric, Magnetic, and Electromagnetic Fields
optocon.de (PDF; 2,5 MB)

Spin-charge converters

GaAs may have applications in

spintronics Spintronics (a portmanteau meaning spin transport electronics), also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-sta ...

as it can be used instead of

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...

in spin-charge converters and may be more tunable.

Safety

The environment, health and safety aspects of gallium arsenide sources (such as

and

) and industrial hygiene monitoring studies of

metalorganic Metal-organic compounds (jargon: metalorganics, metallo-organics) are a class of chemical compounds that contain metals and organic ligands, which confer solubility in organic solvents or volatility. Compounds with these properties find applicatio ...

precursors have been reported. California lists gallium arsenide as a

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...

, as do

IARC IARC may refer to: * International Aerial Robotics Competition * International Age Rating Coalition * International Agency for Research on Cancer * International Arctic Research Center * Israel Amateur Radio Club The Israel Amateur Radio Club (IA ...

and ECA, and it is considered a known carcinogen in animals. On the other hand, a 2013 review (funded by industry) argued against these classifications, saying that when rats or mice inhale fine GaAs powders (as in previous studies), they get cancer from the resulting lung irritation and inflammation, rather than from a primary carcinogenic effect of the GaAs itself—and that, moreover, fine GaAs powders are unlikely to be created in the production or use of GaAs.

References

Cited sources

External links

Case Studies in Environmental Medicine: Arsenic ToxicityFacts and figures on processing gallium arsenide
{{Authority control Arsenides Inorganic compounds Gallium compounds IARC Group 1 carcinogens Optoelectronics III-V semiconductors III-V compounds Solar cells Light-emitting diode materials Zincblende crystal structure