130-563: Gallium nitride ( Ga N ) is a binary III / V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure . Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic , high-power and high-frequency devices. For example, GaN is the substrate that makes violet (405 nm) laser diodes possible, without requiring nonlinear optical frequency doubling . Its sensitivity to ionizing radiation
260-748: A JAS-39 Gripen fighter. Saab already offers products with GaN based radars, like the Giraffe radar , Erieye , GlobalEye , and Arexis EW. Saab also delivers major subsystems, assemblies and software for the AN/TPS-80 (G/ATOR) India's Defence Research and Development Organisation is developing Virupaakhsha radar for Sukhoi Su-30MKI based on GaN technology. The radar is a further development of Uttam AESA Radar for use on HAL Tejas which employs GaAs technology. GaN nanotubes and nanowires are proposed for applications in nanoscale electronics , optoelectronics and biochemical-sensing applications. When doped with
390-503: A by-product during the processing of the ores of other metals. Its main source material is bauxite , the chief ore of aluminium , but minor amounts are also extracted from sulfidic zinc ores ( sphalerite being the main host mineral). In the past, certain coals were an important source. During the processing of bauxite to alumina in the Bayer process , gallium accumulates in the sodium hydroxide liquor. From this it can be extracted by
520-400: A direct bandgap semiconductor in the 1960s ushered in the most important stage in the applications of gallium. In the late 1960s, the electronics industry started using gallium on a commercial scale to fabricate light emitting diodes, photovoltaics and semiconductors, while the metals industry used it to reduce the melting point of alloys . Gallium does not exist as a free element in
650-519: A gain medium , a mechanism to energize it, and something to provide optical feedback . The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (power increases). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that
780-471: A lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode . That is possible due to the light being of a single spatial mode. This unique property of laser light, spatial coherence , cannot be replicated using standard light sources (except by discarding most of the light) as can be appreciated by comparing the beam from a flashlight (torch) or spotlight to that of almost any laser. A laser beam profiler
910-628: A passive , protective oxide layer. At higher temperatures, however, it reacts with atmospheric oxygen to form gallium(III) oxide , Ga 2 O 3 . Reducing Ga 2 O 3 with elemental gallium in vacuum at 500 °C to 700 °C yields the dark brown gallium(I) oxide , Ga 2 O . Ga 2 O is a very strong reducing agent , capable of reducing H 2 SO 4 to H 2 S . It disproportionates at 800 °C back to gallium and Ga 2 O 3 . Gallium(III) sulfide , Ga 2 S 3 , has 3 possible crystal modifications. It can be made by
1040-716: A phosphor . Gallium also forms sulfides in lower oxidation states, such as gallium(II) sulfide and the green gallium(I) sulfide , the latter of which is produced from the former by heating to 1000 °C under a stream of nitrogen. The other binary chalcogenides, Ga 2 Se 3 and Ga 2 Te 3 , have the zincblende structure. They are all semiconductors but are easily hydrolysed and have limited utility. Gallium reacts with ammonia at 1050 °C to form gallium nitride , GaN. Gallium also forms binary compounds with phosphorus , arsenic , and antimony : gallium phosphide (GaP), gallium arsenide (GaAs), and gallium antimonide (GaSb). These compounds have
1170-464: A broad spectrum of light or emit different wavelengths of light simultaneously. Certain lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit . All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. A laser consists of
1300-591: A by-product is defined as that amount which is economically extractable from its host materials per year under current market conditions (i.e. technology and price). Reserves and resources are not relevant for by-products, since they cannot be extracted independently from the main-products. Recent estimates put the supply potential of gallium at a minimum of 2,100 t/yr from bauxite, 85 t/yr from sulfidic zinc ores, and potentially 590 t/yr from coal. These figures are significantly greater than current production (375 t in 2016). Thus, major future increases in
1430-504: A chain reaction. The materials chosen for lasers are the ones that have metastable states , which stay excited for a relatively long time. In laser physics , such a material is called an active laser medium . Combined with an energy source that continues to "pump" energy into the material, it is possible to have enough atoms or molecules in an excited state for a chain reaction to develop. Lasers are distinguished from other light sources by their coherence . Spatial (or transverse) coherence
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#17328485013181560-436: A coherent beam has been formed. The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier. For the gain medium to amplify light, it needs to be supplied with energy in
1690-499: A complex low-coordinated structure in which each gallium atom is surrounded by 10 others, rather than 11–12 neighbors typical of most liquid metals. The physical properties of gallium are highly anisotropic , i.e. have different values along the three major crystallographic axes a , b , and c (see table), producing a significant difference between the linear (α) and volume thermal expansion coefficients. The properties of gallium are strongly temperature-dependent, particularly near
1820-419: A device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather as a high-gain optical amplifier that amplifies its spontaneous emission. The same mechanism describes so-called astrophysical masers /lasers. The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to
1950-508: A gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies. An example of a suitable material is titanium -doped, artificially grown sapphire ( Ti:sapphire ), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science ), for maximizing
2080-480: A given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching . The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers. The lasing medium in some dye lasers and vibronic solid-state lasers produces optical gain over
2210-408: A greater volatility than ZnCl 2 : all of these predictions turned out to be true. Gallium was discovered using spectroscopy by French chemist Paul Emile Lecoq de Boisbaudran in 1875 from its characteristic spectrum (two violet lines) in a sample of sphalerite . Later that year, Lecoq obtained the free metal by electrolysis of the hydroxide in potassium hydroxide solution. He named
2340-399: A higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE. Conserving energy, the electron transitions to a lower energy level that is not occupied, with transitions to different levels having different time constants. This process is called spontaneous emission . Spontaneous emission is
2470-471: A laser beam, it is highly collimated : the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction , that can only remain true well within the Rayleigh range . The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle that varies inversely with the beam diameter, as required by diffraction theory. Thus,
2600-471: A laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state : gas, liquid, solid, or plasma . The gain medium absorbs pump energy, which raises some electrons into higher energy (" excited ") quantum states . Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In
2730-401: A laser to be focused to a tight spot, enabling applications such as optical communication, laser cutting , and lithography . It also allows a laser beam to stay narrow over great distances ( collimation ), a feature used in applications such as laser pointers , lidar , and free-space optical communication . Lasers can also have high temporal coherence , which permits them to emit light with
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#17328485013182860-418: A multi-level system as a method for obtaining the population inversion, later a main method of laser pumping. Townes reports that several eminent physicists—among them Niels Bohr , John von Neumann , and Llewellyn Thomas —argued the maser violated Heisenberg's uncertainty principle and hence could not work. Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth
2990-437: A person's hands at normal human body temperature of 37.0 °C (98.6 °F). Gallium is predominantly used in electronics . Gallium arsenide , the primary chemical compound of gallium in electronics, is used in microwave circuits, high-speed switching circuits, and infrared circuits. Semiconducting gallium nitride and indium gallium nitride produce blue and violet light-emitting diodes and diode lasers . Gallium
3120-441: A process called pumping . The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a flash lamp or by another laser. The most common type of laser uses feedback from an optical cavity —a pair of mirrors on either end of the gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of
3250-462: A quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle . The emitted photon has a random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission . A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to
3380-432: A seminar on this idea, and Charles H. Townes asked him for a copy of the paper. In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in
3510-678: A silicon substrate. High-voltage (800 V) Schottky barrier diodes (SBDs) have also been made. The higher efficiency and high power density of integrated GaN power ICs allows them to reduce the size, weight and component count of applications including mobile and laptop chargers, consumer electronics, computing equipment and electric vehicles. GaN-based electronics (not pure GaN) have the potential to drastically cut energy consumption, not only in consumer applications but even for power transmission utilities . Unlike silicon transistors that switch off due to power surges, GaN transistors are typically depletion mode devices (i.e. on / resistive when
3640-484: A single surface-mount device. Integration means that the gate-drive loop has essentially zero impedance, which further improves efficiency by virtually eliminating FET turn-off losses. Academic studies into creating low-voltage GaN power ICs began at the Hong Kong University of Science and Technology (HKUST) and the first devices were demonstrated in 2015. Commercial GaN power IC production began in 2018. In 2016
3770-431: A small volume of material at the surface of a workpiece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point. Other applications rely on the peak pulse power (rather than the energy in the pulse), especially to obtain nonlinear optical effects. For
3900-685: A suitable transition metal such as manganese , GaN is a promising spintronics material ( magnetic semiconductors ). GaN crystals can be grown from a molten Na/Ga melt held under 100 atmospheres of pressure of N 2 at 750 °C. As Ga will not react with N 2 below 1000 °C, the powder must be made from something more reactive, usually in one of the following ways: Gallium nitride can also be synthesized by injecting ammonia gas into molten gallium at 900–980 °C at normal atmospheric pressure. Blue, white and ultraviolet LEDs are grown on industrial scale by MOVPE . The precursors are ammonia with either trimethylgallium or triethylgallium ,
4030-945: A thin film of GaN deposited via metalorganic vapour-phase epitaxy (MOVPE) on sapphire . Other substrates used are zinc oxide , with lattice constant mismatch of only 2% and silicon carbide (SiC). Group III nitride semiconductors are, in general, recognized as one of the most promising semiconductor families for fabricating optical devices in the visible short-wavelength and UV region. The very high breakdown voltages , high electron mobility , and high saturation velocity of GaN has made it an ideal candidate for high-power and high-temperature microwave applications, as evidenced by its high Johnson's figure of merit . Potential markets for high-power/high-frequency devices based on GaN include microwave radio-frequency power amplifiers (e.g., those used in high-speed wireless data transmission) and high-voltage switching devices for power grids. A potential mass-market application for GaN-based RF transistors
Gallium nitride - Misplaced Pages Continue
4160-479: A variety of methods. The most recent is the use of ion-exchange resin . Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50 ppm, about 15% of the contained gallium is extractable. The remainder reports to the red mud and aluminium hydroxide streams. Gallium is removed from the ion-exchange resin in solution. Electrolysis then gives gallium metal. For semiconductor use, it
4290-646: A very narrow frequency spectrum . Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations as short as an attosecond . Lasers are used in optical disc drives , laser printers , barcode scanners , DNA sequencing instruments , fiber-optic and free-space optical communications, semiconductor chip manufacturing ( photolithography , etching ), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in
4420-430: A wide bandwidth, making a laser possible that can thus generate pulses of light as short as a few femtoseconds (10 s). In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached
4550-492: A wide range of technologies addressing many different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode. In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up between pulses. In laser ablation , for example,
4680-498: Is a chemical element ; it has the symbol Ga and atomic number 31. Discovered by the 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 ( aluminium , indium , and thallium ). Elemental gallium is a relatively soft, silvery metal at standard temperature and pressure . In its liquid state, it becomes silvery white. If enough force
4810-424: Is a common starting reagent for the formation of organogallium compounds, such as in carbogallation reactions. Gallium trichloride reacts with lithium cyclopentadienide in diethyl ether to form the trigonal planar gallium cyclopentadienyl complex GaCp 3 . Gallium(I) forms complexes with arene ligands such as hexamethylbenzene . Because this ligand is quite bulky, the structure of the [Ga(η -C 6 Me 6 )]
4940-489: Is a halogen. They also react with alkyl halides to form carbocations and GaX 4 . When heated to a high temperature, gallium(III) halides react with elemental gallium to form the respective gallium(I) halides. For example, GaCl 3 reacts with Ga to form GaCl : At lower temperatures, the equilibrium shifts toward the left and GaCl disproportionates back to elemental gallium and GaCl 3 . GaCl can also be produced by reacting Ga with HCl at 950 °C;
5070-404: Is a transition between energy levels that match the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process. When an electron is excited from one state to that at
5200-544: Is also emerging as a promising candidate for 5G cellular base station applications. Since the early 2020s, GaN power transistors have come into increasing use in power supplies in electronic equipment, converting AC mains electricity to low-voltage DC . GaN is a very hard ( Knoop hardness 14.21 GPa), mechanically stable wide-bandgap semiconductor material with high heat capacity and thermal conductivity. In its pure form it resists cracking and can be deposited in thin film on sapphire or silicon carbide , despite
5330-477: Is also required for three-level lasers in which the lower energy level rapidly becomes highly populated, preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode. In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper " Zur Quantentheorie der Strahlung " ("On
Gallium nitride - Misplaced Pages Continue
5460-540: Is also used in the production of artificial gadolinium gallium garnet for jewelry. Gallium is considered a technology-critical element by the United States National Library of Medicine and Frontiers Media . Gallium has no known natural role in biology. Gallium(III) behaves in a similar manner to ferric salts in biological systems and has been used in some medical applications, including pharmaceuticals and radiopharmaceuticals . Elemental gallium
5590-406: Is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation . The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories , based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow . A laser differs from other sources of light in that it emits light that is coherent . Spatial coherence allows
5720-407: Is an ionic compound strongly insoluble in water. However, it dissolves in hydrofluoric acid , in which it forms an adduct with water, GaF 3 ·3H 2 O . Attempting to dehydrate this adduct forms GaF 2 OH· n H 2 O . The adduct reacts with ammonia to form GaF 3 ·3NH 3 , which can then be heated to form anhydrous GaF 3 . Gallium trichloride is formed by
5850-418: Is an irritant to skin, eyes and lungs. The environment, health and safety aspects of gallium nitride sources (such as trimethylgallium and ammonia ) and industrial hygiene monitoring studies of MOVPE sources have been reported in a 2004 review. Bulk GaN is non-toxic and biocompatible . Therefore, it may be used in the electrodes and electronics of implants in living organisms. Gallium Gallium
5980-448: Is applied to the growth surface in order to create nanoscale roughness. Then, the surface is polished. This process takes place in a vacuum. Polishing methods typically employ a liquid electrolyte and UV irradiation to enable mechanical removal of a thin oxide layer from the wafer. More recent methods have been developed that utilize solid-state polymer electrolytes that are solvent-free and require no radiation before polishing. GaN dust
6110-563: Is applied, solid gallium may fracture conchoidally . Since its discovery in 1875, gallium has widely been used to make alloys with low melting points. It is also used in semiconductors , as a dopant in semiconductor substrates. The melting point of gallium (29.7646°C, 85.5763°F, 302.9146 K) is used as a temperature reference point. Gallium alloys are used in thermometers as a non-toxic and environmentally friendly alternative to mercury , and can withstand higher temperatures than mercury. A melting point of −19 °C (−2 °F), well below
6240-543: Is as the microwave source for microwave ovens , replacing the magnetrons currently used. The large band gap means that the performance of GaN transistors is maintained up to higher temperatures (~400 °C) than silicon transistors (~150 °C) because it lessens the effects of thermal generation of charge carriers that are inherent to any semiconductor. The first gallium nitride metal semiconductor field-effect transistors (GaN MESFET ) were experimentally demonstrated in 1993 and they are being actively developed. In 2010,
6370-413: Is called an optical amplifier . When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser. For lasing media with extremely high gain, so-called superluminescence , light can be sufficiently amplified in a single pass through the gain medium without requiring a resonator. Although often referred to as a laser (see, for example, nitrogen laser ), the light output from such
6500-415: Is contained in known reserves of bauxite and zinc ores. Some coal flue dusts contain small quantities of gallium, typically less than 1% by weight. However, these amounts are not extractable without mining of the host materials (see below). Thus, the availability of gallium is fundamentally determined by the rate at which bauxite, zinc ores, and coal are extracted. Gallium is produced exclusively as
6630-753: Is efficient at transferring current, and this ultimately means that less energy is lost to heat. GaN high-electron-mobility transistors (HEMT) have been offered commercially since 2006, and have found immediate use in various wireless infrastructure applications due to their high efficiency and high voltage operation. A second generation of devices with shorter gate lengths will address higher-frequency telecom and aerospace applications. GaN-based metal–oxide–semiconductor field-effect transistors ( MOSFET ) and metal–semiconductor field-effect transistor ( MESFET ) transistors also offer advantages including lower loss in high power electronics, especially in automotive and electric car applications. Since 2008 these can be formed on
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#17328485013186760-462: Is emitted by stimulated emission is identical to the photon that triggered its emission, and both photons can go on to trigger stimulated emission in other atoms, creating the possibility of a chain reaction . For this to happen, many of the atoms or molecules must be in the proper excited state so that the photons can trigger them. In most materials, atoms or molecules drop out of excited states fairly rapidly, making it difficult or impossible to produce
6890-421: Is formed by single-frequency quantum photon states distributed according to a Poisson distribution . As a result, the arrival rate of photons in a laser beam is described by Poisson statistics. Many lasers produce a beam that can be approximated as a Gaussian beam ; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with
7020-443: Is frequently used in the field, meaning "to give off coherent light," especially about the gain medium of a laser; when a laser is operating, it is said to be " lasing ". The terms laser and maser are also used for naturally occurring coherent emissions, as in astrophysical maser and atom laser . A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by
7150-427: Is further purified with zone melting or single-crystal extraction from a melt ( Czochralski process ). Purities of 99.9999% are routinely achieved and commercially available. Its by-product status means that gallium production is constrained by the amount of bauxite, sulfidic zinc ores (and coal) extracted per year. Therefore, its availability needs to be discussed in terms of supply potential. The supply potential of
7280-421: Is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical, or destroying the laser by producing excessive heat. Such lasers cannot be run in CW mode. The pulsed operation of lasers refers to any laser not classified as a continuous wave so that the optical power appears in pulses of some duration at some repetition rate. This encompasses
7410-605: Is just above room temperature, and is approximately the same as the average summer daytime temperatures in Earth's mid-latitudes. This melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990 (ITS-90) established by the International Bureau of Weights and Measures (BIPM). The triple point of gallium, 302.9166 K (29.7666 °C, 85.5799 °F),
7540-562: Is low (like other group III nitrides ), making it a suitable material for solar cell arrays for satellites . Military and space applications could also benefit as devices have shown stability in high radiation environments . Because GaN transistors can operate at much higher temperatures and work at much higher voltages than gallium arsenide (GaAs) transistors, they make ideal power amplifiers at microwave frequencies. In addition, GaN offers promising characteristics for THz devices. Due to high power density and voltage breakdown limits GaN
7670-823: Is not found in nature, but it is easily obtained by smelting . Very pure gallium is a silvery blue metal that fractures conchoidally like glass . Gallium's volume expands by 3.10% when it changes from a liquid to a solid so care must be taken when storing it in containers that may rupture when it changes state. Gallium shares the higher-density liquid state with a short list of other materials that includes water , silicon , germanium , bismuth , and plutonium . Gallium forms alloys with most metals. It readily diffuses into cracks or grain boundaries of some metals such as aluminium, aluminium – zinc alloys and steel , causing extreme loss of strength and ductility called liquid metal embrittlement . The melting point of gallium, at 302.9146 K (29.7646 °C, 85.5763 °F),
7800-405: Is not the result of random thermal processes. Instead, the release of a photon is triggered by the nearby passage of another photon. This is called stimulated emission . For this process to work, the passing photon must be similar in energy, and thus wavelength, to the one that could be released by the atom or molecule, and the atom or molecule must be in the suitable excited state. The photon that
7930-399: Is one of the four non-radioactive metals (with caesium , rubidium , and mercury ) that are known to be liquid at, or near, normal room temperature. Of the four, gallium is the only one that is neither highly reactive (as are rubidium and caesium) nor highly toxic (as is mercury) and can, therefore, be used in metal-in-glass high-temperature thermometers . It is also notable for having one of
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#17328485013188060-545: Is that of a half-sandwich . Less bulky ligands such as mesitylene allow two ligands to be attached to the central gallium atom in a bent sandwich structure. Benzene is even less bulky and allows the formation of dimers: an example is [Ga(η -C 6 H 6 ) 2 ] [GaCl 4 ]·3C 6 H 6 . In 1871, the existence of gallium was first predicted by Russian chemist Dmitri Mendeleev , who named it " eka-aluminium " from its position in his periodic table . He also predicted several properties of eka-aluminium that correspond closely to
8190-489: Is to heat an object; some of the thermal energy being applied to the object will cause the molecules and electrons within the object to gain energy, which is then lost through thermal radiation , that we see as light. This is the process that causes a candle flame to give off light. Thermal radiation is a random process, and thus the photons emitted have a range of different wavelengths , travel in different directions, and are released at different times. The energy within
8320-504: Is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser that is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high-energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping
8450-441: Is typically expressed through the output being a narrow beam, which is diffraction-limited . Laser beams can be focused to very tiny spots, achieving a very high irradiance , or they can have a very low divergence to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length ) along
8580-463: Is unique among the light isotopes in having only electron capture as a decay mode, as its decay energy is not sufficient to allow positron emission. Gallium-67 and gallium-68 (half-life 67.7 min) are both used in nuclear medicine . Gallium is found primarily in the +3 oxidation state . The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners indium and thallium . For example,
8710-500: Is used by the US National Institute of Standards and Technology (NIST) in preference to the melting point. The melting point of gallium allows it to melt in the human hand, and then solidify if removed. The liquid metal has a strong tendency to supercool below its melting point / freezing point : Ga nanoparticles can be kept in the liquid state below 90 K. Seeding with a crystal helps to initiate freezing. Gallium
8840-430: Is used to measure the intensity profile, width, and divergence of laser beams. Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties. The mechanism of producing radiation in a laser relies on stimulated emission , where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon that was predicted by Albert Einstein , who derived
8970-580: The AN/TPQ-53 radar system to replace two medium-range radar systems, the AN/TPQ-36 and the AN/TPQ-37 . The AN/TPQ-53 radar system was designed to detect, classify, track, and locate enemy indirect fire systems, as well as unmanned aerial systems. The AN/TPQ-53 radar system provided enhanced performance, greater mobility, increased reliability and supportability, lower life-cycle cost, and reduced crew size compared to
9100-454: The Ga(OH) 4 anion. Gallium hydroxide, which is amphoteric , also dissolves in alkali to form gallate salts. Although earlier work suggested Ga(OH) 6 as another possible gallate anion, it was not found in later work. Gallium reacts with the chalcogens only at relatively high temperatures. At room temperature, gallium metal is not reactive with air and water because it forms
9230-410: The phase of the emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than
9360-421: The transverse modes often approximated using Hermite – Gaussian or Laguerre -Gaussian functions. Some high-power lasers use a flat-topped profile known as a " tophat beam ". Unstable laser resonators (not used in most lasers) produce fractal-shaped beams. Specialized optical systems can produce more complex beam geometries, such as Bessel beams and optical vortexes . Near the "waist" (or focal region ) of
9490-497: The "pencil beam" directly generated by a common helium–neon laser would spread out to a size of perhaps 500 kilometers when shone on the Moon (from the distance of the Earth). On the other hand, the light from a semiconductor laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam employing
9620-667: The AN/TPQ-36 and the AN/TPQ-37 systems. Lockheed Martin fielded other tactical operational radars with GaN technology in 2018, including TPS-77 Multi Role Radar System deployed to Latvia and Romania . In 2019, Lockheed Martin's partner ELTA Systems Limited , developed a GaN-based ELM-2084 Multi Mission Radar that was able to detect and track air craft and ballistic targets, while providing fire control guidance for missile interception or air defense artillery. On April 8, 2020, Saab flight tested its new GaN designed AESA X-band radar in
9750-498: The Earth's crust, and the few high-content minerals, such as gallite (CuGaS 2 ), are too rare to serve as a primary source. The abundance in the Earth's crust is approximately 16.9 ppm . It is the 34th most abundant element in the crust. This is comparable to the crustal abundances of lead , cobalt , and niobium . Yet unlike these elements, gallium does not form its own ore deposits with concentrations of > 0.1 wt.% in ore. Rather it occurs at trace concentrations similar to
9880-464: The FETs to maintain costs similar to silicon power MOSFETs but with the superior electrical performance of GaN. Another seemingly viable solution for realizing enhancement-mode GaN-channel HFETs is to employ a lattice-matched quaternary AlInGaN layer of acceptably low spontaneous polarization mismatch to GaN. GaN power ICs monolithically integrate a GaN FET, GaN-based drive circuitry and circuit protection into
10010-670: The Quantum Theory of Radiation") via a re-derivation of Max Planck 's law of radiation, conceptually based upon probability coefficients ( Einstein coefficients ) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. In 1928, Rudolf W. Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant predicted using stimulated emission to amplify "short" waves. In 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and effected
10140-503: The Soviet Union, Nikolay Basov and Aleksandr Prokhorov were independently working on the quantum oscillator and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion . In 1955, Prokhorov and Basov suggested optical pumping of
10270-403: The [Ar]3d core. This phenomenon recurs with mercury with its "pseudo-noble-gas" [Xe]4f 5d 6s electron configuration, which is liquid at room temperature. The 3d electrons do not shield the outer electrons very well from the nucleus and hence the first ionisation energy of gallium is greater than that of aluminium. Ga 2 dimers do not persist in the liquid state and liquid gallium exhibits
10400-614: The acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers . Modern physics describes light and other forms of electromagnetic radiation as the group behavior of fundamental particles known as photons . Photons are released and absorbed through electromagnetic interactions with other fundamental particles that carry electric charge . A common way to release photons
10530-476: The beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. Lasers are characterized according to their wavelength in a vacuum . Most "single wavelength" lasers produce radiation in several modes with slightly different wavelengths. Although temporal coherence implies some degree of monochromaticity , some lasers emit
10660-425: The blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source; this permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps . The first device using amplification by stimulated emission operated at microwave frequencies, and
10790-405: The by-product production of gallium will be possible without significant increases in production costs or price. The average price for low-grade gallium was $ 120 per kilogram in 2016 and $ 135–140 per kilogram in 2017. Laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation . The word laser
10920-448: The carrier gas being nitrogen or hydrogen . Growth temperature ranges between 800 and 1100 °C . Introduction of trimethylaluminium and/or trimethylindium is necessary for growing quantum wells and other kinds of heterostructures . Commercially, GaN crystals can be grown using molecular beam epitaxy or metalorganic vapour phase epitaxy . This process can be further modified to reduce dislocation densities. First, an ion beam
11050-456: The commercialization of high-performance blue LEDs and long-lifetime violet laser diodes, and to the development of nitride-based devices such as UV detectors and high-speed field-effect transistors . High-brightness GaN light-emitting diodes (LEDs) completed the range of primary colors, and made possible applications such as daylight-visible full-color LED displays, white LEDs and blue laser devices. The first GaN-based high-brightness LEDs used
11180-425: The crustal value in zinc ores, and at somewhat higher values (~ 50 ppm) in aluminium ores, from both of which it is extracted as a by-product. This lack of independent deposits is due to gallium's geochemical behaviour, showing no strong enrichment in the processes relevant to the formation of most ore deposits. The United States Geological Survey (USGS) estimates that more than 1 million tons of gallium
11310-583: The density of gallium as 4.7 g/cm , the only property that failed to match Mendeleev's predictions; Mendeleev then wrote to him and suggested that he should remeasure the density, and de Boisbaudran then obtained the correct value of 5.9 g/cm , that Mendeleev had predicted exactly. From its discovery in 1875 until the era of semiconductors, the primary uses of gallium were high-temperature thermometrics and metal alloys with unusual properties of stability or ease of melting (some such being liquid at room temperature). The development of gallium arsenide as
11440-561: The effect of nonlinearity in optical materials (e.g. in second-harmonic generation , parametric down-conversion , optical parametric oscillators and the like). Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent; that is, the pulses (and not just their envelopes ) are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research. Another method of achieving pulsed laser operation
11570-526: The element "gallia", from Latin Gallia meaning ' Gaul ', a name for his native land of France. It was later claimed that, in a multilingual pun of a kind favoured by men of science in the 19th century, he had also named gallium after himself: Le coq is French for 'the rooster', and the Latin word for 'rooster' is gallus . In an 1877 article, Lecoq denied this conjecture. Originally, de Boisbaudran determined
11700-486: The exceptions of quartz, graphite, gallium(III) oxide and PTFE ), making it mechanically more difficult to handle even though it is substantially less toxic and requires far fewer precautions than mercury. Gallium painted onto glass is a brilliant mirror. For this reason as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers. Gallium does not crystallize in any of
11830-409: The first enhancement-mode GaN transistors became generally available. Only n-channel transistors were available. These devices were designed to replace power MOSFETs in applications where switching speed or power conversion efficiency is critical. These transistors are built by growing a thin layer of GaN on top of a standard silicon wafer, often referred to as GaN-on-Si by manufacturers. This allows
11960-656: The first GaN CMOS logic using PMOS and NMOS transistors was reported with gate lengths of 0.5 μm (gate widths of the PMOS and NMOS transistors were 500 μm and 50 μm, respectively). GaN-based violet laser diodes are used to read Blu-ray Discs . The mixture of GaN with In ( InGaN ) or Al ( AlGaN ) with a band gap dependent on the ratio of In or Al to GaN allows the manufacture of light-emitting diodes ( LEDs ) with colors that can go from red to ultra-violet. GaN transistors are suitable for high frequency, high voltage, high temperature and high-efficiency applications. GaN
12090-595: The first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping , which was experimentally demonstrated two years later by Brossel, Kastler, and Winter. In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference in Ottawa , Ontario, Canada. After this presentation, RCA asked Weber to give
12220-477: The first measurement of the high field electron velocity in GaN in 1999. Scientists at ARL experimentally obtained a peak steady-state velocity of 1.9 × 10 cm/s , with a transit time of 2.5 picoseconds, attained at an electric field of 225 kV/cm. With this information, the electron mobility was calculated, thus providing data for the design of GaN devices. One of the earliest syntheses of gallium nitride
12350-470: The freezing point of water, is claimed for the alloy galinstan (62–95% gallium, 5–22% indium , and 0–16% tin by weight), but that may be the freezing point with the effect of supercooling . Gallium does not occur as a free element in nature, but rather as gallium(III) compounds in trace amounts in zinc ores (such as sphalerite ) and in bauxite . Elemental gallium is a liquid at temperatures greater than 29.76 °C (85.57 °F), and will melt in
12480-597: The gate-source voltage is zero). Several methods have been proposed to reach normally-off (or E-mode) operation, which is necessary for use in power electronics: GaN technology is also utilized in military electronics such as active electronically scanned array radars. Thales Group introduced the Ground Master 400 radar in 2010 utilizing GaN technology. In 2021 Thales put in operation more than 50,000 GaN Transmitters on radar systems. The U.S. Army funded Lockheed Martin to incorporate GaN active-device technology into
12610-419: The hydrated gallium ion, [Ga(H 2 O) 6 ] . Gallium(III) hydroxide , Ga(OH) 3 , may be precipitated from gallium(III) solutions by adding ammonia . Dehydrating Ga(OH) 3 at 100 °C produces gallium oxide hydroxide, GaO(OH). Alkaline hydroxide solutions dissolve gallium, forming gallate salts (not to be confused with identically named gallic acid salts) containing
12740-404: The largest liquid ranges for a metal, and for having (unlike mercury) a low vapor pressure at high temperatures. Gallium's boiling point, 2676 K, is nearly nine times higher than its melting point on the absolute scale , the greatest ratio between melting point and boiling point of any element. Unlike mercury, liquid gallium metal wets glass and skin, along with most other materials (with
12870-422: The laser power inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the lasing threshold . The gain medium will amplify any photons passing through it, regardless of direction; but only
13000-501: The lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall into that category. Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as a continuous-wave ( CW ) laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers lase in several longitudinal modes at
13130-414: The latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property
13260-503: The linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible. In 1963, Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics . A coherent beam of light
13390-402: The literal cavity that would be employed at microwave frequencies in a maser . The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in
13520-431: The longest-lived (half-life 3.261 days). Isotopes lighter than gallium-69 usually decay through beta plus decay (positron emission) or electron capture to isotopes of zinc , while isotopes heavier than gallium-71 decay through beta minus decay (electron emission), possibly with delayed neutron emission , to isotopes of germanium . Gallium-70 can decay through both beta minus decay and electron capture. Gallium-67
13650-522: The lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission. The gain medium is put into an excited state by an external source of energy. In most lasers, this medium consists of a population of atoms that have been excited into such a state using an outside light source, or an electrical field that supplies energy for atoms to absorb and be transformed into their excited states. The gain medium of
13780-412: The maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power. A mode-locked laser is capable of emitting extremely short pulses on
13910-498: The medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially . But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power, the net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of
14040-452: The melting point. For example, the coefficient of thermal expansion increases by several hundred percent upon melting. Gallium has 30 known isotopes, ranging in mass number from 60 to 89. Only two isotopes are stable and occur naturally, gallium-69 and gallium-71. Gallium-69 is more abundant: it makes up about 60.1% of natural gallium, while gallium-71 makes up the remaining 39.9%. All the other isotopes are radioactive, with gallium-67 being
14170-502: The mismatch in their lattice constants . GaN can be doped with silicon (Si) or with oxygen to n-type and with magnesium (Mg) to p-type . However, the Si and Mg atoms change the way the GaN crystals grow, introducing tensile stresses and making them brittle. Gallium nitride compounds also tend to have a high dislocation density, on the order of 10 to 10 defects per square centimeter. The U.S. Army Research Laboratory (ARL) provided
14300-404: The object is not random, however: it is stored by atoms and molecules in " excited states ", which release photons with distinct wavelengths. This gives rise to the science of spectroscopy , which allows materials to be determined through the specific wavelengths that they emit. The underlying physical process creating photons in a laser is the same as in thermal radiation, but the actual emission
14430-509: The order Al > Ga > In and as a result organogallium compounds do not form bridged dimers as organoaluminium compounds do. Organogallium compounds are also less reactive than organoaluminium compounds. They do form stable peroxides. These alkylgalliums are liquids at room temperature, having low melting points, and are quite mobile and flammable. Triphenylgallium is monomeric in solution, but its crystals form chain structures due to weak intermolecluar Ga···C interactions. Gallium trichloride
14560-451: The order of tens of picoseconds down to less than 10 femtoseconds . These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy–time uncertainty ), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such
14690-418: The photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification. In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas
14820-409: The power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course, even a laser whose output is normally continuous can be intentionally turned on and off at some rate to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the period over which energy can be stored in
14950-708: The presence of dimethyl ether as solvent, GaH 3 polymerizes to (GaH 3 ) n . If no solvent is used, the dimer Ga 2 H 6 ( digallane ) is formed as a gas. Its structure is similar to diborane , having two hydrogen atoms bridging the two gallium centers, unlike α- AlH 3 in which aluminium has a coordination number of 6. Gallane is unstable above −10 °C, decomposing to elemental gallium and hydrogen . Organogallium compounds are of similar reactivity to organoindium compounds, less reactive than organoaluminium compounds, but more reactive than organothallium compounds. Alkylgalliums are monomeric. Lewis acidity decreases in
15080-564: The product can be condensed as a red solid. Gallium(I) compounds can be stabilized by forming adducts with Lewis acids. For example: The so-called "gallium(II) halides", GaX 2 , are actually adducts of gallium(I) halides with the respective gallium(III) halides, having the structure Ga [GaX 4 ] . For example: Like aluminium , gallium also forms a hydride , GaH 3 , known as gallane , which may be produced by reacting lithium gallanate ( LiGaH 4 ) with gallium(III) chloride at −30 °C: In
15210-662: The properties of the emitted light, such as the polarization, wavelength, and shape of the beam. Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics . In the classical view , the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom . However, quantum mechanical effects force electrons to take on discrete positions in orbitals . Thus, electrons are found in specific energy levels of an atom, two of which are shown below: An electron in an atom can absorb energy from light ( photons ) or heat ( phonons ) only if there
15340-494: The reaction of gallium metal with chlorine gas. Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules, Ga 2 Cl 6 , with a melting point of 78 °C. Equivalent compounds are formed with bromine and iodine, Ga 2 Br 6 and Ga 2 I 6 . Like the other group 13 trihalides, gallium(III) halides are Lewis acids , reacting as halide acceptors with alkali metal halides to form salts containing GaX 4 anions, where X
15470-473: The reaction of gallium with hydrogen sulfide ( H 2 S ) at 950 °C. Alternatively, Ga(OH) 3 can be used at 747 °C: Reacting a mixture of alkali metal carbonates and Ga 2 O 3 with H 2 S leads to the formation of thiogallates containing the [Ga 2 S 4 ] anion. Strong acids decompose these salts, releasing H 2 S in the process. The mercury salt, HgGa 2 S 4 , can be used as
15600-547: The real properties of gallium, such as its density , melting point , oxide character, and bonding in chloride. Mendeleev further predicted that eka-aluminium would be discovered by means of the spectroscope , and that metallic eka-aluminium would dissolve slowly in both acids and alkalis and would not react with air. He also predicted that M 2 O 3 would dissolve in acids to give MX 3 salts, that eka- aluminium salts would form basic salts, that eka-aluminium sulfate should form alums , and that anhydrous MCl 3 should have
15730-457: The relationship between the A coefficient , describing spontaneous emission, and the B coefficient which applies to absorption and stimulated emission. In the case of the free electron laser , atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics . A laser can be classified as operating in either continuous or pulsed mode, depending on whether
15860-729: The same structure as ZnS , and have important semiconducting properties. GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony. They exhibit higher electrical conductivity than GaN. GaP can also be synthesized by reacting Ga 2 O with phosphorus at low temperatures. Gallium forms ternary nitrides ; for example: Similar compounds with phosphorus and arsenic are possible: Li 3 GaP 2 and Li 3 GaAs 2 . These compounds are easily hydrolyzed by dilute acids and water. Gallium(III) oxide reacts with fluorinating agents such as HF or F 2 to form gallium(III) fluoride , GaF 3 . It
15990-410: The same time, and beats between the slightly different optical frequencies of those oscillations will produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a few nanoseconds or less. In most cases, these lasers are still termed "continuous-wave" as their output power is steady when averaged over longer periods, with
16120-481: The simple crystal structures . The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell . Within a unit cell, each atom has only one nearest neighbor (at a distance of 244 pm ). The remaining six unit cell neighbors are spaced 27, 30 and 39 pm farther away, and they are grouped in pairs with the same distance. Many stable and metastable phases are found as function of temperature and pressure. The bonding between
16250-425: The two mirrors, the output coupler , is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors are flat or curved ), the light coming out of the laser may spread out or form a narrow beam . In analogy to electronic oscillators , this device is sometimes called a laser oscillator . Most practical lasers contain additional elements that affect
16380-416: The two nearest neighbors is covalent ; hence Ga 2 dimers are seen as the fundamental building blocks of the crystal. This explains the low melting point relative to the neighbor elements, aluminium and indium. This structure is strikingly similar to that of iodine and may form because of interactions between the single 4p electrons of gallium atoms, further away from the nucleus than the 4s electrons and
16510-410: The very high-frequency power variations having little or no impact on the intended application. (However, the term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of the round-trip time.) For continuous-wave operation, the population inversion of the gain medium needs to be continually replenished by a steady pump source. In some lasing media, this
16640-597: The very stable GaCl 2 contains both gallium(I) and gallium(III) and can be formulated as Ga Ga Cl 4 ; in contrast, the monochloride is unstable above 0 °C, disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as GaS (which can be formulated as Ga 2 (S ) 2 ) and the dioxan complex Ga 2 Cl 4 (C 4 H 8 O 2 ) 2 . Strong acids dissolve gallium, forming gallium(III) salts such as Ga(NO 3 ) 3 (gallium nitrate). Aqueous solutions of gallium(III) salts contain
16770-485: Was at the George Herbert Jones Laboratory in 1932. An early synthesis of gallium nitride was by Robert Juza and Harry Hahn in 1938. GaN with a high crystalline quality can be obtained by depositing a buffer layer at low temperatures. Such high-quality GaN led to the discovery of p-type GaN, p–n junction blue/UV- LEDs and room-temperature stimulated emission (essential for laser action). This has led to
16900-598: Was called a maser , for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first called optical masers , until "microwave" was replaced by "light" in the acronym, to become laser . Today, all such devices operating at frequencies higher than microwaves (approximately above 300 GHz ) are called lasers (e.g. infrared lasers , ultraviolet lasers , X-ray lasers , gamma-ray lasers ), whereas devices operating at microwave or lower radio frequencies are called masers. The back-formed verb " to lase "
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