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| Names | |
|---|---|
| IUPAC name Gallium nitride | |
| Other names gallium(III) nitride | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.042.830 |
| UNII | |
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| Properties | |
| GaN | |
| Molar mass | 83.730 g/mol[1] |
| Appearance | yellow powder |
| Density | 6.1 g/cm3[1] |
| Melting point | > 1600 °C[1][2] |
| Insoluble[3] | |
| Band gap | 3.4 eV (300 K, direct) |
| Electron mobility | 1500 cm2/(V·s) (300 K)[4] |
| Thermal conductivity | 1.3 W/(cm·K) (300 K)[5] |
Refractive index (nD) | 2.429 |
| Structure | |
| Wurtzite | |
| C6v4-P63mc | |
a = 318.6 pm,c = 518.6 pm[6] | |
| Tetrahedral | |
| Thermochemistry | |
Std enthalpy of formation(ΔfH⦵298) | −110.2 kJ/mol[7] |
| Hazards | |
| GHS labelling: | |
 | |
| Warning | |
| H317 | |
| P261,P272,P280,P302+P352,P321,P333+P313,P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Safety data sheet (SDS) | Sigma-Aldrich Co.,Gallium nitride. Retrieved on 18 February 2024. |
| Related compounds | |
Otheranions | Gallium phosphide Gallium arsenide Gallium antimonide |
Othercations | Boron nitride Aluminium nitride Indium nitride |
Related compounds | Aluminium gallium arsenide Indium gallium arsenide Gallium arsenide phosphide Aluminium gallium nitride Indium gallium nitride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Gallium nitride (GaN) is a binaryIII/Vdirect bandgapsemiconductor commonly used in bluelight-emitting diodes since the 1990s. Thecompound is a very hard material that has aWurtzite crystal structure. Its wideband gap of 3.4 eV affords itspecial properties for applications inoptoelectronics,[9][10][11] high-power and high-frequency devices. For example, GaN is the substrate that makes violet (405 nm) laser diodes possible, without requiring nonlinear opticalfrequency doubling.
Its sensitivity toionizing radiation is low (like othergroup IIInitrides), making it a suitable material forsolar cell arrays forsatellites. Military and space applications could also benefit asdevices have shown stability in high radiation environments.[12]
Because GaN transistors can operate at much higher temperatures and work at much higher voltages thangallium arsenide (GaAs) transistors, they make ideal power amplifiers at microwave frequencies. In addition, GaN offers promising characteristics forTHz devices.[13] Due to high power density and voltage breakdown limits GaN 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 inpower supplies in electronic equipment, convertingACmains electricity to low-voltageDC.
GaN is a very hard (Knoop hardness 14.21 GPa[14]: 4 ), mechanically stablewide-bandgap semiconductor material with highheat capacity and thermal conductivity.[15] In its pure form it resists cracking and can be deposited inthin film onsapphire orsilicon carbide, despite the mismatch in theirlattice constants.[15] GaN can bedoped withsilicon (Si) or withoxygen[16] ton-type and with magnesium (Mg) top-type.[17][18] However, the Si and Mg atoms change the way the GaN crystals grow, introducingtensile stresses and making them brittle.[19]Galliumnitride compounds also tend to have a highdislocation density, on the order of 108 to 1010 defects per square centimeter.[20]
TheU.S. Army Research Laboratory (ARL) provided the first measurement of the high field electronvelocity in GaN in 1999.[21] Scientists at ARL experimentally obtained a peaksteady-state velocity of1.9×107 cm/s, with atransit time of 2.5 picoseconds, attained at anelectric field of 225 kV/cm. With this information, theelectron mobility was calculated, thus providing data for the design of GaN devices.
One of the earliest syntheses of gallium nitride was at the George Herbert Jones Laboratory in 1932.[22]
An early synthesis of gallium nitride was by Robert Juza and Harry Hahn in 1938.[23]
GaN with a high crystalline quality can be obtained by depositing a buffer layer at low temperatures.[24] Such high-quality GaN led to the discovery of p-type GaN,[17] p–n junction blue/UV-LEDs[17] and room-temperature stimulated emission[25] (essential for laser action).[26] This has led to 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-speedfield-effect transistors.[citation needed]
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 bluelaser devices. The first GaN-based high-brightness LEDs used a thin film of GaN deposited viametalorganic vapour-phase epitaxy (MOVPE) onsapphire. Other substrates used arezinc oxide, withlattice constant mismatch of only 2% andsilicon carbide (SiC).[27] 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.[citation needed]
The very highbreakdown voltages,[28] highelectron mobility, and highsaturation velocity of GaN has made it an ideal candidate for high-power and high-temperature microwave applications, as evidenced by its highJohnson's figure of merit. Potential markets for high-power/high-frequency devices based on GaN includemicrowaveradio-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 RFtransistors is as the microwave source formicrowave ovens, replacing themagnetrons currently used. The large band gap means that the performance of GaN transistors is maintained up to higher temperatures (~400 °C[29]) than silicon transistors (~150 °C[29]) because it lessens the effects ofthermal generation of charge carriers that are inherent to any semiconductor. The first gallium nitride metal semiconductor field-effect transistors (GaNMESFET) were experimentally demonstrated in 1993[30] and they are being actively developed.
In 2010, the firstenhancement-mode GaN transistors became generally available.[31] Only n-channel transistors were available.[31] 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 asGaN-on-Si by manufacturers.[32] This allows 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.[33]
GaN power ICs monolithically integrate a GaN FET, GaN-based drive circuitry and circuit protection into a single surface-mount device.[34][35] 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 the first GaNCMOS 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).[36]
GaN-based violetlaser diodes are used to readBlu-ray Discs. The mixture of GaN withIn (InGaN) orAl (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.[27]
GaN transistors are suitable for high frequency, high voltage, high temperature and high-efficiency applications.[37][38] GaN is efficient at transferring current, and this ultimately means that less energy is lost to heat.[39]
GaNhigh-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.[40]
GaN-based metal–oxide–semiconductor field-effect transistors (MOSFET) and metal–semiconductor field-effect transistors (MESFET) also offer advantages including lower loss in high power electronics, especially in automotive and electric car applications.[41] Since 2008 these can be formed on a silicon substrate.[41] High-voltage (800 V)Schottky barrier diodes (SBDs) have also been made.[41]
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 forpower transmissionutilities.
Unlike silicon transistors that switch off due to power surges,[clarification needed] GaN transistors are typicallydepletion mode devices (i.e. on / resistive when 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:[42][43]
GaN technology is also utilized in military electronics such asactive electronically scanned array radars.[44]
Thales Group introduced theGround Master 400 radar in 2010 utilizing GaN technology. In 2021 Thales put in operation more than 50,000 GaN Transmitters on radar systems.[45]
TheU.S. Army fundedLockheed Martin to incorporate GaN active-device technology into theAN/TPQ-53 radar system to replace two medium-range radar systems, theAN/TPQ-36 and theAN/TPQ-37.[46][47] The AN/TPQ-53 radar system was designed to detect, classify, track, and locate enemy indirect fire systems, as well as unmanned aerial systems.[48] 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 the AN/TPQ-36 and the AN/TPQ-37 systems.[46]
Lockheed Martin fielded other tactical operational radars with GaN technology in 2018, includingTPS-77 Multi Role Radar System deployed toLatvia andRomania.[49] In 2019, Lockheed Martin's partnerELTA Systems Limited, developed a GaN-basedELM-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 designedAESAX-band radar in aJAS-39 Gripen fighter.[50] Saab already offers products with GaN based radars, like theGiraffe radar,Erieye,GlobalEye, and Arexis EW.[51][52][53][54] Saab also delivers major subsystems, assemblies and software for theAN/TPS-80 (G/ATOR)[55]
India'sDefence Research and Development Organisation is developingVirupaakhsha radar forSukhoi Su-30MKI based on GaN technology. The radar is a further development ofUttam AESA Radar for use onHAL Tejas which employsGaAs technology.[56][57][58]
GaN nanotubes and nanowires are proposed for applications in nanoscaleelectronics, optoelectronics and biochemical-sensing applications.[59][60]
When doped with a suitabletransition metal such asmanganese, GaN is a promisingspintronics material (magnetic semiconductors).[27]
GaN crystals can be grown from a molten Na/Ga melt held under 100 atmospheres of pressure of N2 at 750 °C. As Ga will not react with N2 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 at900–980 °C at normal atmospheric pressure.[63]
Blue, white and ultravioletLEDs are grown on industrial scale bymetalorganic vapour-phase epitaxy (MOVPE).[64][65] The precursors areammonia with eithertrimethylgallium ortriethylgallium, the carrier gas beingnitrogen orhydrogen. Growth temperature ranges between800 and 1100 °C. Introduction oftrimethylaluminium and/ortrimethylindium is necessary for growing quantum wells and other kinds ofheterostructures.
Commercially, GaN crystals can be grown usingmolecular beam epitaxy or MBE. This process can be further modified to reduce dislocation densities. First, an ion beam 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-statepolymer electrolytes that are solvent-free and require no radiation before polishing.[66]
GaN dust is an irritant to skin, eyes and lungs. The environment, health and safety aspects of gallium nitride sources (such astrimethylgallium andammonia) and industrial hygiene monitoring studies ofMOVPE sources have been reported in a 2004 review.[67]
Bulk GaN is non-toxic andbiocompatible.[68] Therefore, it may be used in the electrodes and electronics of implants in living organisms.
These devices offer lower loss during power conversion and operational characteristics that surpass traditional silicon counterparts.
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