Gallium nitride

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 the mismatch in their lattice constants. 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 108 to 1010 defects per square centimeter. The U.S. Army Research Laboratory (ARL) provided the first measurement of the high field electron velocity in GaN in 1999. Scientists at ARL experimentally obtained a peak steady-state velocity of , 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. == Developments ==

One of the earliest syntheses of gallium nitride 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, (essential for laser action). 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-speed field-effect transistors. LEDs 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 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. GaN transistors and power ICs 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 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 and they are being actively developed. In 2010, the first enhancement-mode GaN transistors became generally available. Only n-channel transistors were available. This allows the FETs to maintain costs similar to silicon power MOSFETs but with the superior electrical performance of GaN, and consists of growing GaN on silicon wafers using MOCVD Epitaxy. 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. For power applications, GaN HEMTs are available with a range of different levels of integration, including discrete, cascode, ICeGaN and integrated gate drive. GaN ICs monolithically integrate a GaN FET, GaN-based drive circuitry and circuit protection into 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. CMOS logic In 2016 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). == Applications ==

LEDs and lasers 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 Ga allows the manufacture of light-emitting diodes (LEDs) with colors that can go from red to ultra-violet. GaN 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 transistors (MESFET) also offer advantages including lower loss in high power electronics, especially in automotive and electric car applications. Since 2008 these can be formed on a silicon substrate. • the implantation of fluorine ions under the gate (the negative charge of the F-ions favors the depletion of the channel) • the use of a MIS-type gate stack, with recess of the AlGaN • the integration of a cascaded pair constituted by a normally-on GaN transistor and a low voltage silicon MOSFET • the use of a p-type layer on top of the AlGaN/GaN heterojunction Radars 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 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 the AN/TPQ-36 and the AN/TPQ-37 systems. 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 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. Turkish Aselsan company delivered the first GaN-based Turkish AESA radar, ALP 300-G, to the Turkish Armed Forces in May 2024. Nanoscale GaN nanotubes and nanowires are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications. Spintronics potential When doped with a suitable transition metal such as manganese, GaN is a promising spintronics material (magnetic semiconductors). == Synthesis ==

Bulk substrates 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: : 2 Ga + 2 NH3 → 2 GaN + 3 H2 : Ga2O3 + 2 NH3 → 2 GaN + 3 H2O Gallium nitride can also be synthesized by injecting ammonia gas into molten gallium at at normal atmospheric pressure. Metal-organic vapour phase epitaxy Blue, white and ultraviolet LEDs are grown on industrial scale by metalorganic vapour-phase epitaxy (MOVPE). The precursors are ammonia with either trimethylgallium or triethylgallium, the carrier gas being nitrogen or hydrogen. Growth temperature ranges between . Introduction of trimethylaluminium and/or trimethylindium is necessary for growing quantum wells and other kinds of heterostructures. Molecular beam epitaxy Commercially, GaN crystals can be grown using molecular beam epitaxy or MBE. MBE growth of GaN can be divided into two categories, including ammonia-MBE (NH3-MBE) and plasma assisted MBE (PA-MBE). In NH3-MBE, NH3 is used as the nitrogen source, while a nitrogen RF plasma is used in PA-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-state polymer electrolytes that are solvent-free and require no radiation before polishing. == Safety ==

GaN dust 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. == See also ==