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Gallium nitride

Gallium nitride (GaN) is a binary III-V compound semiconductor with the chemical formula GaN, typically crystallizing in the hexagonal wurtzite structure.^[1] It features a direct bandgap of 3.4 eV at room temperature, which enables efficient optoelectronic performance in the blue and ultraviolet wavelengths.^[1] First synthesized in 1932 through the reaction of ammonia with molten gallium, GaN gained prominence in the late 20th century for its potential in solid-state lighting and high-power devices.^[2]^[3] As a wide-bandgap material, GaN offers superior electrical properties compared to silicon, including high electron mobility of 990–2000 cm²/V·s, high breakdown voltage, and no reverse recovery losses in power switching.^[4] It also demonstrates excellent thermal stability and cooling capability, allowing operation at elevated temperatures and slew rates up to 150 V/ns.^[4] Mechanically, GaN is exceptionally hard, with a wear rate of 10⁻⁷ to 10⁻⁹ mm³/N·m—three to five orders of magnitude lower than silicon's 10⁻⁴ mm³/N·m and approaching that of diamond—though its durability decreases in humid environments.^[5] GaN's applications span optoelectronics and power electronics, revolutionizing technologies like energy-efficient LEDs (achieving >150 lm/W efficiency) and laser diodes for high-speed data transmission up to 15 Gbit/s.^[4] In power devices, it enables compact, high-efficiency converters for 5G base stations, electric vehicles, aerospace systems, and satellites, with power amplifiers exceeding 150 W.^[4] Additionally, its radiation hardness and mechanical stability support uses in space solar cells, RF components, and sensors resistant to harsh conditions.^[5]^[6]

Properties

Chemical properties

Gallium nitride (GaN) is a binary III-V semiconductor compound with the chemical formula GaN.^[7]^[8] GaN exhibits thermal instability at elevated temperatures, decomposing above 1000°C in vacuum or low-pressure environments into elemental gallium and nitrogen gas via the reaction GaN → Ga + ½N₂.^[9]^[10] To prevent decomposition during processing, an overpressure of nitrogen is typically maintained.^[9] GaN decomposition typically occurs above ~900–1100°C depending on ambient conditions (e.g., higher in N₂, lower in H₂ or vacuum). In terms of reactivity, GaN demonstrates high chemical inertness at room temperature, resisting dissolution in water, most acids, and bases.^[11]^[12] However, it dissolves slowly in hot concentrated alkali solutions, such as sodium hydroxide (NaOH), forming sodium gallate and ammonia.^[13]^[12] Synthesis of GaN often encounters stoichiometry challenges due to the volatility of nitrogen precursors, resulting in non-stoichiometric films with nitrogen vacancies (V_N) that act as shallow donors and influence electrical properties.^[14] In bulk form, GaN shows excellent biocompatibility, exhibiting non-toxicity and compatibility with human cells, which supports its potential use in medical implants such as biosensors or neural interfaces.^[15]^[16]

Physical and mechanical properties

Gallium nitride (GaN) predominantly adopts the wurtzite crystal structure, a hexagonal form characterized by lattice constants of a = 3.189 Å and c = 5.185 Å. This structure arises from the tetrahedral coordination of gallium and nitrogen atoms, with the c-axis aligned along the direction of closest packing. A metastable zincblende (cubic) phase exists under specific growth conditions, such as molecular beam epitaxy on cubic substrates, but it is less stable than the wurtzite form due to higher energy.^[17]^[18] The material exhibits a density of 6.15 g/cm³, reflecting its compact atomic arrangement in the wurtzite lattice. GaN does not melt congruently at ambient pressure, instead decomposing into gallium and nitrogen above approximately 1000°C in inert atmospheres; however, under high pressure exceeding 6 GPa, it achieves stoichiometric melting near 2220°C, enabling bulk crystal growth via methods like ammonothermal processing.^[19]^[20] Thermal properties of GaN are influenced by phonon scattering and defect concentrations. The thermal conductivity ranges from 1.3 to 2.3 W/cm·K at room temperature, with higher values achieved in low-defect crystals due to reduced phonon-defect scattering; this range supports efficient heat dissipation in high-power applications. The specific heat capacity is approximately 42 J/mol·K near room temperature, consistent with its lattice vibrational modes in the wurtzite structure.^[21]^[22] Mechanically, GaN demonstrates exceptional hardness, with a Knoop hardness of 14.21 GPa, attributed to strong Ga-N covalent bonds. Its Young's modulus is around 300 GPa, indicating high stiffness, but this also contributes to brittleness, as the material lacks ductility and fractures under tensile stress without significant plastic deformation. These properties make GaN suitable for robust device structures but challenging for flexible applications.^[23]^[24] The non-centrosymmetric wurtzite structure imparts piezoelectric properties to GaN, generating electric polarization under mechanical stress. The longitudinal piezoelectric coefficient d_{33} is 3.7 pC/N, enabling applications in sensors and actuators where strain-induced voltage is utilized.^[25]

Electronic properties

Gallium nitride (GaN) is a wide-bandgap semiconductor with a direct bandgap of 3.4 eV at room temperature, which enables applications requiring high breakdown voltages, with a critical electric field strength exceeding 3 MV/cm.^[26]^[27] This bandgap arises from the electronic band structure, where the conduction band minimum and valence band maximum both occur at the Γ point in the Brillouin zone, confirming its direct bandgap nature.^[28] The effective masses of charge carriers are approximately 0.2 m₀ for electrons and 0.8 m₀ for holes, influencing their transport behavior.^[28] Charge transport in GaN is characterized by high electron mobility, reaching up to 2000 cm²/V·s in undoped material at room temperature, while hole mobility is significantly lower, typically in the range of 10–200 cm²/V·s due to the heavy hole effective mass and strong phonon scattering.^[29]^[30] Doping plays a crucial role in modulating conductivity: n-type doping is readily achieved with silicon (Si), which introduces shallow donor levels approximately 20 meV below the conduction band edge, facilitating efficient electron provision.^[31] In contrast, p-type doping with magnesium (Mg) is challenging due to its deeper acceptor level around 200 meV above the valence band maximum, resulting in high activation energy that limits hole concentration at room temperature.^[32] Defects significantly impact GaN's electronic properties, with nitrogen vacancies acting as shallow donors that contribute to unintentional n-type conductivity.^[33] Additionally, deep-level defects are associated with a yellow luminescence band at approximately 2.2 eV, arising from transitions involving these levels within the bandgap.^[34]

Optical properties

Gallium nitride (GaN) is a direct bandgap semiconductor with a bandgap energy of approximately 3.4 eV at room temperature, enabling strong optical absorption for photon energies above this threshold, which corresponds to wavelengths shorter than 365 nm.^[35] This property makes GaN highly suitable for ultraviolet optoelectronics, as the material exhibits minimal absorption and high transparency in the visible spectrum (wavelengths >400 nm), with low reflection below the bandgap energy.^[36]^[37] The refractive index of GaN is wavelength-dependent, typically ranging from 2.3 to 2.5 across the visible and near-infrared regions, which influences its use in photonic structures.^[38] This dispersion can be accurately modeled using the Sellmeier equation, with parameters for wurtzite GaN given by:

n^2 = 0.97344 + \frac{3.80128\lambda^2}{\lambda^2 - 0.07704^2} + \frac{0.59917\lambda^2}{\lambda^2 - 0.32445^2} - \frac{3 \times 10^{10} \lambda^2}{\lambda^2 - (5 \times 10^{10})^2}

where \lambda is in micrometers.^[38] Due to its wurtzite crystal structure, GaN displays birefringence, characterized by distinct ordinary (n_o) and extraordinary (n_e) refractive indices; at a wavelength of 633 nm, these are approximately n_o \approx 2.33 and n_e \approx 2.42, respectively.^[38] Photoluminescence in GaN reveals near-band-edge emission centered around 365 nm in the ultraviolet range, arising from radiative recombination of excitons or band-to-band transitions.^[39] Defect-related emission bands are also prominent, including green luminescence around 2.3–2.4 eV (approximately 510–540 nm) and yellow luminescence near 2.2 eV (about 560 nm), often attributed to carbon-related or vacancy complexes in high-purity samples.^[40] The exciton binding energy in bulk GaN ranges from 20 to 30 meV for the A, B, and C excitons, sufficient for partial room-temperature stability and contributing to efficient radiative processes.^[41] In high-quality undoped GaN, the internal quantum efficiency for near-band-edge photoluminescence exceeds 50%, approaching 100% in optimized homoepitaxial layers, underscoring the material's potential for efficient light emission.^[39]

History and development

Discovery and early research

Gallium nitride (GaN) was first synthesized in polycrystalline form in 1932 at the George Herbert Jones Laboratory of the University of Chicago by W. C. Johnson, J. B. Parsons, and M. C. Crew through the direct reaction of liquid gallium with gaseous ammonia at temperatures between 900°C and 1000°C. This method produced a grayish-white powder that was identified as GaN via chemical analysis and X-ray diffraction, marking the initial preparation of the compound despite its instability at atmospheric pressure above approximately 800°C. In the following years, further characterization efforts focused on the compound's thermal stability and structure. Robert Juza and Harry Hahn conducted detailed studies in 1940 on the formation heats and decomposition of various metal nitrides, including GaN, prepared by reacting gallium with ammonia, confirming its stoichiometric composition and wurtzite crystal structure.^[42] Early attempts to grow single crystals in the 1950s and 1960s faced significant challenges due to GaN's high dissociation pressure of nitrogen, requiring elevated pressures to stabilize the material. Initial high-pressure experiments, reaching up to several thousand atmospheres, were explored to enable crystal growth from the melt or solution, though yields remained low and crystals were small. During the 1960s and 1970s, researchers investigated the polymorphic phases of GaN, identifying the stable wurtzite (hexagonal) form under ambient conditions and the metastable zincblende (cubic) phase under specific epitaxial growth setups. Concurrently, the inherent n-type conductivity observed in undoped GaN was attributed to native nitrogen vacancies acting as shallow donors, a defect mechanism confirmed through electrical and optical measurements. These early materials suffered from high defect densities, with dislocation concentrations often exceeding 10^8 cm⁻² in polycrystalline samples, alongside purity limitations from unintentional impurities like oxygen and carbon that affected electronic properties.^[43] A pivotal advancement came in 1969 when H. M. Manasevit and W. I. Simpson-Deerfield demonstrated the epitaxial growth of single-crystal GaN films using metalorganic chemical vapor deposition (MOCVD) with trimethylgallium and ammonia precursors on insulating substrates, opening pathways for thin-film research despite persistent challenges in quality.

Key technological breakthroughs

One of the pivotal advances in gallium nitride (GaN) technology occurred in the mid-1980s when Hiroshi Amano and colleagues developed the low-temperature buffer layer technique for growing GaN films on sapphire substrates. This method involved depositing a thin GaN buffer layer at approximately 600°C prior to high-temperature epitaxial growth, which dramatically reduced threading dislocation densities from over 10^{10} cm^{-2} to around 10^8 cm^{-2}, enabling the production of higher-quality single-crystal GaN films essential for device performance.^[44] A major breakthrough in achieving p-type doping for GaN came in the early 1990s through the work of Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura. While earlier efforts had used low-energy electron beam irradiation to activate Mg-doped GaN, Nakamura demonstrated in 1992 that simple thermal annealing in a nitrogen ambient at temperatures above 700°C could effectively remove hydrogen passivation, yielding low-resistivity p-type GaN with hole concentrations up to 10^{18} cm^{-3} and enabling the fabrication of functional p-n junctions. This innovation, refined by 1993, overcame the longstanding challenge of p-type conductivity in wide-bandgap nitrides and paved the way for bipolar devices. The cumulative impact of these doping and growth advancements was recognized with the 2014 Nobel Prize in Physics awarded jointly to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura for the invention of efficient blue light-emitting diodes (LEDs) based on GaN. Their work transformed GaN from a material plagued by defects into a platform for high-efficiency optoelectronics, with blue LEDs achieving external quantum efficiencies exceeding 50% by the mid-1990s.^[45] In parallel, the 1990s saw the development of high electron mobility transistors (HEMTs) leveraging AlGaN/GaN heterostructures, where the first observation of a two-dimensional electron gas (2DEG) at the interface was reported by M. Asif Khan and colleagues in 1993. This 2DEG exhibited a sheet carrier density of approximately 10^{13} cm^{-2} and electron mobility exceeding 1500 cm²/V·s at room temperature, attributed to the strong piezoelectric and spontaneous polarization fields in the nitride system, which confined electrons without intentional doping and enabled high-frequency, high-power RF applications. Building on these foundations, Shuji Nakamura's team demonstrated the first continuous-wave violet laser diode in 1996 using an InGaN/GaN/AlGaN multiple quantum well structure grown on sapphire. Operating at a wavelength of 417 nm with threshold current densities around 3 kA/cm², this device marked the realization of semiconductor lasers in the blue-violet spectrum, crucial for applications like high-density optical storage.^[46]

Commercialization and recent advances

The commercialization of gallium nitride (GaN) technology began in the 1990s with the development of optoelectronic devices, particularly light-emitting diodes (LEDs). In 1993, Nichia Corporation achieved a major milestone by developing and commercializing the world's first high-brightness blue LED using GaN, which was previously considered technologically challenging.^[47] This breakthrough enabled the creation of white LEDs through phosphor conversion, where blue light from the GaN LED excites a yellow phosphor coating to produce broadband white light; Nichia initiated full-scale production of these phosphor-converted white LEDs in 1996.^[48] These advancements revolutionized solid-state lighting, paving the way for energy-efficient applications in displays, backlighting, and general illumination. Entering the 2000s, efforts focused on reducing costs and expanding into power and radio-frequency (RF) applications, with GaN-on-silicon substrates emerging as a key strategy to leverage existing silicon manufacturing infrastructure. In 2001, Cree Inc. introduced the first commercial GaN high-electron-mobility transistors (HEMTs) for base station amplifiers, targeting microwave applications and demonstrating GaN's potential for high-power RF performance.^[49] This period also saw initial commercialization of GaN-on-Si devices in the mid-2000s, which offered scalability and lower substrate costs compared to GaN-on-sapphire or GaN-on-SiC, facilitating broader adoption in consumer and industrial electronics.^[50] Post-2014, GaN technology experienced rapid growth, particularly in power devices, driven by demand for efficient energy conversion in consumer electronics, renewable energy systems, and electric vehicles. The power GaN device market, valued at approximately $347 million in 2023, is projected to reach $2.2 billion by 2030, reflecting a compound annual growth rate (CAGR) of over 30%, fueled by advancements in high-voltage transistors and integrated circuits.^[51] This expansion has been supported by industry consolidation and investments exceeding $1.25 billion since 2023, enabling cost-effective production scaling.^[52] From 2020 to 2025, GaN integration advanced significantly in electric vehicles (EVs), with applications in power electronics such as onboard chargers and DC-DC converters to improve efficiency and reduce size; for instance, GaN devices began appearing in EV inverters around 2021 to handle high-frequency switching with minimal losses.^[53] In RF domains, GaN amplifiers have become essential for 5G base stations and are positioning for 6G, with recent prototypes achieving record power-added efficiency of 66% at 13 GHz for sub-millimeter-wave applications.^[54] Production innovations include Infineon's pioneering of 300 mm silicon wafer-based GaN manufacturing in 2024, which increases chip yield by 2.3 times per wafer and supports high-volume automotive and industrial deployment.^[55] In 2025, further scaling efforts advanced with Imec launching a 300 mm GaN program in October to develop CMOS-compatible power devices using state-of-the-art equipment, aiming for full capabilities by year-end to enhance efficiency in datacenters and EVs.^[56] Additionally, in November, GlobalFoundries licensed GaN technology from TSMC to accelerate U.S.-manufactured power solutions for datacenters, industrial, and automotive applications, with products expected in late 2026.^[57] Addressing key challenges has been crucial for widespread adoption, including defect reduction in epitaxial layers to below 10^6 cm⁻² through optimized growth techniques like mask-offset methods, which minimize dislocations and improve device reliability.^[58] Additionally, the development of enhancement-mode GaN transistors, which operate normally off for safer power switching, has progressed with prototypes of GaN complementary metal-oxide-semiconductor (CMOS) logic circuits demonstrated in 2022, enabling integrated digital control in high-power systems.^[59]

Synthesis and fabrication

Bulk crystal growth

Bulk crystal growth of gallium nitride (GaN) refers to the production of thick, freestanding single-crystal substrates, which serve as native platforms for subsequent device fabrication, offering superior structural quality compared to heteroepitaxial approaches. These substrates are essential for reducing defects in high-performance optoelectronic and power devices, as they minimize lattice mismatch issues inherent to growth on foreign substrates like sapphire or silicon. The primary established methods for bulk GaN growth are high-pressure solution growth using sodium-gallium flux and hydride vapor phase epitaxy (HVPE), each addressing the material's high thermodynamic stability and decomposition challenges under ambient conditions. High-pressure solution growth, often employing a sodium (Na) flux with gallium (Ga), enables the dissolution of nitrogen into the metallic melt to form GaN crystals under controlled conditions. This process typically operates at pressures of 3–5 MPa (approximately 30–50 atm) and temperatures of 700–900°C, allowing for the crystallization of GaN boules with diameters up to 50 mm. The Na flux enhances nitrogen solubility, facilitating seeded growth where a seed crystal is immersed in the Ga-Na-N solution, promoting the preferential formation of the wurtzite polytype essential for device applications. Growth rates in this method are relatively modest, on the order of 10–50 μm/h, due to the limited solubility of GaN in the flux, but it yields crystals with exceptionally low defect densities. Hydride vapor phase epitaxy (HVPE) provides a vapor-phase alternative for bulk GaN production, utilizing gallium chloride (GaCl) precursor and ammonia (NH₃) in a hot-wall reactor. Growth occurs at temperatures around 1000–1100°C, achieving high rates of 100–500 μm/h, which enables the rapid deposition of thick layers (up to several millimeters) that can be removed from the substrate to form freestanding boules. However, HVPE is prone to parasitic deposition and strain-induced cracking, often limiting initial defect-free areas to approximately 1 cm², though optimizations like multi-step growth have expanded viable sizes. This method's scalability stems from its atmospheric pressure operation, contrasting with solution-based techniques. Key challenges in bulk GaN growth include the inherently low solubility of nitrogen in metallic fluxes, which constrains growth rates and boule sizes, and the need for precise polytype control to suppress unwanted cubic inclusions that degrade electrical properties. Additionally, managing thermal stresses during cooling and achieving uniform doping remain hurdles, as GaN's high equilibrium nitrogen pressure above 900°C promotes decomposition without adequate containment. Despite these, native bulk substrates exhibit dislocation densities of 10⁴–10⁶ cm⁻², significantly lower than the 10⁸–10¹⁰ cm⁻² typical of epitaxial layers on non-native substrates, enabling improved carrier mobility and device reliability. Commercial availability of bulk GaN substrates emerged in the early 2000s, with companies like Sumitomo Electric and Mitsubishi Chemical leading production using HVPE and ammonothermal variants of solution growth, respectively. By 2020, substrates up to 6 inches (150 mm) in diameter were routinely offered, supporting applications in laser diodes and power electronics, with Sumitomo achieving mass production of 4-inch wafers and demonstrating prototypes for larger formats. As of 2024, 6-inch substrates dominate the market (over 43% share), while 8-inch and larger formats are in development and early production to meet growing demand in power electronics and RF applications.^[60] These advancements have driven market growth, with high-quality n-type and semi-insulating options now standard for homoepitaxial device fabrication.

Epitaxial growth techniques

Epitaxial growth techniques for gallium nitride (GaN) primarily involve depositing thin films on foreign substrates to enable device fabrication, with metalorganic chemical vapor deposition (MOCVD, also known as MOVPE) and molecular beam epitaxy (MBE) as the dominant methods. MOCVD utilizes trimethylgallium (TMGa) as the gallium precursor and ammonia (NH3) as the nitrogen source, typically at substrate temperatures of 1000–1100°C to ensure efficient precursor decomposition and high crystalline quality.^[61] A low-temperature AlN buffer layer, deposited at around 900–1000°C prior to the main GaN growth, is essential to mitigate the lattice mismatch with the substrate and promote uniform nucleation, resulting in smoother films with reduced defect densities.^[61] Growth rates in MOCVD typically range from 1 to 5 μm/h, allowing for efficient production of multilayer structures suitable for optoelectronic devices.^[62] Molecular beam epitaxy (MBE) offers precise control over composition and doping through ultra-high vacuum conditions, using elemental gallium from effusion cells and active nitrogen from either an RF plasma source (N2) or cracked ammonia (NH3). Growth occurs at lower temperatures of 700–800°C compared to MOCVD, enabling in situ monitoring via reflection high-energy electron diffraction (RHEED) for atomic-level precision.^[63] However, MBE growth rates are slower, generally less than 1 μm/h, making it ideal for research on novel heterostructures but less common for high-volume manufacturing.^[63] Common substrates for GaN heteroepitaxy include sapphire (Al2O3), silicon carbide (SiC), and silicon (Si), selected based on cost, availability, and compatibility with device integration. Sapphire is the most prevalent due to its chemical stability and low cost, despite a significant in-plane lattice mismatch of approximately 16% with GaN, which necessitates buffer layers to accommodate strain.^[61] SiC provides a closer lattice match of about 3.5%, enabling higher-quality films with fewer initial defects, though its higher cost limits widespread use. Silicon substrates offer advantages for integration with CMOS processes but suffer from a 17% lattice mismatch and severe thermal bowing due to differences in coefficients of thermal expansion, often requiring advanced strain management.^[64] Threading dislocations, arising from lattice mismatch, propagate from the substrate interface and degrade device performance by scattering carriers and reducing mobility. To manage these defects, epitaxial lateral overgrowth (ELO) techniques are employed, where selective growth on patterned substrates (e.g., with SiO2 masks) allows dislocations to bend and terminate at sidewalls, achieving densities as low as 10^6 cm^{-2} in overgrown regions compared to 10^8–10^{10} cm^{-2} in planar films. Patterned sapphire substrates further enhance this by promoting lateral coalescence during initial nucleation, effectively filtering dislocations without additional masking steps. In industrial production, particularly for light-emitting diodes (LEDs), MOCVD remains the dominant technique due to its scalability and ability to handle large wafer sizes. Systems from manufacturers like Aixtron, such as the CRIUS series, enable high-throughput growth on multiple 4-inch or larger wafers, supporting the mass production of GaN-based LEDs with uniform thickness and composition control.

Advanced and emerging methods

Ammonia-based molecular beam epitaxy (MBE) variants, such as NH₃-MBE, enable the growth of high-quality GaN films by utilizing ammonia as a nitrogen source, achieving stable homoepitaxial growth over a wide range of flux ratios and temperatures while maintaining low defect densities.^[65] This approach supports step-flow growth modes that enhance structural integrity, particularly in nitrogen-rich conditions, leading to smoother interfaces compared to traditional plasma sources. Plasma-assisted MBE complements these variants by providing an ultrahigh vacuum environment with low background impurity concentrations, allowing for precise control of active nitrogen flux up to 3.5 μm/h equivalent to GaN growth rates, which is essential for producing purer films with reduced unintentional doping.^[66] Migration-enhanced epitaxy (MEE), often integrated with these MBE techniques, alternates the supply of gallium and nitrogen sources to promote atomic migration on the surface, resulting in significantly smoother GaN films on sapphire substrates without requiring buffer layers, as evidenced by reflection high-energy electron diffraction patterns showing improved crystallinity.^[67] Nanowire growth of GaN via selective area epitaxy using metalorganic chemical vapor deposition (MOCVD) allows for the fabrication of vertically aligned structures on patterned substrates, typically achieving diameters of 50–200 nm through controlled precursor flows and low fill-factor patterns.^[68] The nanoscale geometry of these nanowires inherently filters threading dislocations from the underlying substrate, enabling dislocation-free cores that improve optical and electrical performance in nano-optoelectronic devices.^[68] Two-dimensional (2D) GaN has been realized through exfoliation from bulk or epitaxial layers using sonochemical methods in solvents like isopropyl alcohol, yielding free-standing monolayer sheets with thicknesses around 0.3 nm and lateral dimensions up to 300 nm.^[69] Direct chemical vapor deposition (CVD) on graphene substrates, reported since 2016, stabilizes the hexagonal phase of 2D GaN by leveraging graphene's lattice for epitaxial alignment, often forming hybrid structures suitable for advanced electronics.^[69] The monolayer bandgap of 2D GaN is approximately 5.3 eV, enabling applications in deep-ultraviolet optoelectronics due to its wide direct bandgap and high thermal stability.^[69] Porous GaN structures are fabricated via electrochemical etching of n-type GaN films, typically in electrolytes like oxalic acid or KOH under voltages of 5–20 V, producing uniform nanopores with diameters of 50–200 nm and depths up to 44 μm while preserving single-crystallinity.^[70] Advances from 2020 to 2025 have optimized this process for higher porosity (up to 60%) and reduced defects, enhancing biocompatibility for biomedical scaffolds that promote human mesenchymal stem cell adhesion and spreading, particularly at pore sizes of 80–95 nm.^[70] Hybrid approaches integrating GaN with ultra-wide bandgap materials, such as GaN-on-Ga₂O₃ heterostructures, have emerged through plasma-assisted MBE on nitridated β-Ga₂O₃ substrates, achieving low lattice mismatch and full-width at half-maximum values below 200 arcsec in X-ray diffraction.^[71] Prototypes developed in 2023 demonstrate rectifying p-n junctions with on/off ratios of 10–100 and unintentional doping levels of 10¹⁶–3×10¹⁷ cm⁻³, paving the way for vertical power devices that combine GaN's high mobility with Ga₂O₃'s breakdown field exceeding 8 MV/cm.^[71]

Applications

Optoelectronic devices

Gallium nitride (GaN) and its alloys, particularly InGaN and AlGaN, have revolutionized optoelectronic devices by enabling efficient emission and detection in the blue, green, and ultraviolet spectral regions due to their direct wide bandgap properties. These materials form the basis for high-performance light-emitting diodes (LEDs), laser diodes, photodetectors, and emerging display technologies, where quantum well structures enhance carrier confinement and radiative recombination efficiency. Blue and ultraviolet LEDs primarily utilize InGaN/GaN multiple quantum wells (MQWs) as the active region, achieving internal quantum efficiencies (IQEs) exceeding 80% through optimized epitaxial growth and strain management. In the 1990s, early demonstrations by Nakamura et al. produced InGaN/AlGaN double-heterostructure blue LEDs with output powers around 1 mW and external quantum efficiencies of about 2.7%, marking a shift from low-brightness prototypes to commercially viable devices. By the 2010s, advancements in defect reduction and light extraction led to wall-plug efficiencies surpassing 100 lm/W for blue LEDs, enabling widespread adoption in solid-state lighting and displays. UV LEDs, leveraging AlGaN barriers for higher bandgaps, extend emission to wavelengths below 365 nm, with IQEs approaching 50% in recent structures. White LEDs are commonly realized by coating blue InGaN/GaN LEDs with yellow-emitting phosphors, such as yttrium aluminum garnet (YAG), to produce broadband white light for general illumination. This phosphor-converted approach has driven luminous efficacies from under 50 lm/W in early 2000s devices to over 200 lm/W by 2020, surpassing traditional fluorescent lamps and contributing to energy savings in global lighting. The high efficiency stems from the blue LED's strong output combined with phosphor's spectral conversion, achieving color rendering indices above 80 while maintaining low thermal loads. Violet laser diodes based on InGaN/GaN MQWs, operating at 405 nm, were pivotal for optical data storage, powering Blu-ray discs with data densities exceeding 25 GB per layer through tighter focus enabled by the shorter wavelength. Nakamura's group at Nichia demonstrated continuous-wave operation in 1996, evolving to high-power devices (>100 mW) by the mid-2000s for commercial Blu-ray systems. Green laser diodes, targeting 515-530 nm, employ higher indium content in InGaN wells but face challenges from indium segregation, which causes compositional inhomogeneity and reduces quantum efficiency below 10% in early prototypes; mitigation via interface engineering and low-temperature growth has improved thresholds to under 1 kA/cm² in recent years. Solar-blind ultraviolet photodetectors exploit AlGaN's tunable bandgap (above 4 eV for Al content >40%) to achieve high selectivity against visible light, with responsivities exceeding 100 mA/W at 265 nm in Schottky or p-i-n structures. These devices, often grown on AlN substrates to minimize dislocations, exhibit external quantum efficiencies over 50% and rejection ratios greater than 10^4 for wavelengths beyond 280 nm, making them ideal for flame detection and missile warning systems. Back-illuminated designs further enhance gain through avalanche multiplication while suppressing dark currents below 10 nA/cm². In display applications, GaN-based micro-LEDs have advanced augmented reality (AR) and virtual reality (VR) systems with pixel sizes below 10 μm, enabling resolutions over 2000 ppi and brightness exceeding 10^6 cd/m². Between 2022 and 2025, innovations in wafer-scale GaN-on-Si integration and sidewall passivation reduced efficiency droop in sub-5 μm pixels, achieving external quantum efficiencies above 20% for blue emission and facilitating full-color arrays via quantum dot color conversion.

Power electronics

Gallium nitride (GaN) high electron mobility transistors (HEMTs) have emerged as a key technology in power electronics due to their superior switching performance compared to silicon-based devices. These lateral devices typically achieve breakdown voltages exceeding 600 V, with specific on-resistances below 50 mΩ·cm², enabling efficient operation in high-voltage applications.^[72]^[73] For instance, GaN HEMTs demonstrate on-resistances as low as 0.92 mΩ·cm² at 600 V breakdown, supporting switching frequencies greater than 1 MHz that minimize losses in power conversion systems.^[74] This capability stems from GaN's high electron mobility and wide bandgap, allowing for faster charge carrier transport and reduced energy dissipation during transitions.^[75] In practical applications, GaN HEMTs excel in fast chargers and electric vehicle (EV) inverters. By 2018, commercial 65 W USB-C chargers utilizing GaN technology were introduced, enabling compact designs with up to three times faster charging than silicon equivalents while halving size and weight.^[76] In EVs, GaN-based 800 V inverters reduce conduction losses by approximately 50% relative to silicon MOSFETs, improving overall system efficiency and enabling higher power densities for traction drives.^[77] GaN devices operate in either enhancement-mode (normally off) or depletion-mode (normally on) configurations; the latter, which is inherent to standard GaN HEMTs, often employs cascode setups with low-voltage silicon MOSFETs to achieve safe, enhancement-like behavior and prevent unintended conduction.^[78] Since 2018, integrated GaN circuits incorporating drivers have further simplified designs by combining power transistors with control circuitry, reducing external components and enhancing reliability.^[79] Efficiency advantages in GaN power electronics are quantified by the figure of merit (V_br² / R_on), which reaches approximately 10^8 V²/Ω·mm for enhancement-mode GaN transistors versus 10^6 V²/Ω·mm for silicon superjunction MOSFETs, representing a 100-fold improvement and highlighting GaN's potential for lower conduction and switching losses.^[80] Effective thermal management leverages GaN's high thermal conductivity, around 130 W/m·K, which facilitates heat dissipation in dense modules and supports operation at elevated temperatures without significant performance degradation.^[81] Market adoption has grown, with GaN integrated into solar inverters for higher conversion efficiencies and data center power supplies, including those powering NVIDIA GPUs by 2023, where it enables compact, high-reliability systems for AI workloads.^[82]^[51] In 2025, advancements include Imec's launch of a 300 mm GaN program for cost-effective power devices, Infineon's introduction of 100 V automotive-qualified GaN transistors, and GlobalFoundries' licensing of GaN technology for datacenter and automotive applications, as of November 2025.^[56]^[83]^[57]

Radio frequency and microwave devices

Gallium nitride (GaN) high electron mobility transistors (HEMTs) have become a cornerstone in radio frequency (RF) and microwave devices due to their superior power density, efficiency, and high-frequency performance compared to traditional materials like gallium arsenide (GaAs).^[84] In RF amplifiers, GaN HEMTs achieve output power densities exceeding 5 W/mm at 10 GHz, with power-added efficiency (PAE) surpassing 60%, enabling compact designs for high-power applications.^[84] For instance, GaN-on-Si HEMTs have demonstrated 6.1 W/mm output power and 65% PAE at 10 GHz under specific biasing conditions.^[84] These attributes stem from GaN's wide bandgap and high electron mobility, allowing operation at elevated voltages and temperatures without significant degradation.^[85] In telecommunications, GaN-based power amplifiers are integral to 5G base stations, particularly for mm-wave bands, where they deliver up to 100 W output power with efficiencies over 50%.^[86] This contrasts with GaAs amplifiers, which typically achieve around 30% efficiency in similar roles, making GaN preferable for energy-efficient, high-throughput networks.^[87] Doherty configurations using GaN HEMTs further enhance back-off efficiency, supporting the dynamic power demands of 5G massive MIMO systems while reducing operational costs.^[88] For radar applications, GaN enables advanced active electronically scanned array (AESA) systems with extended range and reliability. The AN/TPQ-53 counterfire radar, upgraded with GaN transmit-receive modules in the 2010s, provides detection ranges up to 20 km in 360° search mode and 60 km in 90° search mode, improving target acquisition for artillery and rocket threats.^[89] Similarly, Thales' Ground Master 400 employs GaN technology for full 360° azimuthal coverage, detecting high- to low-altitude targets with robust performance in dense environments.^[90] These systems leverage GaN's high power handling to achieve greater sensitivity and faster scan rates compared to legacy GaAs-based radars. In satellite communications and defense, GaN devices offer low noise figures below 2 dB and exceptional radiation hardness, critical for space environments.^[91] GaN HEMTs have demonstrated noise figures of 1.7–1.99 dB across 8–10 GHz, supporting high-sensitivity receivers in jammed or noisy scenarios.^[91] Their tolerance to radiation doses exceeding 10^15 protons/cm² with minimal parameter shifts makes them suitable for orbital platforms, as evidenced by Lockheed Martin's integration in space radar prototypes since the late 2010s.^[92]^[93] Monolithic microwave integrated circuits (MMICs) incorporating GaN have advanced hybrid systems by combining GaN's power amplification with GaAs's low-noise front-ends, particularly in the 2020s.^[94] These integrations yield broadband performance from 1–100 GHz, with GaN MMICs providing high output power density in defense transceivers while GaAs handles signal reception, reducing overall system complexity and size.^[94]

Emerging applications

Gallium nitride (GaN) holds promise in spintronics due to its wide bandgap and compatibility with ferromagnetic doping, particularly in GaMnN alloys that facilitate spin injection into non-magnetic semiconductors. Theoretical models predict Curie temperatures exceeding 300 K for diluted magnetic (Ga,Mn)N semiconductors, enabling potential room-temperature ferromagnetism essential for spintronic devices.^[95] Research on these materials has progressed since the early 2000s, with experimental observations of ferromagnetic ordering up to 300 K in n-type GaMnN epitaxial films, though debates persist on the intrinsic versus extrinsic origins of the magnetism.^[96] Recent advances, including circularly polarized light emission at 300 K under magnetic fields, underscore GaN-based structures' viability for spin-polarized transport in opto-spintronics.^[97] In nanoscale devices, GaN nanowires exhibit high sensitivity for gas sensing applications, leveraging their large surface-to-volume ratio and chemical stability. For instance, InGaN/GaN multi-quantum well nanowires achieve a limit of detection of 3 parts per billion (ppb) for NO₂, surpassing regulatory thresholds and enabling trace-level environmental monitoring.^[98] GaN quantum dots further extend nanoscale potential in quantum computing, serving as platforms for qubit realization through confined electron spins. Early theoretical work on GaN/AlN quantum dots highlights their suitability as single-qubit emitters, with strong built-in electric fields aiding spin manipulation.^[99] More recent demonstrations include optically controlled spin gates in GaN quantum dots, where dipole-dipole interactions enable entanglement between qubits at cryogenic temperatures.^[100] Quantum technologies benefit from GaN's defect engineering, particularly for single-photon sources. Defect-based emitters in GaN, such as those involving carbon or silicon impurities, produce bright, photostable single photons, with 2023 studies characterizing their optical dipole orientations and enabling deterministic control.^[101] These defects exhibit ultrafast spectral diffusion on picosecond timescales, which can be harnessed for linewidth narrowing in quantum optics applications.^[102] While primarily observed in the 600–700 nm range, stress-tunable defects in GaN offer potential extension to ultraviolet wavelengths for integrated quantum networks.^[103] Integration with diamond nitrogen-vacancy (NV) centers enhances collection efficiency; transfer-printed GaN solid immersion microlenses boost fluorescence extraction from laser-written NV centers by factors exceeding 10, facilitating hybrid quantum systems.^[104] Biomedical applications leverage GaN's biocompatibility, positioning it as a candidate for implantable devices. Unlike many semiconductors, GaN demonstrates non-toxicity and supports peptide attachment without adverse cellular responses, critical for long-term neural interfaces.^[105] Porous GaN scaffolds, fabricated via advanced etching techniques, mimic the extracellular matrix to promote cell adhesion, proliferation, and tissue regeneration in bone engineering.^[70] GaN demonstrates high biocompatibility with minimal inflammatory response in vitro, advancing applications in neural implants where its wide bandgap enables stable bioelectronic signaling.^[106] In renewable energy, GaN's high-efficiency power electronics are emerging in hydrogen production systems, supporting compact, high-voltage components for electrolyzers. Prototypes incorporating GaN devices achieve system efficiencies over 70% in alkaline and PEM configurations, reducing energy losses in large-scale H₂ generation.^[107] This integration addresses scalability challenges, with 2024 advancements targeting cost-effective green hydrogen pathways through improved stack durability and performance.^[108]

Safety and environmental considerations

Health and toxicity

Gallium nitride (GaN) exhibits low acute toxicity via oral and dermal routes, though specific LD50 values for GaN are not fully established. Dust and nanoparticle forms of GaN can cause respiratory irritation upon inhalation, particularly fine particles smaller than 5 μm, which may penetrate deep into the lungs and induce pulmonary inflammation and fibrosis similar to that observed with other respirable particulates. Skin and eye contact with GaN powder may lead to irritation or dermatitis, manifesting as redness, itching, or sensitization in sensitive individuals.^[7] In biocompatibility assessments, bulk GaN has demonstrated non-cytotoxic properties in cell culture studies, supporting cell adhesion and growth without interference, and showing no degradation or leaching of gallium ions in aqueous environments. This stability makes GaN suitable for biomedical implants, where it promotes neurite extension in neural cells and complies with general biocompatibility evaluation principles for medical devices.^[109] Long-term exposure risks for GaN appear limited, with no evidence of carcinogenicity reported in toxicological evaluations, distinguishing it from more hazardous gallium-based semiconductors like gallium arsenide. While free gallium ions from soluble compounds can bioaccumulate in the liver and bone, potentially disrupting iron metabolism, the chemical stability of GaN prevents significant ion release under physiological conditions.^[110]^[111]^[109] During synthesis via metalorganic vapor phase epitaxy (MOVPE), precursors such as trimethylgallium (TMGa) and ammonia pose greater hazards than the final GaN product, with TMGa being pyrophoric and highly toxic by inhalation or skin contact, and ammonia causing severe respiratory and ocular irritation.^[112]

Handling and environmental impact

In the production of gallium nitride (GaN) via metalorganic chemical vapor deposition (MOCVD), workplace safety protocols emphasize robust ventilation systems to manage precursor gases, particularly ammonia (NH3), with exposure limits maintained below 25 parts per million (ppm) to prevent respiratory irritation. Personal protective equipment (PPE), including chemical-resistant gloves, goggles, and suits, is required when handling gallium-containing spills, as metallic gallium reacts slowly with water to produce hydrogen gas, posing a potential fire hazard.^[113] Waste management in GaN manufacturing focuses on recycling gallium from spent wafers and substrates, often through processes like ball milling, annealing, and acid leaching to recover over 90% of the metal, minimizing resource depletion.^[114] Nitrogen emissions from epitaxial growth exhausts, primarily unreacted NH3, are controlled via thermal oxidation or scrubbing systems in fabrication facilities to comply with air quality standards and reduce atmospheric release.^[115] Environmentally, GaN exhibits low persistence in soil and water due to its insolubility in neutral aqueous solutions, limiting leaching and long-term contamination from solid waste. Unlike soluble gallium salts, GaN does not bioaccumulate in ecosystems, as its inert ceramic structure prevents dissociation and uptake by organisms.^[116] Lifecycle assessments of GaN production highlight its energy intensity, with MOCVD processes consuming approximately 2 kWh per square centimeter of wafer area, primarily due to high-temperature reactors and cleanroom operations, contributing significantly to the overall carbon footprint.^[117] Implementing gallium recycling in the supply chain can reduce lifecycle environmental impacts by up to 50%, particularly in energy use and raw material extraction.^[118] Under the European Union's REACH regulation, GaN is registered and classified under CLP as Skin Sensitisation Category 1 (H317: May cause an allergic skin reaction), requiring appropriate labeling and safe handling, though exempt from authorization or restriction requirements for most industrial uses.^[119] GaN-containing waste electrical and electronic equipment falls under the Waste Electrical and Electronic Equipment (WEEE) Directive, which mandates separate collection and sets general recycling targets (e.g., 85% collection rate for large household appliances as of 2019), with a revision expected in 2026 to address critical raw materials.^[120]

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Jan 30, 2025 · Measurements indicated that the GaN LNA achieved a small-signal gain of 19 − 20 dB and a noise figure of 1.70 − 1.99 dB in the 8 − 10 GHz range.
[87]
Gallium Nitride (GaN) Radiation Hardness for Space Electronics
Studies have shown that GaN HEMTs can withstand proton fluences exceeding 1e15 protons per square centimeter with minimal degradation in electrical ...
[88]
U.S. Army Awards Lockheed Martin Contract Extending AN/TPQ-53 ...
Oct 8, 2018 · The US Army awarded Lockheed Martin a contract modification to insert Gallium Nitride (GaN) into the AN/TPQ-53 (Q-53) radar as part of the full rate production ...
[89]
GaAs and GaN MMICs: Key component of defense RF electronic ...
These devices offer the best combination of high-frequency operation, low noise, high linearity, and high output power density of any semiconductor technology.
[90]
High Curie temperature in diluted magnetic semiconductors (B, Mn ...
The ferromagnetism in (Ga, Mn)N remains a subject of debate, some experiments reported the room-temperature ferromagnetism [10–12] and attributed the high T C ...
[91]
[PDF] Wide bandgap GaN-based semiconductors for spintronics
Feb 6, 2004 · The predicted. Curie temperature of AlMnN is greater than 300 K and recently a Curie temperature of more than 340 K has been observed for AlN:Cr ...<|separator|>
[92]
Spintronics in GaN‐Based Semiconductors: Research Progress ...
Nov 6, 2024 · At an external magnetic field of 8 T and temperatures of 150 and 300 K, the researchers observed circularly polarized light with a degree of ...
[93]
InGaN/GaN multi-quantum well nanowires: Enhanced trace-level ...
Jul 1, 2024 · The limit of detection (LOD) for the InGaN/GaN-MQW2 sensor is 3 parts per billion (ppb), significantly lower than the NO2 threshold value of 53 ...
[94]
[0807.5024] GaN/AlN Quantum Dots for Single Qubit Emitters - arXiv
Jul 31, 2008 · We study theoretically the electronic properties of c-plane GaN/AlN quantum dots (QDs) with focus on their potential as sources of single ...
[95]
Optically Controlled Spin Gate Using GaN Quantum Dots
Apr 15, 2022 · The interaction between two quantum bits enables the creation of entanglement, the two-particle correlations that are at the heart of quantum ...
[96]
[PDF] Optical Dipole Structure and Orientation of GaN Defect Single
Oct 5, 2023 · ABSTRACT: GaN has recently been shown to host bright, photostable, defect single-photon emitters in the 600−700 nm wavelength range that are.
[97]
Ultrafast spectral diffusion of GaN defect single photon emitters - ADS
Our work provides insight into the ultrafast spectral diffusion in GaN defect-based single photon emitter systems and contributes toward harnessing the ...Missing: UV | Show results with:UV
[98]
First-Principle Prediction of Stress-Tunable Single-Photon Emitters ...
Our work sheds light on the possible origin of defect-based single photon emission in GaN and provides an effective method to achieve room-temperature single ...
[99]
Additive GaN Solid Immersion Lenses for Enhanced Photon ...
Aug 30, 2023 · We report increased fluorescent light collection efficiency from laser-written nitrogen-vacancy (NV) centers in bulk diamond facilitated by micro-transfer ...Introduction · Fabrication Method · Results and Discussion · Author Information
[100]
Research Finds Gallium Nitride is Non-Toxic, Biocompatible
Oct 24, 2011 · “The first finding is that GaN, unlike other semiconductor materials that have been considered for biomedical implants, is not toxic. That ...
[101]
GaN aids biomedical implantation - News - Compound Semiconductor
Mar 27, 2014 · The researchers worked with GaN because it is one of the most promising semiconductor materials for use in biomedical applications. They also ...
[102]
[PDF] 2024 - Hydrogen Production Technologies Subprogram Overview
Develop high-temperature electrolyzer technologies able to meet stack targets of $125/kW at 1.2 A/cm2 and. 1.28 V with a 40,000-hour lifetime by 2026. • Develop ...
[103]
Hydrogen production – Global Hydrogen Review 2024 - IEA
Installed water electrolyser capacity reached 1.4 GW by the end of 2023 and could reach 5 GW by the end of 2024. China leads in terms of committed projects and ...
[104]
[PDF] Gallium nitride, powder and pieces - Kurt J. Lesker Company
Jul 3, 2006 · See "Section II" LD 50/LC 50: No toxicity data recorded. SECTION 6 : Emergency And First Aid Procedures. Physical Health Hazard: HEALTH ...
[105]
https://news.ncsu.edu/2011/10/wmsivanisevicganpeptides/
[106]
Toxicity of indium arsenide, gallium arsenide, and ... - PubMed
Aug 1, 2004 · Although acute and chronic toxicity of the lung, reproductive organs, and kidney are associated with exposure to these semiconductor materials.Missing: nitride long-
[107]
Medical Applications and Toxicities of Gallium Compounds - PMC
Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this ...Missing: nitride | Show results with:nitride
[108]
Wide-Bandgap Semiconductors: A Critical Analysis of GaN, SiC ...
This review provides a comprehensive roadmap for sustainable WBG semiconductor manufacturing, bridging materials innovation, energy efficiency, and industrial ...
[109]
[PDF] Gallium Safety in the Laboratory L. C. Cadwallader June 21, 2003
Jun 27, 2003 · Care should be taken when handling spills to minimize exposure. Overall, gallium and galinstan do not pose a large toxicity hazard. Flow Loop ...
[110]
Recycling process for recovery of gallium from GaN an e-waste of ...
The developed process can treat and recycle any e-waste containing GaN through ball milling, annealing and leaching.
[111]
Burning beats scrubbing in LED fabs - Compound Semiconductor
May 11, 2011 · The two most common gas by-products of the GaN MOCVD manufacturing process are ammonia (NH3) and hydrogen. Both of these gases are highly ...Missing: ventilation | Show results with:ventilation
[112]
On the solubility of gallium nitride in supercritical ammonia-sodium ...
No clear dependence of GaN solubility on temperature was resolvable, while most solubility values were determined to be within a band of 0.03-0.10 mol% GaN, ...<|control11|><|separator|>
[113]
Gallium: Environmental Pollution and Health Effects - ResearchGate
Ga-linked waste may contaminate the water and air but Ga levels in ambient water and air quality are not standardized at present.
[114]
Cradle-to-Gate Life Cycle Assessment (LCA) of GaN Power ... - MDPI
Jan 20, 2024 · This study aims to assess the environmental impacts of producing a GaN semiconductor power device. Since the normally-off GaN devices offer the ...
[115]
GaN Sustainability Report: “Electrify Our World”
Feb 14, 2022 · The report includes a third-party Lifecycle Assessment (LCA) of GaN technology according to ISO14040/14044, the international standard for ...
[116]
[PDF] SAFETY DATA SHEET - Fisher Scientific
Mar 30, 2024 · May cause long-term adverse effects in the environment. Do not allow material to contaminate ground water system. Persistence and Degradability.