Gallium nitride
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| Gallium nitride | |
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| IUPAC name |
Gallium nitride
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| Identifiers | |
| CAS number | 25617-97-4  |
| PubChem | 117559 |
| RTECS number | LW9640000 |
| Properties | |
| Molecular formula | GaN |
| Molar mass | 83.73 g/mol |
| Appearance | yellow powder |
| Density | 6.15 g/cm3 |
| Melting point |
>2500°C[1] |
| Solubility in water | Reacts. |
| Band gap | 3.2 eV (300 K, direct) |
| Electron mobility | 440 cm2/(V·s) (300 K) |
| Thermal conductivity | 1.3 W/(cm·K) (300 K) |
| Refractive index (nD) | 2.429 |
| Structure | |
| Crystal structure | Wurtzite |
| Space group | C6v4-P63mc |
| Coordination geometry |
Tetrahedral |
| Hazards | |
| EU Index | Not listed |
| Flash point | Non-flammable. |
| Related compounds | |
| Other anions | Gallium phosphide Gallium arsenide Gallium antimonide |
| Other cations | Boron nitride Aluminium nitride Indium nitride |
| Related compounds | Aluminium gallium arsenide Indium gallium arsenide |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor commonly used in bright 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. Its sensitivity to ionizing radiation is low (like other group III nitrides), making it a suitable material for solar cell arrays for satellites. Because GaN transistors can operate at much hotter temperatures and work at much higher voltages than Gallium arsenide (GaAS) transistors, they make ideal power amplifiers at microwave frequencies.
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[edit] Physical properties
GaN is a very hard, mechanically stable material with large heat capacity.[2] 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.[2] GaN can be doped with silicon (Si) or with oxygen[3] to N-type and with magnesium (Mg) to p-type;[4] however, the Si and Mg atoms change the way the GaN crystals grow, introducing tensile stresses and making them brittle.[5] Gallium nitride compounds also tend to have a high spatial defect frequency, on the order of a hundred million to ten billion defects per square centimeter.[6]
GaN-based parts are very sensitive to electrostatic discharge.[7]
[edit] Developments
High crystalline quality GaN can be obtained by low temperature deposited buffer layer technology.[8] This high crystalline quality GaN led to the discovery of p-type GaN,[4] p-n junction blue/UV-LEDs[4] and room-temperature stimulated emission[9] (indispensable for laser action).[10] 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.
High-brightness GaN light-emitting diodes (LEDs) completed the range of primary colors, and made applications such as daylight visible full-color LED displays, white LEDs and blue laser devices possible. The first GaN-based high-brightness LEDs were using a thin film of GaN deposited via MOCVD on sapphire. Other substrates used are zinc oxide, with lattice constant mismatch only 2%, and silicon carbide (SiC).[11]
Group III nitride semiconductors are recognized as one of the most promising materials for fabricating optical devices in the visible short-wavelength and UV region. Potential markets for high-power/high-frequency devices based on GaN include microwave radio-frequency power amplifiers (such as 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 than silicon transistors. First gallium nitride metal/oxide semiconductor field-effect transistors (GaN MOSFET) were experimentally demonstrated in 1993[12] and they are being actively developed.
[edit] Applications
GaN, when doped with a suitable transition metal such as manganese, is a promising spintronics material (magnetic semiconductors). A GaN-based violet laser diode is used in the Blu-ray disc technologies, and in devices such as the Sony PlayStation 3. The mixture of GaN with In (InGaN) or Al (AlGaN) with a band gap dependent on ratio of In or Al to GaN allows to build light-emitting diodes (LEDs) with colors that can go from red to blue.[11]
Nanotubes of GaN are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications[13]
GaN HEMTs have been offered commercially since 2006, and have found immediate home in various wireless infrastructure applications due to their high efficiency and high voltage operation. Second generation technology with shorter gate lengths will be addressing higher frequency telecom and aerospace applications.[citation needed]
[edit] Synthesis
GaN crystals can be grown from a molten Na/Ga melt held under 100 atm 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 + NH3 → GaN + H2O
[edit] Safety
The toxicology of GaN has not been fully investigated. The 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 recently in a review.[14]
[edit] See also
[edit] References
- ^ T. Harafuji and J. Kawamura (2004). "Molecular dynamics simulation for evaluating melting point of wurtzite-type GaN crystal". Appl. Phys. 96: 2501. doi:.
- ^ a b Isamu Akasaki and Hiroshi Amano (1997). "Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength Light Emitters". Jpn. J. Appl. Phys. 36: 5393-5408. doi:.
- ^ Information Bridge: DOE Scientific and Technical Information - Document #434361
- ^ a b c Hiroshi Amano, Masahiro Kito, Kazumasa Hiramatsu and Isamu Akasaki (1989). "P-Type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI)". Jpn. J. Appl. Phys. 28: L2112-L2114. doi:.
- ^ Shinji Terao, Motoaki Iwaya, Ryo Nakamura, Satoshi Kamiyama, Hiroshi Amano and Isamu Akasaki (2001). "Fracture of AlxGa1-xN/GaN Heterostructure —Compositional and Impurity Dependence". Jpn. J. Appl. Phys. 40: L195-L197. doi:.
- ^ lbl.gov, blue-light-diodes
- ^ Hajime Okumura (2006). "Present Status and Future Prospect of Widegap Semiconductor High-Power Devices". Jpn. J. Appl. Phys. 45: 7565-7586. doi:.
- ^ H. Amano et al. (1986). "Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer". Applied Physics Letters 48: 353. doi:. http://link.aip.org/link/?APL/48/353.
- ^ Hiroshi Amano, Tsunemori Asahi and Isamu Akasaki (1990). "Stimulated Emission Near Ultraviolet at Room Temperature from a GaN Film Grown on Sapphire by MOVPE Using an AlN Buffer Layer". Jpn. J. Appl. Phys. 29: L205-L206. doi:.
- ^ Isamu Akasaki, Hiroshi Amano, Shigetoshi Sota, Hiromitsu Sakai, Toshiyuki Tanaka and Masayoshi Koike (1995). "Stimulated Emission by Current Injection from an AlGaN/GaN/GaInN Quantum Well Device". Jpn. J. Appl. Phys. 34: L1517-L1519. doi:.
- ^ a b Morkoç, H. (1994). "Large-band-gap SiC, III-V nitride, and II-VI ZnSe-based semiconductor device technologies". Journal of Applied Physics 76: 1363. doi:.
- ^ Asif Khan, M. (1993). "Metal semiconductor field effect transistor based on single crystal GaN". Applied Physics Letters 62: 1786. doi:.
- ^ Goldberger et al. (2003). "Single-crystal gallium nitride nanotubes". Nature 422: 599-602. doi:.
- ^ Shenaikhatkhate, D (2004). "Environment, health and safety issues for sources used in MOVPE growth of compound semiconductors". Journal of Crystal Growth 272: 816. doi:.
[edit] Further reading
- Isamu Akasaki and Hiroshi Amano: "Breakthroughs in Improving Crystal Quality of GaN and Invention of the p–n Junction Blue-Light-Emitting Diode" Japanese Journal of Applied Physics, Vol. 45, No. 12, 2006, pp. 9001–9010.
- Isamu Akasaki and Hiroshi Amano: " Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength Light Emitters" Japanese Journal of Applied Physics, Vol. 36, 1997, pp. 5393–5408.
- Jacques I. Pankove, T. D. Moustakas, Gallium Nitride (GaN) II: Semiconductors and Semimetals, Academic Press, 1998 (ISBN 0-12-752166-6)
- Shuji Nakamura, Gerhard Fasol, Stephen J Pearton The Blue Laser Diode: The Complete Story, Springer Verlag, 2nd Edition (October 2, 2000)
- UC Santa Barbara Professor Shuji Nakamura to receive Prince of Asturias Award.
[edit] External links
- AGAPAC - Advanced Gan Packaging (EU FP7 research project) EU FP7 funded project coordinated by Thales Alenia Space, France.
- The Wide Bandgap Semiconductor Materials and Devices Group at MIT.
- The Cambridge center for galium nitride (GaN).
- Photonics Sources Group, Tyndall National Institute GaN and other photonics research at the Tyndall National Institute, Ireland.
- External MSDS Data Sheet.
- Ioffe data archive
- National Compound Semiconductor Roadmap page at ONR
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