Gallium(III) nitride

Gallium nitride (GaN) is a direct-bandgap semiconductor material of wurtzite crystal structure with a wide (3.4 eV) band gap, used in optoelectronic, high-power and high-frequency devices. It is a binary group III/group V direct bandgap semiconductor. 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 GaAs transistors, they make ideal power amplifiers at microwave frequencies.

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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] "There are a huge number of defects in gallium nitride compounds -- a hundred million to ten billion per square centimeter."^[6]

GaN based parts are very sensitive to electrostatic discharge.^[7]

Developments

The high crystalline quality of GaN can be realized 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 (LDs), 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).

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.

Applications

GaN, when doped with a suitable transition metal such as manganese, is a promising spintronics material (magnetic semiconductors).

Nanotubes of GaN are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications^[11]

GaN-based blue laser diodes are used in the HD-DVD and 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.

Safety and toxicity aspects

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^[12].

See also

• Schottky diode
• Semiconductor devices
• Molecular-beam epitaxy
• Epitaxy

References

1. ^ [http://dx.doi.org/10.1063/1.1772878 Harafuji, Tsuchiya and Kawamura, J. Appl. Phys. 96, 2501-2512 (September 1, 2004)
2. ^ ^{a b} Isamu Akasaki and Hiroshi Amano, "Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength Light Emitters", Jpn. J. Appl. Phys. Vol.36(1997) 5393-5408 doi:10.1143/JJAP.36.5393
3. ^ [1]
4. ^ ^{a b c} Hiroshi Amano, Masahiro Kito, Kazumasa Hiramatsu and Isamu Akasaki, "P-Type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI)", Jpn. J. Appl. Phys. Vol. 28 (1989) L2112-L2114, doi:10.1143/JJAP.28.L2112
5. ^ Shinji Terao, Motoaki Iwaya, Ryo Nakamura, Satoshi Kamiyama, Hiroshi Amano and Isamu Akasaki, "Fracture of AlxGa1-xN/GaN Heterostructure —Compositional and Impurity Dependence—", Jpn. J. Appl. Phys. Vol. 40 (2001) L195-L197, doi:10.1143/JJAP.40.L195
6. ^ lbl.gov, blue-light-diodes
7. ^ Hajime Okumura, "Present Status and Future Prospect of Widegap Semiconductor High-Power Devices", Jpn. J. Appl. Phys. Vol. 45 (2006) 7565-7586, doi:10.1143/JJAP.45.7565
8. ^ Applied Physics Letters, Volume 48, Issue 5, pp. 353-355 [2]
9. ^ Hiroshi Amano, Tsunemori Asahi and Isamu Akasaki, "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. Vol. 29 (1990) L205-L206 doi:10.1143/JJAP.29.L205
10. ^ Isamu Akasaki, Hiroshi Amano, Shigetoshi Sota, Hiromitsu Sakai, Toshiyuki Tanaka and Masayoshi Koike, "Stimulated Emission by Current Injection from an AlGaN/GaN/GaInN Quantum Well Device", Jpn. J. Appl. Phys. Vol.34(1995) L1517-L1519 doi:10.1143/JJAP.34.L1517
11. ^ Goldberger et al, Nature 422, 599-602 (10 April 2003)
12. ^ Journal of Crystal Growth (2004); doi:doi:10.1016/j.jcrysgro.2004.09.007

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.
• Shuji Nakamura, Gerhard Fasol, Stephen J. Pearton, The Blue Laser Diode : The Complete Story, Springer; 2nd edition, October 2, 2000, (ISBN 3-540-66505-6)
• 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)
• UCSB Press release describing Shuji Nakamura's work.

Commercial links

• Informative commercial link to Trimethylgallium and other metalorganics.
• Interactive Vapor Pressure Chart for metalorganics.