Gallium nitride

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Gallium nitride
GaNcrystal.jpg
Wurtzite polyhedra.png
Names
IUPAC name
Gallium nitride
Identifiers
25617-97-4 YesY
ChemSpider 105057 YesY
Jmol 3D model Interactive image
PubChem 117559
RTECS number LW9640000
  • InChI=1S/Ga.N YesY
    Key: JMASRVWKEDWRBT-UHFFFAOYSA-N YesY
  • InChI=1/Ga.N/rGaN/c1-2
    Key: JMASRVWKEDWRBT-MDMVGGKAAI
  • [Ga]#N
Properties
GaN
Molar mass 83.73 g/mol
Appearance yellow powder
Density 6.15 g/cm3
Melting point >2500 °C[1]
Insoluble[2]
Band gap 3.4 eV (300 K, direct)
Electron mobility 440 cm2/(V·s) (300 K)
Thermal conductivity 1.3 W/(cm·K) (300 K) [3]
2.429
Structure
Wurtzite
C6v4-P63mc
a = 3.186 Å, c = 5.186 Å [4]
Tetrahedral
Vapor pressure {{{value}}}
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
Gallium arsenide phosphide
Aluminium gallium nitride
Indium gallium nitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
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,[5][6] high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without use of nonlinear optical frequency-doubling.

Its sensitivity to ionizing radiation is low (like other group III nitrides), making it a suitable material for solar cell arrays for satellites. Military and space applications could also benefit as devices have shown stability in radiation environments.[7] Because GaN transistors can operate at much higher temperatures and work at much higher voltages than gallium arsenide (GaAs) transistors, they make ideal power amplifiers at microwave frequencies.

Physical properties

GaN crystal

GaN is a very hard (12±2 GPa[8]:4), mechanically stable wide bandgap semiconductor material with high heat capacity and thermal conductivity.[9] 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.[9] GaN can be doped with silicon (Si) or with oxygen[10] to n-type and with magnesium (Mg) to p-type;[11] however, the Si and Mg atoms change the way the GaN crystals grow, introducing tensile stresses and making them brittle.[12] Gallium nitride compounds also tend to have a high dislocation density, on the order of a hundred million to ten billion defects per square centimeter.[13]

Developments

GaN with a high crystalline quality can be obtained by depositing a buffer layer at low temperatures.[14] Such high-quality GaN led to the discovery of p-type GaN,[11] p-n junction blue/UV-LEDs[11] and room-temperature stimulated emission[15] (indispensable for laser action).[16] 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 of only 2% and silicon carbide (SiC).[17] Group III nitride semiconductors are in general recognized as one of the most promising semiconductor family for fabricating optical devices in the visible short-wavelength and UV region.

The very high breakdown voltages,[18] high electron mobility and saturation velocity of GaN has also 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 (such as 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[19]) than silicon transistors(~150°C[19]), because it lessens the effects of thermal generation of charge carriers that are inherent to any semiconductor. The first gallium nitride metal semiconductor field-effect transistors (GaN MESFET) were experimentally demonstrated in 1993[20] and they are being actively developed.

In 2010 the first enhancement-mode gallium nitride transistors became generally available.[21] These devices were designed to replace power MOSFETs in applications where switching speed or power conversion efficiency is critical. These transistors, also called eGaN FETs, are built by growing a thin layer of GaN on top of a standard silicon wafer. This allows the eGaN FETs to maintain costs similar to silicon power MOSFETs but with the superior electrical performance of GaN.

Applications

LEDs

GaN-based violet laser diodes are used to read Blu-ray Discs. When doped with a suitable transition metal such as manganese, GaN is a promising spintronics material (magnetic semiconductors). The mixture of GaN with In (InGaN) or Al (AlGaN) with a band gap dependent on 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.[17]

High frequency, high voltage, high temperature, high efficiency

GaN HEMTs 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. Second generation technology with shorter gate lengths will be addressing higher frequency telecom and aerospace applications.[22]

GaN based MOSFET and MESFET transistors also offer advantages including lower loss in high power electronics, especially in automotive and electric car applications.[23]

GaN-based electronics (not pure GaN) has the potential to drastically cut energy consumption, not only in consumer applications but even for power transmission utilities. MIT spinout Cambridge Electronics Inc's claim their transistors have at most one-tenth the resistance of such silicon-based transistors. This allows for much higher energy efficiency, and orders-of-magnitude faster switching frequency. This has huge implications not only for energy usage of power electronics systems, but their physical size and stability. Unlike silicon transistors which switch off due to power surges, GaN transistors are typically depletion mode (i.e. on / resistive when the gate-source voltage is zero), however the company along with US government and university assistance developed GaN transistors via materials engineering to also be available as enhancement mode ("normally off") devices, just as silicon based transistors.[24]

Nanoscale

GaN nanotubes are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications.[25]

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

Molecular beam epitaxy

Commercially, GaN crystals can be grown using molecular beam epitaxy. 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.

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 recently in a review.[26]

Bulk GaN is non-toxic and biocompatible,[27] and therefore may be used in the electrodes and electronics of implants in living organisms.

See also

References

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Mion, Christian (2005). "Investigation of the Thermal Properties of Gallium Nitride Using the Three Omega Technique", Thesis, North Carolina State University.
  4. ↑ Bougrov V., Levinshtein M.E., Rumyantsev S.L., Zubrilov A., in Properties of Advanced Semiconductor Materials GaN, AlN, InN, BN, SiC, SiGe. Eds. Levinshtein M.E., Rumyantsev S.L., Shur M.S., John Wiley & Sons, Inc., New York, 2001, 1–30
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Gallium Nitride as an Electromechanical Material. R-Z. IEEE 2014
  9. ↑ 9.0 9.1 Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Wetzel, C.; Suski, T.; Ager, J.W. III; Fischer, S.; Meyer, B.K.; Grzegory, I.; Porowski, S. (1996) Strongly localized donor level in oxygen doped gallium nitride, International conference on physics of semiconductors, Berlin (Germany), 21–26 July 1996.
  11. ↑ 11.0 11.1 11.2 Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Preuss, Paul (11 August 2000). Blue Diode Research Hastens Day of Large-Scale Solid-State Light Sources. Berkeley Lab., lbl.gov.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ 17.0 17.1 Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ 19.0 19.1 Why Gallium Nitride?
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ 2010 IEEE Intl. Symposium, Technical Abstract Book, Session TH3D, pp. 164–165
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ http://phys.org/news/2015-07-silicon-gallium-nitride-electronics-drastically.html
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  27. ↑ Shipman, Matt and Ivanisevic, Albena (24 October 2011). "Research Finds Gallium Nitride is Non-Toxic, Biocompatible – Holds Promise For Biomedical Implants". North Carolina State University

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