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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.
GaN is a very hard, mechanically stable material with large heat capacity. 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. GaN can be doped with silicon (Si) or with oxygen 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. "There are a huge number of defects in gallium nitride compounds -- a hundred million to ten billion per square centimeter."
The high crystalline quality of GaN can be realized by low temperature deposited buffer layer technology. This high crystalline quality GaN led to the discovery of p-type GaN, p-n junction blue/UV-LEDs and room-temperature stimulated emission (indispensable for laser action). 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.
Nanotubes of GaN are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications
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.
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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gallium(III)_nitride". A list of authors is available in Wikipedia.|