Gallium nitride

Gallium nitride
IUPAC name[hide] Gallium nitride
Identifiers
CAS number	25617-97-4 Y
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	3.4 eV (300 K, direct)
Electron mobility	440 cm2/(V·s) (300 K)
Thermal conductivity	1.3 W/(cm·K) (300 K)
Refractive indexnD) (	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 Gallium arsenide phosphide Aluminium gallium nitride Indium gallium nitride
(what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)Y
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. 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. 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.

Physical properties

GaN is a very hard, mechanically stable wide bandgap semiconductor material with high heat capacity and thermal conductivity. 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 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. and making them brittle.

Developments

High crystalline quality GaN can be obtained 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, 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 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, high electron mobility and saturation velocityJohnson's Figure of Merit. 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 and they are being actively developed. of GaN has also made it an ideal candidate for high-power and high-temperature microwave applications, as evidenced by its high

Applications

A GaN-based violet laser diode is used in the Blu-ray disc technologies, and in devices such as the Sony PlayStation 3. GaN, when doped with a suitable transition metal such as manganese, 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 blue.

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.GaN based MOSFET transistors also offer many advantages in high power electronics, especially in automotive and electric car applications.Nanotubes of GaN are proposed for applications in nanoscale electronics, optoelectronics and biochemical-sensing applications

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 + 2 NH₃ → 2 GaN + 3 H₂O

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.