Aluminium nitride
| Aluminium nitride | |
|---|---|
| |
| Systematic name | Aluminum Nitride |
| Other names | aluminum(III) nitride |
| Appearance | crystalline solid, bluish white |
| Molecular formula | AlN |
| Molar mass | 40.988g/mol |
| CAS number | |
| Density | 3255 kg.m-3 |
| Modulus of elasticity (GPa) | 310 GPa |
| Melting point | 2200 °C |
| Boiling point | 2517 °C |
| Disclaimer and references | |
Aluminum nitride (AlN) is a nitride of aluminum. Its wurtzite phase (w-AlN) is an extremely wide bandgap (about 6.0 eV) semiconductor material which has potential application for deep ultraviolet optoelectronics.
History
AlN was first synthesised in 1877, but it was not until the middle of the 1980s that its potential for application in microelectronics was realised due to its relative high thermal conductivity for an electrical insulating ceramic (100-190 W/m•°K ). This material is of interest as a non-toxic alternative to beryllia. Metallization methods are available to allow AlN to be used in place of alumina and BeO for many electronic applications. AlN is synthesised by carbothermal reduction of alumina or by direct nitridation of aluminium.
Aluminum nitride has a hexagonal crystal structure and is a covalent bonded material. The use of sintering aids and hot pressing is required to produce a dense technical grade material. The material is stable to very high temperatures in inert atmospheres. In air, surface oxidation occurs above 700°C. A layer of aluminum oxide forms which protects the material up to 1370°C. Above this temperature bulk oxidation occurs. Aluminum nitride is stable in hydrogen and carbon dioxide atmospheres up to 980°C. The material dissolves slowly in mineral acids through grain boundary attack, and in strong alkalis through attack on the aluminum nitride grains. The material hydrolyzes slowly in water.Aluminium nitride is resistant to attack from most molten salts including chlorides and cryolite.
Applications
Currently there is much research into developing light emitting diodes to operate in the ultraviolet using the gallium nitride based semiconductors and, using the alloy aluminium gallium nitride, wavelengths as short as 250 nm have been reported. The bandgap of AlN allows a wavelength of around 200 nm to be achieved, in principle. However, there are many difficulties to be overcome if such emitters are to become a commercial reality. Because of the high cost of AlN it has been mainly developed for military aeronautics and transport fields.
See also
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