Methods of AlN Crystal Growth

AlN, as third-generation semiconductor material, is not only an important blue light and ultraviolet light material, but also an important packaging, dielectric isolation and insulation material for electronic devices and integrated circuits, especially suitable for high-temperature and high-power devices. In addition, AlN and GaN have a good thermal match and chemical compatibility, AlN used as GaN epitaxial substrate, can significantly reduce the defect density in GaN devices, improve device performance.

Due to the attractive application prospects, the preparation of high-quality, large-size AlN crystals has received great attention from researchers at home and abroad. Currently, AlN crystals are prepared by solution method, direct nitriding of aluminium metal, hydride gas-phase epitaxy and physical vapour phase transport (PVT). Among them, the PVT method has become the mainstream technology for growing AlN crystals with its high growth rate (up to 500-1000 μm/h) and high crystal quality (dislocation density below 103 cm-2).

The growth of AlN crystals by the PVT method is accomplished by sublimation, gas phase transport and recrystallisation of AlN powder, and the growth environment temperature is as high as 2 300 ℃. The basic principle of growing AlN crystals by the PVT method is relatively simple, as shown in the following equation:

2AlN (s) ⥫⥬ 2 Al (g) ＋ N2 (g)

The main steps of the growth process are as follows: (1) sublimation of AlN raw powder; (2) transport of gas-phase components of the raw material; (3) adsorption of gas-phase components on the growth surface; (4) surface diffusion and nucleation; and (5) desorption process [10]. Under standard atmospheric pressure, AlN crystals begin to decompose slowly into Al vapour and nitrogen only at about 1 700 ℃, and the decomposition reaction of AlN intensifies rapidly when the temperature reaches 2 200 ℃.

TaC material is the real AlN crystal growth crucible material in use, with excellent physical and chemical properties, excellent thermal and electrical conductivity, chemical corrosion resistance and good thermal shock resistance, which can effectively improve the production efficiency and service life.

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