RF Growth of Bulk GaN and AIN

Aluminium, gallium and indium nitride belong to a family of materials described as peritectic compounds. A peritectic compound is defined as a compound that transforms, at the peritectic temperature and atmospheric pressure, according to the reaction  

In the case of aluminium nitride, the decomposition is into liquid aluminium and nitrogen gas. This decomposition is the impediment to the growth of AIN bulk crystals using conventional melt growth processes. 

Limited information exists for growing AIN [2-5] at high temperatures and pressures, using sublimation or solution growth techniques. Only one published technique describes the growth of AIN from a melt of AIN [6], 

Solution growth utilises the ability of a solvent, such as Fe or Ca3N2, to take a solute into solution at a reduced temperature and precipitate the solute at an even lower temperature. The solution is contained in a crucible, and like the sublimation technique, the crucible generally fails during the lengthy growth experiments required to obtain crystals of appreciable size. 

One technique that addresses both container reaction and impurity inclusions is a high pressure, RF, melt growth process. With this process, the material is inductively heated by RF energy, oscillating at frequencies between 450 kHz and 4 MHz. Power levels up to 100 kW are available to produce melt temperatures of the order of 2600°C. To prevent decomposition, the chaige is contained in a nitrogen over-pressure of 10 to 100 atm. The liquid aluminium nitride is self-contained in a water-cooled skin, which prevents both container reaction and deleterious inclusions. 

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