A thermocyclic process was introduced to increase the particle size and purification of AlN powder for use as a source in growing single crystals. The particle size increase that occurred during thermocyclic process was theoretically verified by thermodynamic analysis. Thermodynamics-driven process conditions were experimentally optimized for producing large particles. The thermocyclic process not only caused particle growth but also improved the purity of the AlN powder. During repetitive sublimation and condensation cycles, the low-boiling, non-condensing impurities were eliminated by vaporization. Chemical analysis confirmed that the amounts of free carbon, oxygen, and metallic impurities were reduced after thermocyclic process. With non-purified and purified AlN powders, we grew bulk crystals of AlN and compared the chemical purity of crystals by SIMS measurement. The experimental result confirmed that AlN crystal grown by purified AlN powder having similar to 30 mm particle size and 99.999% purity exhibited improved crystal quality.

Keywords: AlN powder; Particle size control; Purification; Thermocyclic process; Crystal Growth