Free nucleation of aluminum nitride single crystals in HPBN crucible by sublimation

Clear and colorless aluminum nitride (AlN) single crystal thin platelets up to 60 mm2 were prepared at 2100 °C and 800 Torr in hot-pressed boron nitride (HPBN) crucibles by free nucleation in a graphite furnace. Crystals grown in HPBN crucibles typically form thin platelets with the fastest growth rate (above 400 μm/h) occurring in the c-axis direction. Growth striations frequently run the length of the crystals, probably due to the presence of boron in the growth environment. Raman spectra and X-ray topography reveal that the crystals have good structural quality. Emissions peaks around 4.10 eV, 3.90 eV, and 3.70 eV were observed in the photoluminescence spectrum, suggesting that boron from the boron nitride crucible may incorporate into the AlN crystals as hexagonal boron nitride.