Crucible selection in AlN bulk crystal growth

Growth of AlN bulk single crystals by sublimation of AlN powder was carried out in a resistively heated reactor at temperatures up to 2300°C. A variety of crucible materials, such as BN, W, Ta, Re, ZrO₂, TaN, and TaC, were evaluated. Our studies have shown that the morphology of crystals grown by spontaneous nucleation strongly depends on the growth temperature and contamination in the reactor. Crucible selection had a profound effect on contamination in the crystal growth environment, thus influencing nucleation, coalescence, and crystal morphology. Spontaneously grown single crystals up to 15 mm in size were characterized by x-ray diffraction (XRD), x-ray topography (XRT), glow discharge mass spectrometry (GDMS), and secondary ion mass spectrometry (SIMS). Average dislocation densities were on the order of 10 ³ cm^-3, with extended areas virtually dislocation-free, while high-resolution XRD showed rocking curves as narrow as 7 arcsec.