Seeded growth of AlN bulk crystals in m- and c-orientation

Seeded growth of AlN boules was achieved on m-(1 0 1- 0) and c-(0 0 0 1-) orientations by physical vapor transport (PVT). The single crystalline m- and c-plane seeds were cut from freestanding AlN single crystals. AlN boules 12 mm in diameter and 7 mm in height were grown at source temperatures around 2280 °C in N₂ atmosphere at 500 Torr of total pressure. Under identical process conditions, the m- and c-plane boules exhibited the same growth rates, 150-170 μm/h, and similar expansion angles, 22-27°, which indicated that the growth was controlled by the thermal profile inside the crucible rather than by crystallographic differences. X-ray rocking curve analysis and Raman spectroscopy confirmed that both m- and c-plane grown crystals possessed high crystalline quality. The dislocation density in both crystals was non-uniform and in the range 10²-10⁵ cm^-2, as characterized by X-ray topography.