Comparative study of initial growth stage in PVT growth of AlN on SiC and on native AlN substrates

The main issue in homoepitaxial growth of aluminum nitride (AIN) on native seed substrates appears to be aluminum oxynitride poisoning of seed surface leading to polycrystalline growth at 1750-1850 degrees C. This is well below the lowest growth temperature appropriate for physical vapor transport (PVT) of bulk AIN, which is about 2150 degrees C. Contrary, heteroepitaxial growth of AIN on SiC is relatively easy to achieve because of natural formation of a thin molten layer on the seed surface and VLS growth of AIN via the molten buffer layer. The most critical issue of AIN growth on SiC is cracking of the grown layer upon cooling as a result of different thermal expansion. Optimization of seeded growth process can be achieved by proper choice of SiC seed orientation and by use of ultra-pure starting material.