Formation of needle-like and columnar structures of AlN

The present study focused on understanding the formation of needle-like and columnar structures by investigating the initial nucleation of aluminium nitride (AlN) on SiC substrates with SEM, AFM, and XRD. The grown AlN consisted of high concentration (∼8×104 cm−2) hexagonal hillocks (HHs) that originate from threading dislocations in the substrate. The KOH etching technique has been used to examine the origin and formation process of HHs and defect reduction in the grown AlN crystals. A model is introduced to explain the AlN HH formation. The SEM result shows that the AlN columnar structure was formed by merging of needles, which are grown exactly on completed AlN HHs, followed by a lateral growth.