Growth anisotropy in the GaN/Al2O3 system

The crystallographic aspect of gallium nitride epitaxy on sapphire were investigated for the vapor phase epitaxy system GaCl/NH₃/HCl/N₂. For this purpose, thick layers of doped gallium nitride were deposited on hemispheres of Al₂O₃ single crystal with the three fold axis of the corundum structure perpendicular to the basal plane. Complete characterization of these layers has been carried out including Laue back diffraction, scanning electron microscopy and cathodoluminescence. After growth, sections were cut along the main crystallographic planes and the growth rate was measured as a function of the substrate orientation. The observed relationship for epitaxy has been interpreted in terms of three-dimensional matching between the gallium nitride and corundum structures.