Growth defects in GaN layers on top of (0001) sapphire: a geometrical investigation of the misfit effect

For GaN layers grown on (0001) Al2O3 a geometrical approach is proposed in order to explain the formation of {10 (1) over bar 0} inversion domain boundaries. As the epitaxial relationship is due to the continuation of anion stacking along the growth direction, the gallium atoms of the first layers have choices of sites to occupy. Therefore, islands related either by displacement vectors corresponding to the usual stacking fault of the hcp structure or inversion domains can form naturally on the (0001) sapphire surface. The inversion domains were found to be generated mostly at surface steps, where they are shown to minimize the large misfit along the c axis (20%).