The defect structure of GaN film grown on sapphire by plasma-assisted molecular beam epitaxy depended upon the growth temperature and thickness of the aluminum nitride buffer layer. High-resolution X-ray diffraction was used to measure symmetric (00•2) and asymmetric (10•2) rocking curve (ω-scans) broadening, which allowed the estimation of screw threading dislocation and edge threading dislocations densities, respectively. For GaN grown on lower-temperature buffer, the density of screw threading dislocations was increased while the density of edge threading dislocations was decreased. Further examination revealed that the edge threading dislocation was closely related to stress in GaN films and that the screw threading dislocation was controlled by AlN surface roughness. Since the GaN defect was dominated by edge threading dislocations, the total number of threading dislocations was also effectively suppressed with the use of lower-temperature buffer with appropriate thickness.

The Effect of AlN Buffer Growth Parameters on the Defect Structure of GaN Grown on Sapphire by Plasma-Assisted Molecular Beam Epitaxy. Y.Y.Wong, E.Y.Chang, T.H.Yang, J.R.Chang, Y.C.Chen, J.T.Ku, C.T.Lee, C.W.Chang: Journal of Crystal Growth, 2009, 311[6], 1487-92