The structures of thin (0.2 to 0.6μ) GaN epilayers which had been grown directly onto 6H-type SiC(00•1) by plasma-assisted molecular beam epitaxy were studied. The X-ray reciprocal space maps of the GaN(00•2) reflection revealed negligible inhomogeneous strain within the layer, but a comparatively large orientational spread of the GaN c-axis. However, X-ray rocking-curve measurements showed that this mosaicity steadily decreased with film thickness. The density of threading defects, as detected by transmission electron microscopy, decreased sharply with distance from the GaN/SiC interface and finally reached a value of less than 5 x 109/cm2 at a layer thickness of 0.5μ.

Structural Characterization of Thin GaN Epilayers Directly Grown onto On-Axis 6H-SiC(00•1) by Plasma-Assisted Molecular Beam Epitaxy. B.Yang, A.Trampert, B.Jenichen, O.Brandt, K.H.Ploog: Applied Physics Letters, 1998, 73[26], 3869-71