The structural properties of thin GaN epilayers which had been grown directly onto on-axis 6H-SiC (00•1) by means of plasma-assisted molecular beam epitaxy were studied. The use of X-ray measurements showed that the crystalline perfection of the layers steadily improved with film thickness. The density of threading defects, as detected by using transmission electron microscopy, was found to decrease markedly with distance from the GaN/SiC interface and to reach a final value of less than 5 x 109/cm2 at a layer thickness of 0.5μm.

Structural Properties of GaN Epilayers Directly Grown onto On-Axis 6H-SiC(0001) by Plasma-Assisted MBE. A.Trampert, O.Brandt, B.Yang, B.Jenichen, K.H.Ploog: Journal of Crystal Growth, 1999, 201-202, 407-10