High-quality and almost crack-free GaN epitaxial layers were obtained by inserting a single AlGaN interlayer between the GaN epilayer and a high-temperature AlN buffer layer on Si (111) substrate via metalorganic chemical vapour deposition. The effect of the AlGaN interlayer upon the structural properties of the resultant GaN epilayer was investigated. Optical microscopy and Raman scattering spectroscopy confirmed that the AlGaN interlayer had a marked effect in introducing a relative compressive strain into the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy revealed that a significant reduction in both screw and edge threading dislocations was achieved in GaN epilayers by inserting AlGaN interlayers.

The Effect of Single AlGaN Interlayer on the Structural Properties of GaN Epilayers Grown on Si (111) Substrates. Y.X.Wu, J.J.Zhu, D.G.Zhao, Z.S.Liu, D.S.Jiang, S.M.Zhang, Y.T.Wang, H.Wang, G.F.Chen, H.Yang: Chinese Physics B, 2009, 18, 4413