Defect formation in GaN grown on vicinal 4H-SiC (0001) substrates

We report a comparative study of wurtzite GaN epilayers prepared by Metal Organic Chemical Vapor Deposition on 4H-SiC substrates of orientation vicinal to the (0001) (misorientation 0°, 3.4°, and 8°). Structural analysis using X-ray diffraction, defect-selective etching methods, and (High Resolution-) Transmission Electron Microscopy provides direct evidence for a higher number of defects in GaN epilayers grown on the 8° misoriented substrate compared to the 3.4° and 0° misoriented substrates. We found strong differences in morphology of the GaN epilayers and in type and density of the defects formed during growth on both vicinal and nominally exact oriented SiC substrates. The formation of clusters of defects and the non-uniform distribution of strain, resulting in preferential cracking of the GaN films along the [110] direction, are both results of growth on misoriented substrates. Based on experimental results, the growth mechanism is discussed and a model explaining the defect formation is proposed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)