A study was made of how defects in SiC substrates influence the crystallographic properties of AlGaN/GaN layers deposited by metal-organic vapor phase epitaxy and by molecular beam epitaxy. Double-crystal reflection X-ray topography, exploiting symmetrical (00▪8) and (00▪12) reflections and CuKα radiation (1.54Å), were used to image dislocations, micro-pipes and low-angle boundaries in SiC substrates. The lattice strain near to the core of a micro-pipe defect was estimated to be of the order of 10-7. The substrates investigated exhibited radial patterns of strain and, primarily, of tilt of the order of tens of arcsec. After deposition of the AlGaN and GaN layers, DCXRT images were generated from the substrate (00▪8) or (00▪12) and GaN epitaxial layer (00▪4) reflections. Full-width at half-maximum values ranging from ~100 to 300arcsec were typical of the GaN reflections, while those of the 4H–SiC reflections were ~20–70arcsec. Micropipes, tilt boundaries, and inclusions in the SiC were shown to produce structural defects in the GaN layers. A clear correlation between SiC substrate defects and GaN defects was established.

SiC Substrate Defects and III-N Heteroepitaxy. B.D.Poust, T.S.Koga, R.Sandhu, B.Heying, R.Hsing, M.Wojtowicz, A.Khan, M.S.Goorsky: Journal of Physics D, 2003, 36[10A], A102-6