This study addressed how defects in SiC substrates influence the crystallographic properties of AlGaN/GaN layers deposited by metallorganic vapour phase epitaxy and by molecular beam epitaxy. We employed double crystal reflection x-ray topography using symmetric (0008) and (00012) reflections with CuKα radiation (λ = 1.54 Å) to image dislocations, micropipes, and low angle boundaries in SiC substrates. Lattice strain near the core of a micropipe 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 (0008) or (00012) and GaN epitaxial layer (0004) reflections. Full-width at half-maximum values ranging from ~100 to 300 arcsec were typical of the GaN reflections, while those of the 4H–SiC reflections were ~20–70 arcsec. 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 has been established.