Effect of defects on the luminescence in semipolar InGaN/GaN quantum wells on planar and patterned m-plane sapphire substrate

The correlation between luminescence and defects was investigated by the structural and optical analyses of semipolar InGaN/GaN quantum wells (QWs) grown on a planar m-plane sapphire substrate and patterned m-plane sapphire substrate using metal organic chemical vapor deposition. Scanning electron microscopy images indicated that the semipolar InGaN/GaN QWs grown on the planar substrate had high density of small arrowhead-like features on the surface, while those grown on the patterned sapphire substrate (PSS) had low density of large arrowhead-like features. Moreover, for the PSS sample, low defect regions were formed by periodically aligned patterns that reduced defect density, as verified by transmission electron microscopy. The monochromatic cathodoluminescence images revealed that the luminescence of the planar sample was affected by the arrowhead-like features and high internal defect density, whereas that of the PSS sample was more influenced by the regions with reduced defects, as indicated by bright spotty features. Furthermore, the microphotoluminescence mapping images showed increased In incorporation where the arrowhead-like features were present. In particular, for the PSS sample, the wavelength of the luminescence from the reduced defect region was approximately 5?nm shorter than that from the region with a high density of internal defects. This result suggests that In incorporation was also increased in the high defect region.