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Realization of phosphor-free white-light emitters is becoming an important milestone on the road to achieve high quality and reliability in high-power white-light-emitting diodes (LEDs). However, most of reported methods have not been applied to practical use because of their difficulties and complexity. In this study we demonstrated a novel and practical growth method for phosphor-free white-light emitters without any external processing, using only in-situ high-density GaN nanostructures that were formed by overgrowth on a silicon nitride (SiNx) interlayer deposited by metal organic chemical vapor deposition. The nano-sized facets produced variations in the InGaN thickness and the indium concentration when an InGaN/GaN double heterostructure was monolithically grown on them, leading to white-color light emission. It is important to note that the in-situ SiNx interlayer not only facilitated the GaN nano-facet structure, but also blocked the propagation of dislocations.

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 cathodolumine-scence 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.