Characterization of a-plane GaN layers grown on patterned r-sapphire substrate by metal organic chemical vapor deposition

Non-polar a-plane GaN layers were grown on planar and hemispherical micro- and nano-patterned r-sapphire substrates (PSS) by metal organic chemical vapor deposition (MOCVD). Double Crystal X-ray Rocking Curve (DCXRC) and Transmission Electron Microscopy (TEM) analyses showed that the crystal quality of a-GaN grown on the micro-PSS was the best among three kinds of r-sapphire substrates, which was attributed to defect reduction through lateral overgrowth on the hemispherical patterns. The intensity of the near band-edge emission (NBE) at 3.4eV from a-GaN on the micro-PSS was increased by about 30 times compared with that of the conventional a-plane GaN on planar r-sapphire, while the yellow emission spectrum at 2.2eV was the lowest among the three samples. Comparison of the micro-photoluminescence mapping image and the cross-section TEM also showed high and low defect regions on the planar section and hemisphere, respectively.