A nonpolar a-Plane GaN grown on a hemispherical patterned r-Plane sapphire substrate

A high-quality a-plane GaN layer with a pit-free, mirror-like surface was grown on a hemispherical patterned r -plane sapphire substrate (PSS) by metal-organic chemical vapor deposition. The use of the r-plane PSS reduced the density of defects such as basal plane staking faults and threading dislocations of the a-plane GaN. The low-temperature-photoluminescence intensity of the emissions at 3.25 and 3.39 eV related with the defects increased along with the near-band-edge emission at 3.46 eV. The intensity of yellow emission at 2.2 eV on the PSS was remarkably decreased, which indicates the improvement of the crystal quality because of the defect reduction. The InGaN light emitting diode grown on the PSS showed an output power of 7.4mW at 100 mA, which was about 7 times higher than that on the planar substrate.