High efficiency GaN-based light-emitting diodes ͑LEDs͒ are demonstrated by a nanoscale epitaxial lateral overgrowth ͑NELO͒ method on a SiO 2 nanorod-array patterned sapphire substrate ͑NAPSS͒. The transmission electron microscopy images suggest that the voids between SiO 2 nanorods and the stacking faults introduced during the NELO of GaN can effectively suppress the threading dislocation density. The output power and external quantum efficiency of the fabricated LED were enhanced by 52% and 56%, respectively, compared to those of a conventional LED. The improvements originated from both the enhanced light extraction assisted by the NAPSS and the reduced dislocation densities using the NELO method.

This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide ͑SiO 2 ͒ were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy ͑HVPE͒. The passivation of the sidewalls coated with SiO 2 prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.

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The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template. The investigation of x-ray diffraction showed that the strain in a-plane GaN grown on r-plane sapphire could be mitigated. The average threading dislocation density estimated by transmission electron microscopy was reduced from 3 ϫ 10 10 to 3.5ϫ 10 8 cm −2 . From the temperature-dependent photoluminescence, the quantum efficiency of the a-plane GaN was enhanced by the nanorod epitaxial lateral overgrowth ͑NRELOG͒. These results demonstrated the opportunity of achieving a-plane GaN films with low dislocation density and high crystal quality via NRELOG.