Whispering gallery modes in GaN microdisks, microrods and nanorods grown by MOVPE

Self-assembled GaN microdisks, micro-and nanorods were grown by a mask-free and self-catalyzed metal-organic vapor phase epitaxy method. The morphology of the structures is analyzed by scanning electron microscopy. All rods have a hexagonal shape with smooth sidewall facets and sharp edges. Depending on the deposition of a GaN nucleation layer prior to growth of GaN rod structures the diameter of the rods can be adjusted. Nanorods with diameters down to 400 nm as well as microrods and disks with diameters up to 5 mu m can be achieved. The optical properties of the rods are investigated utilizing a combined scanning electron microscopy and cathodoluminescence system. Electron beam excitiation of GaN rods leads to a typical GaN spectrum showing GaN near band edge emission at 369 nm and broad yellow defect luminescence at 560 nm. Enhanced emission is located at the top of the rod. By fixing the focussed electron beam at a sidewall position of a single GaN rod, whispering gallery modes are observed in the cathodoluminescence spectrum. Depending on the diameter of the micro-/nanorods the spectral position of the modes as well as the spectral distance between the modes can be adjusted. Quality factors up to 475 are measured. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei