Deterministically-grown GaN microrods on a mask-free plateau patterned substrate

In this study, a polished plateau-patterned sapphire substrate (PP-PSS) was developed to grow epitaxial GaN microrods using an AlN buffer layer via pulsed metal–organic chemical vapor deposition. The diameter of the plateau region could be easily adjusted in the range of 600–1600 nm by altering the polishing time, allowing the selective growth of the GaN microrods in only the plateau region and subsequent deposition on the AlN layer. The GaN microrod growth mechanism on the PP-PSS was explained using the morphology of the grown GaN microrods. Transmission electron microscopy revealed that the single-crystalline GaN microrods had a GaN (0002) d spacing of 0.263 nm, and a measured lattice constant ratio of the (0001) and (10 1‾ 0) planes of 0.535, which is similar to the theoretical value of 0.532 for a fully relaxed GaN. Through Raman spectroscopy, the GaN microrod E₂ (high) mode was 566.70 cm⁻¹, which was shifted by only 0.50 cm⁻¹ compared to that of the strain-free reference. These results suggest that stress-free GaN microrod epitaxial growth is possible on PP-PSS.