Fabrication of high-aspect ratio GaN nanostructures for advanced photonic devices

High-aspect-ratio GaN-based nanostructures are of interest for advanced photonic crystal and core-shell devices. Nanostructures grown by a bottom-up approach are limited in terms of doping, geometry and shape which narrow their potential application areas. In contrast, high uniformity and a greater diversity of shape and design can be produced via a top-down etching approach. However, a detailed understanding of the role of etch process parameters is lacking for creating high-aspect ratio nanorods and nanopores. Here we report a systematic analysis on the role of temperature and pressure on the fabrication of nanorod and nanopore arrays in GaN. Our results show a threshold in the etch behaviour at a temperature of ~ 125 °C, which greatly enhances the verticality of the GaN nanorods, whilst the modification of the pressure enables a fine tuning of the nanorod profile. For nanopores we show that the use of higher temperatures at higher pressures enables the fabrication of nanopores with an undercut profile. Such a profile is important for controlling the optical field in photonic crystal-based devices. Therefore we expect the ability to create such nanostructures to form the foundation for new advanced LED designs.