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. Display Omitted Impact of the temperature and the pressure on nanorods profileIdentification of critical temperature of 125°C for etching vertical nanorodsDiscussion on the impact of the temperature/pressure on the etching mechanisms in nanorod and nanopore arraysIdentification and control of the key parameters needed to control the nanostructure profiles for the fabrication of advanced photonic crystal devices.