Fabrication of Tapered and Cylindrical GaN Nanowires Using Nanosphere Lithography

Nanowires fabricated using the top-down method can offer high uniformity and precise morphology. However, achieving well-controlled dry and wet etching processes is essential to produce large-area uniform nanowires. It is also interesting to have control on their shape, since tapered structures can have favorable light extraction properties, whereas cylindrical shapes are preference for electronics or photodetection. This paper presents a comprehensive study on the fabrication of GaN nanowires using a top-down approach facilitated by nanosphere lithography. We focus on optimizing both dry and wet etching processes to achieve high-aspect-ratio nanowires with controlled shapes. The final wet etching step, critical for shaping the nanowires, was performed with a crystallography-selective method, resulting in nanowires with vertical m-plane facets or tapered structures, depending on the initial diameter of the spheres. This demonstrates the process's adaptability to control nanowire geometry.