Achieving Ultra-long GaN Nanorod Growth by Lowering Nucleation Energy Via Surface Modification for Optical Sensors

We introduce a pit-formation method on a GaN substrate to obtain ultra-long GaN nanorods (NRs) grown homoepitaxially through hydride vapor phase epitaxy (HVPE) without an additional catalyst or a complex lithography procedure. The pits were created by annealing and nitridation at a high temperature on the GaN substrate; thus, GaN NRs were pinned at the pits during growth processes. The nucleation barrier of the GaN NR can be lowered by creating pits on the GaN substrate, leading to a higher possibility of triggering NR growth at a higher growth temperature. The conditions of the growth temperature were found to critically influence the NR aspect ratio and height. The GaN NRs with c-orientation achieves an ∼11.2 μm height in average in 20 min where the maximum height reaches 12.7 μm. The possible diffusion pathway of Ga adatoms was also discussed to reach the maximum height of a GaN NR at various growth temperatures. In addition, room-temperature cathodoluminescence measurements on the GaN NRs show a GaN-related near band gap emission peak and the luminescence intensity is even better than that of the GaN substrate. Such ultra-long GaN nanorods with the optical properties can be evaluated for sensing materials.