Extraction Efficiency in GaN Nanorod Light-emitting Diodes Investigated by Finite-difference Time-domain Simulation

The light extraction efficiency (LEE) in GaN-based nanorod light-emitting diode (LED) structures is investigated using a three-dimensional (3-D) finite-difference time-domain (FDTD) simulation. The LED structure is composed of a p-GaN layer, InGaN/GaN active layers, and an n-GaN layer grown on a sapphire substrate, and the active layers are positioned at the center of the rods. The LEE for top or bottom emission shows a periodic behavior as the radius of a rod varies, which can be interpreted by the creation of radial resonant modes inside the nanorod cavity. The LEE in a nanorod array is found to be quite high. For an optimized nanorod LED structure, it can be >90%, which is higher than that of current high-efficiency LED structures by around 10%. Due to the potential of very high LEE, the nanorod LED structure is expected to be a good candidate for future high-efficiency LEDs.