Modification of far-field radiation pattern by shaping InGaN/GaN nanorods

In this work, we report on the fabrication of "golftee," "castle," and "pillar" shaped InGaN/GaN nanorod light-emitting diode (LED) arrays with a typical rod diameter of 200 nm based on nanoimprint lithography, dry etching, and wet etching. The photoluminescence (PL) integral intensities per active region area for "golftee," "castle," and "pillar" shaped nanorod samples were found to be 2.6, 1.9, and 2.2 times stronger than that of a conventional planar LED. Additionally, the far-field radiation patterns of the three different shaped nanorod samples were investigated based on angular resolved PL (ARPL) measurements. It was found that the sharp lobes appeared at certain angles in the ARPL curve of the "golftee" sample, while broad lobes were observed in the ARPL curves of the "castle" and "pillar" samples. Further analysis suggests that the shorter PL lifetime and smaller spectral width of the "golftee" sample were due to the coupling of photon modes with excitons, which also led to the observed high efficiency and directional emission pattern of the "golftee" sample. Finally, three dimensional finite difference time domain simulations were carried out to study the near-field distribution of the "golftee," "castle," and "pillar" shaped nanorods. The simulation results showed not only a strong enhancement of the electric field in the nanocavities of the three nanorod structures but also a reduction of the guided modes into the nanorod substrate for the "golftee" shaped structure.