Influence of Size of ZnO Nanorods on Light Extraction Enhancement of GaN-Based Light-Emitting Diodes

We investigate the influence of size of ZnO nanorods on the light extraction efficiency (LEE) enhancement of GaN-based light-emitting diodes (GaN-LEDs). ZnO nanorods with different sizes are hydrothermally grown on patterned indium-doped tin oxide (ITO) electrodes of the GaN-LEDs in zinc acetate aqueous solutions of different concentrations. Measurements are conducted for the LEE enhancement of the LEDs with ZnO nanorods, compared to these without ZnO nanorods. The results suggest that the LEE of the LEDs with ZnO nanorods increases with the increasing size of ZnO nanorods. However, a saturation trend for the LEE improvement is also observed, which is attributed to the maximum limitation of light coupled into ZnO nanorods from GaN-based LEDs, and the reflection is increased by the increasing top surface of the ZnO nanorods.