Light extraction enhancement of GaN based light emitting diodes by ZnO nanorod arrays

This study examined the effects of the alignment of ZnO nanorod arrays (NRAs) on the light extraction enhancement of GaN-based light emitting diodes (LEDs), where ZnO NRAs were synthesized hydrothermally. The shape of the ZnO NRAs was controlled using seed layers for flower and vertical structures. Numerical analysis based on the two-dimensional (2D) finite difference of time domain (FDTD) method showed that the extraction efficiency of LED with bare (without ZnO NRA), vertical ZnO NRA and flower shaped ZnO NRA was 37%, 60% and 49%, respectively. The optical output power of the LEDs with vertical ZnO NRA and flower ZnO NRA was improved by 50% and 30% compared to that of the LED without ZnO NRA at an input current of 100 mA. These results suggest that the vertical alignment of ZnO NRA is important for enhancing the light extraction of GaN based LEDs.