Fabrication of zinc oxide hemispheres array and its application into solid state LEDs

To improve the light extraction efficiency (LEE) for GaN-based blue light emitting diodes (LEDs), we proposed a zinc oxide (ZnO) hemispheres array on top of an indium tin oxide (ITO) electrode. The ZnO hemispheres array was produced with two-step hydrothermal growth technique. First, a periodic ZnO seed dots array was fabricated by laser interference lithography (LIL) followed by ZnO sputtering. Then, it was dipped into a nutrient solution for the growth of flower-like ZnO structure consisting of omni-directional nanorods at each ZnO seed dot. In the secondary growth step, a growth inhibitor, which was electrostatically adsorbed on the top facet of ZnO nanorods, suppressed the c-axial growth. Only lateral growth was activated to form a ZnO hemisphere by merging the neighboring ZnO nanorods. The ZnO hemispheres array was incorporated into the ITO contact surface of the GaN-based blue LEDs, and the LEE was enhanced by 20% at 20 mA compared to that of the LED without it.