In recent years, even though the light output of GaN-related LED continues to increase, the brightness is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs. In this study, we utilize the ZnO nanotip with aqueous solution and flip-chip technique to increase the light extraction of GaN LEDs. Electroluminescence (EL) and angular optical distribution are used to measure the light output intensity of LED. In the results, ZnO nanotip after thermal annealing with N2O ambiance decrease the ZnO defects. Flip-chip LED has higher light intensity ( 1.25 times) than conventional one in vertical emitting area ( at 0 angles). The enhancement of light output is duo to the reduction of light absorption from the metal contact and Fresnel¡¦s transmission losses. Finally, we fabricate a high brightness LED with above light enhancement design. EL intensity of LED is increased about 1.38 times than conventional one. Therefore, we can manufacture a LEDs array with above designs to obtain high light output for future solid-state illumination.

The length of ZnO nanotip can be controlled by the deposition time, and the crystal of ZnO nanotip can be enhanced by a thermal annealing at 300oC in this study.The thickness of TiO2 on ITO/glass also can be controlled by the deposition time in this investigate. There are three major parts in this study : 1. (1). The control of thickness of TiO2 film and length of ZnO nanotip and (2). the difference of their photocatalytic activities are two major parts. 2. The relationship between the surface area and the photocatalytic activities of TiO2 powder (P25) and film. 3. The improvement of photocatalytic activity was utilized by the hetrojunction of ZnO nanotip/TiO2 and TiO2/ZnO nanotip, and the P25 is used as a reference for all measurements.