In this study, a low-resistant and high-transparent ohmic contact to p-GaN layer using an indium-zinc oxide (IZO)/(oxidized-Ni/Au) contact system was investigated to enhance light extraction of GaN-based light-emitting diodes (LEDs). Improvement in the light output of GaN-based blue LEDs as a function of the IZO film thickness was examined and an optimum thickness of around 300 nm has been found. Under an injection current in the 10-50 mA range, as compared to the case without IZO film, about 35-28% improvement in light output power (Lop) has been obtained. Comparisons of Lop and its reliability for LEDs with an IZO or indium-tin oxide transparent conduction layer were also made. In addition, compared to IZO/GaN samples without the patterned surface, the LEDs fabricated using a patterned IZO surface show a 23.1% improvement in Lop at 20 mA. (c) 2006 Elsevier B.V. All rights reserved.