Interfacial adhesion between an indiumtin oxide (ITO)/Ni/Ag/Ni/Au p-electrode, and Au and Ni/Au seeds in vertical GaN-based light emitting diodes (LEDs) was enhanced by O-2 plasma cleaning treatment of the Au surface in the p-electrode. However, AES and REELS analyses of the Au surface in the p-electrode detected surface damage to the p-electrode and photoresist (PR) passivation structure from O-2 plasma cleaning. W/Ni and Al/Ni adhesion layers were introduced in the Au seed to increase interfacial adhesion between Au seed and untreated PR passivation. Forward leakage current as low as 0.91 nA at 2 V was observed for the vertical LED with the Al/Ni/Au seed, for which adhesion strength to O-2 plasma-cleaned Au and untreated PR was 141.2 MPa and 62.8 MPa, respectively. (C) 2010 Elsevier B.V. All rights reserved.