For thin-GaN LED, Al layer is often incorporated with NiO-Au to form a highly reflective NiO-Au/Al p-GaN contact. Both electrical and optical characteristics of NiO-Au/Al contact exhibited poor thermal stability. X-ray photoelectron spectroscopy (XPS) results showed that the poor thermal stability attributed to the diffusion of Al atoms into GaN epi layer. To prevent Al diffusion, a Ni barrier layer was placed between Al and NiO-Au layer. The specific contact resistance of the NiO-Au/ Ni/Al was maintained on the order of 10(-2) Omega-cm(2), up to 600 degrees C. XPS results confirmed the function of the Ni barrier layer. Low Al level was detected in GaN epi layer. (c) 2005 The Electrochemical Society.