In order to form low-resistance ohmic contacts with p-type GaN, InGaN/GaN multiple quantum-well light-emitting diode wafers were treated with boiled aqua regia before Ni/Au (5nm/5nm) film deposition. It was shown that surface treatment with aqua regia could effectively remove oxide from the surface of the p-GaN layer and revealed defect-pits whose density was almost the same as the screw dislocation density estimated by X-ray rocking curve measurements. This suggested that the metal atoms of the Ni/Au transparent electrode of light-emitting diode devices could diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with aqua regia had to be chosen so as to avoid an increase in threading dislocation-induced leakage current.

Effect of Surface Treatment of GaN Based Light Emitting Diode Wafers on the Leakage Current of Light Emitting Diode Devices. L.J.Wang, S.M.Zhang, J.H.Zhu, J.J.Zhu, D.G.Zhao, Z.S.Liu, D.S.Jiang, Y.T.Wang, H.Yang: Chinese Physics B, 2010, 19[1], 017307