To form low-resistance ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers were treated with boiled aqua regia prior to Ni/Au (5nm/5nm) film deposition. The surface morphology of wafers and the current–voltage characteristics of fabricated light emitting diode devices were investigated. It was shown that surface treatment with boiled 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 measurement. It suggested that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices might diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.

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