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Formation process of high reflective Ni/Ag/Au Ohmic contact for GaN flip-chip light-emitting diodes

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3 Author(s)
Liann-Be Chang ; Department of Electronic Engineering, Chang-Gung University, 259, Wen-Hwa 1st Road, Kwei-Shan, Taoyuan, Taiwan 333, Republic of China ; Shiue, Ching-Chuan ; Ming-Jer Jeng

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The combinations of Ni, Ag, and Au which form both Ohmic and reflective multilayer contacts for flip-chip light-emitting diode applications are examined. A strong interdiffusion of Ohmic metals and GaN during the annealing process is found to result in poor reflectance (63% at the wavelength of 465 nm). The authors propose a two step metallization method, the Ni/Ag double layer is first deposited/annealed followed by the deposition of Au, to improve the correspondent reflectivity (as high as 92%). This method is different from the conventional one step Ni/Ag/Au formation method in which these three metals are deposited together and then annealed. The secondary ion mass spectrometry depth profiles indicate that a wide interdiffusion region existed only in the conventional one step formation samples; thus the low reflectivity of Ni/Ag/Au-annealed contacts can be attributed to the strong interdiffusion of Ohmic metal into GaN. Their proposed two step metallization method avoids the strong interdiffusion and improves the reflectivity effectively.

Published in:

Applied Physics Letters  (Volume:90 ,  Issue: 16 )