High reflective p-GaN/Ni/Ag/Ti/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) applications

The fabrication of high reflective Ni/Ag/(Ti, Mo)/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) are proposed and considered, Ni/Ag/Au Ohmic contacts are also fabricated to compare their resulting reflectivities. From secondary ion mass spectrometry (SIMS) depth profiles, it indicates that the Au in-diffusion occurs in Ni/Ag/Au contacts after annealing. It is considered that Au in-diffusion, which is intermixed with Ag, Ni and GaN in Ni/Ag/Au contacts after annealing, is responsible for the resulting low reflectance (63% at the wavelength of 465 nm). To avoid Au in-diffusion and enhance the reflectivity, a diffusion barrier metal (Ti or Mo) between Ni/Ag and Au is fabricated and examined. It is demonstrated and found that an insertion of diffusion barrier metal of Ti enables to block Au diffusion effectively and also improve the reflectivity significantly, up to 93%.