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The barrier effect of Pt and Ni has been investigated in the Ti/Al/Pt/Au and Ti/Al/Ni/Au Ohmic contacts to n-GaN, respectively. Severe indiffusion of Pt and Au has been found in the 800 °C annealed Au/Pt/Al/Ti/n-GaN samples. However, Ni does not penetrate into the n-GaN and shows better barrier effect for preventing Au penetration into Au/Ni/Al/Ti/n-GaN samples. The reaction between Ga and Pt has also been identified in the samples annealed at 600 °C. At the same time, the electrical degradation was found for the Ti/Al/Pt/Au samples aged at 600 °C. However, no obvious degradation was found for the aged Ti/Al/Ni/Au samples. It is suggested that the reaction between Ga and Pt may cause the electrical degradation of the Ti/Al/Pt/Au metallization system.

The diffusion barrier effect of Pt has been investigated in Ti/Al/Pt/Au ohmic contacts to n-GaN. Severe indiffusion, outdiffusion of Pt and outdiffusion of Ga have been found in 450 ?C annealed samples according to the Rutherford backscattering spectrometry (RBS) results. At the same time, the reaction between Ga and Pt has also been identified by glancing angle synchrotron irradiation x-ray diffraction (GASIXRD) in the samples annealed at 450 ?C. A higher annealing temperature causes Pt to indiffuse into GaN and react with GaN further. As a result, electrical degradation of the Ti/Al/Pt/Au metallization system was found for samples aged at 600 ?C. In contrast, no obvious degradation was found for the aged Ti/Al/Ni/Au samples. According to the RBS and GASIXRD results, it is suggested that the formation of Ga3Pt5 may cause degradation in the electrical properties of the Ti/Al/Pt/Au metallization system.

The temperature dependent diffusion and epitaxial behavior of oxidized Au/Ni/p-GaN ohmic contact were studied with Rutherford backscattering spectroscopy/channeling (RBS/C) and synchrotron X-ray diffraction (XRD). It is found that the Au diffuses to the surface of p-GaN to form an epitaxial structure on p-GaN after annealing at 450 °C. At the same time, the O diffuses to the metal–semiconductor interface and forms NiO. Both of them are suggested to be responsible for the sharp decrease in the specific contact resistance ( ρ c ) at 450 °C. At 500 °C, the epitaxial structure of Au develops further and the O also diffuses deeper into the interface. As a result, the ρ c reaches the lowest value at this temperature. However, when annealing temperature reaches 600 °C, part or all of the interfacial NiO is detached from the p-GaN and diffuses out, which cause the ρ c to increase greatly.

The annealing time-dependent diffusion behavior of oxidized Au/Ni/p-GaN ohmic contact was studied with Rutherford backscattering spectroscopy/Channeling (RBS/C). It was found that, at 500 °C, 1 min annealing caused obvious indiffusion of Au, O and outdiffusion of Ni. And the Au even has diffused to the p-GaN/metal interface. According to the annealing time-dependent RBS spectra and referring to the correspondent specific contact resistance of the samples, it is suggested that indiffusion of Au and formation of NiO at the interface are among the critical mechanisms for the formation of low resistance ohmic contact with Au/Ni/p-GaN contact structure.