Metal contacts to n-GaN

Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 8C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current–voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current–voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 8C. The surface of Au and Ti/Au contacts annealed at 900 8C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 8C. X-ray diffraction examinations showed, that new Ti2N, Au2Ga and Ga3Ti2 interface phases formed in Ti/Au contact at 900 8C, new Ti2N phase formed in Ti/Al contact at 700 and 900 8C, as well as new AlN interface phase developed in Ti/Al contact at 900 8C.