Effect of Co 60 gamma-radiation on interactions between phases in the Au-Ti-Al-Ti-n-GaN contacts

We consider radiation effects in the Au-Ti-Al-Ti-n-GaN multilayer metallization when the contact structures, both initial and after rapid high-temperature annealing in the nitrogen atmosphere, are exposed to Co 60 gamma-irradiation up to doses of 4·108 R, 109 and 2·109 R. The initial contact structures do not change substantially under irradiation, and the layered structure of metallization remains unchanged. Thermal annealing at 700 degrees centigrade damages the contact layered structure due to enhancement of interdiffusion at the interfaces between phases. The morphological and structural transformations in the contact metallization which were induced by thermal annealing enhance mass transfer of metallization components under radiation action. In this case, after gamma-irradiation up to a dose of 2·109 R, titanium and gallium appear at the metallization surface, while oxygen penetrates into the whole contact structure, and big amounts of it are observed in the GaN near-surface layer. A correlation was found between the contact resistivity and radiation-enhanced mass transfer of oxygen into the GaN near-surface layer. (authors)