Low resistance Al/Ti/n-GaN ohmic contacts with improved surface morphologyand thermal stability

The Al/Ti/n-GaN ohmic contact and multilayer variations on this contact are widely used because of the low contact resistivities they provide to n-GaN . However, there are few reports that reveal the influence of the atomic ra tio of Al to Ti on the contact resistivity, thermal stability and surface m orphology of the contacts. This study reveals that the ratio of Al to Ti st rongly influences all of these characteristics. All contacts in this study had atomic ratios of Al to Ti higher than 1. Those contacts with ratios of Al to Ti less than 3 required higher annealing temperatures or longer annea ling times to reach comparable contact resistivities compared to the more A l-rich contacts. On the other hand, the less Al-rich contacts provided seve ral advantages. They exhibited smooth surface morphologies even after they were annealed at temperatures near 1000 degrees C, and they suffered much l ess severe degradation during long-term aging at 600 degrees C. These findi ngs are explained by differences in the phases formed after annealing.