Effect of rapid thermal annealing on the composition of Au/Ti/Al/Ti ohmic contacts for GaN-based microdevices

The homogeneity of Au/Ti/Al/Ti ohmic contacts for AlGaN/GaN devices was analyzed as a function of the thickness of the Ti barrier (30 nm < d < 90 nm). After rapid thermal annealing, the Al out-diffusion is induced even for the thickest Ti barrier, accompanied by Au in-diffusion and the oxidation of the surface. Uniform contacts were found only for d > 50 nm, although several compositional deficiencies were identified in the distribution maps obtained with the ion microprobe, including the formation of craters. A clear interplay between Ti and Au was found, suggesting the relevance of lateral flows during the rapid thermal annealing.