The behavior of Ni/Au contacts under rapid thermal annealing in GaN device structures

The effect of rapid thermal annealing (RTA) on Ni/Au contacts on P-type GaN was investigated in terms of surface morphology and diffusion depth of metallic species. Ni/Au contacts were evaporated on the P-type 0.5 mu m thick top layer of a GaN P/N homojunction. Optical micrographs revealed that the contact morphology degrades when annealed above 800 degrees C for 1 min. At the same time, both Ni and Au atoms strongly diffuse in the P-type layer and even can reach the junction for a I min long annealing at 900 degrees C, therefore making the junction structure unoperable. This behavior was evidenced using the Auger voltage contrast (AVC) technique.