High-temperature structural behavior of Ni/Au contact on GaN (0001)

We investigated the structural evolution of the Ni/Au contact on GaN (0001) during annealing in N-2, using in-situ x-ray diffraction, anomalous x-ray scattering, and high resolution electron microscopy. GaN decomposition occu rred mostly along GaN dislocations at temperature higher than 500 degreesC. The decomposed Ga diffused into Au and Ni substitutional positions, and th e decomposed nitrogen reacted with Ni, forming Ni4N. Interestingly, Ni4N wa s grown epitaxially. The epitaxial relationship of the Ni4N, Au, and Ni was identified as M (111)//GaN (0002) and M[1 -1 0]//GaN[1 1 -20] (M= Ni4N, Au , and Ni). At dislocation free regions, however, the atomically smooth inte rface remained intact up to 700 degreesC. Remarkable improvement of device reliability is expected in the contact on dislocation free regions compared with the contact on dislocations.