Phase formation in Ni/InP contacts

The reaction of Ni films with InP is of technological interest because of the importance of Ni in ohmic contacts to n-type InP. However, numerous discrepancies are found in the literature concerning the Ni/InP reaction. In this study, bulk and thick film diffusion couples are examined in light of the Ni–In–P phase diagram, and many of the apparent discrepancies in the literature are clarified. Segregation of In and P into Ni–In and Ni–P binary phases is found to be an intermediate stage of the reaction, which is most easily observed in the reaction of thicker Ni layers with InP substrates. However, the Ni2InP ternary phase is found in the final stage of the reaction of Ni films on InP substrates, as predicted by the phase diagram. This sequence of phase formation differs dramatically from that observed in the other Ni/III–V systems that have been examined, and these differences are discussed.