Metallurgical study of Ni/GaAs contacts. I. Experimental determination of the solid portion of the Ni-Ga-As ternary-phase diagram

X-ray diffraction on powders and single crystals has been performed to determine the limits of homogeneity and crystallographic data of metallic ternary phases which occur in the bulk Ni-Ga-As system and to draw the solid portion of the phase diagram. The samples were prepared in closed, small-volume containers to prevent the formation of gas-phase products. Five ternary phases which crystallize in hexagonal symmetry and are all structurally derived from the NiAs type were evidenced. Among them, three phases show hexagonal superlattices: a(3)1/2×3c, 2a×4c, and 3a×2c which denote ordered structures. Neither nickel nor ternary phases are in thermodynamic equilibrium with GaAs, in contrast to the binaries NiGa, Ni2 Ga3, and NiAs which are. The bulk-phase diagram determined in this study provides a framework within which most of the experimental data concerning the products of reactions at Ni/GaAs interfaces can be understood.