Phase equilibria in the In-Co-As system at 475°C

Phase equilibria in the In-Co-As system are established at 475°C, using X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA). The phases indium, CoAs(α), CoAs2(α) and CoAs₃ are shown to be in thermodynamic equilibrium with InAs. A ternary phase of unknown crystal structure, with a narrow range of homogeneity centered about the composition Co_0.48In_0.37As_0.15, is found to exist in this system. A quaternary, 600°C In-Ga-Co-As phase diagram sample is also analyzed in the present study, and shows that cobalt-rich CoGa is in thermodynamic equilibrium with In_0.63Ga_0.37As. These results, in conjunction with previous investigations of the Ga-Co-As system, suggest that CoAs(α) would be suitable as a thermodynamically stable contact material to In_xGa_1-xAs for any value of x. However, there may be some practical problems associated with the fabrication of CoAs(α) using conventional deposition methods. It is further suggested that both stoichiometric and cobalt-rich CoGa should be studied as potentially stable contact materials to In_xG_1-xAs, and in particular to In_0.53Ga_0.47As, which is among the most technologically important compositions of the In_xGa_1-xAs semiconductor alloy.