The ternary compound Fe3Ga2-xAsx:: A promising candidate for epitaxial and thermodynamically stable contacts on GaAs

Solid state phase equilibria in the ternary Fe-Ga-As phase diagram have been established at 600 degrees C using X-ray diffraction, scanning electron microscopy and EDX microprobe analysis as experimental techniques. The existence of a ternary phase, expressed by the general chemical formula Fe3Ga2-xAsx (0.20 less than or equal to x less than or equal to 1.125), which crystallizes in hexagonal symmetry and derives structurally from the NiAs-type structure, has been evidenced. The original feature of the diagram is the occurrence of a tie line between this ternary phase and the semiconductor GaAs. It is the first time that such a ternary phase M-x(Ga,As)(y) (M = transition metal) has been found to be in thermodynamic equilibrium with GaAs. Based on hexagonal-pseudocubic crystallographic considerations, this phase Fe3Ga2-xAsx presents real possibilities to be epitaxied on GaAs. Therefore, this compound appears as a unique candidate to obtain a quasi-ideal metal/GaAs contact, both thermodynamically stable and single-crystalline. For this purpose, we have studied the solid state interdiffusions in epitaxial (70 nm Fe)/GaAs(001) heterostructures grown at room temperature and annealed at 450 degrees C in ultra-high vacuum conditions. The epitaxial growth of the Fe3Ga2-xAsx compound on GaAs(001) has been proved but, for an annealing temperature of 450 degrees C, the binary compound Fe,As, which is not found in thermodynamic equilibrium with GaAs, coexists as patches at the interface. This indicates that annealing at higher temperature should lead to a quasi-ideal Fe3GaAs/GaAs(001) contact. (C) 1997 Elsevier Science S.A.