Phase stability versus the lattice mismatch of (100)Co_1-xGa_x thin films on (100)GaAs

Thin films of the intermetallic compound Co_1-xGa_x, which has a broad homogeneity range and a continuously variable lattice constant, were grown on the (100) GaAs surface by molecular beam epitaxy. The stoichiometry of the films and the cleanliness of the substrates were determined in situ by Auger electron spectroscopy. The identity and orientation of the phases present in the films were determined ex situ by x-ray diffraction (XRD). The films were annealed to various temperatures in N₂ and reexamined by XRD to detect any chemical interactions between the Co_1-xGa_x and GaAs. Films of Co_1-xGa_x deposited with a 2% lattice mismatch (x = 0.5) reacted with the substrate to produce CoGa₃ at 600 deg;C, whereas films with no detectable mismatch (x = 0.61) did not react until they had been heated to 800 °C.