Single crystal films of GaSbyAs_1-y and AlxGa_1-x SbyAs1-y alloys having compositions within the miscibility gap can be prepared using nonequilibrium growth techniques. These alloys were grown lattice matched to InP by molecular beam epitaxy/ Transmission electron microscopy studies of these alloys grown on (100) InP at 500-560 deg C show evidence of compositional modulation due to spinodal decomposition similar to that of InGaAsP grown by vapor phase epitaxy on InP used for laser diodes emitting at approx 1.5 mu m. From the studies of optical microscopy, X-ray diffraction, and photoluminescence measurements at both room temp. and liquid helium temp., these epitaxial layers are considered of high quality for optoelectronic device applications in the wavelength range of 0.65-1.7 mu m lattice matched to InP substrates.