Ge-Related Faceting and Segregation during the Growth of Metastable (GaAs)1-x(Ge2)x Alloy Layers by Metal--Organic Vapor-Phase Epitaxy

(GaAs)_1-x(Ge₂)_x alloy layers, 0<x<0.22, have been grown by metal-organic vapor-phase epitaxy on vicinal (001) GaAs substrates. Transmission electron microscopy revealed pronounced phase separation in these layers, resulting in regions of GaAs-rich zinc-blende and Ge-rich diamond cubic material that appears to lead to substantial band-gap narrowing. For x = 0.1 layers, the phase-separated microstructure consisted of intersecting sheets of Ge-rich material on {115}B planes surrounding cells of GaAs-rich material, with little evidence of antiphase boundaries. Atomic force microscopy revealed {115}B surface faceting associated with the phase separation.