Ge-related faceting and segregation during the growth of metastable (GaAs)(1-x)(Ge-2)(x) alloy layers by metal-organic vapor-phase epitaxy

(GaAs)(1-x)(Ge-2)(x) alloy layers, 0<x<0.22, have been grown by metal-organ ic vapor-phase epitaxy on vicinal (001) GaAs substrates. Transmission elect ron microscopy revealed pronounced phase separation in these layers, result ing 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, wit h little evidence of antiphase boundaries. Atomic force microscopy revealed {115}B surface faceting associated with the phase separation. (C) 1999 Ame rican Institute of Physics. [S0003-6951(99)01310-8].