Atomic Ordering and Phase Separation in MBE GaAs1-xBix

Transmission electron microscopy studies of GaAs_1?xBi _x layers grown at low temperature by molecular beam epitaxy have revealed evidence of both atomic ordering and phase separation. In layers containing up to ∼10% Bi, the two variants of CuPt_B-type atomic ordering on { 111 } B planes were observed and this is believed to be associated with the surface reconstruction present during growth. In a sample containing ∼13% Bi, no atomic ordering was observed but instead an anisotropic platelike structure was present that is believed to result from phase separation, possibly associated with the surface segregation of excess Bi during growth. Both of these effects are expected to have significant effects on the electrical and optical properties of the material.