TEM evaluation of ordered and modulated structures in GaAsSb crystals grown on (110)InP substrates by molecular beam epitaxy

Ordered and modulated structures in GaAsSb grown on (110)InP substrates by molecular beam epitaxy, has been evaluated by transmission electron microscopy. In the electron diffraction pattern from the GaAsSb, superstructure spots associated with CuAu-I type ordered structure are found. When the offset angle of the substrates increases, the ordering becomes stronger. The ordering becomes also stronger with increasing growth temperature in the range 470-530°C. In high resolution images of the crystal, areas with doubling in periodicity of 220 and 200 lattice fringes are observed locally, which is due to CuAu-I type ordering, indicating that the ordering is not perfect and that ordered regions are likely to be microdomains. Modulated structure are also found in both the ⟨001⟩ and ⟨11¯0⟩ directions. Coarse and fine modulated structures are clearly observed, and the periodicity of the coarse structure in the ⟨001⟩ direction is much longer than that in the ⟨11¯0⟩ direction. These findings lead us to conclude that atomic ordering and spinodal decomposition of the crystal are competing on the growth surface via surface diffusion of deposited atoms