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

摘要

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/spl deg/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.