MISORIENTATION DEPENDENCE OF EPITAXIAL-GROWTH ON VICINAL GAAS(001)

The misorientation direction dependence of the transition from growth by the formation and coalescence of two-dimensional clusters to growth by step advancement has been examined systematically with reflection high-energy electron-diffraction (RHEED) measurements during molecular-beam epitaxy on GaAs(001). Accompanying simulations of a solid-on-solid model have reproduced qualitatively all of the dominant features of the measured RHEED through comparisons based upon the step densities of the simulated surfaces. We have reported earlier that the Ga flux and misorientation-angle dependence of RHEED on vicinal GaAs(001) surfaces misoriented towards the [010] direction can be both qualitatively and quantitatively reproduced by a suitably parametrized solid-on-solid model. Here, we have modified the model to account for the anisotropy in the surface kinetics expected for surfaces misoriented along the [110] and [110]BAR directions. Two distinct origins of this anisotropy have been considered, both separately and together: one that is based only on the nearest-neighbor environment and one that is based on attempt frequencies for migration, which is independent of the nearest-neighbor environment. Both effects can contribute to the anisotropy of the diffusion constant and to the temperature at which growth becomes dominated by step advancement, but the growth-front morphologies differ considerably in the two cases. Although diffraction effects have impeded direct quantitative comparisons between measured RHEED and simulated step density on these surfaces, qualitative conclusions can still be made and simulated morphologies can be compared with scanning tunneling microscopy. Our comparisons suggest that the origin of the anisotropic growth-mode transition stems mainly from anisotropic incorporation kinetics, modeled by the nearest-neighbor environment, rather than anisotropic adatom mobility. Moreover, even if the mobility is anisotropic, the favored direction is orthogonal to that reported by others.