ANISOTROPIC DIFFUSION AND ISLAND FORMATION IN THE MBE GROWTH OF SI(001)

The effect of anisotropic diffusion on the process of island formation and growth during the early stages of molecular beam epitaxy of Si on Si(001) is studied. The theoretical treatment in terms of a rate-limi ting step predicts strong growth anisotropy for the isotropic (1:1) an d anisotropic (1000:1) diffusion models. Although, in the case of anis otropic diffusion, the direction of easy diffusion is perpendicular to the direction of preferential island growth, Monte Carlo simulations show that the experimental STM data on island densities and island sha pes can be reproduced by both models. Elongate island formation is, in the first place, an effect of anisotropic lateral interactions, while the migration anisotropy has a minor effect on the island shapes. It somewhat suppresses shape anisotropy at low temperatures and slightly enhances that at high temperatures.