Step instability of the In0.2Ga0.8As (001) surface during annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [1 (1) over bar0] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton-Cabrera-Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [1 (1) over bar0] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.