Abstract
We have studied, in the equilibrium state, the multiatomic step (multistep) structure only a few nanometers high on GaAs(001) vicinal surfaces grown by metalorganic chemical vapor deposition (MOCVD). Annealing (growth interruption) straightens multistep edges, but even after the annealing the multistep on the [1̄10]-misoriented surface is straighter than the multistep on the [110]-misoriented surface. This indicates that the free energy of the [1̄10]-step is lower than that of the [110]-step. Step bunching on this vicinal surface is caused by the formation of two facets with different orientations.