Formation and stability of large step-free areas on Si(001) and Si(111)

We have created arrays of step-free regions on Si(111) and Si(001) starting with fabricated square ridge structures and using high-temperature annealing. The conditions for the formation of step-free regions are different on the two surfaces due to differences in the temperature dependences of the surface structures and different diffusion characteristics. The step-free regions are unstable against the formation of circular vacancy pits due to the supersaturation of vacancies at large distances from atomic steps and the invasion of pre-existing steps from the surrounding barriers. The effects of electromigration on the behavior of the sublimation pits are different on the two surfaces. On Si(001) the details of the step arrays depend markedly on whether direct or alternating current heating is used. With direct-current heating the pits are no longer concentric. The effect can be explained by electromigration and the anisotropic mobility of adatoms on the reconstructed Si(001) surface. The major type of point defect on the terraces at high temperature can be inferred from the observation of vacancy or adatom clusters after quenching.