An hypothesis on the role of oxygen in the Si(111)-1 × 1 → 7 × 7 phase transition

Abstract

On the basis of the more important role of the corner holes than the adatoms in characterizing the Si(111)-7 × 7 reconstruction and on the basis of the strong affinity of oxygen to the Si surface, the role of oxygen in the Si(111)-1 × 1 → 7 × 7 phase transition has been discussed. Since the Si(111) surface held around the transition temperature in UHV is a dynamic system where O 2 adsorption, SiO sublimation and oxygen outdiffusion in the Si substrate are in equilibrium, it is concluded that the equilibrium oxygen concentration around the transition temperature can have a value of the order of 10 13 oxygen/cm 2 and that an oxygen-free surface cannot be obtained. Based on this conclusion a model of stacking fault triangle formation induced by the incorporation of oxygen has been proposed. The reason why only n × n structures with odd n are observed experimentally can successfully be explained by in-phase merging of the stacking fault fronts. The growth of 7 × 7 domains with triangular shapes from the step edges can be explained quite well by assembling the stacking fault triangles and the unfaulted triangles. The dynamic aspect of the 1 × 1 ⇆ 7 × 7 phase transition has been shown to be an example of precursor phenomena in the first-order phase transition.