Arsenic adsorption onto silicon stepped surfaces: a study at semiempirical level

As adsorption onto Si surfaces vicinal to ( 100) has been studied using the Hartree - Fock method at a semiempirical level and a cluster model of the surface steps. The simulation conditions apply to the dilute limit of the adsorbate concentration. Accordingly, one As atom is placed on the step in a substitutional or interstitial location, either above or below the surface. The optimal configuration of the system is evaluated from a steepest-descent energy minimization. The central finding is that As is preferably adsorbed in the interstitial location and the physical explanation is that this location allows both a stronger electrostatic coupling with the surface and a lower stress than in the case of the substitutional impurity. This result represents a significant divergence with respect to the known properties of the bulk impurity. It can, however, consistently account for known features of heteroepitaxial growth of As on Si(100).