A. Antons, R. Berger, K. Schroeder, and S. Blügel

Experimental observations of island growth during homoepitaxy on surfactant(As, Sb)-covered Si(1l1 ) are explained by ab initio calculations of the structure and binding energies of small clusters of Si-adatoms. We show that on Si(lll):As the growth of double-layer steps with (1 x 1) structure is established already at an island size containing four Si-adatoms. On the contrary, on Si(lll):Sb the growth proceeds by an alternating sequence of (1 x 1) and ( SQR(3) x SQR(3)) structures with monolayer steps. We find that individua1 Sb-trimers are nucleated on Si(l1l):Sb(l x 1) terraces leading to a ( SQR(3) x SQR(3)) Sb-trimer structure on top of (1 x 1) terraces.