Origin of homoepitaxial faulted island growth on the Si(111) surface

Silicon homoepitaxy on Si(111) substrates has been studied using a novel growth technique which allows new details of the growth mechanism to be investigated, In agreement with earlier studies the growth of faulted Si(111) islands is observed, Under low-temperature growth conditions these faulted structures are the dominant growth nuclei on the surface, The preference for metastable structures is shown to be intimately related to the manner in which the rest-layer structure of the Si(111)-(7 x 7) reconstruction is gradually transformed into a bulk (1 x 1) structure - a transformation that is a prerequisite for Si(111) homoepitaxial growth. Nucleation is seen to occur rapidly following transformation of small triangular regions of rest-layer to a bulk (1 x 1) structure, However, nucleation events are explicitly avoided for which the island's edge runs along or closely parallel to the dimer rows that border these (1 x 1) regions. This repulsive interaction is suggested to result from excessive tensile stress due to rebonding along. the island's step-edge, The repulsion is largest for the case of unfaulted islands since these islands and the (1 x 1) regions in which they are found always point in the same [11 (2) over bar] direction. Under these conditions, faulted-island nucleation is favored since these islands point in the opposite [(1) over bar (1) over bar 2] direction which largely avoids this repulsive interaction. (C) 1998 Elsevier Science B.V. All rights reserved.