In-situ RHEED study of growth processes in the initial stage of SiGe alloy film deposition by gas source molecular beam epitaxy

Abstract

Growth processes in the initial stage of SiGe alloy film deposition on (100)Si surfaces by molecular beam epitaxy using Si 2H 6 and GeH 4 have been studied over the whole composition range by in-situ RHEED observation. In the Ge-rich range, the sequence in the initial growth processes is the same as that of Ge on Si, that is, the growth of (1) two-dimensional (2D) layers with an (8×2) surface superstructure, (2) {811}-faceted islands having a 〈111〉 doubly-ordered structure and (3) {311}-faceted islands. The critical thicknesses at which these growth stages change increase markedly with decreasing Ge composition. On the other hand, in the growth of Si- rich alloy films, the growth of 2D layers with a (2×1) surface structure continued until the growth was stopped, for example, up to as thick as 380 monolayers, and the (8×2) structure is observed on the as-grown surfaces after stopping the growth and cooling down to room temperature. The (8×2) superstructure and the {811}-facet structure with the 〈111〉 double ordering are considered to be energetically stable structures constructed of Si and Ge atoms for the respective thicknesses and compositions of Ge and Si atoms.