Effects of hydrogen on the formation of SiGe/Si heterostructures
In this report, we review and discuss our results obtained on the surface segregation of Ge atoms and surfactant effects of hydrogen atoms in Si overlayer growth on Ge/Si(100) by gas-source molecular beam epitaxy (GSMBE) using GeH/sub 4/ and Si/sub 2/H/sub 6/. The layer-by-layer growth rate of the Si overlayers was observed in-situ by reflection high-energy electron diffraction (RHEED) intensity oscillation periods.
Studies on the suppression of Ge segregation during Si overgrowth on GE(n ML) / Si(100) substrates by gas-source MBE
Surfactant effects of hydrogen atoms on the Ge segregation during Si growth on Ge/Si(100) substrates by Si 2 H 6 -source molecular beam epitaxy have been studied. The layer-by-layer growth rates were examined in-situ by reflection high energy electron diffraction (RHEED) intensity oscillation periods. The growth rate of Si overlayers decreases exponentially with increasing Si thickness and eventually approaches to that of Si/Si(100) homoepitaxial growth at substrate temperatures of 440-550°C, which corresponds to the change in surface coverage of Ge atoms. The decay length of the surface concentration of Ge atoms is suppressed by an increase in Si 2 H 6 gas pressure. These facts can be explained as an effect of H atoms existing on the growing surface. Furthermore, the atomic mixing phenomenon in the initial stage of growth is observed, which is related with the strain of Ge layers. The addition of excess hydrogen atoms during Si growth leads to a further reduction of the decay length under the appropriate growth condition and to the island growth at higher temperatures and for lower Si 2 H 6 pressures.
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 2 H 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.