First principles calculations of the local arrangement of silicon hydrides on the Si( [formula omitted])-c(2×4) surface

Abstract

Using first principles total energy calculations, we have studied the energetics and structural properties of silicon trihydride (SiH 3) and dihydride (SiH 2) species adsorbed on the Si(0 0 1)-c(2 × 4) surface. These are fragments produced in the chemical vapor deposition of silane and disilane on Si(0 0 1). It is found that in the absence of hydrogen atoms, the SiH 2 subunit prefers to be adsorbed in the on-dimer site (on top of a Si dimer) rather than in the intra-layer site (between two Si dimers of the same row). However, if we consider the two hydrogen atoms produced in the dissociation of the SiH 4 molecule, the relative stability of the two sites is reversed. These results are in good agreement with experiments that found the SiH 2 fragment to be located at the intra-row site only. We have also considered the dissociation of SiH 4 into a SiH 3 fragment and a hydrogen atom. It is found that the SiH 3 fragment and the hydrogen atom are both attached to Si dangling bonds. The lowest energy configuration involving a trihydride radical is metastable with respect to the lowest energy configuration involving a dihydride radical. A similar situation is found for the adsorption of a Si 2H 6 molecule. The configuration with trihydride fragments is less stable than the configuration with dihydride fragments.