First principles calculations of the local arrangement of silicon hydrides on the Si(0 0 1)-c(2×4) surface

Using first principles total energy calculations, we have studied the energetics and structural properties of silicon trihydride (SiH3) and dihydride (SiH2) 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 SiH2 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 SiH4 molecule, the relative stability of the two sites is reversed. These results are in good agreement with experiments that found the SiH2 fragment to be located at the intra-row site only. We have also considered the dissociation of SiH4 into a SiH3 fragment and a hydrogen atom. It is found that the SiH3 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 Si2H6 molecule. The configuration with trihydride fragments is less stable than the configuration with dihydride fragments.