First principles total energy calculations of the adsorption of germane and digermane on Si(0 0 1)-c(2 × 4)

First principles total energy studies are performed to investigate the energetics, and the atomic structure of the adsorption of germane (GeH4), and digermane (Ge2H6) on the Si(0 0 1)-c(2 × 4) surface. It has been observed experimentally that adsorption of Ge2H6 is a dissociative process, which first yields GeH3 and then GeH2 fragments as products. We first study the adsorption of GeH2 considering two different models; the intra-row and the on-dimer geometries. Our results show that the on-dimer site is more stable than the intra-row geometry by 0.44 eV. This is not a surprise since in the absence of H atoms, adsorption in the on-dimer site leaves no dangling bonds. In contrast, when the GeH2 fragment is considered together with two H atoms, the intra-row geometry is favored energetically as compared with the on-dimer site, in good agreement with experiment. Similar results have been previously obtained for the adsorption of SiH2 on Si(0 0 1). Digermane adsorption is explored according to two different geometries. In the first one, we have considered the adsorption as two GeH3 fragments, while in the second, we have considered the adsorption as two GeH2 fragments plus 2 H fragments. In good agreement with experiments, it is found that the latter geometry is energetically more favorable.