Adsorption of GeH2 on the Si(0 0 1) surface

We present results of ab initio calculations, based on pseudopotentials and the density functional theory, for the adsorption of germanium dihydride (GeH2) on the Si(0 0 1) surface, which is thought to take place during the atomic-layer-epitaxy process. Three adsorption sites are considered: (i) on-dimer (or bridge) site, (ii) an intrarow position between two neighbouring Si dimers with hydrogenated surface (GeH2+H+H), and (iii) an intrarow position under GeH2 rich condition (GeH2+GeH2). The atomic structure and surface electronic states for these structures are presented and the results are discussed in relation to recent experimental works, as well as recent theoretical work on the adsorption of SiH2. In particular, we find that all the three models are characterised by much longer Si–Si dimer length than on the clean Si(0 0 1)-(2×1) surface. We also find that for all these models the fundamental band gap is free of surface states and the system remains fully passivated. We do not find any significant energy difference between the first two models, although the on-dimer structure provides unfavourable Ge–Si bond angle.