We present results of nb initio calculations, based on pseudopotentials and
the density functional theory, for the dissociative adsorption of Si2H6 on
the Si(001) surface. Various models are considered, containing H and the r
adicals SiH3 and SiH2. Models based on the SiH2 radical were considered wit
h three adsorption sites: (i) an on-dimer position, (ii) an intrarow positi
on between two neighboring Si dimers in the same dimer row, and (iii) an in
ter-row position between adjacent Si dimer rows. The intrarow and bridge ge
ometries are considered with and without the saturation of the Si dangling
bonds with hydrogen. For the 2 x 1 surface reconstruction, the on-dimer geo
metry is energetically more favorable than the inter-row geometry. For the
2 x 2 reconstruction, without hydrogen passivation of the Si dangling bonds
, the on-dimer and intrarow geometries leave the system fully passivated. W
ith hydrogen passivation of the Si dangling bonds, the on-dimer geometry is
more favorable than the intrarow geometry.