Density functional study of XH4 (X=Si and Ge) reactivity upon dissociative adsorption onto the Si(100) surface

Total energy calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) and ultrasoft pseudopotential approximation and an analysis tool of atom-resolved density of states (ADOS) have been used to investigate (1) the energetic profiles for the possible initial dissociative adsorption of XH4 (X=Si and Ge) onto the Si(100)-(2 x 2) surface to evaluate their reactivity and (2) the effect of surface electronic states of Si(100)-(2 X 2) on gaseous molecular precursors XH4 (X=Si and Ge) during initial dissociative adsorption to understand the factors governing their reactivity. Our calculated lower-energy barrier for initial dissociative adsorption of GeH4 is due to the forming of stronger bond of Si-H between H within GeH4 and buckled-down Si atom on the Si(100)-(2 X 2) surface accompanying the larger extent of unbuckling of the buckled Si=Si dimer on the Si(100)-(2 X 2) surface at the transition state. Our evaluated better reactivity for GeH4 than SiH4 (a factor of around 14.6) is slightly larger than observed higher reactivity for GeH4 than SiH4 (a factor of between 2 and 5 depending on the incident kinetic energy) employed supersonic molecular bean techniques. Finally, our calculated ADOS indicate that the surface electronic states of buckled Si==Si dimer on the Si(100)-(2 x 2) surface energetically favorably participate in the transition state during GeH4 initial dissociative adsorption to reduce the energy barrier, i.e., enhance its reactivity, in comparison with SiH4 initial dissociative adsorption onto the Si(100)-(2 X 2) surface under the same reaction conditions. (C) 2003 Wiley Periodicals, Inc.