Density Functional Study of the Effect of SiH₄/GeH₄ and Si(001)/Ge(001) on Gas‐Surface Reactivity during Initial Dissociative Adsorption

Abstract

Ultrasoft pseudopotential total energy calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) has been used to investigate 1) the energetic profile for the initial dissociative adsorption of XH4 (X = Si and Ge) onto Si(001) and Ge(001) surfaces to evaluate their gas‐surface reactivity in comparison with relevant measured gas‐surface reactivity using supersonic molecular beam techniques, and 2) the effect of different gaseous molecular precursors, i.e. XH4 (X = Si and Ge), and different surfaces, i.e. Si(001) and Ge(001), on their gas‐surface reactivity during initial dissociative adsorption. Our evaluated gas‐surface reactivity for GeH4 is approximately a factor of 18.45 better than that for SiH4 on Si(001)‐(2×2) surface. This calculated result is about three to four times higher than observed gas‐surface reactivity (as much as a factor of 5 depending on the incident kinetic energy) derived from measured gas‐surface reactivity using supersonic molecular beam techniques. We believe that the better evaluated gas‐surface reactivity for GeH4 than SiH4 is due to 1) the forming of a stronger bond of Si‐H between H within GeH4 and buckled‐down Si atom on the Si(001)‐(2×2) surface and 2) the smaller distortion of Ge‐H bond within GeH4 at the transition state. Additionally, our evaluated gas‐surface reactivity for SiH4 on Si(001)‐(2×2) surface is approximately a factor of 21.69 better than SiH4 on Ge(001)‐(2×2) surface. This calculated result is about two times higher than observed gas‐surface reactivity. We attributed this better evaluated gas‐surface reactivity for SiH4 on Si(001)‐(2×2) surface to 1) the smaller distortion of Si‐H bond within SiH4 and 2) the nature of weaker bond of Ge‐H between H within SiH4 and buckled‐down Ge atom on Ge(001)‐(2×2) surface in comparison with that of stronger bond of Si‐H between H within SiH4 and buckled‐down Si atom on Si(001)‐(2×2) surface even though there is the slightly shorter bond length of Ge‐H between H within SiH4 and buckled‐down Ge atom on Ge(001)‐(2×2) surface at the transition state.