DFT study on dissociative adsorption of SiH4 and GeH4 on SiGe(1 0 0)-2 × 1 surface

SiH4 and GeH4 dissociative adsorptions on a buckled SiGe(1 0 0)-2 × 1 surface have been analyzed using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(1 0 0)-2 × 1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH4 and GeH4 reactions with four dimers of Si∗-Si, Ge∗-Si, Ge∗-Ge, and Si∗-Ge (∗ denotes the protruded atom). On a half H-covered surface, the energy barriers for silane and germane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. Rate constants are also calculated using the transition-state theory. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence in dimer form. If the surface Ge is present in form of Ge∗-Ge, the surface reactivity decreases as the Ge∗-Ge content increases. If the surface Ge prefers to be in form of Ge∗-Si at low Ge contents, the surface reactivity increases first, then decreases at high Ge surface contents when Ge∗-Ge prevails. The calculated rate constant ratio of GeH4 adsorption on Si∗-Si over Ge∗-Ge at 650 °C is 2.1, which agrees with the experimental ratio of GeH4 adsorption probability on Si(1 0 0) over Si(1 0 0) covered by one monolayer Ge. The experimental ratio is 1.7 measured through supersonic molecular beam techniques. This consistency between calculation and experimental results supports that one monolayer of Ge on Si(1 0 0) exists in form of Ge∗-Ge dimer.