Adsorption mechanisms of tertiarybutylarsine on Ga- and As-rich GaAs(001) surfaces

The adsorption of tertiarybutylarsine (TBAs) on GaAs(001) surfaces was studied by supersonic molecular beam experiments. It was found that TBAs molecules were chemisorbed on arsenic-rich c(4×4) and gallium-rich (4×6) surfaces at room temperature by a precursor-mediated mechanism. But no TBAs molecules stuck on arsenic-rich (2×4) surfaces at room temperature. The angular dependence of desorbed (or reflected) TBAs molecules was explained by trapping/desorption and direct inelastic scattering processes of the incident TBAs. The former angular dependence was described by cosn θ and n close to unity, which suggested that the activation barrier in the TBA trapping/desorption is very small for GaAs(001) surfaces. From the time-of-flight experiments for desorbed TBAs, the activation energy in TBAs desorption from the (2×4) surface was 17.5 kcal/mol and those from (4×6) were 8.2 kcal/mol and 6.9 kcal/mol. These adsorption results were reasonably explained by a model based on the surface reconstruction of each surface.