Arsenic dimer dynamics during MBE growth: Theoretical evidence for a novel chemisorption state of As_2 molecules on GaAs surfaces

Results of first-principles calculations are reported for the adsorption of As2 molecules on the stable surface reconstructions of the GaAs (001) surface, including adsorption paths and barriers for strongly bound sites. It is shown that a novel chemisorption state acts together with an intermediate physisorbed plateau in the total energy to hold the As2 molecules near the surface and funnel them into strongly bonding sites during epitaxial growth, and that this state can explain the transition from the b2s2 3 4d to the cs4 3 4d reconstruction under low-temperature, very arsenic-rich conditions. [S0031-9007(99)09336-9]