Reexchange Controlled Diffusion in Surfactant-Mediated Epitaxial Growth: Si on As-Terminated Si(111)

For a Si adatom on the Si(111) surface passivated by an As surfactant layer the adatom diffusion barrier ( E_D), the exchange barrier ( E_EX) for incorporation, and the energy gain ( E_B) due to incorporation into the As layer are calculated using an ab initio total energy and force method. We found that the activation energies for surface diffusion and exchange are similar in size and much smaller than the activation energy for the reexchange ( E_REEX) process ( E_D∼E_EX≪E_REEX = E_EX+E_B). We propose that adatoms are rapidly incorporated into the As layer and the effective diffusion is determined by the reexchange process.