Defect energetics and impurity incorporation mechanisms at the arsenic-passivated Si(100) surface

Theoretical calculations show that defect properties of the Si(100) and Si( 100):As surfaces are completely different. Large atomic relaxations around vacancies near the Si(100) surface cause chemical rebonding and defect heal ing that greatly lowers their formation energies. However, passivation of t he surface by a monolayer of As induces substantial structural rigidity in the near-surface region. This reduces atomic relaxations and raises vacancy formation energies to high values, inhibiting vacancy mediated processes n ear the surface. The formation energies of silicon interstitials near the A s-passivated surface are significantly lower than those of vacancies, which favors an interstitial mode of arsenic incorporation into the bulk during in diffusion. These results explain the observed uniformity of the Si(100): As surface and the high level of electrical activation of in-diffused As.