Clustering of boron into a vicinal Si(100) surface: a quantum mechanical study at semiempirical level

In this work the equilibrium configurations of boron impurities into a silicon surface, vicinal to (100), are studied using the Hartree–Fock method at semiempirical level. Clusters containing up to five boron atoms are considered. These impurities are either of a substitutional or of an interstitial type and are placed at the step edge. The most stable defect shape is evaluated relaxing the system to an energy minimum with a steepest descent approach. The results indicate that the impurities remain clustered and are stabilized by the formation of bonds considerably shorter than the normal interatomic distance in crystalline silicon. Due to the tensile strain so generated, the step reconstructs strongly and the disorder promotes the hybridization of the boron–silicon bonds. Owing to these interactions, the binding energies of the clustered atoms acquire a functional dependence on the step structure which seems in agreement with experiments.