DISSOCIATION OF B₂H₆ AND ADSORPTION OF THE FRAGMENTS OF B₂H₆ ON THE STEPPED Ge(100) SURFACE

Abstract

In this work, the p-type doping of the S A type stepped Ge(100) surface by a diborane ( B 2 H 6) gas flow has been simulated by the possible dissociation and adsorption models. The most probable dissociation model of B 2 H 6 and adsorption models of the fragments of B 2 H 6 on the stepped Ge(100) surface have been determined by the local minimum total energy and/or binding energy calculations based on the Density functional (B3LYP/6-3g) and Hartree–Fock (HF/STO-3g) theories, respectively. The present calculations have shown that, the step region (for both up and down terraces) of the stepped Ge(100) surface has the most attractive sites for BH3 molecules determined to be the first dissociation fragments of B 2 H 6 by an external energy of ~ 1.3 eV. It has been found that, at the first step of the adsorption, BH3 can dissociate to BH2 and BH fragments on the stepped Ge(100) surface. While BH3 and BH2 products prefer to be attached to a single surface Ge atom, BH is bridged between two adjacent surface Ge atoms. According to the present optimization calculations, the p-type doping process of the stepped Ge(100) surface has started with the adsorption of BH3 on the electron deficient site (buckled down) of the Ge dimer bond close to the step edge and ended with the substitutional occupation of the Ge site in the layers of the surface by B atom. The beginning of the p-type doping of the stepped Ge(100) surface has been illustrated by the electronic states of B appeared in the optical energy gap of Ge very close to the edge of the HOMO.