DISSOCIATION OFB2H6AND ADSORPTION OF THE FRAGMENTS OFB2H6ON THE STEPPEDGe(100)SURFACE

In this work, the p-type doping of theSAtype steppedGe(100)surface by a diborane (B2H6) gas flow has been simulated by the possible dissociation and adsorption models. The most probable dissociation model ofB2H6and adsorption models of the fragments ofB2H6on the steppedGe(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 BH3molecules determined to be the first dissociation fragments ofB2H6by an external energy of ~ 1.3 eV. It has been found that, at the first step of the adsorption, BH3can dissociate to BH2and BH fragments on the steppedGe(100)surface. While BH3and BH2products prefer to be attached to a single surface Ge atom, BH is bridged between two adjacent surfaceGeatoms. According to the present optimization calculations, the p-type doping process of the steppedGe(100)surface has started with the adsorption of BH3on the electron deficient site (buckled down) of theGedimer bond close to the step edge and ended with the substitutional occupation of theGesite in the layers of the surface byBatom. The beginning of the p-type doping of the steppedGe(100)surface has been illustrated by the electronic states ofBappeared in the optical energy gap ofGevery close to the edge of the HOMO.