Effects of Strain on Diborane Dissociative Adsorption and Boron Incorporation on Si0.5Ge0.5(001)-2 x 1 Surfaces

Abstract

This study investigates the surface reaction pathway of the diborane dissociative adsorption on the Si0.5Ge0.5(001)-2 x 1 surface by using density functional theory. The impact of biaxial strain on the kinetics and thermodynamics of the reactions and on the subsequent boron incorporation in the lattice is additionally evaluated. The strain affects both the thermodynamic drive for boron incorporation and the activation energies of surface reactions involving BH3 fragments. Specifically, as the strain changes from compressive to tensile, the energy barrier for BH3 dissociation on the surface progressively increases, resulting in a rate reduction of the B adsorption process. Concurrently, the driving force for incorporating B atoms into the first atomic layers of the surface decreases, reducing the probability of its occurrence. The reported mechanisms are studied on two different surface models, either having a Si or a Ge subsurface atomic layer. The simulations on these two surface configurations reveal that the embedding of B atoms is favored in substitutional sites with larger numbers of Si nearest-neighbors.