LEDGE INTERACTIONS AND STRESS RELAXATIONS ON SI(001) STEPPED SURFACES

Excess energies and stresses of flat and vicinal stepped surfaces on Si(100) with striped domains of single- and double-layer ledges are calculated using the Stillinger-Weber empirical potential. Energies of stepped structures relaxed by molecular-dynamics simulations are compared to results of electronic-structure calculation in the tight-binding approximation for comparable cell dimensions, with qualitative agreement in the prediction of relative stability among the various ledges. Relaxed atomic configurations for a range of ledge-ledge separations from 8 to 320 angstrom are obtained by energy minimization. It is shown that stepped surfaces have excess energies lower than that of the flat surface for ledge separations greater than 16 angstrom. Calculations of in-plane stresses on the surfaces show that the energy-lowering mechanism is an elastic relaxation induced by the initial discontinuity in the stress component across the ledge. These results are discussed in the context of current understanding of elastic interaction effects on the stability of stepped surfaces.