Equilibrium configuration of atomic steps on vicinal Si(001) surfaces with external biaxial strain

We determine the equilibrium configuration of atomic steps on vicinal Si(001) surfaces with applied biaxial tensile strain by computing the elastic relaxation energy associated with different possible step configurations, in which spontaneous step creation is allowed. As a function of decreasing sample miscut, we find that the equilibrium configuration changes from a ''normal'' array of straight steps, to an arrangement of triangular steps which are in out-of-phase alignment on adjacent terraces at intermediate miscut, to a ''striped'' phase with long parallel fingers at a low miscut. These results are in qualitative agreement with recent experiments on Si(001) surfaces which show spontaneous step creation due to applied biaxial tensile strain and/or heavy boron doping.