Formation and morphology of step bunches during B-segregation on vicinal Si(111)

Degenerately boron-doped vicinal Si(111) substrates were annealed at high temperatures to achieve complete saturation of the ‘dangling bonds’ by surface segregating boron atoms under reconstruction to the Si(111) ( 3 × 3 ) R 30 ∘ phase. Different cooling procedures were applied to obtain well ordered superstructures. The surface morphology of the prepared substrates was studied by spot profile analysis of low energy electron diffraction (SPA-LEED). The splitting of the diffraction peaks into multiple satellites points to the formation of step bunches of different inclination (equivalent to different terrace widths) during the segregation process due to changes in the surface free energy. A model with step bunches consisting of steps with monoatomic or biatomic heights and large (111)-oriented terraces is developed to explain our results. Steep step bunches with short terraces and biatomic step heights are formed independently of the preparation process while flat step bunches with large terraces are dissolved with increasing annealing time.