STEP TOPOGRAPHY OF SI(001) VICINALS, CLEAN AND AFTER DEPOSITION OF AS, SB AND BI

We have used high-resolution LEED and AES on a spherically shaped samp le to investigate the polar and azimuthal dependence of the step topog raphy of Si(001) vicinals and its change by As, Sb and Bi adsorption. The well-established smooth transition on clean Si from single (S) to double (D) layer steps between 1.5 degrees and 6 degrees in the [110] azimuth is completely changed. After deposition at 300 K and equilibra tion by annealing at 970 less than or equal to T less than or equal to 1000 K the average step height for 0.75 less than or equal to theta(A s) less than or equal to 1 ML becomes four layers (F) for all azimuths and miscut angles. No preferential orientation of the As adsorption d imers with respect to the F-step edges is observed. For Sb (720 less t han or equal to T less than or equal to 770 K), theta(Sb) approximate to 1 ML and for Bi (600 less than or equal to T less than or equal to 750 K), S-steps are formed in all azimuths and for miscuts up to 100 f rom (001). These topography changes can be understood in terms of stra in modifications induced by the adsorbates. Before complete desorption , both As and Sb induce c(4 X 4) patterns in all azimuths, connected w ith coverages of 0.25 ML. Also Bi induces a c(4 X 4) pattern but it is developed best at 920 K where Bi is already completely desorbed. Miss ing Si-dimer structures without adsorbate (Bi case) or with As or Sb f illing the missing dimer sites are proposed.