STM STUDY OF SURFACE RECONSTRUCTIONS OF SI(111)B

The scanning tunneling microscope is used to study the boron-doped Si( 111) surface as a function of annealing times and temperatures. The su rface structure is found to be determined by the concentration of B. W hen the substitutional B concentration is less than 1% of the top 1X1 bilayer atoms, the surface is largely 7X7 but surrounded by adatom-cov ered 1X1 regions (which have higher B concentration). When the B conce ntration is more than 3%, the whole surface will be adatom-covered 1X1 regions including (root 3 X root 3)R 30 degrees structures. The (root 3 X root 3)R 30 degrees domains will increase with the B concentratio n. Because 7X7 can only exist in the region with low B concentration, the growth of 7 X 7 is slowed down. Further annealing at 560 degrees C can convert 2X2, c(4X2) into 7X7 and 9X9. Sides of the 7X7 domain pre ferentially grow along the three equivalent [11 $$($) over bar 2] dire ctions. The adatom-covered 1X1 regions are bounded by faulted halves o f the 7X7 domains. The dark sites of 7X7 are observed and counted. The y are further interpreted in terms of a B substitution model. The patt ern of bright and dark atoms in (root 3 X root 3)R 30 degrees domains is analyzed and a criterion for a B stabilized Si-(root 3 X root 3)R 3 0 degrees structure is obtained.