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 surface structure is found to be determined by the concentration of B. When the substitutional B concentration is less than 1% of the top 1×1 bilayer atoms, the surface is largely 7×7 but surrounded by adatom-covered 1×1 regions (which have higher B concentration). When the B concentration is more than 3%, the whole surface will be adatom-covered 1×1 regions including (3 × 3) R30° structures. The (3 × 3) R30° domains will increase with the B concentration. Because 7×7 can only exist in the region with low B concentration, the growth of 7×7 is slowed down. Further annealing at 560°C can convert 2×2, c(4×2) into 7×7 and 9×9. Sides of the 7×7 domain preferentially grow along the three equivalent [112] directions. The adatom-covered 1×1 regions are bounded by faulted halves of the 7×7 domains. The dark sites of 7×7 are observed and counted. They are further interpreted in terms of a B substitution model. The pattern of bright and dark atoms in (3 × 3) R30°domains is analyzed and a criterion for a B stabilized Si-(3 × 3) R30°structure is obtained.