STM study of surface reconstructions of Si(111):B

Abstract

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