B-induced reconstruction on Si(100)-(2×1) surface studied with scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been used to study the surface structure of a heavily B-doped Si(100) substrate prepared by high-temperature annealing. Images show distinctive atomic features induced by the surface segregation of B atoms. In the unoccupied state images, the dominant feature appeared as a pair of protrusions embedded in a dark frame, while in the occupied state images, the apparent height of protrusion pairs was reduced and the separation between the two protrusions decreased. Two types of protrusion pairs were observed. It is noted that the buckling states of Si dimer rows on both sides of the protrusion pairs are different from those reported previously. It was also found that the density of the protrusion pairs increased with annealing time. In some regions, the protrusion pairs tend to assemble together into small patches with a (2×2) reconstruction. The mechanism of forming B-induced protrusion pairs is discussed.