An in-situ high temperature scanning tunnelling microscopy study of the boron-induced √3 × √3 reconstruction on the Si(111) surface

Abstract

In-situ high temperature scanning tunnelling microscopy (STM) measurements were performed on vacuum-annealed, boron-doped Si(111) wafers. The samples were p-type with an atomic boron concentration of ∼ 10 19 cm −3 which were chosen such that after ultra-high vacuum processing at up to 1250°C and annealing at 600°C they gave rise to co-existence of both 7 × 7 and √3 × √3R30° surface terminations. After the initial “flashing” of the sample to 1250°C, we observe pinning of a variety of reconstructions due to the random out-segregation of boron to the surface. Prolonged annealing at the measurement temperature of 600°C was observed to give rise to the agglomeration of the boron into well-defined √3 × √3 regions. In the measurements, we observe preferential directions for the in-plane boundaries between √3 × √3 and 7 × 7 regions, showing clearly the importance of dimerisation as a strain relief mechanism between these regions. Detailed observations reveal the lateral diffusion of boron and silicon in the √3 × √3 regions as a function of time. The data are discussed in terms of the various controlling processes at the surface.