AN IN-SITU HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY STUDY OF THE BORON-INDUCED ROOT-3X-ROOT-3 RECONSTRUCTION ON THE SI(111) SURFACE

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 similar to 10(19) cm(-3) which were chosen such that after ultra-high vacuum processing at up to 1250 degrees C and annealing at 600 degrees C they gave rise to co-existence of both 7 X 7 and root 3 X root 3 R30 degrees surface terminations. After the initial ''flashing'' of the sample to 1250 degrees 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 degrees C was observed to give rise to the agglomeration of the boron into well-defined root 3 X root 3 regions. In the measurements, we observe preferential directions for the in-plane boundaries between root 3 X root 3 and 7 X 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 root 3 X root 3 regions as a function of time. The data are discussed in terms of the various controlling processes at the surface.