A METASTABLE (ROOT-3X-ROOT-3)R30-DEGREES RECONSTRUCTION OF THE SI(111) SURFACE, INDUCED BY SILICON ADATOMS

Reflection high-energy electron diffraction (RHEED) studies of Si(111) growth using silane reveal that the growing surface exhibits two equi librium structures as a function of growth temperature: a (1 x 1):H st ructure for temperatures below 600 degrees C, and (7 x 7) for temperat ures higher than 600 degrees C. Starting from the (1 x 1):H surface, t wo structural pathways are identified upon H desorption when silane fl ux is interrupted. In the growth temperature range 570-600 degrees C, the (1 x 1):H surface transforms directly to the (7 x 7) surface. At l ower growth temperatures, a metastable (root 3 x root 3)R30 degrees st ructure is observed as an intermediate step during the transformation from the (1 x 1) to the (7 x 7) surface. The formation of the (root 3 x root 3)R30 degrees structure can be explained by the redistribution of excess Si adatoms present on the surface during growth.