Photoemission studies of the surfactant-aided growth of Ge on Te-terminated Si(100)

The interactions of Ge adatoms with a Si(100) surface terminated by an ordered layer of Te have been studied in detail using XPS, SXPS, STM and LEED. It has been demonstrated that the Te layer has a surfactant action on the growth mode of the Ge in that the two dimensional growth regime is extended to at least 200 A and the Te is seen to segregate to the growing Ge surface. The surface reconstruction of the Ge layer changes from (1 × 1) in the initial stages to (2 × 2) as growth proceeds and the surface population of Te is reduced. SXPS line shape analysis has indicated that the initial stages of Ge incorporation are characterised by the formation of small islands above those surface Si sites not fully coordinated with Te. Continued growth of such islands is, however, restricted due to their high surface free energy with respect to the surrounding Te-terminated areas. Ge atoms therefore site-exchange with Te atoms in bridge sites, thus becoming incorporated onto the Si lattice and displacing the Te to bridge sites on the growing surface. In this manner islanding is prevented and two-dimensional growth continues beyond the critical thickness. No evidence is seen for any significant incorporation of the Te within the growing Ge layer.