SURFACE STRUCTURAL-CHANGES DURING THE INITIAL GROWTH OF GE ON SI(111)7 X 7

Reconstruction and the surface morphology of Ge layers on Si(111)7 x 7 during the initial growth stages were studied by reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). The behavior of the Ge layer subjected to a thermal process was clarified by solid-phase epitaxy (SPE). By systematically varying the deposition thickness and temperature, the growth mode was confirmed to be the Stranski-Krastanov mode and the three-dimensional islands were found to form at 6.5 angstrom (equivalent to 4 ML). The 5 x 5 reconstructed structure was found to be characteristic of the low coverage (below the critical thickness) and high-temperature annealing (450-650-degrees-C). The double-step SPE, i.e., 5 angstrom Ge deposition (below the critical thickness) followed by 2 angstrom Ge deposition (over the critical thickness), revealed an apparent increase in the critical thickness. The results show that the 5 x 5 reconstructed structure is derived from intermixing Ge into the Si substrate.