Formation of Ge nanoislands before the completion of a wetting layer in the Ge/Si(1Â 1Â 1) system

The formation of Ge nanoislands directly on Si(1 1 1) surface before the completion of a wetting layer was studied by scanning tunneling microscopy and Raman scattering spectroscopy. The mechanism of the wetting layer formation in the Ge/Si(1 1 1) system depends on the rate of Ge deposition. Within the temperature range 350-500 °C, with Ge deposition rates of the order of 10−3 bilayers/min, the Ge wetting layer is formed by the multilayer growth mechanism. Therefore, the arrays of Ge islands with the densities of 109-1012 cm−2, depending on the rate of Ge deposition, appear directly on the Si surface during the evolution of the wetting layer. The height of Ge islands is limited by 3 bilayers. The lateral dimensions depend on the coverage of Ge and on the growth temperature. A series of lines related to the quantization of the phonon spectrum along the growth direction [1 1 1] was observed in the spectra of Raman scattering by optical phonons of Ge nanoislands.