The initial stages of Ge growth on vicinal Si(001) studied by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) is employed to follow the initial room temperature growth of Ge dimer layers on clean vicinal Si(001)-(1 x 2 ). The experimental data shows structure in the region of 2.4 eV which chan ges sign depending on Ge dimer orientation. Comparison with microscopic cal culations for one monolayer and two monolayer Ge coverages reveals excellen t agreement with experiment, demonstrating that surface states localised on Ge dimers are responsible for the RA response in the region of 2.4 eV. Thi s provides the first clear and unambiguous proof that RAS can be sensitive to dimer orientation. The origin of RA growth oscillations, their relations hip to dimer orientation, and variation with monitoring energy are definiti vely explained for the Ge/Si(001) system. (C) 1999 Elsevier Science B.V. Al l rights reserved.