Reflectance anisotropy spectroscopy of clean and Sb covered Ge(001) surfaces and comparison with clean Si(001) surfaces

Reflectance anisotropy (RA) spectra of clean, dimerized Si and Ge (001) surfaces with (2×1), p(2×2), and c(4×2) surface unit cells and Sb covered Ge(001) with a (2×1) unit cell are calculated using a local orbital hybrid density functional theory approach. The weight of Fock exchange in the DFT Hamiltonian is chosen so that bulk dielectric function critical point transition energies and dielectric constants for Si and Ge agree with experimental values. The RA spectrum calculated for the c(4×2) phase of Si(001) is in excellent agreement with experiment. RA spectra calculated for Ge(001) clean surface phases show two prominent minima below 2 eV. The RA spectrum of the clean Ge(001)–(2×1) surface was measured at room temperature down to 0.4 eV and found to be in agreement with currently available experimental data above 1.5 eV. These RA spectra show a single minimum in the range up to 2 eV, but do not show a second minimum where another minimum is predicted by calculation. Wavefunction amplitudes at the Γ‾ point of the surface Brillouin zone for the two occupied surface states of Si(001)’c(4×2).